a biomechamcal analysis of a sit-to-stand...
TRANSCRIPT
A BIOMECHAMCAL ANALYSIS OF A SIT-TO-STAND TRANSFER AMONG THE ELDERLY
by
Lorraine Cathleen Hughes
Submitted in pamal fùifihent ofthe requirements for the de8fee of Masters of Science
at
Dalhousie University Ha1ifq Nova Scotia
Marck 1999
O Copyright by Lorraine CaMeen Hughes, 1999
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Table of Contents
COPYRIGHT AGREEMENT l ? 0 = 1 = m
LIST OF TABLESm W
BIOMECHAN~CS OF CHAR-RIS~NG ............................ ,., ......................................................................... 10 Jorn KMTICS ,...,...,..-. --..--.+.. - -....---o..- ......-......... ................................................... 12 CHAIR-RISIN& STRATEGY .................................................................................................................... 15 JOINT POWERS ............................................................................................~....................................... 16
....................................................................................................... THE INFLUENCE OF CHAlR HETGHT 17 The influence of chair height on chair-rising mmeuver- ..............................................~.................. 20
T H E ~ ~ c E o F AGE ...................................................................................................................... 22 THE INFLUENCE OF S T R E N ~ ............................................................................................................. 23
S~engrh trainingfor the elder& ..................................................................................................... 26 SUMURY OFTHE BEVIE~KOF- -.----...-......-.___. C............C............C.... CC................. 26
RESEARCH DE SiGN.. ......................................................................................................................... 2 % SUBJECT RECR- ............................................................................................*......................... 29 -AL PR- üRE. ...............-................ ... .-....-... .................................. ..............-+. ........... 29
Sir-to-stmd ~ansfem .................................................................................................................... 29 Strengîh measuremenk -..-.-..-- -.-.- , ....-,..--.. ................ ...........-. ................. 31
--ATION ................................................................................................................. . . . . 32 ~~~~~~~~~c meamwne nts. . -,,.......-. ..... ,, .....--.. ............................... ......,.............. 32 ...................................................................... Xtitemac &a ................,.... ................................. 33
.......... ............... Force pi@onrr, , ....,-..,.,-.-.,..~o,.. .....-... ..........---........ 33 Labormwy choir- .................................................. - ....................... ....oi..oi. .................................... 33 Saength measzuements -,.,.---..-..-.. ...-.--..- ... .......... ........-...,,..... .... .....-.... ...... 35
DATA REDUCXiON ..,....- . ,............,..,. ........... .,,. ............................ 36 Kinenrm-c data .,...... .............-.............--.... .- .. ......... ......-. . - .. ...-....-..-.... -.* .... . 3 7 Kïnetic &a, ............................. .....-....-..... ....--....... ..-. ..........-...... .......-.............. ........+............ 38 Cuvariance mea~ufes 6eîweenjointntomenîs o f@cr:e.,.-,-... ..... - .... --.- ............................. 38 Joint powier and tord amount of wrk done- .............. .-- ., ..,.. ...... .......-......... ... ...-.. . 3 9
DATA ANALYS~S ...,-......- ...,.......,..-.,,n'....stS--...........stS.....stS.....stS.stS........-.....,..,.......... U] . . W2hitz d j e c t reltc16rlip ........-..-.-...............................................-....... ~.....~...C....C......CC.CC.C 41 Dependent me- S..,.... . - . ...,.-....,-..n'Iln..S...S...S.S........S.S.S.S...S..S...S.S..........S.S.....S...... . 41 Joint m e ~ c u ~ p a u i e r cmd total mount of work done, .~...UI------...pauier.pauier.......t--....- ......-. 42
DISCUSSION .....-----y---------.pp- 62
CONCLUSIONS AND RECOMMENDATIONSs 76
APPENDIX D 94
List of Figures
FIGURE 1. DXAGRAMDEMON~TING THE CHANGE IN VOLTAGE OUTPUT WlTH TWE .................................................. OCCURRENCE OFBACK-OFF AND THIGH-OFF. 3 4
FIGURE 3. EMEMBLE AVERAGES OF TRE J O W MOMENTS OF FORCE AT THE HP, KNEE AND ANKLE FOR 1 1 SUBJECTS. MOMENTS WERE NORMALIZED TO BODY MASS AND REPRESENTTHE SUMOF THE RIGHT AND LEET SIDES. EXI'ENSORMOMEN'L'S ARE NDICATED BY 3- VALUES. DOTTED LINES REPRESENT k 1 STANDARD DEVTlATION. ... .s f
mGURE 4: h&AN HP MOMENT VERSUS MEAN KNEE MOMENTDURING THE EXTENSION PHASE OF THE STS TRANSFER FOR ALL SUSJECTS ACROSS THREE CHAR HEIGHT C O M ~ ~ ~ O N S . THE WNE OF BEST n~ IS SHOW FOR THE DATA POINTS. ..................... -5 5
FIGURE 5: h&W KNEE MOMENT VERSUS MEAN ANKLE MOMENT DURING THE EXTENSION E%IASE OF THE STS TRANSFER FOR AU SWBJECTS ACROSS THREE CHAIR HEIGHT CONDITIONS, P 1 ; A E F I " O N IS REPORTED AS POSlTIVE, TEE LINE OF BEST FIT IS SHOWNFORTHEDATAPO~S. ............... ,..~~...C.CCCC..C.CCC.C .............. , . , . . , , .CCC~C~CC~CCCC55
FIG~uRE 6. ENSEMBLE AVERAGES OF THE JOIEFT MECHANICAL POWERS AT THE HP, KNEE AND ANKLE FOR I 1 SUB~ECTS. RIE MECHAMCAL POWERS WERE NO- TO B0DYMASSAM)REPRESENT~sUMOFTHERIG~ANDLEETSIDES. POWER GENERATION IS INDICATED BY + VALUES WHILE POWER ABSORPTION IS INDICATED BY
.......................... - VALUES. DOTTED LINES REPRESENT * I STANDARD DEVIATIUN, .57
FIGURE B 1. -TIC DIAGRAM OF THE LABORATORY SET UP DURING THE DATA COLLECTION..,+ ....................................................................................................... 84
FIGURE C 1. FORCE LENGTH CURVE FOR EIGHT RESISTIVE BANDS. NUMBER SIGN REFERS ................................................................................. TO THE # OFRESI!3TiVEtBANI)S 88
FIGURE C 3. FORCE -LENGTH CURVE, NUMBER SIGNREFERS TO THE # OF RESBTIVE .................................................................................................................... BANDS 92
FIGURED 1. EFFECTOFINCREASINGTEIE~OFTHELEGEX~~~ENSIONONTEIE ACCELERATION OF THE SLIDING SEAT. E1GElT RESISTNE BANDS WERE USED. ........... 97
List of Tables
TABLE 2, ANTHROPOMETRIC DATA AND DESCRP'ïIVE DATA FOR SUBJECTS . ,.. . ,. . . , , . . . . . . . *. -32
TABLE 3 . C ~ U R HEIGEIT AS A PERCENTAGE OF KNEE HEIGHT . . . . . . , . . . . . . .. . - . . - -. . . . - . . . . - -. . . . . . - - - - 3 5
TAsLE 4, bURA CLASS CORRELATION COEFFICIENT VALUES FOR THE DEPENDENT MEASURES ,.,...,, ,,.. ...UREURE..URE.UREURE.... * * ... . *...*..* . . . . . - . - . . - - . - - . . . . . . . . * . . . 44
'hE3LE 5. MEANS AND STANDARD DEVIATTONS FOR THENORMALaED MOMENTS W-G) AT TKIGH-OFF FOR GROUPS 1 & II . , ,. . . ,, ,.,. , . . .. .. -. +*.. .. .. ,. .. ... .. ...-.., .,. ,. . .- ..- ...-.,.. . . ...... . .. 47
TABLE 6. h@WS AND STANDART) DEVIATIONS OF THE PEAK NORMALIED MOMENT OF FORCES WG) FOR GRoUPS 1 & II. ... .. ... .. .... . .... .. . ... .. ..... ... . . . . . . . . .. ... ...... .. . .. .,... . .- 48
TABLE 7, CV VALUES FOR THE HP* KNEE AND ANKLE ACROSS DETEENT CHAIR HEIGHTS WHENGROUPS WERECOMBINED .,.,...........INED. INED..INED .... INED...INED...-.. .... ,.-.,.,..--....... .................., 50
TABLE 8, COVAMANCE VALUES FOR THE MEAN JOINT MOMENTS BETWEEN GROUPS 1 AND n (GI GW AND COND~ONS. ü m s ARE REPORTED IN (NWKG)~ . ..... ....... . . . .. .. . .. 53
TAEU 9. COVARIANCE MEASURES FORTHE MEAN JOINT MOMENTS FOR GROUPS 1 & II ACROSS ALL CHAIR HEIGHT CONDITIONS.. , ,..,ITf.. ... . . ... . . ., . ... . . . . . . . ,. . . . . . . . . . . . . . 5 4
TABLE 1 O. CV VALUES FOR THE EXP, KNP: AND AEIRLE POWER-TIME CURVES ACROSS DIFFERENT CHAfR HEIGHTS. GRoUPS WERE COMBINED . . . . . ... . . . . -. . . . - , . .. .. . . . . . .. . . . ,. . . . ,. . . . 56
TABLE 1 1. MEANS AND STANDARD DEVIATIONS OF THE NORMALlZED WORK DONE (J/KG) FOR GROUPS 1 & 11 .-.. .,.,. . . .,. .. . .. . .. ,.. ..... .*.. .,., . . . . . , .. . . . . . . . . . . . . . .,. . . .. ,.. ,, . ,,.. -. -58
TABLE 12. SUBJECTS PERFORMANCE ON THE SHUTIZE 2000 .. ..... . . . , . . , . . . . . ,, . . . . . . . . ,,. . . . . . .. . . 5 9
TABLE 13. COMPARISONOF THE AMOüNT OF WORK REQUIRED TO RAISE THE COM FROM A CHAIR SET AT DlEEEENï HEIGFïïS TO THE PERFORMANCE ON THE SHUTTLE ~000. Ums AREIN JOULES ....... ....+ rSS~~SSSSS..SSS. .SC.t t t .C.C. . . .CC.CCCCCCCCCCCCCCCCCtCCCCCCC.CCCC rrr...........r... 60
TABLE 14. COMPARED VALUES OF PEAK NORMAtlZED MOMENFS OF FORCE (NM(KG) FOR THE SIT-TGSTAND TRANSFER, TEE MOMENTS OF FORCE REPRESENT~ SUM OF TEE RIGHT AM) LEET PEAR MCMENTS AT THE HP, KNEE AND ANKLE - .. ,. , , . , , . . . .. ,,,. . . . .. ,- .. , . - 67
............ . TABLE c 2 STATISTICAL RESULTS OBTAINED FROM THE REGRESSION ANALYSIS: 87
TABLE c 5 . STATISTICAL RESULTS EROM THE REGRESSION ANALYSTS WlTH THE OüïLiER 90
TABLE c 6 . STATISTICAL RESULTS FROM THE REGRESSION ANALYSlS WITHOUT THE 0- ................................................................................................................. 91
........................ . T m c 7 ~ I C T E D FORCE CALCULATIONS W~TH 8 RESISTIVE BANDS 93
............. TABLE E 1 : SUGGESED CUT-ûFF FREQüENCIES OBTAINED FROM BIOMECH @ -99
TABLE F 2- SUUMARY OF THE ANOVAS ON THE MAGNlTUDE VARIABLES FOR THE WïîEiiN ............................................................................................ SuBJEcTRELIABïm 104
TABLE F 3 . SUMMARY OF TEE GNOVAS ON THE TEMPORAL VARIABLES FOR WlTHIN- ....................................................................... SUBJEaRELIAsriUrr ....,,,........... ,., 105
Rising fiom a chair is an important fuu~*onaI actnnty which people daily perform The aim of îhis study was to quant@ the joint kinetics and enqetics of the Iower iimb during the sit-to-stand transfa for different chair heights among an elderly population The variables and@ included the moments of force at thigh-og peak moments of force and the totai amount of work &ne to amplete the transfer at the hip, hee and ankle joints. In addition, a covariance masure was used to assess Iower h b synergy. As a second purpose, the relationship between the minimum chair height nom which an older person was abfe to successfiilly rise was compared to their performance on the Shuttle 2000.
Eleven healthy, elddy subjects (10 fernales and 1 d e ) with a mean age of 79 years participated in the study. Subjects were gruuped by stature with Group 1 being > 1.63 m (n=4) and Group II being < 1.63 m (n=7). Subjects in Group I rose fiom 0.400, 0.435 and 0.470 m while subjects in Group II rose from 0.38OP 0-415 and 0.450 m For each triai, the subjeas rose fiom the chair without arm assistance and with th& feet in a standardized position on a force plaflorm.
A sagittal piane view of the movement was recorded usin& a vide0 canera. The ground reaction forces were mea~u~ed using a Kistla force pIatform and ND converted using an IBM compatible computa at a sampling rate of 300 Hi. The video data were reduced ushg the Peak Performance Technologies System O to obtain the raw coordinate data for a four-link segment model. Subsequent kinematic and kuietic andyses were perfomed us@ BIOMECH @, a motion anaiysis software package.
Eüsing f?om the low chair height repuired significantiy more knee moment at thigh-off compared to rising fiom both the middle and high chair heights in Group II (t =-3.523, df 16, p < 0.05; t = -3.875 df 16, p < 0.05, respe*iveIy). A similar trend was observed in Group 1 although not StrdiSticalIy signincanî. SignisEantry more hip extensor moment at thigh-off was however requind in Group I when rising fiom the middie height compared to the low chau heïght ( t = -3.098, df 16, p < 0.05). Risuig h m the Iow chair height reqpired si@cantiy more ptalr knee moment cornparrd to rising nom the highest chair height in Group II (t = -3.289, df I6+ p < 005). A sigdicant hcrease in the totai amount of work done Iit the hwt was obsaved in ôoth p u p s when rising fiom the lowest chair height compared to the highest chair height (t a = -3.3 54, t a = -5.374, df 16, p < 0.05). ûveraii, the comCance measure across aII groups war 48.0 % for the hiphee and -14.0 % for the kn-ûnlde* This, the hip-knee moment patterns exhiibit some degne of sharing in the O& task. CormerseIy, the kneeankle moment patterns seem to work quite independentiy fkom each other.
The S W e 2000 ia its present state wps unable to Qscnrmnat * * -
e among dBierent strength capabilities since the majority of the subjects compIetai the exercise wa6 maximum resistance-
1 would like to sincerely achowledge my supervisor, Dr. John Kozey, for his expert
advice and encouragement tbroughout my undergraduate and graduate degrees. Above
dI, his wisdom and patience thoughout the entire project were greatly appreciated.
1 wodd also Wre to thank my cornmittee members, Drs. Cheryl Kozey, Carol Putriam and
Phil Campagna for their advice and assistance on this project.
1 wodd like to extend my appreciation to Don Made04 James Crouse and Dave
Grimshire for their technicd assistance. 1 wodd aIso Iike to thank Steve Redman for bis
assistance during the data collection and reduction and to Wade Blanchani for his
statisticai advice.
A sincere th& you to Amy Kwoiq Fem Delamae, Steve Leblanc and Drew Campbeii
for their support and fnendship.
I wouid aiso lüre to extend my appnciation to the volunteers who participateci in this
study and to ecknowiedge the Naturd Science and Engineering Research Council for
their financial support.
FinalIy, 1 wish to thaiik rny parents, Barbara a d Frank Hughes. 1 am especiaiiy gratefbi
for their support and encomgement throughout this joumey.
Introduction
Rising fiom a chair is an important fimctional aaMty that individuals fiequentiy
perform durhg the day. As it has been found to be one of the most biomechanicaiiy
demancihg activities of daily living that individuals carry out (Riley, Schenlcman, Mann
& Hodge, 1991). it is not surprishg to h d that an estimatecf two million individuais in
the United States, aged 65 and ova, qerience some degree of diffcufty when rishg
fiom a seaîed position (Hughes, Myers, & Schezikman, 1996). Since the ab- to
successfully execute the sit-to-stand motion is essentid for independent M g (Hughes &
Scheiihnan, 1996), older individuais unable to cise d o u t assistance incsease their nsk
of being institutionalized and perhaps more importantly to Nner fiom diseases associated
with their immobility (Aiexander, Schultz & Wamick, 199 1).
A component of many rehabiiitative progcams designed to improve a patient's
mobiiity is the successful completion of the sït-to-stand traasfer @oorenbosch, Harlaar,
Roebroeck & Lankhorst, 1994). Furthemore, physical paformance tests designed to
assess fiuictional mobiiity among the eldaly often incorporate chair rising tasks. In orda
for these propms and assessments to be effective, an understandhg of the various
fmors a t r i g one's abiiity to rise &ont a chair is required. Recent biomechanid
research in the field hss made major contributions in d o u s areas including the
importance of chair design and Mirent chak rishg techniques for the successfiil
cornpIetion of the task
One area requiring mer bvestrCgation is the importance of the lower exttemity
muscles durhg the sït-testand movement. To date ody a few studies have inchdeci a
complete kuietic andysis on the normal sit-testand trandk Most h e concentrated on
a single joint or have ewamined the &ect of altering various conditions on seIeded
kinetic variables. For exampk ElIn and associates (1979) d y l e d the knee forces in
two maie subjccts as t k y rose âom a normal chair without usbg their anm. At the time
tlÿa subjects Iost contact Wnh the seat, the compressive knee joint force which was
paralle1 to the long axis of the tibia was caiailated to be as high as seven-times body
weight wMe the patelio-femoral forces rangeci between two- to six-times body weight.
For comparative purposes, reported tibio-femoral forces range between three- to four-
times body weight d d g level walkh&t walking up and down a ramp and ascending and
descendhg stairs (Seedhom & Terayama, 1976). Ahhough the study's limiteci n m b a of
subjects and age range reduces the generaluability of the resuits, the high knee forces are
an indicatioa of the amount of stress enwuntered at this joint for this movemeat. In a
later study, Ellis, Seedhom and Wright (1984) examined the effect of chair height on
lmee joint forces on eighteen subjects and found that both the knee joint forces and the
muscle forces were Iess when nshg fkom a high chair in cornparison to a Iow chair with
and without ann use.
Moments of force are fkquentfy determineci in the shidy of human movement as
they provide an estimate ofthe net remit of aiI internai forces acting at a part idu joint.
In thcory they include the moments due to muscies, ligaments, joint fiction and
stnichtral cozlstraislts (Wiier, 1991) and are indicative of the amount of stress ocamhg
at a joint (Bwdett, Habasevich, Pisciotta & Simon, 1985). Severai studies have
concentraîed on determining peek moment offorce at the hip, knee and aakle durhg the
chair rise. In 1988, Fieckensteitt and associates restricted then subjects' initiai knee
flexion angle in order to aramine its effect on the peak moment of force at the hip while
rishg nom a chair. When the initiai Lnee fiexion was 75 degrees, the subjects had to
exaggaate theu forward movement ofthe uppedmdy and arms h order to cornpiete the
rise. As a result, the peak hip extemr moment tncreased fiom 142 Nm to 253 Nm.
AIthough theu findings were bssed on a group ofyoung heaithy mbjects (mean age 25.4
y-), the large hip exteasor moment raises conam for individuais s u f f i fiom eitha
ha or hip joint diseases or bah.
Wnh respect to assessmems using joint kinetics, Wimer (1991) emphasized the
importance of examining the entire Iowa lunb raîher than f d g on a single joint
since it may provide idormafiton as to how one joint can compensate for the Iack of
support at another joint and siüI enable the indMdud to complete the task. He
introduced the concept of support synergy whereby variations in the hip moment pattern
are compensated by opposite changes in the knee and ankle moment patterns. These
trade-offs account for the Iow varîability observeci in the support moment despite the
considerably high variabitity in the individuai joint-moment patterns within and between
subjects. The support moment represents the net tendency of the lower limb to extend
and is the summation of the moments of force at the ankle7 knee and hip with extensor
moments as positive (Wier, 1980). Trade-ofi have been found to occur between
moments across joints for subjects walking at difEerent cadences. In an attempt to
quanti@ these trade-offs in the moment pattern, a covafisu1ce measure bas been used. A
high covarrCance measure (100%) indicates a high correlation between the two adjacent
joints. A low covariance measure indicates that the individual moment panans of the
adjacent joints are unreiated and acting independently of each other (Winier, 1989). To
date no sit-to-stand studies have examineci the lower limb synergy for this task in terms
of the degree of covariance.
Another kinetic variable that provides information on the role of muscles relates
to the energetics and in particular the mecbanid power at each joint. This variable
provides the rate with which mechanical work is done by the muscles and acts as an
hdicator of m u d a r effort for c o n d c and eccentric ~ 0 ~ 0 1 1 s (Andrews, 1983).
Concentric contractions genagte power whiie eccentric codractions absorb power. The
area under each phase ofthe power-thne curve is equd to the mechanical work done and
identifies periods of powa generation and absorption.
Few sit-to-stand studies hrive andyzed the mechanical power at the hip, knee and
ankie joints. In 1994, C m and Gentile examineci the influence of ana movement on the
mechanics of the sit-to-stand d m . A cornparison was made between naturai a m
movernent, rebcted am movement and a pointjng condition Six subjects performed
the rise with chair height standardized to lower ieg Iength. Iacluded in thir anaiysis was
a description of the pow-tune curves. EssentÏalIy power was generated at al1 three
joints during the majority of the extension phase for ail conditions. Coghiin and
McFadyen (1994) also included a power analysis in a shidy examining transfer strategies
among n o d and low back pain abjects. Sidarly to Carr and Gentile's findings,
power generatiou was seen across all joints. The type of strategy used inauenceci both
the paaeni of the power-time m e and the total amount of work done at each joint.
ûther assessments of variables such as chair height on the joint kinetics of the sit-
to-stand have been examined to a limited extent and few have focused on the elderly. In
1985, B u n i a and colleagues compared the peak moments of force during nsing tiom
two types of chairs differing in chair height. The sarnpie population included ten heaithy
male subjects and four male subjects with lower extfemity disabiiities. The subjects were
asked to rise tiom a standard chair of height 0.43 m and &om a specially designed chair
of height 0.64 m with and without ann assistance. While the d e plantamexor moment
did not signincamly change in either situation, significantly smaiIer peak hip and knee
extensor moments were obsaved when rising fiom the higher chair in cornparisou to the
lower chair without ami assistance (Burdett a al., 1985).
out of the three lower extremity joints, Rodosky and colleagues (1989)
demonstrateci that cheu height had the peatest impact on the moment acting at the kne
when subjects rose nom an d e s s chair. The authors observed a 50% reduction in the
moment required at the knee as chair height increased Born 65% of the subject's knee
height to 111%. Sina it is not uncornmon for older pasoas to fhd thernseIves faced
with the challenge of rising f?om a Iow ch& M e r data is naded on the &kt of chair
height on the joint kinetics and eaefgetics of the enth lowa limb among the elderly
popuIation.
It is a weli known f a th with UiaeaSmg age, skdetai muscIe undergoes bath
structural and hctionai changes kcIudmg a reduction in musde mass and muscIe
strength ( L d I , Taylor & Sjostrom, 1988). Lower extremity strrngth is a fùndamentd
component of the seiwrimotor hc t ion which supports mobility (Wolfson, Judge,
Whipple & King, 1995) and consequently when muscle strength tiills below a certain
threshoId the individual's a b w to complete various mobility reiated activitiw may
becorne impaireci (Young 1986).
Of the few studies that have investigated the relative importance of strength in
rising f h m a chair, there is some debate. For example, Hughes et ai. (1996) focused on
the role of knee exteiisor strength in chair king and found that hctionaily impaued
older ad& requed 97% of their available strength to rise tiom their lowest successftI
chair height. In contrast, a youager, hedthier group required ody 39% of their avaiIable
strength at the Iowest chair height. An isometrk measure of knee extaisor strength for
the eIdedy was obtained for each subject using a Cybex dynamometer with the hee
placed at 60 degrees of flexioe In contrast, Schultz, Aiexander and Ashton-Miller
(1992) found in their anaiysis of the sit-to-stand task that the repuireci strength to rise
ftom a chair feii well below the d m u m voluntary joint moment strengths reporteci in
the üterature for elderly individuais. Th& resrihs suggest that the reduction in muscle
strength that is normally associateci with aging may not be a ümituig factor in chair rishg
among the eldery and that there are other fistors which may have a more signincant role.
AdaiittedIy, while these studies differ in their opinions, it is importaut to reaiize
tbt the researchers used dinerent m m e m e n t mahodologies and popdations to obtain
a meastre of strength avaüability. Given the many factors which inf'iuence strength
measuremeas, saiigth values h d in the litemwe can vary immenseLy. Exampies
incrude imet - and iPtra - subject within the population king studied (Le. the
pnsence or absence ofdisease), the joint angfes at *ch tEw measurements were taken as
welI as whether or not the type of c0ntractr90n was isometric or idcinetic (Schula 1995).
Oae of the difficuIties when evaluting the relationship between strength and
fiinctional performance relates to the fact that it is difficuft to directIy measure muscle
strength in the same way the muscle is used fiinctiody (Hughes et aL, 1996). In most
sit-to-staad studies a measure of maximum voluntary strength, isornetric or isokindc,
was used to iadicate an individuai's strength availability (Hughes et ai., 1996; Kotake,
Dohi, Kajiwara, Sumi, Koyama & Mima, 1993; Schuhz a al., 1992). This value was
then comparai to the required joint moments to complete the sit-to-stand task. An
important issue is whether or not a maximm isomeaic or isokinetic strength value is a
valid measure to compare to the strength requkements to rise fiom a seated position and
to the task itself. m e may exkt other measures that are perhaps more representative of
the task reqyirements of a sit-to-stmd task movement which incorporates the use of ail
three joints.
Although some studies have designed a device to meastue Ieg extensor power in
an attempt to relate power output with fiinctiod perfocm811ce (Bassey et ai., I99I), onIy
one study has used a Keiser leg press to obtain similar meamrements among older
persans (EarIes, Judge & Gunnarsson, 1997). The focus of the fatter study was to
determine whether strength or powa was more comlated with the outcorne measures of
a physicai performance test. The test f d on the amount of time requbd to complete
various tasks including fwe chair rises. This may be a more usefid meihod in identifying
oider aduhs at risk of becoming bctionaily dependent es wefl as an effective streagth
training device for this population.
In summary, three important areas of research were eX8mUled in an effort to
increase our understanding ofthe pediormance ofa h c t i o d sit-testand task among the
eIderIy. These included the joint-moment t h e histories, joint powas and a h c t i o d
measure 0fstrengt.h
Purpose o f the stady
The a h ofthis study was to quant@ the joint betic and energetic patterns in the
Iowa limb as older abjects completed the sit-to-stand movement fiorn various chair
heights. Specific attention was paÏd to the moments at tbigh-off and to the magnitude of
the peak moments at the hip, knee and ankie. Lower iimb synergy was assessed using a
covariance measure for the d o u s chair height conditions. Fuctiier, the power patterns at
each joint were quakatively describeci. This description included the identification of the
number of power phases and the total amount of mechanical work perfiomed during the
sit-testand ûarisfei for each joint.
As a second purpose, the relationship between the mlliimum chair height fiom
which older pasons were able to rise and thek performance on a leg extension exercise
device was sramined. The Shuttle 2000 is an exacise device designed for rehabilitative
purposes and accommodates a wide range ofdiffaent strength capabilities. It involves a
simple Ieg extension and was used to obtain a functionai measure of lower actremity
strength. The total amount of work reqked to raise the body's center of mass fiom a
seated position was ais0 compared to the amom of work r-ed to extend the leg on
the S W e 2000,
The objective of this study was to test the following nuil hypotheses:
1) The moments of force at the hip, hee, and d e at the tirne of thigh-off were not
s ign indy affecteci by changes in chair height.
2) The peak moments of force at the hip, knee and ankie during the sit-to-stand ta&
were not sigaincantiy affecteci by changes in chair height.
3) The totaI amount of work done during the sit-twtand task for each joint was not
signincaatly a&cted by changes in chan height.
The htent of this study wuas to observe the e f k t of chair height and its innuence
on an etderIy pason's ab* to successfully rise, therefbre certain limitations,
delimitations and 8ssu111ptioas wae imposed on the study. For instance9 it Eus been
show that various factors affect the reproducibility of the sit-to-stand traasfer; therefore
a Iimitation to the study was the standardized conditions impIemented to aiiow vaiid
cornparisons to be made between chair rises set at different chair heights. A delimitation
to the study was the criteria used to select the population. The mclusion criteria r@ed
the subjects to be h e fiom any known neuromudar or severe mudoskeletai
âisorders and be medically stabL EiderIy persons d e r i n g fiom hypertension, coronary
heart d i s e . , blindness, lower extremity amputations or severe degenerative joint
diseases were exciuded nom the study.
Bilateral symmetry between right and Iefl legs was assumed (Baer & Ashbum,
1995). Another assumption was that a two-dimensional biomechimical model of the
lower extrexnity was appropriate for descnig the movement. According to
Ellis, Seedhom et ai. (1984), using a t w ~ e n s i o t l d model is weii founded shce for
this movement, the medio-lateral forces are considend to be d. It was ais0 assumeci
that the head arms and tninL muid be modeled as one segment (HAT segment). ûne
final assumption was that the i n d a i forces associatesi with the acceleration ofthe lower
srtremity were aegügible during the Ieg extensions on the Shuttle 2000.
Although the focus of this research was on the elderly, it is important to realize
that eiderly Îndividuals are not the oniy ones to mence difncuity in rising fiom a
mted position and hence pf8~t~~cai hdings may be us& for individuais d ' i g fkom
arthritis, neuroiogicai or otha musculoskeIetai diseases.
MechuuCcd power (Watt@: is the work paformed p e r d tirne, and is used to qymtifjr
the rate of g a i d g or absorbing energy by muscles or the rate of change of energy of a
segment or body system. Joint mechiinid power is the product ofthe moment offorce
and anguiar velocify at the jonit. At any given the, soime miscies aossing a joint can be
generating while others are absorbing energy: the net rate of energy generation or
absorption is evident in the joint mechanicd power (Wînter, 1991).
Positive Work (Jouies): is the work doue by concentrically acting muscles and e q d s
the time integrai of the joint mechanical power during the tïme the muscle is shortening
(winter, 1991).
Negative Work (Joub): is the work doue by eccentridly acting muscles and equais
the the integral of the joint mechanical power d u h g the time the muscles are
Iengthening (Wimter, 199 1).
Muscular Strength (Nm): Maximum force a muscle or muscle group cm genetate
(Wiimore & Costili, 1994). In this study the one-repetition maximum (1-RM) is defineci
as the maximum amount of teasion (number of resistive bands) the individual can
successttlly leg extend on the Shunle 2000. The Iower limb must be completely
extendeci.
Ti ied "Up and Go" Test (s): Test used to r u e u e fûnctiond mobility in a frai1 elderly
pason. It requires the older person to rise fkom a standard armchair (seat height 4541q
arm height 65 cm), waik three meters, tum, walk back and sit d o m The score is the
amount of tirne required to complae the test (Pdsiadio & Richardson, 1991).
Unruccmsful chair rise: arose when any of the hllowing situations ocmrred: (1) the
subjects were mble to Mt the buttocks off the seat, (2) were unable to cise without
unfolding thek arms or lady, (3) rose but felI back and thus neva reached a fil1 standing
posture (Hughes, Myers et ai., 1996).
An understanding of the dynamics involveci in a sit-to-siand transfer is r e e d to
evduate the influence of chair height on an older petson's ability to rise fkom a chair-
This chapter gives a brief o v e ~ e w of the biomechanics involveci in chair-rising as weU
as pertinent information relateci to the present stuciy. N d y , this chapter discusses the
effect of chair-rishg strategy, chair height, age and strength on the completion of the sit-
to-stand transfer,
Biomechanics o f chabrishg
The goal of the sit-to-stand task is to move the body's center of mus upward
Erom a sitting to a standing position without Iosing balance (Roebroeck, Doorenbosch,
Harlaar, Jacobs & Laakborst, 1994)* To fk&!itate the process of analyzhg the sit-to-
stand motion, the has been d ~ d e d into several phases. Key events cm then be
ideatined within each phase. This may assist physicians and therapists in understanding
the reasons for their patients' inabiiity to rise fiom a chair and tbus improve therapeutic
intervention by enabling them to ide* where the diEcuity O-s during the rise
(Ikeda, Schenkman, Riley & Hodge, 1991). Aithougb the taminology and manna in
which researchers choose to i d e the phases o h differ, most have highhghed
smiilar events. Researchers oîten use the iinear kinematics of the center of mass to define
the phases (Roebroeck et al., 1994; Pai & Rogers, 1990).
The four phases describeci by Schenkman and associates (1990) are bnefly
discussed to provide a generai overvkw of the sit-to-stand hematics. They include the
flexion-momenhim phase, the morneatum-transfer phase, the exîension phase and the
stabiiization phase. The flexion-momentum phase generates uppa-body momentun and
is recognized by a forward and sfightly downward movement of the body's c e n i a of
mass (KeIIey, Daims & Wood, 1976; Schmlmiea, Berger, RiIey, Mann & Hodge, 1990).
During this phase, the hip is undergohg fie2cion. M e the Ime's anguk displacement
remPins pnmariIy unchaaged. A smelI amount of domiflexion genaally occurs at the
Seat off S a t e s the momentum-transfi phase. During this phase, the translation
of the body's center of mass changes nom a predominandy horizontal direction to a
vertical one. Hexe, the body's center of mass is decelerating in the horizontal direction
while accelerating in the vertical direction The upper-body momentum generated in the
first phase is tramferreci to the taai body. This phase chalIenges a person's stabiiity
since it initiates the transition between a the-point support system provided by the seat
and feet to a two-point system provided by ody the feet (Riiey et ai., 1991; Pai & Rogers,
1990; Hughes, Weiner, Scbenkma. Long & Studenski, 1994). The extension phase is
characterized by the verticai displacement of the center of mass. During the latter two
phases, both the hip and knee are undergohg extension while the d e is chamterïzed
by plantadexion. During the last phase, the dispIacement of the cester of mass becomes
stabiiized. Researchers rarely d y z e this phase because of the diflicuity encountaed in
detennining when quiet stance is reached (Ikeda et ai., 1991; Schenlonan et aL, 1990).
PrMous studies have examineci the impact of aitering various eqmhentai
conditions on the duration of the phases. Since performance time has ban uscd as an
indicator of chair-rishg difficulty, med sit-to-stand &dies have aiso used the d d o n
of the phases to make cornparisons among y m g and 01d d i t s (Aiexander a al., 1991,
Ikeda a ai., 199 1). Aiexander and associates #amined ody two phases in their shidy,
namely the time between the initiation of movement and lift-off and the the between
W-off and termination of the transfk. When rising without the hands, the older p u p
spent s i g d i d y more time in the first phase than did the younga poup despite
comparable total performance times. The authors wncluded that total t h e to rise may
not distinguish betwezn modaste perfiormance difficuities among the young and dd.
Ikeda and associates (1991) aiso examinai the influence of age on rising h m a
chair. Specincally they compareci the timing of the fht three phases denned by
Schenkman a ai. (1990) mong a heahhy olda group to data previously collecteci on a
younga group. Rising unda a prescribed tirne* the eidedy subjects rose nom o backless
chair stmdardized to 80 % Ime height wahout the use oftheir anns. Bo& the timing and
duration ofthe phases among the oider group were simt7ar to the younger p u p . Despite
similar petformance times, the older subjects spent les the in the mornenttm transfer
phase and sIightly more the in the extension phase dian did the younger group. These
findings suggest that dividing the sit-to-stand motion into phases is beneficiai since
performance merences may then be identifieci-
Joint kinetics
Few sit-to-stand studies (STS) have measured the reaction forces between the seat
and the subject and thus in most cases the jouit kinetics have been reported ftom the
instant of seat o E Frrrthermore, most kinetic assessments have concentrated on a single
jomt or have examined the effect o f aitering various conditions on selected kinetic
variables,
During the extension phase, the hip and hee typically experience extensor
moments while the ankle experiences a plantadexor moment. The extensor moments at
the hip and knee usuaily decrease as the transf'er progresses while the plantarflexor
moment at the ankie remains fairly constant.
The joim kinetics of the sit-testand task have been determineci using both static
and dynamic methods. Under a static anaiysis, the acceIerations of the Iower extremity
are assumed to be smalI and therefore the inert~~al forces are neglected. Hughes et ai.
(19%) pmvide suppohg evidence fOr this 85sumption as a cornparison was made
between the two approaches for the hee joim forces and moments. Ushg a "ground up"
approach to calnilate the joint moments offorce at the hee, the authors reported fbding
no signincant differences ôetween the peak knee moments usuig either method. The
mean percent merence in maximum hiee extensor moment for the yomg group was
- 0.4 i 0.9 % wMe for the efdedy group it was 12 I 1.6 %. Both ofwhich were not
sigdicady diffient nom zero. Io addition, the dynamic forces with respect to the
static forces were 2 9 I 2.1 % whiie the moments produced by the anguln acceIeration
with respect to the strtic moments wae 1.5 f 1.3 %. B d on these values the authors
c01~:iudeâ that a static d y s î s was an ecauate m d o d to estimate the joim moments and
forces ofa sît-to-stand transfer. In their study the focus was on the biet joint and ody
one parameter of the moment time m e was compared (peak knee extensor moment).
In 1990, Müier compared the biomechanics of rising fkom a chair or bed between
young and older maie subjects. A cornparison was made between the predicted momems
of force at seat off using a static versus dynarnic mode1 and assuming bilaterai symmetry.
The dyaamic moments of force at the hip, knee and ankle calculated usuig the ground
reaction forces were compareci to those calailateci using a "top down" approach that
negiected the inertial loads. A static "top dom" approach relies solely on the joint
angular displacements and on the anthropometnc data to calculate the moments of force.
The direction proceeds inferiorly *out having access to the ground reaction force data
The greatest Merence between the two methods for rising without arm assistance was
seen at the hips with 43 Nm for the young group and 41 Nm for the ofda group. At the
knee, the différence was 15.1 Nm for the young and oniy 3 Nm for the older subjects
while for the ankie, a difference of 6 Nm and 13 Nm for the young and old respectively,
was observeci. Although a diffaent parameter was examined in this shidy, the srnail
dinerences at the Lwe are in agreement with Hughes et a l ' s (1996) findings. Thus, the
identity of the joint is an important derion for choosing benveen a static and dynamic
mode1.
Recentiy a shidy evaluated the intersegmentai d m c s of a sit-testand
movement (Cmsbie, Herbert & Bridson, 1997). Six maie subjects participated in the
study of mean age 23.5 years. The authors compared a "top down" approach to the
"ground up" approach for estimating mscIe moments at the hip, knee and ankle.
Differences between the two methods for determinia8 muscIe moments avmged less
than 0.04 NmlKg. The authors coacluded that a "top down" dynamic approach was a
vaIid method to estimate moments and tbat the ermr introduced as a r e d t of predicting
the kinematics ofthe HAT segment and workuig downwards was negiigible.
Of the few sit-testand studies that hve used s 'top dom" appmach, most have
negiected the memal Io&. Sc- and associates (1992) in their anaiysis of the sit-to-
stand cask determined the required moments at seat off for three groups diBering in age
and in abÏfity to rise without a m assistance. Experimental data was obtained nom an
eariier study and included body configurations and hand force data Seat height was
adjusteci to easure the subject's thigh was horizontai and the Iower legs were pIaced at
70' to the horizontal. Subjects rose at a self-selected speed. Ushg a '%op dom" siatic
approach, the joint reaction forces and moments were caicuiated for a 10 segment link
model. Of the three Iowa extfemity joint moments, the knee expexienced the greatest
exterrsor moment after seat off,
SimiIariy, Kotake and associates (1993) used a "op down" static approach to
estirnate the hip and knee exteasor moments r@ed to nse nom a seated position.
Twelve male subjects, age 22 to 40, rose fiom a stool adjusteci to knee height with their
arms foIded across their chest. The moments of force were determined for the sit-to-
stand wrnpleted a a natural speed. The biomechanical model used the weight of
the uppa-body and thigh to estimate the moments acting at the hip and knee and the
i n d forces were negiected. The peak kaee extasor moment occu~red at seat off and
was greaterthan the hip mensor moment, which occurred shortly t h d e r .
In summary, oniy two studies have compared the joint kinetics using a static
mode1 and a dynamic model and wm importantiy, ody one kinetk parameter was
compareci. Future research in this wa is r@ed to M y understaad the ConseQuence of
n Jecthg the iaertiai louis on the predicted joint moments of force of the Iowa limb
and shodd examine the methodoIogy associateci with the determination of the point of
application of the extanal forces. The consequeme of using a 'top dom" vasus a
"ground up" approach shouid aIso be d e d in fbrther d a
Chair-rising strategy
Rishg fiom a chair r w e s large hip and knee extensor moments. Both the
acperimentd protocd and chair rise strategy play an important d e in determinhg which
of the two joints sustain the Iarger moments. For instance, Doorenbosch et al. (1994)
examineci the effect of full tnink flexion prior to seat off on the kinematics, kinetics and
1eveI ofEMG activation of various leg muscles. Nie young subjects performed the sit-
to-stand tratlsfer using two strategies. They rose under a prescribed time with th& hands
on their hips from a chair height set to knee height. The first strategy was refend to as
the ''naturaI sit-to-stand t rans f i i (NSTS) and required subjects to rise in a nomai
manna. The second strategy was refetred to as the "sit-to-stand with fÙii fiexion"
(FSTS) and requued the subjects to accentuate tnink flexion prior to seat off:
Signincamly higher hip extensor moments and Lower biee extensor moments wen
observai when subjects perfonned the sit-testand transfer ushg the second strategy
(FSTS) versus the first strategy (NSTS). The subjects aiso experienced a higher plantar
flexor moment at the ankle using the second strategy VSTS). Under the nrst m e g y the
knee sustained the largest extensor moment white unda the second strategy it was the
hip. The authors mncluded that individuils suffiring fiom muscle weakness may adopt
diffèrent strategies to help d u c e the recphed joint moments at the affected joint.
It is not unusuai for individuals suSering fkom arthntis to experience restncted
range of motion in the affecteci area. Fleckmstein and associates (1988) examined the
effect of limiting the degree o f initiai knee flexion during the sit-to-stand trader on the
peak hip extemr moments. Ten young subjects rose âom a 44 cm high stooi *out
the use oftheir a m under varyUig amounts of initiai knee flexion (lOSO varius 75" fkom
fidl extension). A dynemic anaiysis was wed tu estirnate the muscle moments at the hip
and kaee. Restricting the degree of knee flexion to 75" resuited in a p a t e r forward
movement of the upper-body aed a sisnificantiy higher peak hip extensor moment
Higher peak knee extensor moments were a h observeci ahhou& not Statisticaiiy
si@cant. For bot6 conditions, peak hee exmuor moment was greater tben the peek
hip extensor moment,
In 1994, Coghlin and McFadyen examineci transfer strategÎes among normal and
low back pain subjects. Using a dynamic mode4 the moments of force at the hip, knee
and ankle were detefmined for a chair heigtrt standardized to knee height. Two types of
rishg strategies were identified among the normal subjects: a C%ip-ttunk stnitegy" and a
'hee strate&'. No& stibjects who exhibiteci hiam moments at the kaee in
cornparison to the hip were classined under the '7caee mate&. In the %p-tnink
strategy", subjects flexed theu tnuiks m e r forward and sdiibited much higher
moments at the hip in cornparison to the knee. U ' this strategy, as tnink fiexion
increased, a shfk in the displacement of the body's center of mass towards the carter of
pressure was observed for tbese subjects. It was suggested that the "hip-trunk strategr
o f f d stabiiity since the center of mass is over the base of support for a Ionger paiod of
tirne. The low back pain subjects used no distinct strategy. Evidentiy these subjects
atternpted to share the Ioad by distntbuting the moments of force at the hip and knee more
evenly (Coghlin & McFadyen).
Previous studies have show that chair height, initiai foot position, speed of
movement, and type of biomecbaniCd mode1 infiuence the joint W c s of the sit-to-
stand transfer, (Burdett et al., 1985; Shepherd & K04 1993; Pai & Rogers, 199 1; Hughes
et al., 1996; Müla, 1990). In aunmary, when the acperimentd protocoi and chair rising
strategy are taken h o consideration, valid compuÏsons can be made between diffient
studies with respect to the joint kinetics.
Joint powtrs
In 1994, Carr and Gentile examineci the effect of a m movement on the
biomectianics of r i s k g nom a chair. Six male subjects with a mean age of 24 years
performed the rise under thne conditions. Condition 1 r@ed the subjects to rise using
a prderred arm movement. Condition 2 r-ed the subjects to point with th& right
ann as they compIeted the cftair rise whiîe Condition 3 reqpired the subjects to hoId a rod
ushg bot6 bauds. AU subjects rose at a ~e~sefected spad fiom a chair height
standardized to lower leg length. The analysis ewmined the three conditions in terms of
the kinematics, the joint kioetics and mechanical powm at the hip, knee and d e .
In terms of the joint-moment pattern, Conditions 1 and 3 were very similar with
o d y a smaii merence at the end of the movement. For the preferred arm movement
(Condition I), both the hip and knee moments beaime fiexor moments at the end of the
transfer while for the restricted condition (Condition 3) the change in polanty did not
occur. The pointhg condition exhicbiteci fluchiations in the joint-moment patterns in
compm*son to the other two conditions. The peak moments of force at the hips were
greater than the values at the knee and ankie across conditions.
The power-time w e s were caiculated by muItip1ying the instantanmus joint-
moments of force by the joint mguiar velocities. According to the authors, power was
generated during most of the extension phase at aü three joints across conditions. The
amount of work doue at each joint, which is the integrd of the power-time curve, was not
report&
As previously mention& Coghün and McFadyen (1994) examined transfer
sttategies used in nsing nom a chair. Their analysis also included the mechanical joint
power-time m e s and amount of work done at the hip, knee and ankle. Ahhough both
the c ~ p ü u n k strate&' and 'Iwe s t r a t e generated puwa at the hip during the
extension phase, subjeas who used the "hip-mmk" megy generated more power at the
bip and less at the knee in cornparison to the '(knee-strate&'. The profile of the power-
time c w e s was determined by the strategy and conse~ueatly the amo- ofwork done at
each joint was also affecteci by the strategy used.
The influence of chair height
h 1993, Weiner and associates examinai the range of chair heights found in a
mimber of settings fieqmtly visited by older mdividuais. It wa9 fôund that chair heig&ts
typidy range fiom 30.5 to 45.7 cm. Thus it is not uncommon in appüed settiags* for
olda pefsolls to nnd h s e l v e s faced with the c6alIenge ofrising nom a low chair-
As chair height demeases, the position of the cemer of mass ofthe HAT and thigh
segments relative to the hee joint is Iowered thus making W-off more mechanidly
demanding (Schenkman, RiIey & Pieper, 1996). An hcrease in moment arm Iength
between the body's center of mass and the h e e joint results in an increase in lmee
extensor moments. Hmce it is not surpriskg to find that chairs whose vemcal height MI
below knee height generaiiy make rising more ciifficuit for elderly individuals to
successfhliy complete (Hughes & Schenkman, 1996).
Studies have show that higher chairs facilitate the tramfer task. Out of the three
lower extremity joints, Rodosky and colleagues (1989) demonstrated that chair height
had the greatest impact on the moment aaing at the knee when subjects rose fiom an
d e s s chair. Ten young healthy subjects participated in the study. Usuig a dynamic
aaalysis of the motion, the authors obsenred a 50% reduction in the moment requked at
the hiee as chair height incnesed fkom 65% of the subject's lmce height to I 15%. Only
a small difference in the moments of force at the bip was seen between the lowest and
highest chair height whiie the ankle was d e c t e d by changes in chair height.
Siniilarlyt Eilis et ai. (1984) reporteci a reduction in knee joint and musde forces
when heahhy rnibjects rose from a high seat in cornparison to rising fiom a Iow seat The
primary interest of their study was to examine the joint and muscle forces acting at the
knee as subjects rose 6om a specidy designed chair which recordeci the r d 0 1 1 force
between the chair and penon. The authors used a twodimensionai model of the hee
and assumeci the Ioad was @y dmded betwesn both Iegs. In thek model the inertiai
loads of the lowa ext~emity wete mglected and moments about the hip, hee and ankfe
w a e then determind Reductions in knee jouit and muscle forces were reposted between
8 and 56 % when rising firom a high chair thPa fiom a low chair. The population studied
in this study inciuded young healthy aduhs.
H@es et ai. (1996) alao obsaved s i @ d y higher peak knee adensor
moments when chan height was decreased among the young and functionaIIy impaired
elderly. Chair heights rangeci between 0.33 m and 0.58 m and increased in 0.05m
increments. Since the authors found no difference in the moments of force using a
dynamic mode1 versus a static model, ody the results obtained f?om the static aoalysis
were reportecl in their study.
In Burdett et al. study (1985), peak moments offorce at the hip, h e e and ankie
wae detefmined using a static ncialysis for two types of chairs ciSiering in height. The
cornparison in chair heights was 0.43 m and 0.64 m. The study focuseci on healthy
subjects and on subjects with Iower sttremity disabilities. Both the hip and knee
extensor moments were significantly reduced when rising fkom the higher chair without
a m assistance while no sipifkant différences were seen at the ankle arnong both groups.
Converseiy, Munro and colleagues (1998) found that chair height had no
signincaat d i on the net knee moments at Se8f-ofE Twelve elderly subjects SUffering
fkom rheumatoid artbritis participated in the study. A cornparison was made between
nsing fkom a low (0.45m) and a high chair (0.54m) with and without the use of an ejector
mechanisie The protocol required the subjects to use the amrests and to keep their fea
on the forceplate during the transfer. Load ceiis wae used to ooiiect the v e r h i forces
exerted on esch armrest by the subjects. An inverse dynamic approach was used to
estimate the moments of force at the adde and knee at seat-ofE The authors
hypothesized that the elderly subjects used a particufar swtegy that lessened the Ioad
acting at the hee joint at seet off. No signincant differences were found in the net d e
moments. A complete kinetic analysis on the lower iimb wodd have provided greater
insight into which strategy the eiderIy subjects used to owipIete the transfér.
CollectkeIy, these studies have shown that regadess ofthe modehg technique,
chair height reduces the peak moments at the kme. However, it is not cIear based upoa
these studies what the &ect is at the m e and hip. Since most have eitha fOcused ody
the knee joint or have examineci the infiuence of chair height on young hedthy subjects,
there is a nad to examine the Muence of chair heigk on aU three joints of the Iower
limb in an eIdaly population,
The influence o f chair height on chair-rishg maneuver.
The impact of chair height on the maneuver used to rke fiom a chair has recently
gained attention as researchers atternpt to understand the compensatory mechanians used
to overcome the diniculty encountered when rising fiom a low chair. Chair-rising
stracegies exist on a coutinuum with the momenhim strategy at one end of the spectnim
and the stabilization strategy at the d e r end (Hughes a al., 1994). While the
momenhim strategy Uivolves generatùig uppebody momeritum in order to rise, the
stabilization strategy relies mainly on movemeiits that tend to increase stability and
involves very Iittle momentum generatioa Momentun is the product of mass and
velocity and is related to the klietic energy of the system (Schenkman et ai., 1990).
In Hughes et al.% study (1994), elderly subjects rose without arm assistarice fmom
six different seat heighds that ranged between 0.43 and 0.56m An unsuccessful trial
occurred when after 10 seconds fiom the start s i g d , the subject had not reached a
standing posture. Attention was paid to the movement of the tnmk, buttocks and f-
since they ai i affect the Iocation of the center of mass relative to the base of support
provided by the fm. Two kinemafic memes were used to ideatifjr which strategy the
subjects tended to use in otder to rise fiom a chair. They included the horizomal tnink
velocity and the horizontal distance between the body's center of mass and the base of
support provided by the feet (COMlBOS). hdividuais whose btizontai tnmk velocity
was 10 c d s or more and who did not reduce the COlWBOS vaiue by more than 5 cm
were classined under the "momentun strate&. For the "stabiiization strate&', the
horizontal üunk velocity was 7.5 c d s or Iess and the COMBOS distance was decreased
by more than 5 cm. EIderly subjects who did not meet the cntaia for either strate= were
dassined under a 'ccombined strategy"-
Of the twenty pubjects, efeven used the "momentum strate&', four used the
c c s t a b ~ ~ n strate&' and five e1dedy subjects used the cccombined stmtegf'. At the
IOW chair heights, the percentage of successfbi rÎses was Iess in the stabilization a d
combined strategies in cornpanson to the momentum strategy. The authors speculated
that there is a greater dependence on the joint-moment required at the knee to rise when
eitfier the stabhtion or combined stnaegy is appiied. Wfi M e or no momentum,
higher dependence on the knee extensors is required. More important, d subjects
experienced greater success as chair height increased irrespective of the strategy used.
According to the authors, the cgmomentum strate&' requires a higher degree of
posiural control since the person must generate SUfEicient momentum to Bse yet stül
maimain their balance when standing posture is ceacheci. In contrast, the "stabiiization
strate&' atternpts to reduce the distance between the center of mass and base of support
and is genedy performed more slowly than the 'hiomentum strate&'. It requires less
postural conttol at the end ofthe task
ui 1996, Schenkman and coileagues d e d how individuais manipuiated theu
upper and lower body momentwn when chair height decreased. The authon compared
performsulce characteristics between young and old heaithy subjects. T d anguiar
velocity was used as a measure of upper-body momenhim A stmdardized protocol
required the subjects to rise under a presmîed t h e without arm assistance and to keep
theV feet statbuary. Unda these constrained conditions, b t h p u p s inaeased theu
upper-body momenhM to accommodate the decreases in chair height.
A s M a r invesbCgation was conducteci on eiderly persans with moderate
bctional impairment (Hughes & Schenkman, 1996). Eldaly experiencing difficulty
with any o f the foiiowing tasks were c W e d as hctionally impair&: (1) the inability
to descend four conseeuthe stsits, step-ove~step; (2) the inability to rise fiom a 0.33 m
high chair, or (3) a Iowest successfui chair hei* Iess than the subject's knee height The
eIderLy voImeers were asked to rise without the use of thek anris fiom a Sefies of
different heigbts (mge was between 0.33 m to 0.58 ru). Speed of movement was not
controiied The resuhs of the study indicated that the subjects compe11~8ted for the
deçrease in chair height by simuhaneow1y attemptmg to maease bot6 momeritum and
stabiirn,. Based on merai kinematic measures @p flexion veIocity, time to use and
distance between the centa of mass and base of support), the authon conchided that the
fbnctionally impriired elderIy placed more emphasis on achieving stabiiity ratha than
successfùiiy rising fkom a low chair.
Ln summary, these fiduigs wouid suggest that for the eideriy, the abiIity to
mahain balance is a determinant nidor for the type of strategy used to complete the rise.
Since the type of stnitegy used may reflect possible baiance irnpairments, Hughes and
Schenkman (19%) provide guideliaes for i d e n m g strategies withùi a clinicai setting
muneiy the speed oftnink movement, foot movement and total time to rise shodd be
monitored as the person completes the rise.
Tbe influence of age
As for the influence of age on the biomechanics of rising, Alexander and
coiIeagues (1991) maimned the angular displacement of the rh& thigh and tnink in the
elderly and the young. Chair hei* was standiudized so that the subjects sat upright with
I IO0 ofknee flexion. The older ad& flexed their legs and tnmks mon and extended
their thighs to a greater extent than the younger addts when rising fiorn a chair without
the use of thek arms.
As previously mentioned, Ikeda and associates (1991) compareci the timing of
Schenlnnan's phases and magnitude of the peak joint angIes and veIocities for a
controiied sit-to-stand movement emong a young and ofd group. Few kinematic
difEîiences were found b e e n the two grwps. Whüe the head position differed
between the two groups, no diffaeaces were seen in relation to the joint agies or
velocities. Using an inverse dynamics approach the pacentage of difference between
groups for knee and hip moment of forces was ody 7 % and 6 respectively. The
sunilanties ktween the right and Ieft sides in the oIda group support the assumption thot
heaIthy olda individu ai:^ exhliit symmetry. For exampIe, mean diffierences for
m81Limum d e and hip joînt angles wexe 1 % and 2 %, respecheiy. Differences
between right and Ieft hip and knee moments were Il% and 13 %, respedvely. These
results would be scpected in an asymptomatic abject.
The influence of stmngth
Although many possible hctors may contribute to an elderly person's inability to
successfùily rise 60m a ci&, severai studies have recently focused on the relative
importance of strength in chair-tising among the elderly. One of the diffcuIties when
evaiuating the relatiomhip between strmgth and ninctiooal perfomce relates to the
election of an appropriate strength measurernent device. As of y* no test rneasures
strength of the muscfe groups involved as they are used ~ct ionai iy (Hughes et ai.,
1996). Most sit-to-stand studies have used a uni-joint m e a x e of maximum vobtary
strength eaher isometnc or isokinetic, to indicate an individuai's strength availabiiity
(Hughes et al., 1996; Kotake et al., 1993; Schultz et ai., 1992). This value was then
compand to the required joint-moments to cornpiete the sit-tocstand task.
Schultz and associates (1992) in their analysis of the sit-to-stand task compared
the cetpireci moments for seaî-off to ~emgth data reporteci in the literature. Chair height
was adjusted to epsure the subjects thigh' were horizontal and the Iower legs at 70' to
the horloatal. Rising without their anns, the required joint-moments for the elderly
(mean age 72 years) were below the isomaric strength vahies published in the Iiterature.
The authors mncIuded thet strength may not play as criticaI a role in cwrising as hsd
been previousLy thought Their findings seem to disape with the opinion ofHughes and
associates (19%). Different methodoIogies make cornpuisons between studies difficuIt
and therefore cenfuI analysis is w82r8nted when drawing coacIusions.
The vaIidity in making comprriscms to strength d i t e s reported m the titerature is
debatable since t h q can vary immenseLy es a resuk of different methodobgîes of
strength testing Many factors inciudmg muscle length, muscle veiocityr muscle
activation as weiI as gender and body size are known to have an effèct on one's s~rength
producing capabilities (Chapman, 1985; NdonaI Isometntc Mbscle Streagt4 1996).
Hughes et al. (1996) examineci the role of lmee extemr strength in limithg the
Iowest chair height f?om which functionally impaired eiderly individuais couid
successfiilly rise. Measurements of maximum knee isometric strength and required
moments to complete the tramfer were determineci for each abject. The authon defïned
maximum isomebic streagth as the maximum extensor moment produceci using a Cybex
dynamometer with the knee placed in a position of 60° of flexion. Fu~zctional impairment
was defineci as the inability to descend four c o d v e stairs, step-over-sep, d o u t
using the handrail and to rise fiom a 0.33 m high chair. Performances were compareci to
those of young heaithy individuais.
Requiced knee moments were d d a t e d at s e v d different chair heights for both
groups. Chair heights rmged fiom 0.33 to 0.58 m and increased in increments of 0.05 m.
Subjects rose fiom a backless chair without am assistance. Of the eleven fbctionaI1y
impaired eldedy individuais wne were able to rise fiom the lowest irnposed chair height
of0.33 rn and ody four were &le to rise fkom a chair height of 0.38 m. This height
was approximately 82.3 K of the individuai's knee height. Aithough the authors found
no signifcant Mience between the recpked moments between either gmup, the elderly
were signincantly weaker in muscle strength. When the authors presented the requïred
moments as a percent of the iadividuais' avdable strength, the elderiy required 97 % of
their avaiIabIe isometric strength at the Iowest chair height while the young required oniy
39 % w b rising fiom a chair height of0.33 m.
In an attempt to gain a betta understanding of the role of muscle men@ in
relation to physicaf @ormance, Brown, Sinacore and Kost (1995) regesseci values of
hip extension, ha extension and p l m m flexion bah separateIy and in combination with
the amoimt of tirne recpked to complete m*ous activities. Strength data were obtained
using a band-heId dynamometa. An isokinetic dynamometer was aiso used to oobtain an
isometrk measure of hee extension strength. The knee was pl& at an angle of 45".
Specinc rewihs were obtained rising fiam a chan of varÏous heighss. When the streagth
d u e s wae regcessed separateIy, non-si@catt reIationships wae o k e d for aü three
different cboir heights (0.457-, 0.406- and 0.356 rn chairs). Hbwever* when the strength
dues for aü three joints were added and normaiized to body weight, a significant
association between sirength and rising fiom a 0.356 m chair was observed. Brown and
associates concludeci that even though the minimum amount of strength required to
complete a specifk task remains unclear, the need to maintain and improve strength in
key muscle groups is a necessity.
Many studies have used maximum isornetric strength as a masure of strength
availability and related these dues to the joint torqw reqtrirements to mmplete the sit-
to-stand task. How comparable these measurements of physicai performance are in
relation to the hctiond tasks remains questionable. Firstly, this method requires
selecting appropriate joint angles and angular velocities at which to rneasure strength
isometridy or isokiIieticaily in order to compare these values to required moments of
the task Hence the d e r i a used to select at what angle maximum voluntary strength is
measured is important. SecondIy, one is attempting to compare the mengui rwements
of a rnuiti-joim task to singie+joint strength data.
As an alternative to using individuai measmes of maximum isometric strength at
specinc joints, EarIes and associates (L997) used a Keiser leg press to obtah uniiateral
strength measurements in a sarnple of230 oider persans. The focus of this study was to
determine whaher strength or powa is a bmer predictor of fûnctional ability. Streiigth
was defineci as force times distance (work) whiIe powa was work over tirne. These
measurements were relateci to timed scores of various mks Uicluding the tirne to rise
fkom a chair fie times. The authors found that power is mon indicative of hctionai
ability within an elderly population. Although the authors did not specify the height of
the chair in their abstract, it be wodd usefbi to determine whether or not the same
concIusions wodd be d r a . ifdecreasing chair height increased chair-ris@ diflicuity.
Strength training for the elderly.
Several studies have shown the benefïts eiderly subjects receive following a
training program. In 1990, Fiatarone and colleagues examined the effect of a high
intensity training program on ii~nctiooal mobility in a group of institutionaiired, fiail
elderIy individuais. The authors tested bnctiooal mobility by determining the amount of
t h e needed to rise fiom a 0.43 rn high c k . Walkîng velocity was also determined for a
6x11 walk. The training protoc01 involved concentric and eccentric contractions over an
eight-week penod. Specifically, the elderly subjects were required to Iift an appropriate
Ioad fiom 90 "of knee flexion to &II extension and then lower theu Ieg. Significant gains
in knee extensor strength and fiinctiond mobiIity were seen at the end of the study. For
example, one of the three subjects who was unable to successfiilly rise €tom the chair
without using their arms was able to do so after the training. Similarly, Fiatarone and
colleagues (1994) noticed considerable improvements in lower extremity strength,
wallcing velocity and stair clunbing power a f k their elderly subjects (mean age 87.1
years) participateci in a ten-week strength training program. Hip extensors were either
trained on a cable - pdey system or on a double leg press. Both studies highiight the
benefits of using a dynamic form of strength testing.
Summary of the review of literature
The present review of hierature has identified three important areas of research
FÏÏstly, few sit-testand -dies have examined the role of chair height on al1 three joints
of the Iower Iimb among an elderly popuhtioe Revious studies have either focused on
the kinematics or have ody assessed the kinetics at one joint (Hughes, Myers et ai., 1996;
Schenkman et a1.,1996). Exaaiinr'ng the individual joim-moment patterns at the adde,
knee and hip provide valuable information as to how one joint can compensate for the
Iack of support at another joint and di enable the person to compfete the task (Wimter,
1991). In addition, no &-testand study has examined the Iower IÏrnb synergy using a
measure ofcovananCe. SecondlyT the influence ofchan height on the joint energetics has
not been examined among an elderfy population ThirdIy, few sit-to-stand studies have
compared a hctional measure of strength to the successfif completion of the chair rise.
In summary, with these issues highlighted, the present study was deveIoped to assess the
influence of chair height on the joint kinetics and energetics of the lower Iimb in rising
fîom a chair among an older popdation.
Methodology
This chapter provides a detailed description of the methods and procedures used
to cofiect the data for this research project. Specincally, the research design, abject
recruitment, testing protocoi, instrumentation, data reduction and d y s i s are described
ia detail.
Resurch design
The design of the present study was quasi experimentai since there was no control
group nor was randomization to a group possibk. The purpose of a quasi experhental
design is to M the design to senings more like the real world while d l controiiing for as
many of the threats to interna1 vaiidity as possible (Thomas & Nelson, 1990).
The necessary s a f i precautiom were taken by the researcher to protect the rights
and w e k e of ail subjects participating in the snidy. NameIy, the right to privacy, the
right to rmiain anonymous, the right to confidentlCality, the right to withdraw and the right
to expect experimenter respom'bility were ensureci (Thomas & Nelson, 1990). The
equipment used to coiiect the data met aU standards for s a f i and therefore the nsks
were considered srnail. In any case, the e1derIy subjects were instntcted to inform the
researcher immediately ifat any tune they feit discornfort. The subjecîs wae informed
oftheir rights and d e n consent was obtained fkom aii subjects @or to data collection.
The study received ethicai approvai fiom the Research Ethics Committee of the QEII
HeaIth Science Centre.
AU subjects performed a sit-to-stand transfer nom varying chair heights unda
standardized conditions. Since the eldaly subjects smed as th& own coatrols, any
noticeable change in the seIected parameters provideû the bssis for drawing coac1usions
about tée imposed tr-ent (Jbsent6aI & Rosnow, 1991). In eqmhentai research, any
variation in the dependent MnabIe is thought to be due to the independent variabfe. In
tsrms ofcause and &ecf the independent varïabIe is the presumed catise and the
dependent is the presumed effîect (Singleton, Straits & Straits, 1993). The dependent
variabIes in the present shidy were the se1ected joint kinetic and energetic parameters
(moments of force, joint mechanical power and work done) wMe the independent
variable was chair height.
Eleven heaithy elderly subjects (10 fernaie and 1 male) wae chosen to participate
in the study. Subjects were recniited by two primary means. They were either part of a
larger study that examined the Timed TJp and Go' test (Rea4 1998) or from various
retirement homes located within the Halifax community. Ai1 subjects were Living
independently in the communifl and fke 50m any known oithopaedic, nez~~ornuscular or
cardiovascuiar diseases. The inclusion dais reqùred al i subjects to complete the
Timed Wp and GO' test which is a h c t i o d mobility test that requins the person to rise
nom a standard arm chair, waik three meters, hrm. wak back and sit down (PodsiadIo &
Richardma, 199 1).
This study reqired the abjects to participate in two separate data collection
conditions. The subjects participateci in a series of sit-to-stand trials and on another
occasion a series of Iower extremity strength meames were collecteci.
The sit-to-stand trials were conducted in the CliaicaI Locomotor Ftmction
Laboratory located in the Nova Scotia Rebabilitation Centre. The weight, heigbt md
d e r selected anthropometric dimensions for each abject were recordeâ prior to the sit-
to-stand transfers. f i e e height was defined as the verticai distance nom the floor to the
tibiai plateau. Since the subjects were mstnicted to wear th& seKseIlected, ffat shas
dUnag the rise, ai i measurements were taken with their shoes oa.
The elderly subjects rose in a random order, nom three different chair heights.
Subjects were grouped by stature with Group I being greater than 1.63111 (n=4) and Group
II being less than I.63m (~7). The puping was chosen based upon a physical
constraint in the chair adjustrnent system. Subjects in Group 1 rose nom 0.400m, 0.435m
aad 0.470m whiie subjects in Group II rose fkom 0.380m, 0.415m and 0.450m By
accounting for ciifferences in body height, the imposeci level of chair rising dïEcuity was
comparable for aM subjects. These heights wae chosen since they approxïmated a
variety of chair heights individuals routinely encounter rit home and in the community
(Alexander, Koester & Gninawalt, 1996). Table 1 presents the fmpency distribueion of the
irmdnxnized order of chair heights for each mdition.
Table 1. Rindoaaod ocder o f chair height settings caair height
Low Middie w 3 h
Condition 1 2 5 4
Condition 2 4 2 S
Condition 3 5 4 2
The elderly subjects p d o d the sit-to-stand transfers with their feet positioned
on a force platform while being videotaped. A standard starting position was used to
reduce triai-to-triai variability- For aii aiais, this position reqybed the subjects to have
their back in contact with the baciuest, arms folded across thek chest, and thek féet in the
subjects prefierred position A aahnaI foot position was selected and maintained for aii
trials within each chair height. Foat position was staudardized within a partCcuiar height
by outlining euh foot on a clear sheet of papa which was piaced on the force phtform,
Bilaterai symmetry ofthe motion was assumeci and qyked thst the hed ofeach fwt be
placed the same distance fiom the edge ofthe force platform Since Baer and Ashbum
(1995) speculated that prescrii timing mi@ aher the sit-testand transfer, the dderiy
subjects rose at P seKseiected speed.
To accommodate the subjects' preferred foot position in the thtee chair height
conditions; the set up required the middIe fiont Ieg of the chair to be placed on the force
platform whiie the other Iegs ofthe chair remaineci adjacent to the platform. To eliminate
the chair's minimal contribution to the applied forces; the force platfom, with the midds
nont kg of the chair on it, was zen, bdmced prior to data collection
Subjects practiced the sit-to-stand ta& at each height until they felt cornfortable
with the transfer. Five trials were coliected at each chair height with rest paiods
provided as needed. A trial was coasidered unsuccessful when any one of the foilowing
situations occmed: (1) the subjects were unable to lift the buttocks off the seat, (2) were
unable to rise without uafoldiug their anns or Iastiy, (3) the subjects rose however fell
back and never completely reached a standiag posture (Hughes et al., 1996).
Strength testing was pedionned in the Ceutre for Work and Heahh, Daihousie
UniverSay. ûnce the eldetly subject had becorne Miiaxized with the exercise machine
(Shuttie 2000) and had completed the w m up exercises, a one-repetition maximum was
determineci. With both fat placed on the footplate, the subjects were asked to sIowIy
push against the plate untü their Iowa Iunb was completely extended. The resistance
was increased in an incrementai faohion until the one-cepetition maximum (1-RM) was
reached. The 1-RM was dehed as the maMmum amount of tension (nimber of resistive
bands) the individuai couid succesdUy extend on the SSuttle 2000. A successfirl triai
recpired the Iower limb to be compIete1y extended. A second trial was permitteci if the
&st attempt was r m s u c c e s ~ . A goniorneter was used to meamne the inchdeci hip, knee
and ankie mgles for each subject prior to each aial. Since both their legs were used, a
b i l a t d strmgth measurement was obtaïned Rest periods were provided as needed.
A f k the 1-RM was determined, cooI down exercises foiiowed. GuÎdeIines h m the
Elderfit booklet (Makrïdes & Campagna, 1992) were foIIowed for the warm up and cool
d o m exercises-
Both the number ofresistive bands and distance traveied by the sliduig seat were
recorded The device was caliirated to allow for the caldation of the actual force
produced and work done for a successfiil triai.
Table 2 presents a summary of the anthropometric and descriptive data for each
subject. Prior to the sit-to-stand triais, subjects body weight and height were measured
using a standard medicai scaie (Mectu Scaies Inc.). A measuring tape was used to
masure the individuais body segment Iengths and the knee height (I<H). An
aatbropornetn*~ data sheet with the individuai body segments defineci is presented in
Appendk A. APthropometric tables (Winta, 1990) wae used to locate each segment's
center of m s and moments ofinertia
Table 2. Aathropometric data and descriptive data for subjects
Go' (s) A 82 79.5 1.67 I 0.456 13.2 B 78 60.4 1.62 C 81 702 1.58 D f7 72.0 1.58 F 85 83.4 1.70 G 82 58.2 1.69 H 74 63.1 1.63 I 81 672 1.67 J 72 50.7 1-52 K 78 57.7 1.53 W 78 70.0 1.62
Mëan 78.9 66-6 1-62
Kincmatic data.
To coflect the khematic data, a sagittal plane view of the rïght side ofthe subjects
was recorded (HïtachÏ V M 2400A) as they completed the sit-to-stand transfer. The actuaI
vide0 samplhg rate was 30 -es per second which when digitized represented an
effective samphg rate of 60 -es per second.
To assist in the videotape analysiq reflective markers were Iocated on the right
side of the body over the followuig bony Iandmarks: nfth metatard, tuberosity of
caicaneous, lateral maileolus offibula, laterai side of the knee joint between the popiiteai
fold and the patella, greater trochanter of &mur, and the greater tuberde of the humerus.
These markers were used as a guide during the digitkation process for definhg the end
of the various segments in the h k segment modeI.
Force platform.
A Kistier force platforni (Type 9807 B) was used to ooiiect the kinetic data duririg
the sit-to-stand transfkr. The p u n d reaction forces and center of pressure vaiues were
measured and IVD converted using an IBM compatible cornputer at a sampIing rate of
300 H z Appendix B outiines the procedures taken to ver@ the refererœ coordinate
system of the force pl&om
hboratocy chair.
CHAIRS Ltd. specindy desigeed the height adjustable chair for this study. The
range in v d d chair height was 0.38m and 0.57m fiom the floor. The chair had a firm
back and seat pan surfàce with no seat dope. Both the seat pan height of the chair and
the width between armrests were ad.stabIe. htring testing the ri@ a r m a was
removed however, as O s a f i precaution, the Ieft armrest was not removed during the sit-
to-stand transfiers-
A simple eIeCtricai device was developed to assist in the determination of various
temporai events during the sit-to-stand ta&. Elecaicaiiy conductive tape was placed on
the chair at the point of contact between the chair and the posterior side of the right thigh
and right scapula representing the contact of the back and ihigh, respecfiveIy. Another
piece of tape was atîached to the subjects such that when they were seated, they wexe in
contact with the tape on the chair. This produced a closed circuit that activateci srna11
LED's which were positioned in the field of view of the vide0 m e e As the subjects
rose they in tum, opened the c i r d and the Iight wodd go off This aIIowed for the
synchronization ofthe temporal events with the vide0 (Figure 1).
Tïm (s)
4 Thig h off 1 Back off
Figure 1. D i a m demonstrrting the change in voltage output rvitli the ocrumace of bacleoff and thighoff.
The height of the ch& was measured nom the anterior, top edge of îhe seat to the
floor. When weighted the chair aIlowed for a 1 cm compression. This was accounted for
in the original chair height seaings. As previously mentioned, subjects were grouped by
stature witb Group 1 behg > 1.63 m and Group II king < 1-63 m. Table 3 presents chair
height as a percentage of knee heighî for each subject. A two-szunpIe t-test asmdng
uneque[ mCance7 reveaied no sipifiant differenœs betweea the groups within either
condition (Iow, middie or bigh).
I 1 I I
E 2
% 1
4 6 8 10 -1 f
O 1
Table 3. Chair height as a pacentage of knee height
SuZlject Ht (m) Group KK(m) Chair heigbt / KH (%) Low MÏdcüe High
Strength was expressed in terms of the amount of work required to perform a
simple 1% extension on the Shuttie 2000. The Shuttie 2000 is an exercise device
designed for rehabilitative purposes. The amoust of resistance was easiiy adjusted and
inaeased in s m d increments over a wide range. Therefore it was considered a suitable
exercise device for the eiderly.
To calculate the mechanical work to pafonn the Ieg extension, the exercise
apparatus was caiibrated using a force transducer. The transducer was a#ached to the
sliding seat of the exercise machine. The voltage output to p d i one resistive band
throughout its range, then two, three and so on was recordeâ and then converteci into
Newtons using a measured caliintioa equatioa A complete description of the method
useâ is found in Appendix C. The data coIIected dururg the caliiration procedure was
later used in a regression d y s i s to dmlop an eqpation capable of predicting the
amom of force reqyked to paform the Ieg extension exercise. A second calibration of
the exercise machine was conducteci at the end of the mdy (E<iucition 1).
Force (N) = 50 ( # resistive bands) - I42.IS
The equation developed was based upon the assumptiou that the inertX Io&
were negiigiile during the leg extension and couM therefore be negiected d u - g the
testing. To ver@ this assumption a rmi*axiaf accelerometer was mounted on the siiding
apparatus of the Shuttie 2000 as one subject perfomed a &es of Ieg extensions at
Merent speeds. Appeiidar D provides a detailed description of the procedures taken to
coliect this information.
The work calcuiations were based on the predicted force obtaiaed âom Equation
1 and the distance between the start and final position of the sliding seat (see Equation 2).
Work(J)=1/2(FI+F,,) * (DI -Do) (2)
where:
F, = predicted force at Do for a @en number of resistive bands (N).
Do = Start position of the siidhg seat (m).
Fi = predicted force at Di for a &en number of resistive bands (N).
Dl = Fihi position ofthe siiding seat (m).
F, accounted for the immediate rise in force the moment the siiding sept began to
move and thaefore represented the krce required to initiate the movement. Do was
dehed as the initial starting position of the siiding seat whaeby Fe was measurable
(Figure C3 m Appendix C). In the present shidy, distance was not a signiscant factor in
Equation 1 and therefore the magnitude of F,, and FI were identical (Appendix C).
Data ttduction
Baseâ on the recommendations fiom Yang and W d s (1983) study on EMG
reiisbiiity* a minimum oftbra tMIs were anaiyzed per subject within each chsir height
condition to improve the reliabiiity ofthe kinematic and kinetic rneasmements.
Kinematic data.
For each triai, the extension phase ofthe sit-to-stand transfer was digitùed using
the Peak Performance Technologies System Q (Version 5.0). The artension phase began at
thigh-oc as d e t d e d by the electricd circuit, and ended when the subjects had
reached a standing posture. The end of movement or standing poshxe was definecl as the
point when the shodder marker had reached a maximum vertical displacement. This.
point was opaationdly defined as the nfth consecutive M e whaeby the shodder
height stabillled. A minimum often -es were digitized prior to thigh-off and past this
visuaiiy determineci point to elirninate end-point problems. The end of movement was
then detennined at a later point. A stationary point was digïtkd to assess the precision
in identifyiag the end of movement. The standard m r tuas withlli f 0.2 cm.
BIOMECH @, a motion d y s i s software package, was used to paform aii
biomechanical anaiysis post digitidon. This incIuded all filtering of the raw digitized
data, g e n d o n ofthe linear and angular kinematic data and the kïnetic data r-ed for
the analysis.
To reduce the noise present in the signal, the raw digitized data were smoothed
using a tao-lag, fod-oideq Iow-pas Butterworth di@ fiIter. The optimal cut-off
fieqyency for each rnarker was determineci using the Noise subprogram withui
BIOMECH @. Appmda E lisor the suggested ait off fieqiencies fm aii triais anaiyzed.
Odonaiiy, the Peak software system experienced difflcuity grabbhg a particuiar
fiame within a triai. This tended to produce a bias in the y position coordinates for the
particuiar fiame. The nattne of the sit-to-stand d e r supportecl the mggesteci low ait
off fieqpencies for these triais and thus minimai signal distoriion was expected since the
fie~uency content of the movement was Iow.
&netic data.
A kinetic analysis was performed on the sit-to-stand t r d e r using BIOMECH @.
A luik segment model cousisting of four segments (foot, sha& thigh aml tnink) was used
in combination with the anthropometric data (Winter, 1990) and kinematic data to
caldate the joint-moments of force at the anlde, Laee and hip using a dynamr0c inverse
solution, The sit-to-stand motion was modeIed as a symmetricai movement and therefore
the masses for the foot, shank and thigh were cioubled for the dys is . Consequentiy all
kînetic and energetic values are presented as the s u . of the two sides. For comparîson to
other related fiterature, it was sometimes necessary to divide these values by two to
detennine the values for one limb.
Covafianct memiires betwee~ joint-momenb offorcc
A covariance measure was used to investigate iftrade-offs in the joint-moments
o f force occurreâ duiing the sit-to-stand task between adjacent joints as has ken s h o w
to occur in walking. Specincaiiy, a wmiance measure was used to assess the trade-offs
between the hip and knee and between the knee and ankie moments. E q d o n (3)
estimateci the amount of ~ 0 ~ 8 1 1 ~ bawan the joint-moments o f force ( W i i , 1995).
The units are in (Nm/kg)2.
da = a'~+ 2~ - drvr (3)
where: dE and dr are the variances of the mean moments at the hip and knee ova the
extension phase.
&is the variance ofthe sum of the mean hip aiid kna moment patterns.
da is the covariCmce baweai the hip and knee moment patterns.
A positive covariance meeslne occurs ifthe d IHr term is Iow. In this case, the
mean moments of force at the hip and knee were apaiencing magaitude changes of
oppogte polonty. Thaefore, if the hip extensor moment increased the hee extaisor
moment c o a ~ e ~ u d y decreased In contrast, anegathe covariance measme occurs ifthe
d t m is hi& ril this caseF the mean moments of force at the hip and knee were
experiencing magnitude changes in the same polarity (Whter, 1989). AccordnigIy, ifthe
hip extensor moment increased, an increase in knee extensor moment aiso occurred.
The covariance m w e , 2, was expressed as a percentage of the maximum
possible covariance (% COV) ushg Equation (4). When the d term is equal to zero,
the covariance term ( c ? ~ ) wii i quai the sum of the variances of the mean moments at
the hip and knee and consequently the COV wiii quai I0W. This is an example of tight
coupihg between the moments of these adjacent joints. In contrast, when the covariance
temn (A) is equal to zero, the individuai joint-moment pattems at the hip and knee are
acting independemly of each other and therefore the % COV is zero (Winter, 1989). A
meastue of covariance between the knee and ankle was obtained using the same
equations.
Joint power and totai imouut of work doue.
The power-tirne curve was generated by multiplying the instmtaneous net muscle
momem Mat joint (j ) by the joint ariguiar velocity o as shown in Equation 5. The
joint anguiar velocities wae obtained by subtractmg the anguiar velocities of the adjacent
segments (Wmer, 1978) and were grnerateci in BIOMECH Q Power generation ocairs
when the joint anguiar velocity is ofthe same polarity as the net muscle moment. Power
absorption occurs when the joint mgular veiocity is of the oppsite polarÏty to the muscie
moment. The Force program within BIOMECH @ dcuiated the totai work done at each
joint for the exteon phase as the int@ of die power-the airve.
P , # = y ( ! , *q(Watts) (5)
To aiiow for comparisons among subjects and across conditions, the kinetic and
energetic variabIes were normalized in amplitude with respect to body mass and in t h e
as a percentage ofthe exîension phase. A Visual Basic Macro, created in Excel (version
%O), the notmalized the data to 1 % intends using an interpolation technique. For
descriptive purposes, the mean ensemble average of the joint-moments and power
pattern for the 11 nibjects were plotted with k 1 standard deviation for each condition.
The coefficient ofvancation (CV) was cdcdated using Equafion 6 w~~ter, 1991):
C V = Z ~ ~ / ~ I xil '100 % (6)
Whee X i is the mean value of the variable at the i th interval
a i is the standard deviaîion of the variable X about X i.
Data andyis
For each chair height, a minimum of thne Ends were analyzed per subject. Out
of nixiety-tbree triais, twelve wae excluded f?om the d y s i s since the joint-moment
patterns for these triais were not reprewmtive ofa normal pattem. A normal pattern was
considered to occur when both the hip and icnee experienced extensor moments at thigh-
off which graduaîiy decreased as the transfi prognssed while the ankle experienced a
plantadexor moment throughout the majority of the extension p h . Of the twelve
trials ornitteci, bug ocnmcd cmdcr the îow EhpP height condition while there were five omined
h m the niiddk and hi@ chair hâgk COllçlitians. U p chsa exambution of the video data and
center of pressure plots, an asymmetricai rise may have ocwred durhg these triais. Two
cornmon observations inciuded a shdhg of the fea backwards and or a roüing to one
side. Accordhg to &@es et ai. (1994). shufning of the feet is characteristic of
individuals using the stabiikation strategy- A is an aaempt to move the base of support
closer to the body's center of mass and co~l~equentiy shorten the dtimïon of the
tmstabïkhg event between siaipg and standing+ This adjustment however, may have
imroduad an agymmetry by m Ionga ha* the he& of each fbot @y aiîgned fiom
the edge ofthe force plate. This wodd have Muenceci the Iocation of the center of
pmsures and co~lse~uently an asymmetry between the kinetk and bernatic data wouId
have o c c ~ e d .
Withh subject nlirbility.
Pnor to any statistid aoalysis, a preliminary test for normaIÏty ushg a modified
Shapiro-W'is test and a normal probability plot on aU of the dependent measures was
performed. No apparent deviations nom normality were found. Given the assumption
the data had a nomial distribution, the within subject reliability on the dependent
variables was assesseci using an ANOVA (GeneraI Linear Model) with the independent
measures of subject, chair height and trials nested within subjects. The intra-class
conelation coenicients @CC) values were dcuiated using the mean square error
associateci with subjezt and triais nested within subjects (Eqyation 7). Detailed tables
presenting the resuits of the ANOVA for each variable are providecf in Appendix F.
Dependent mtirures.
Having established high withui subject reliability on the seIecîed dependent
variables, the mean score values for these rneamres were then anaiyzed using an
ANOVA mode1 with the independent meaSUTes of group, condition withùi grog and
subjects withui groups. In the ANOVA modeI, subjects were specfied as a random
factor and the IeveI of si@cance was set to 0.05. The stati*sticai output for each
dependent meastue is presented in Appendix F. In cases where there wae si@cmt
main effects due to conditions nested within group, a Bonfioni post-hoc test was used
to isoIate the sipifiant dinaences. Since the c o m ~ * s o n s acrosg gpups was n a
reIevant to the present study, the p-dues for the pst-hoc test were manuaiiy caicuiated
for six pairWise comparis0~.
Mer the GLM was performed the standardueci residuais obtsiined nom the mode1
for the selected dependent measures were used to fiutha test for normality. Specincally,
a normal probabiIity plot was constructeci and the results fbm a Ryan-Joiner test of
aormality were evaluated.
Joint mechanicil power and totai amount of woric done.
The joint energetic d y s i s for each subject involved a qualitative description of
the power-time m e for al l joints. Specifically the number of sigdicant periods of
power generation and absorption was determineci. Concenttic contractions generate
power and perform positive work while eccentnc contrstctions absorb power and perform
negative work To determine the totai amount of work done at each joint both the
positive work and negative work were considered.
The purpose of this study was to quantify the joint betics and energetics of the
Iower Iimb dinmg the sit-testand transfer for various chair height conditions arnong an
eldery population. The variables analyzed included the moments of force at the hip,
lmee and ankle at the instant of thigh-off, the peak moments of force at the tliree joints
and the total amount of work done to complete the trarisfer at the three joints. For ease of
cornparison, all kinetk and energetic variables were normalized to body mass and
represent the sum of the right and left sides. In addition, a covariance measure was used
to assess lower limb synergy. As a second purpose, the relaîionship between the
minimum chair height from which an older person was able to successfuliy nse was
compared to their performance on the Shuttie 2000. This chapter describes the resuits
obtained fkom the study.
Subjects descriptive data
The eiderly population consistai of 10 fernales and 1 male with a mean (k ISD)
age of 78 -9 (3.8) years, a mean mass of 66.6 (9.8) Kg and a mean height of 1 -62 (0.06) m
The Timed 'Up and Gu' scores ranged 6om 9.7 to 25.3 seconds with a rnean score of
13.0 (5.1) seconds. This performance test is usefiil for assessing physicai mobiiïty among
the elderly (PodsiadIo & Richardson, 1991). Of the eIeven elderly subjects who
participateci in the present study7 nine scored Iess than 20 seconds. Based on Podsiadlo
and Richardson's findhgs, the Ievel of physicai mobüity for this popuiation was
cwsidered to be hia.
Within subject rrüibiiity
Based on the resuhs obtabeâ nom the m M e d Shapuo-WilLs test for normafity7
the data was assumeci to be normaily distriiuted. As previousIy mentione4 the withùl
subject reliability on alI of the dependent memures wa9 assesseâ uskg an ANOVA
(Gaierd Linear Moder) with the independent measmes ofsubject, chair height and triaIs
nested within subjects. As expected there were SigrifIcant main effects due to subjects
and chair height, the triais withui subjects effect was non-signincant for di of the
selected parameters.
The insa-class correlation coefficients (ICC) for the dependent variables are
presented in Table 4. High ICC vaiues for the jo~mornents of force at thighsff were
found and ranged between 0.95 and 0.99. Similariy the ICC values for the magnitude of
the peak moments of force and mean moments were high and mged between 0.87 and
0.96 and between 0.9 1 and 0.98, respectively. A high level of consistency was aiso
observeci for the amount of work doue at d three joints (0.83 to 0.93). These figures
indicate that the elderiy subjects were consistent withh each chair height condition for
these selected parameters and support the decision to use the within subject mean score
vaiues in al1 M e r statistid anaiysis.
Table 4. Intra ciass correIation cafncient vaiues for the dependent measures
Parameter R, Ankie moment atthigh-off 0.99 hee moment otthigh-off 0.96 Hip momemt atthigh-off 0.95 Peak ankle moment Peak knee moment Peak hip moment Mean anlcie moment Mean kiee moment Mean hip moment Mcm hipimee moment Mean knee-aukie moment work @ lnWa Work @ knee Work @ hip Time to peok ankle moment T h e to p d c knee moment T i t o peak hip moment
The LCC vaiues for the thne to peak moment offorce for the three joints displayed
grmer varkbüifl m&g fiorn O Iow tu modaate levd (0.54 to 0.79). In contrast, the
the to cornplete the extemion phase was highIy reüable with an ICC d u e of0.96.
To confirm the assurnption of normality on each of the dependent masures, a
Ryan-loiner test using the standardized residuals obtained nom the ANOVA mode1 were
used. Spdcally, a normal probability plot was constructeci and the correlation between
the standard residuals and probabiiity score was evaluated. When the observed
conelation wefncients were high and the p-values were greater than the d c a I value
(cc;. O.OS), the assumption of normality was accepteci. For aU dependent measures this
assumption was accepteci. WWith ody one exception, the correlation coefficients and
observed p d u e s were high (R > 0.97, p > 0.1). However, the mean knee moment
experienced a lowa correlation coefficient and p value as a resuit of one obsmation at
the high chair height (R = O.%, p = 0.05). When the no- test was perfonned
without this observation, the values improved signincantiy (R = 0.99, p > 0.1). Since this
observation conformeci to the generai trend of decreasing mean knee moments as chair
height inmeased, it was not considerd as an outlier and was Ieît in the data for M e r
anaiysis and no transformation of the deta was perfiomed.
Figure 2 is an example of a n o d probabiiity plot for the amount ofwork done
at the hip. AU of the normal probability pIots are presented in Appendix G. In summary,
these hdings provide mong evidence of a normal distriiution for aii of the parameters
and thus support the assumptions undedying the stotisticai process used in this study.
Figure 2. Nomai probability plot for the amount of worlr dont at the hip.
Individual dependent measuns
The redts âom the ANOVAs are presented in Appendk F. The Ievei of chair
rising difiiculty at each condition was comparable for both groups since no significant
differences were found between groups for aay of the dependent variabks. There were
signifiaint main effects due to conditions nested within groups and subjects nested within
groups for several dependent variables. For each dependent variable, oniy the resuhs
obtaiwd fiom the pairwise cornparisons withÏn groups were examined. Cornparhg
conditions across groups was not pedormed.
Muscie moments at thigi ta
Table 5 presents the means and standard deviations of the normalized mean
moments of force grnerateci at the hip, knee and d û e a thigh-off (TU). For both
groups, the moments offorce generated &the hip @dh m) wkchranged fiom 1-91 to 2.47
Nm/K& were consistdy higher then the moments generated kt the knee (Mk anü at
the ankle (Ma to) across an three conditions. The Mk to mged fiom 027 to 0.96 NmlKg
while the Ma ro ranged fkom 0.03 to O. 18 Nm/Kg at TO.
Table 5. Means and standard deviations for the normalued moments (Nm/Kg) at thigh- off for Groups I & II
Parameter Group I (n4) Gmup IE (n=7)
Condition 1 2 3 I 2 3
Chair ht 0.400 m 0.435 rn 0.470 m 0.380 m 0.415 rn 0.450 m
Mh t, l.91(.53)a 2.29(.38)' 2.03(.28) 2.23(.28) 2.47(.20) 2.47(.19)
Mk to 0.96 (SI) 0.69 (.40) 0.58 (.38) 0.69 (.311b 0.37 (.161b 0.27 (.151b
Ma t, 0.10 (.OS) 0.17 (4) 0.10 (-32) 0.18 (-35) 0.17 (29) 0.03 (.21)
Grnip i, Condition 1 significmtly diaennt compped to Coidition 2 (p < 0.09. Gmup 4 Conditid si@cantiy d i n i t compnrrd to Conditions 2 ami 3 ( p c 0.05)
There were no significant differences between the groups for the moments of
force at the hip, knee or ankle at thigh-off (FhP = 3.01, p > 0.05; Fbe 1.16 = 3.79,
p > 0.05 and F d e 1.16 = 0.03, p > 0.05). For the hip moment at thigh-oe there was a
signincant main effect due to oonditions nested within group (F *JS = 5.3 1, p < 0.05).
The post-hoc test meaied that chair height had a signincant e f f i in Group I on the hip
moment at thigh-off, SpecScaily the Mh , for Condition 1 was Iowa than Condition 2
(t obi = -3 -098, df= 16, p < 0.05). NO significant cliffierences were seen in Group IL
For the knee moment at thigh-off, a @nificm main effect due to conditions
nested withïn groups was dso obsemd (F 4.16 = 6.03. p < 0.05). The results o f the post-
hoc test revealed that chair height had a siBnificant &ect on the knee moment at thigh-
off within Group IL SpecifIcally the knee moment at thigh-off for Condifion I was
higher than the knee moments at thigh-off for Conditions 2 and 3 (t = -3.523, df 16,
p < 0.05; t = -3.872, âf 16, p < 0.05, respectiVeLy). A simiTar trend wss observeci in
Group 1 ahhougb statistically not Signifïcaut*
For the mean ankle moment at thigh-oe there was no signifiant differences for
conditions nested within group (F +IS = 1.63, p > 0.05).
Peak normaiized joint-moments.
Table 6 presents tée means and standard deviations of the nofmalized peak
moments of force at each joint For both groups, the absolute values for the peak
moments of force at the hîp which mged iiom 1.93 to 2.49 NmlKg were
consistentfy higher than the peak knee (h&&) and peak ankle we*) moments of force
across the three conditions. taaged fiom 0.85 to 1.26 Nm/Kg while % c ~ r rangeci
from 0.57 to 0.69 NmKg.
Table 6. Means and standard devim*ons ofthe peak n o d i z e â moment of forces ~ ~ g ) for Groups 1 & II
Parameter Group 1 (n= 4) Group II (n = 7)
Condition 1 2 3 1 2 3
Ch& ht 0.400 m 0.435 m 0.470 m 0.380 m 0.415 m 0.450 m
Group II, Condition1 sipüicantiy different nom Condition 3 @ c 0.05)
There wae no sipnincant merences between groups for the peak moments of
force at the hip, knee or adde (F bi, 156 = 2.69, p > 0.05; F i, 1 3 5 = 3.10, p > 0.05 and
F us = 0.67, p >O.OS). AWough there was a main effect due to conditions nested
within group (F LIS = 526, p c 0.05) for the peak moment at the hips, the post-hoc tests
revealed that chair height had no &ect on the Mh ,* withlli either group across
c0nditio11s1
For the peak knee moment, signincant différences due to conditions nested
group were found (F +rs =3.41, p < 0.05). The resuIts of the post-hoc test reveded that
chair height had a signiscant effect in Group IL SpecEdy, the peak knee moment for
Condition 1 was signincantly higher thaa Condition 3 (t = -3.289, df 16, p < 0.05). A
similar trend was observeci in Group 1 akhough not statisticdy different
For the pegk moment at the d e , there were no significant differences for
conditions nested within group (F +16 = 1.00, p > 0.05).
Variance and Covariance measum
Prior to presenthg the resuIts obtained on the variance arid covariance measures
between the joint moments, a description ofthe joint-moment tirne patterns is provided.
Figure 3 illustrates the ensemble-averaged moment patterns at the hip, h e e and ankie for
the three chair height conditions aaosr, the subjects. The joint moments of force were
analyzed fiom the instant ofthigh-off untiî the subject had reached a standing posture.
Similar hip, knee and d e moment patterns were seen across di conditions. While the
hip and knee exhibited extensor moments which pduaiiy decreased as the sit-to-stand
movement was completed, the ankle experienced a plantarfiexor moment for the majority
of the extension phase. Occasionaily the anlde experienced a s m d doraexor rnoment
at thigh-oE Appeadix H presents the joint moment offorce patterns by group for each
condition,
In terms of the variabiIity in the individuai joint-moment patterns* a distinct aend
was obsaved across chair height conditions (Figure 3). The coetFcient ofvariation (CV)
generally inoreased as chair height increased flabIe 7). Bath the hip and lmee moment
patterns exhibited moderate vatiability with d u e s mghg nom 47 % to 72 %. Hïgher
variability was seen at the anLle and in particuiar at the highest chair height (55 % to
25 1%).
Table 7. CV values for the hip, lmee and ankle across dEerent chair heights when groups were combuied
Chair height Low MÏddIe High
Hip moment 52% 49% 72%
Knee moment 47% 48% 67%
ArikIe moment 55% 80% 251%
Since the coeEcient of variation does not provide information about possible
interaction between adjacent joints, a covariance measure was used to detemiine if the
variabiiity in the mean moment of one joint was correlateci to the variability in the mean
moment of the adjacent joint (W~iter, 1984). SpecXcdIy a meana measure was
detemüned between the mean hip and knee moments as weU as between the mean knee
and ankle moments.
Using this covariance measure the mean of hip and knee moments are considered
to be exhibiting synergy among one another when low variab- is observed in the
summation ofthe hip and lmee moment term whiie stilI observing high variability in the
individual joint-moment patrems. A positive covariance measure wifi occur as a result of
magnitude changes in opposite polarity in the hip and knee moment patterns. For
example, one vaiue increases while the other one decreases. Low measures of covariance
are interpreted to mean that the moment pmfiIes at the two adjacent joints are actiug
independently (randomly) of each other. Negative masures occur when magnitude
changes occw of the same polanty in the individual joint-moment patterns (Wikter,
1989). In other words, both moments of force simultaneously increase or decrease.
Covariance masures for each group and condition.
Table 8 presents the covariance measures for the mean joint moments offorce by
group and chair height condition. Each group exbibited a moderate Ievel of covariauce
between the mean hip and knee moment (% COVrm) a Condition 1 (iow chair height).
Specincally, the % COVm was 59 % for b u p 1 and for 40 % Group II. For the
combined groups, the covariance mearnrre was aIso moderate, with a vaiue of 53.6 %.
The covarhce measure between the man hee and ankle moment (% COVKA) was
generaily low and much more *able within each group at the Iow chair height.
Specincaiiy, the % COVm was -1 1.0 % for Group I and 8.0 % for Group II. OveraU, the
degree of covan*ance for the combined groups was negiigiiie, with a vaiue of -5.9 %.
At Condition 2 (rniddle chair height), Group 1 and Group II exhiôited less thao 20
% COV= benmen the mean hip and knee moments (18.8 % and 14.5 % respectiveiy).
W i i both grwps cornbineci, the 96 C0Vm rose sligbtIy but was oniy 27.8 %. A low
negative covari*ance was obsaved between the mean knee and ankIe moments for Group
1 and Group II (-27.7 % and -16.9 % resp&eIy)). ûverall, the % COVU was -20.9 %.
At condition 3 (high chair height), the % COV= was moderate and comparable
across groups. Specincally, the % COV= was 59.3 % for Group 5 48.5 % for Group II
and 59. I % for the combineci groups. Agaui. greater &ability was seen across groups in
the % COVU with 0.1 % for Group I and 28.5 % for Group II and -3.1 % for the
Table 8. Covariance values for the mean joint moments between Groups I and II ((3 & GII) and conditions. Units are reported in (Ndg)'
Variance Condition 1 (Iow) Condition 2 (middle) Condition 3 (high)
rka 0.26 4-17 0.03 0.19 0.19 O. 17 0,01 4.37 0.00
An important observation when imefpreting the variauce and covariance measures
in Table 8 is that the covanvanance meaSufe for the wmbined groups (GI & GIi) did not
necessady fàll between GI and OI['s covariance meames (% COV). The % COV
between twm adjacenî joints is directiy infîuenced by the variance in the mean moments
of force and iadirectiy influenceci by the d e r of subjects wahin a group. Detailed
tables presenting the mean moments offorce, standard dmevratiom and variances messures
are fouad in Appendm I for each groq and condftion,
Covariance mcasures across conditions.
Table 9 presents the o v d covariance measure obtained when combining both
groups across the three conditions. The percent c o v ~ c e measure between the mean
hip and knee moments (% ~ O V =) was 48% for the e1derIy subjects across di chair
height conditions. As expected the percent covariance measure between the mean knee
and d e moments (% covd rmauied Iow across d chair height conditions (-14.0 %).
Table 9. Covariance memes for the mean joint moments for Groups 1 & II across al1 chair height conditions Vatiance G I + w (IF 1 l)
2, 0.03 4
&K 0.060
&K 0.049
2, 0.046
2~ 0.026
GK+A 0.098
2, 4.0 12
%mm 48.0
% C O V ~ -14.0
~ E K * 4.52
r AK O. 13
Where: r tefers to the Pearson Rodact Moment Conehticm coefficient * indicates a siBnificant refationship at a 4 . 0 5
Figure 4 is a plot of the average hip moment versus average knee moment and
illustrates the general trend across diffaent chair heights. The CO-variabüity Î n the mean
hip and knee moments across aiî chair height conditions was moderately correlated
(r= = - 0.52, p < 0.05). The negative Pearson Product Moment Correlation coefficient is
an indication of the moderate synergistic relationship beniveen the mean hip and knee
moments. h otha words as the mean hip moment h c r d the mean knee moment
decreased and vice-versa,
1 m Predicted Y 1
Mean Knee moment (NmlKg)
Figure 4: Mean bip moment versus mean h e e moment d u ~ g the extension phase o f the STS tramfer for iII subjects across t h m chair beight conditions. The üne of best fit is s h o w for the data points.
Figure 5 is a plot of the average knee moment versus average ankle moment. No
significant relationship was found between the average knee and ankie moments
(r AR O. 13, p > 0.05). The s m d but positive Pearson Produa Moment ComeIation
coe5cient nconfinns the low negative covariance measure (-14.0%) observeci between
the mean biee aml ankle moments. Though the knee and ankle moments were
experïencing magnitude changes in the same polarity, the joint moments were acting
quite independently o f each d e r since the degree of meance benmen these joints was
minimal,
4. t O 0.t 0.2 0.3 0.4 0.5 0.6 O.?
Mean rnkle moment (NmlKg)
Figure 5: Mean hiee moment versas mean mûde moment daring the utension phase of the STS trrrwfer for dI sabiects icrou tlvce chair height conditionsi Piantainexion ir reportcd as poritive~ The IOie o f krt Bt b sbonn for the dit. pinen
Joint paner-time histories.
Figure 6 displays the ensmble averaged power patterns at the hip, knee and aakle
for the Iow, middle and high chair heights. Simüar power-time curves for each joint were
seen across the chan heights. Both the hip and knee exbibiteci oniy one distinct phase of
power generation tbroughout the extension phase. Peak hip power was greater in
magnitude and generdy occurred earlier in the saension phase than peak knee power.
The hip and knee muscles p d o d more positive than negative w o k In contrast, the
aokle had no distinct power phases and the vaiues were negligile in cornparison to the
hip and knee vaiues. Minimal positive and negative work was doee at this joint.
Of imerest, the hip and hee power w e s generally exhibited l e s variability at
the lowest heght in cornparison to the highest height (see Table IO). Since the
co&cieut ofvariation scores represent a ratio between the standard deviation and mean
score, it is understandabie thpt the CV scores at the ankfe were sigpincaxrtiy inauenceci
by the minimai power vaiues.
Tabk 10. CV values for the hip, h e e and anlde power-time curves aaoss differem chaù heights. Groups were oombhed
Chairheight Low Middie High
Hip Power 78% 112% 117%
Knee Power 40% 38% 62%
AnidePower 168% 596% 500%
Total amount of work done during the estension phase.
Table 1 1 compares the uormalized work done at each joint across ail chair height
conditions. The total work is quai to the area under the power-time curve and represents
the sum of the positive and negative work The amount ofwork doue at the hip (Work h)
which ranged tiom 1.19 to 1.57 J/Kg was consistentiy higher than the amount of work
done at the knee (Work L) and the ankle (Work 3 across the three conditions. Specificaily
the Work k mged Eom 0.59 to 0.99 J/Kg while the Work , ranged f?om 0.02 to 0.09
J/Kg. This is consistent with the remlts obtained with the power-time cwes.
Table I l . Means and standard deviations of the normalued work done (J/Kg) for groups I & 11. Parameter Group 1 (n4) Group II ( ~ 7 )
Condition 1 2 3 1 2 3
Chair ht 0.400 m 0,435 m 0.470 m 0.380 rn 0.415 ni 0.450 m
Work h I.24(.53) 1.35(.33) I. I9(.4I) 1.57(.43) 1.46(.32) 1.52(.4I)
Work 1: 0.99(.32)' 0.93(.28) 0.72(.36). 0.90(20)~ 0.73(. 14) 0.58(. 191b
Work. 0.05(.03) O.û4(.04) 0.09(.08) 0.03(0.03) 0.03(.02) 0.02(.04)
Group L Condition 1 signincady W i t fhnn CancGtion 3 (p < 0.05) b Gfôup II, Condition 1 SZgdïady &keaîErom CondiÉion 3 (g < 0.05)
There were no significant differences betwe!en groups for the total amount of
work done at the hfp, knee or anlde (FhiP U6 = 1.22, p > 0.05; Fhrc 1-16 = 1-34, p > 0.05
and Fd. 1-16 = 4-61, p > 0.05). For the totd amount of work done at the hip, no
significant differences were formd in the conditions nested within group eEect
(F 4-16 = 0.41, p > 0.05). h terms ofthe total amount ofwork done at the knee, there was
a ~ ~ c a n t main effect due to conditions nested wÏthÏn group (F as = 10.42, p < 0.05).
Significantly more work was done at the knee for Condition 1 compared to Condition 3
for both group 1 and LI (t = - 3.354, df 16, p < 0.05; t = -5.374. df 16, p < 0.05,
respective1 y).
For the total amount of work at the adde, there was no significant effect due to
conditions nested with groups (F 416 = 2.21, p > 0.05).
Strength measurements
Nine of the eleven subjects who participated in the sit-to-stand triais dso
performed the leg extension exercise. Medical and personal reasons prevented two
subjects nom participatuig in the leg extension exercise. The intent of this exercise was
to obtain a clinicai measure of strength that may distinguish strength capabilities among
the elderly individuais. Since the Shuttie 2000 involves a muiti-joint task similar to the
sit-to-stand task, it was hypothesized that the performance on the Shuttle 2000 may be
retated to the lowest successfui chair height fiom which an elderly person may rise. As
shown in Table 15 the majority of the abjects (n = 7) succeeded in extending their legs
against the device with maximum resistance (12 resistive bands). The remaining two
subjects were able to extend against eIeven resistive bands. Thuq the Shuttle 2000 in its
present state was unable to discriminate among different strength capabilities.
Table 12. Subiects Performance on the ShuttIe 2000
bands #
W 70.0 1-63 0.831 LIS 91 90 OB7 L2 4572 457.9 58.2
Work caiculations were based on the predicted force and the distance traveled by
the sliduig scat- The predicted forces were calculateci using the regession equation
developed during the caiibration procedure and were infiuenced by the number of
resistive bands (Appendix C). Leg length and the positionhg of the subject on the
exercise machine detennined the distance traveled by the sliding s e a t These factors
innuenced the estimateci amount of work to complete the Ieg extensioo. Two subjects
had exceptionally low values of work 10.2 and 11.9 joules. These values are explained
by the smdi distance d u e s as shown in Table 12.
The performance on the exercise machine was unrelateci to the successfiil
completion of the sit-to-stand ta& SubstantiaUy Iess work was required to complete the
leg extension in cornparison to chair rishg regardless of chair height (Table 13).
Tabk 13. Cornparkon of the amount ofwork required to raise the COM fiom a chair set at différent heights to the performance on the s ~ e 2000. Units are in Joules
Sdj- Group Low Middle High Shuttie
In summary, the within subject reliability was high for the joint moments offorce
at thigh-oe peak moments of force and totai amount of work done. Tirne to peak
moments offorce displayed however more variitbility. nie rewilts of this study bdicate
that chair height had the greatest kinetics effect on the knee joint. A sÏ@cant reduction
in the required knee moments was found in Group II as chair height increased. Aithough
a similar trend was observed in Group I, it was not st8tistidy signincant. A
sipnincantiy higher hip extensor moment at thigh-off was however observed at the
midde chair height competed to the Iow chair height in Group 1. The d e moments
were d k c t e d by changes in chair height In addition, the covariance measme betweea
the hip and knee moment patterns across dBerent chair heights was moderate (48.0 %)
whüe the degree of covariance between the ha and d e moments during the sit-to-
stand tramfier was negligible (- 14.0 %). In temis of the joint enagetics, the totai arnount
of work done at the knee joint fbr both 8foups was signincantiy reduced when nsing
ftom the highest chair height cornpareci to the Lowest chair height. Lady, the r d t s
obtauied on the Shuale 2000 did not relate to the elderly subject's chair rishg
performance.
Discussion
The present study was undertaken for two main reasons. One was to examine the
infItxence of chair height on the joint kmetics and energeiics of the sit-to-stand msfer
among an elderly population. A second reason was to investigate the relationship
between the minimum chair height ftom which an older person was able to rise and their
performance on a leg extension device. Both the fhdings and implications of this study
on the stated hypotheses are discussed in the fouowing chapter.
Eieven hedthy elderly subjects were assigneci to one of two p u p s based upon
their standing posture. Subjects were then required to rise fiom three different chair
heights. The actual chair height settings were group specinc but the range of values
overlapped (Group 1: 0.40 m, 0.435 m, 0.470 m, Group II: 0.380 m, 0.415 tn, 0.450 M,).
Nime of the eleven subjects were capable of rising fkom aiI three heights. While only one
femde subject in Gmup 1 was uosuccessful at the Iowest chair heigbt, a second female
subject in Group II was unable to have her fm f l y on the fbrceplate at the highest
chair beight. B a d on the elderty subjects chair tising perfo~m811ces and on their Tirned
'Up and GO' scores, the IeveI of bctionaI mobility for this popdation was considered to
be reIatively hi&.
Rdiability of the dependent merrures
Acairate assessments in the field of biomechanics depend on the reiiabiiity of the
seIected kinematic and kinetic measurements used to d y z e human rnovernent. In the
present study, the reproduciiiiity of the selected kinetic measuzements in a sit-to-stand
task was assessed. Wahin subject rehabiüty was evaImted uskg an intra-class
correlation coefficient @CC) on aiI of the kinetic and energetic variab1es. TypicaIiy, the
ICC values for the magnitude mCabIes wae gr- than 0.83. These figures indicate
tbat the elderly subjects wen capabIe of reproduciag these measurements with a high
degree ofcoiisistency across diffetent chrir heights- The ternpod measures for peak
moments offorce exhibîted more variab- with d u e s mging fiom 0.54 to 0.79. One
possible reason for the low ICC vdue for the time to peak hip moment is the s m d
betweea subject variance. The effiveness of the ICC score as a measure of reliabiiity
is reduced when subject scores are homogeneous since this resuits in minimal between
subject variance. It is therefore important to aramine the variab- of the scores when
using ICC scores to assess measurement reliability (1- Schenkman, Riley, Lin, 1990;
M e , Pai, Rogers, 1995). Ahhough a significant subject effect was observed in the
study (F = 2.2 1, df = 10.46, p < 0.05), the s m d between subject variance suggests the
subject scores for this variable were homogeneous and thus the ICC score aiay not
accurately refiect the reiiability of this dependent measure.
Joint kinctics
In absolute terms, the hip moments were substantidy greater than those at the
biee and ankie at thigh-off for ail conditions. Similar kdings have previously been
reporteci (Burdett et ai., 1985; Rodoslty a aL, 1989; Carr and Gemile, 1994). Although
the îask of identifying chair rising stratees was not undertaken in this study, it wotdd
appear that with the exception of one subject, the elderIy mbjects employed a 'aiptMik
strate&' in order to wmplete the rise. As pnviously mentioned Cogh(in & McFadyen
(1994) identifieci two types of transfer strcrtegies arnong their control group. In thek
shidy, the protocoI rqubed the subjects to nse at a self-selected speed âom a baciûess
and d e s s chair with their feet in a predetennined position Normd subjects who
flexed their aunk fhrther forward and experïenced higher moments at the hip in
cornparison to the knee were classifiexi under the 'Wp-tnmk stnitegy". Based on the
displacements of the body's center of mass and centa of pressure, the authors
hypothesized that this strategy o f f d stabüity to the pemm since the body's center of
mass was o v a the base of support for a longer penod of tirne. The elderly male subject
in this study @ e n d a reIativeLy higher hee exteiwr moment and Iower hip
extemior moment m cornparison to the femafe subjects and thus t wouid appear fie
attempted to use a ''knee strate&'. SWarIy when Doordosch et al (1994) aompared
two rishg strategies on the net m u d e moments, p a t e r hip extensor moments with
correspondingly smaller knee extensor moments were observeci when subjects used an
excessive trunk flexion In summary, both the experimentd protocol and cbair-rising
strategy have an important mie in d e t e r d g which of the two joints sustain the Iarger
moments.
Two methodologicai issues must be taken into consideration when cornparhg the
redts ofthis study to pubiished values. Firstly, the kinetic mode1 employed in this study
estimated the muscle moments for both legs SimuitaaeousLy and e@y. Therefore the
moment values represent the sum of the lefi and right joint moments of force combined.
For cornparison to other refated litenme, it was sometimes necessary to divide the
moments by two to d a d e the values for one M. Ikeda and associates (1991)
provide supporthg evidence that hedthy older individuais exhibit symmetry while rishg
fimm a chair since differences between the right Pid ieit joint moments at the hip and kna were
only 11 % and 13 %, mpeahdy. Secandly, the prrsmt study used a dynamic biomechicai
mode1 to estimate the moments of force and other hetic parameters. Revious sit-to-
stand studies that have neglected the inertiai loads acting on the Iower iimb may
underestimate the required muscIe moments. Aithough limited research has been
conducteci in this area, a subsdd difference was seen at the hip joint wfien Miller
(1990) compared the predicted moments at thigh-off using a static and dynamic modei
while minimai difrences were seui at the lmee and ankle. The actual comparison of a
mtic to a dynamic mode1 was not paforwd in this study but the dynamic mode1 is
assumed to be a more accurate represeutation ofthe a W motion.
Effect of chair height on the joint kinetics.
Previous shidies have shown that chairs witfi higher seat pans facilitate the
tratlsfer fiom sitting to standing. As chair height increases, the position of the center of
mass ofthe thigh and HAT segments relative to the knee joint is bigher thus msknig iift-
off less mechmidy demanding (Scbenkman a aL, 19%). The main Wor coatnîuting
to the Iowa hee extensor moments at thigh-off is the decrease in moment a m length
between the body's ceider of mess and the ha joint. In the prescrit study, a aignScant
reduction in knee moment at thigh~ff was found in Group II as chair height increased.
Although st&caiLy not differenty a similar trend was obsemd in Group L
An unexpected hding was the signifcant increase in the hip moment at thighsff
at the middIe height compareci to the Iow chair height in Group 1. The different chair
rishg strategy used by the maie subject w i t b Group 1 may account for this observation
As previously rnentioned he appeared to use a ' h h i e e strate&' and consequentIy
experienced lower hip extaisor moments and higher knee extensot moments than the
other two subjects within Group 1 Condition 1. With the d sample size, the low hip
moment at thigh-off for the maie subject had a sub-ai influence on the o v d mean
of the hip moment at thigh-off for this group. It is important to reaiize that the elderly
subjects in the present study were classified into groups based on body stature due to a
physicai constraint in the chair adjusmient system and not on chair nsing stnnegies.
Conversely, the normal subjects in Co- and MiSadyen's (1994) study were grouped
based on the patter~s dispïayed in the mommt-thne m e s and consequentIy were
examinecl separateiy. Chair rising strategy is thus an important &or to consider when
examinhg the moment-time graphs among subjects.
Sisnifiant reductions in peak moments of force have pmiously been reportai as a resuit
of incfeasing chair heigbt (Burdett et ai.. 1985, Rodosky et al., 1989, Hughes et al.,
1996). While there were no signifiant differences in the peak hip moments for either
gcoup, only Group II experienced a significaiit reduaion in peak knee moment. With
respect to the peak hip moment, the r d t s of the preseat study are in agreement with
RodosLy a al.% coaclusioas. Chair height 6ad Mie effect on the magnitude of the peak
hip ff exor moment between the lowest and highest chair height settings since the changes
were less than 12 %- In coiitrast, Burdett et al reporteci a sipificant decrease in peek bip
moment when rising fiom the high chair in cornparison to rishg nom the Iow chair. A
distinguishing ftctor among these studies m cornparison to the present me is
the range of chair heights tested. The difference between the lowest and highest chair
heights was over 0.20 m in Burdett et al. 's study while in the presexst study merences in
chair heights were at most 0.07 m. Thus, the absolute changes which o m e d within this
study shouid be less tbaa the reported différences in the Iiterature. For example, Rodosky
and associates reported a 50Yo reduction in p d knee flexor moment when comparisons
were made between the chair heights set to 65% and 115% ofthe subjects knee height.
The non-adjustable baclrrest combined with the standardized starting position used in this
study prevented higher heights Rom being tested. As well, the elderly subjects were
required to have thek back tgmly against the backrest and feet resting completely on the
fioor, which may affect their sit-testand pdormaace.
Table 14 pcesents published values for the peak moments offorce at the hip, h e e
and ankle fiom several sit-to-stand shidies. At similm chair heights, the observecl peak
exîensor moments at the hip and knee in the present study wae cornparabIe to the
published vatues. Peak ankle p l a n t ~ x o r moments were however Iowa thsn the
published values (Burdett et ai., 1985, Carr & Gentile, 1994, Coghlin & McFadyen,
1994). One possible reason for these lowa d u e s is the initiai foot placement. Foot
placement affects the position of the thigh and sbank with respect to the feet.
Coosequently it influences both the directr0on of the ground reaction forces and the
distance baween the My's center of mass and the base of support provided by the féet
(Shepherd & Koh, 1993). While the eIderiy subjects seIf4eected the foot position at
each condition in the present study, f~ position was standardized in bot6 Cam and
Gentile's and CoghIin and McFadyen's studies. In Btudett et d.'s study, the authors
simply state thst each subject was positioned so tîiat both fat wae on the forceplate.
The present rcwilts wodd suggest thst the eIderIy subjects selected O fwt position that
Iowed the peait phtadexor moments.
Tablc 14. Compered values of peak normalized moments of force (Nm/Kg) for the sit-to-stand transfer. The moments of force represent the sum of the right and left peak moments at the hip, knee and ankte
> J
Bucdett et d. Cam Igt Coghlin & Hughes et Present study
(1 985) Gentile McFadyen al. ( 1 996)
Chair ht 0,43m 0.64m 100% KH 100% I(H 100 % KH 0.40m 0.43Sm 0.47m 0.38m 0,415m 0,45111
Ag@ 33 years 24 years 32 years 78 years 79 years
Kinet io Static Dynamic Dynamic Static
modal
PFA KS HTS
(n=3) (n=2)
Dynamic
Group I(n= 4) Group Il (n- 7)
PFA = Pmfened am condition
KS = "Knw strategy" HST = "Hip-twnk strate&'
KH = "Knw height"
Covariance measure
Kinetic assessrnents which analyze the entire Iower Iimb provide information
showing how one joint can compensate for the lack of support at another joint and s t i l l
enable the individual to complete the task (Wi, 199 1). Substantially high variabiIity
in the hip and hee moment patterns during successive walkllig trials lead Wimter to test
whether or not there was a correlation bmeen what was happening at one joint with the
moment patterns at the 0 t h joints. It was found that these variances were not d o m
and that there exkted a tight coupüng between these joints ("Winter, 1984). To prwent
vertical collapse and to maintain the body's center of m a s within the base of support in
waiking, trade-offs occur between adjacent joints. Winter (1990) introduceà the concept
of support synergy whereby variations in the hip moment patterns are compensated by
opposite changes in the knee and ankie moment patterns. These trade-offs account for
the low miability observeci in the support moment despite the considerably high
vaciability in the individual joint-moment patterns within and between subjects. The
support moment represents the nei tendeacy to extend the Iimb and is the summation o f
the moments of force at the ankie, knee and hip with extensor moments as positive
(Wher, 1980). He illustrated the trade-offs which ocnn between moments for subjects
w a h g at Werent cadences. A one to one trade-off between the hip and knee moments
was obsenred. Subjects tendeci to either exhibit a hip extensw/knee flexor pattern or a
hip flexodknee extensor pattern.
These trade-offs have also ban reported using a rneesure of covariance. To
maintam low variabiiïty in the summation of the hip and knee moment patterns while still
eacountering greater variability in the hdbiduai joint-moment patterns reqyires a certain
degree ofsynergy between the joint-momeat patterns. The conriame measure d l be
high when tkre is a high Ievel of synergy between the two adjacent joints. A positive
covariance measure occur~ when the joint moments of force are experiencing magnitude
c6anges of opposite polanty. Zero covariance is intetpreted to mean that the moment
patterns at the two adjacent joints are unreia!ed and are thus acting independently of each
d e r . A negative cov8tlCance measure occurs wha the joint moments of force are
experiencing magnitude changes of same polarity. Ln walking, the amornt of covariance
between the hip and knee moments in young hedthy adufts typically ranged between 60
and 70 % while heaithy older adults exhriited 57.7 % (Whter, Patla, Frank & Walt,
1990). In geneml, the degree of covariance betwem the mean knee and ankle moments
tends to be lower in cornparison to the mean hip and knee moments.
According to Wrnter (1989), the bi-artidate muscles of the lower timb are partiy
responsible for the tïght couphg obsmed in walking. For instance, the biceps femoris
is both a hip exteasor and a knee flexor. Its &ect on one joint is demonsaated by an
opposite e f f i on the adjacent joint. These muscles enable the individuai jouit-moment
patterns to vary substantiaiiy yet stiIi maintain Iow variabiiity in the support moment. It
is important to rWe however that the bi-artidate muscles are not entirely responsible
for the tight couphg and that the neuromuscular system also has an important role in
ianuencing the joint-moment pattern of the Iower Iimb (Wîrntet-, 1989).
Rising fiom a chair is a multi-joint task requiriag the coordination of muscles
crossing aIi three joints. The prevention of vertical colIapse and postural control are
essentid requirements for the succasfiil completion of the sit-to-stand task as they are in
walking. In the present study, the hip-knee and kneeankie covariance measures were
generally Iower than the values reported by Winia (1990) for waIking. The overall
covariance measure across aü groups was 48.0 % for the hipknee ami -14.0 % for the
knee d e . This shows tht the 6ipknee are not as timy wntrolied as in walkuig but
stiII exhibit some degree of shariag in the ove& task ComrefseLy, the hee-ankie
morneut patterns seem to work quite independently from each other.
Severai siî-to-stand studies have examined the activation of various Iower Iimb
muscIes through d a c e electromyography (KeiIey et aL, 1976; Coghlin & McFadyen,
1994, Roebroeck et d, 1994, Doormbsch et aI., 1994). Of particuiar interest is the
activation ofthe bi-articulate biceps fenoris and nctus fernoris. C o - c o ~ o n between
these antagonistic muscIes hrs ban observed dirrulg the rise. These muscIes have an
important d e in preventiag the vertical coUapse and in muntnming the uppa body
within the base of support provided by the feet ( W i , 1991). The M G activation of
these musdes during the sit-to-stand tramfer provides evidence for the moderate trade-
offs in the mean moments offorœ between the hip and knee.
Ovedl the covariance measure between the ankle and knee was negligible for the
sit-to-stand transfer. A possible expimation relates to the singIe joint muscles, nameIy
the soleus and tibialis anterior. Previous studies suggest that when represented as a
pacentage of total maximum voluntary contraction, both the aoleus and tibialis anterior
have a higher activation Ievel than the gastn,cnemtus at seat off (Roebroeck et al., 1994;
Dooreabosch et al., 1994). According to these studies the EMG signal of the tiiidis
anterior graduaUy decreased after seat off while the soleus mcreased fiom this point. The
gastmcnemius remained fairy constant throughouî the transfer. These EMG activations
would substautiate the low covafftance measures observed between the mean knee and
ankle moments of force during the sit-to-stand W e r . Thus, the single joint muscles
may have a more signifiant role in accomplisbiag the trmsfm than the bi-articulate
Higher corn*ance memes between the mean hip and knee moments of forces
were seen at the Iow and high chair height in cornparison to the middle height. Possible
expIanations for these hdings rehe to the challenges imposed on the r e e m e n t s of
the sit-to-stand tasic, namely the need to prevent verticai coiiapse and maimaui upright
bafance. IndMduais must modify their strategy accordhg to the condition in order to
accomplisfi the sit-testand transfii
The covariance measuce between the mean hip and knee moments reveaied a
moderate correlation between the adjacent joints at the low chair height in cornparison to
the middIe heigbt, with 53 % at the Iow chair height and oniy 27.8 % at the middk
height. Evidentty tighter coupihg between the hip and bee muscIes ocumed at the Iow
chair height in comparison to ~e middIe height. ûne poBsibIe explanation relates to
tnmL movement lndividiials tend to exaggaate the movements wà6m a partidm
strategy at lower chair heights (Hughes et aI., I994). Since the elderly subjects geriedly
extiicbited greater forward leaaing of the trunk at the lower chair height, a greater demand
was most likely pIaced on the bi-articulate muscles to maintain balance during the
transfer and consequentiy a higher Ievel of synergy was observed at this height. At the
low height, the mean d e and knee moments of force were independent of each other.
The middle height represented a standard chair height. The Ievel of difficulty in
terms of baiance control was less demanding at this height in cornparison to the Iow
height and thus Iess coupling between the mean hip and knee moments of forces was
required. Even though the elderly were rishg without the use of thek arms, it would
appear that this chair height had the greatest similarity to a normal sit-to-stand transfer.
Of interest, a higher negative covarjance (-20.9 %) meaSuTe was observed between the
knee and ankle patterns at this chair height in cornparison to the low and high chair
heights (-3.8 % and -3.1 % respectively). In other words an increme in knee extensor
moment was wrrespondingly matched with an uicnase in the plantadlexor moment.
While increasing chair height may have reduced the reqyired knee moments of
force, the relative infiuence of higher chair heights on an elderly person's abüity to
maintain their balance during the traasfer is uncertain since a higher degree of covarCance
between the mean hip and knee moments occuffecl at the higher chair height m
cornparison to the middle chsir height (59.1% vasus 27.8%). One possible reason for
the higher synergy between the mean hip and knee moments relates to the fhct that at the
higher chair heigk an unstabilizing ment may have ocmed. From the vide0
recordings it was obsaved that certain subjects began the transfer by raishg their toes
verticaiiy and placing their weight ont0 their heels. Coll~equentIy at thigh-off. these
subjects experienced a "landhg effets" which may have cmenged th& abüity to
meincain their balance Qring the Sa-twtand W e r . An expianation for the o b s a n d
behaviour relates to the initial starhg position+ As part of the standdiad protocoL the
elderly subjects hed their backs festin8 on the b8ckrest for di rises. The depth of the seat
was however not adjristeci chniiig the study. Although the abjects fm were on the 0mr
whiie sitting, in order for them to complete the nse at this height, they rose ont0 their
heels and tbus introduced an unstabihing event which required tighter couphg between
the hip and knee muscles. Negligible covariance was seen between the mean knee and
ankle moments of force.
Joint eaergeiu
In general the profiles of the power-time cunres resembled both C m and
Gentiie's (1994) and Coghün and McFayen's (1994) redts. Power was generated aaoss
the hip and knee during the extension phase and oniy one signincant power phase was
seen. For aii conditions, peak hip power g e n d y occurred first and was greater in
magnitude than peak knee power. In terms of the total amount of work done.
substantialIy more work was done at the hip thm at the knee durhg the extension phase.
Wle the d c i e n t ofvariation scores (CV) at the hip were much higher in compasison
to the knee, generaliy both decreased as chsir height decreased. Whiie Carr and Gentile
o b m e d higher peak knee power than peak hip power m their study* the type of strategy
influenceci which joint sustaineâ the Iarga powa in Coghiin and McFactyen's snidy.
Subjects classined under the '%iphiptninL strate&* geneed more hip power t h h e e
power while those clessined unda the c'knee-8trategy" generated more hee power t h
hip power.
The power-tirne a m e s at the a d e were more variable. No distinct phases were
seen and the magnitude ofthese phases was small in compmCson to the d e r joints. The
particuiady srnail vaIues infiuenced the CV scons at the low and midâie heigk
Accordmgiy7 the total mount of wort done at this joint in cornpuison to the Lnee and
hip joints was negfigiible. These reaults wen comparabk to bath Carr and Gentile's
(1994) and Cog611li and McFadyen7s (1994) resuits.
When the amotmt of wodc done at eacb joint wcis cornpanxi a ~ o s s chair heigM
conditions, the oniy sigdicant difference occumd at the ha. Substaniially Iess work
was done at the knee for the highest chair height in cornparison to the lowest chair height
for both groups. Ln CoghIia and McFadyenYs (1994) shidy, the type of strategy used
innuenceci the amount of work done at the individual joints. For instance, substantially
more work was done at the knee than at the hip under the '%me strategy" wtiiIe the
reverse was tnie for the c%p-trunk shategy". Table 15 compares the nonnalized work
vaiues of the present study to Coghlin and McFadyen's normal subjects. Only work
vaiues for high chair heights are presented since tbis chair height approximated 100 %
knee height.
Table 15. Cornparison of notmalized work values between studies (JKg)
Parameter Coghh et al. (1994) Present study
KS ( ~ 3 ) S (4) Group I ( n=4) Group II (n=7)
Chair ht LOO % KH 0.470 m 0.450 rn
Work 0.53 1 .O7 1.19 1 .52
Work bec 0.91 O, 17 0.72 0.58
Work 0.05 0.06 0.09 0.02
Where KS is the h e e strategy and EiTS = is the hip-aunk m e g y
Of interest the work vaiues at the hip were higha although comparable to Coghlui
and McFadyen's (1994) C'hip-trunk strate&' whiie the knee values more closely
resembled the "knee-strate&'. The anMe vaiues were low and comparab1e across the
two studies. The higher moments of force in the present study is one possible
scplanation for the hi@= work values. In the present shidy, the dechne Î n knee extensor
moment was more graduai th in Coghllli and McFadyen7s study. Aiso it is possibIe
that the elderiy subjects wmbhed the two strategies.
Strength mmurtmtnts obtaheü fmm the ShWe zoo0
An attempt to relate a hctionaL mcesure oflower atremity men@ to the sit-to-
stand was undertaken in this study. Although nsiag f h m a seated position is a
multi-joint task, most sit-to-stand studies have used a mearmre of maximum voluntary
strength at one joint to estimate an individual's strength avaiiability (Hughes et al., 1996;
Kotake et aI., 1993). The seledion of an appropriate strength measurement device is
difficuit when attempting to relate strength to fùnctiond mobility. As an alternative to
using individual strength measurements at euh joint, an exercise machine involving al l
three joints was used to obtain a bilateral strength measurement. The Shunle 2000 is an
exercise device designed for rehabilitative purposes. It involves a simple leg extension.
Since the majority of the subjects were capable of extendin8 their lower Limb with
maximum resistance, the Shuttle 2000 in its present state was unabte to discriminate
among different strength capabilities.
The Shutîie 2000, located in the Centre for Work and Hdth, is over Meen years
old and the Ievel ofwear and tear on the first eight resistive bands was evident. Although
accordhg to the manufàcturer, the Shunfe 2000 is capable of providing approximately
109 kg ofresistance with 8 resistive bands a - maximum extension (Tippet, 1994), oniy a
maximum of 68 kg of resistance was recordeci at maximum extension with the k s t 8
resistive bands in the present study. This value was bas& on the calibration data. In its
cluiicai environment, certain tension satings on the Shuttle 2000 have presumably been
used more fiecpently than others aud thus the elasticity of the resistive bands has been
reduced on this exercise device. AWough the addition of four new resistive bands
increased the amount of maximum resistance, it had no &ect on irnproving the
sensitivity of the device to detect Merent strength capabiüties.
The strength measurements were expressed in terms of the mechanical work
repked to extend the lower limb. Work cdcuiations were based on the predicted force
and the distance traveled by the sliding backrest. As previously disaissed, leg Iength and
positioning of the abjects on the sliding seat influenced the distance traveled by the seat.
AIthough the shouider m e s s secured the elddy subjects position on the exercise
apparatus, it prevented the staodardbion of the Iower iimb as a resuh of diffecern body
segment lengths. This was apparent for shorter individuais with prrtCcuiariy small trmk
segment Iengths since the initiai stacting position ofthe lower Iunb was in a more
extendeci position thaa for tder indnnduals. Hence ody a short distance was required to
fully extend the Iower limb. Of interest, the newer mode1 of the S h d e 2000 has the
choice of handles Iocated on each side of the sliding seat or the shodder hamess. The
adjustable handes w d d enable individuais of différent body shes to have theif Iower
limb in the same positi011,
The Shuttie ZOO0 may be a suitable device for certain rehabilitaîion exexcises.
Although the 1- RM was unrelated to the lowest chair height nom which an elderly
person may rise, firme research shouid examine its usefiiiness in trainhg kg extmr
power ammg an elderly popdation since chair rise time has been shown to be influenced
by leg extensor power (Skelton, Greig, Davie & Young 1994).
Summaty
In summary, the within subject reliabiiity was high for the joint moments of force
at thigh-oc peak moments of force and totai amount of work done. Time to peak
moments of force demomtrated however more variabiiity. The results of the preseiit
study indicate that chair height had the greatest kinetic and energetic effect on the knee
joint. Signincantly less biee moment was re<iUed to rWe nom the middk and high
chairs in comparison to rising fiom the low chair in Group IL A similar trend was
observeci in Group 1 aIthough not statistically significant. Less work was done at the
knee when rising fiom the highest chair than nsing âom the lowest chair in both groups.
in addition, the covariance rneasure bemeen the hip and knee moment patterns across
différent chair heights was moderate. The hip and Lnee moment patterns were kefore
not as tightiy controiîed as m walling. The degree of conriame b e t w a the h e e and
anlde durÎng the sit-to-stand tramfi= was negligi%Ie. k c e , the icnee and ankie moment
patterns were acting independentiy ofeach other- M y , the Shuttle 2000 in its present
state was unable to disixmmî . * e among different strength capabiiities since the majonty
of the subjects compIeted the amcise with maxÎmm resïstsnce. Further the total
mount of work repuired to raise the body's center of mass fiom a sitting to a standing
position was substantislly higher than the work repuirsd to a d d the Ieg.
Conclusions and Recommendations
The foilowing chapter discusses the implications of the results on the stated nuU
hypotheses and provides recommendations for fimire research in this area.
1) The nuil hypothesis that the moment of force at the hip at the time of thigh-off was
not significantly a&cted by changes in chair height was rejected. The hip moment at
the fime of th@-off was significantiy higher when nsing &om the middle chair
height compared to rising fkom the low chair height specificaily for Group L
2) The nuii hypothesis that the moment of force at the knee at the time o f thigh-off was
not signincantly affecteci by changes in chair height was rejected. The knee moment
at the time of thigh-off was significaatly lower when rishg nom both the high and
midde chair heights cornpareci to rising nom the low chair height specifidy for
Group IL
3) The ndl hypothesis that the moment offorce at the ankle at the time of thigh-off was
not sigdicantiy affected by changes in chair height was not rejectecl.
4) The nuiî hypothesis that the peaL moment of fbrce at the hip was not sigdicantiy
affected by changes in chair hei@ was not tejected.
5) The nui1 hypothesis that the peak moment of force at the hee was not signincantiy
affecteci by changes in chair height was rejected. Th peak moment of force at the
lmee was si@cantiy Iowa when rishg fiom the highest chan height compared to
rising fiom the lowest chair he@t Specincaliy for Group II.
6) The nuil hypothesis that the peak moment offorce a the M e was not signindy
&échd by changes m chag height was not qCecteded
7) The nul1 hypothesis that the totd amount of work done at die hip was not
s ign i f idy & i e d by changes in chair height was not rejected.
8) The nuiI hypothesis that the total amount of work done at the Icuee was not
sisnifieandy affected by changes in chair height was rejected. The totd amount of
work was significantly lower when rising from the highest chair height compared to
rising from the fowest chair height for both groups.
9) The nul1 hypothesis that the totd amount of work done at the d e was not
signincantly affaed by changes in chair height was not rejected.
Summa y and recommendations
Based on the hâings fiom the present anaiysis on the sit-to-stand d e r among
the elderly, the foliowing recommendations can be drawri,
Chair height had the greatest innuence on the joint kinetics and energetics at the knee.
in an appIied d g , elderfy ÏndMduals dering fiom musculoskektd diseases at
the lmee are ttnis able to reduce the stress at this joint by ushg higher chairs. Further
research in this area on a Iarger sample would cl* the effect of chair height on the
hip extensor moments.
Kin& assessrnents on the lower iimb over the entire extension phase are
recommended in fimire sit-to-stand studies for several reasons. By examining the
joint moment patterns across aiI three joints, a gréata understanding of the chair
rising strategy can be achieved. It is important to ide* which joints sustain the
Iarger moments during the movemait. The present study has aIso shown that there is
a need to d e more than one kinetic panmeter in order to obtain a better
understanding of the role of chair height on the sit-to-stand trsasfir. Both the
moments of force at the time of thigh-off and peak moments of force are important
variables to consida as are the joint energetic variables. Lastiy, a measure of
covariance between adjacent joints is also an importam variable to acamine as Et
provides information on lowa limb synergy.
Chair tising strategies shouId be examineci in more detail in orda tu identifjr possib te
impairments or muscle weahesses among the elderly subjects and their innuence on
the joint W * c s and energetics*
Continueci research m this area shouid d e possible gender differences since the
eIderly maIe subject appeared to use O diffaent chair rishg mategy then the f d e
subjects.
5) Mer fûnctionai measmes ofstren@ which incorporate the use of aiI three joints are
needed to examine the relationship between strength and chair rising difECUIty since
the ShunIe 2000 was unable to discnmuiate between Merent strength capabilities.
6) Accordhg to EarIes and associates (1997), power is more indicative of funciional
ability within an elderty population and therefore the beaefits of using the Shuttle
ZOO0 to train leg exteasor power among the elderly should be examineci.
Aiithropometric Data Sheet: DATE:
SUBJECT'S NAME: SUBJECT'S ID -ER: AGE: WEIGHT (kg): EmGKT: (m)
KNEE E3EIGHT (m): (Vertical distance fiom floor to the tiiiai plateau):
CIRCLE CHAIR HEIGHT CATEGORY: A) 0.38m;0.415rn;0.45m OR
Chair height 1: Chair height 2: - Chair height 3: RANDOM H E I Ï SEQUENCE:
JOINT MARKER LOCATION AND BODY SEGMENT LENGTHS:
1. 5 th M e t a t d Phaiangeai Joint 2. Calcaneous 3. L a t d Weolus ofFibuia 4. Latd side of the knee joint (Between pateiIa and popliteal fol& Burdett et ai. 1985) 5. Greater Trochanter of Femw 6. Gceater Tubercle of the humerus
I Toe to Ankle 1 1
S-enî Toc to Heei
I FToor to Ankie 1 I
Length (m) ,
This section lias the steps taken to ensure the reference coordinate system of the force
platfonn located in the Clinical Locomotor Function Laboratory (CLFL) was aIigned
with the reference coordinate system used in BIOMECH a's motion analysis systern
TabIe B1 presents the center of pressure coordinates for a symmetncai Ioad. VaIues
were coilected at six diffaent positions on the Kistler force platform (Figure B 1).
The reference coordinate system of the force platform has the t-aris no& to the
surface with the positive direction poiming away fiom the piatfonn The direction of
the positive Fx axis is towards the door while the direction of the positive Fy axis is
towards the treadmill. The ax coordinate was aiso found to increase positively
towards the door.
W i i respect to BIOMECH 's teference cwrdmate system, the origin (0,O) is at the
boaom left hand corner of the canera's fieid of view and thus moving l& to ri&
increases in the positive direction of the x axis. To account for the reversai in the Fx
component and ax wrnponent of the two systems, the signs of the Fx and Ax
components were muitiplied by -1. A Fortran program was created to adjust the
formaî of the force fiIes obtaiaed fiom the CLFL to the same format of the RF fiTe
used in BIOMECH @.
Tabk B 1. Center of pressure coordinates for the Ioad
Position Ax Av
Chair Cup boards
Figure B 1. Schematic diagim o f the iaboratory set up during tbt data c o i i d o n
This section describes the procedures taken to devdop an eqyation to predict the amount
offorce required to perfomi the 1% extension ou the S h d e 2000.
Part 1: Cdibration of the force transducer
1. The force traosducer was calibrated by appIying known weights and recordhg the
correspondllig output vahe on an d o g u e to digital converter (Table CI). The masses
were cowerted to Newtons (N) by mdtiplying mass* 9.8 1 m/sz.
Table C 1. Calr'bration of the force transducer
Mass (kg) Newtons (N) AD IOÙtE cnbus systw b i s 1 -0 9.81 11.1 2.3 22.1 27.1 3.5 34.3 43.1 4.8 46.6 58.2 7.3 71.1 87.1 9.8 95.6 117.1 123 120.2 146-7
2. Using a regression anaiysiq the foiIowing calibration equation was found:
y (N) = 0.8 18 X (ND unit@ - 4.2 1 (1)
Part 2: Cabration of the CMC Shuttk 2ûûû
1. One end of the force transducer was connecteci to the sliding seat of the exercise
machine while the otha end was attached to a mechanid jack that ensuecl each pull
remaineci static, constant and levei during data wiiection
2. The resistive bands wae individuaily numbaed for identification purposes.
3. The A/D readings for one resistive band, then two, thra and so on were recordeci at
discrete lengths located within the ümits of the sliding seat's range of movement- The
mechanicd jack displaced the siiding seat by approxhateïy 2 cm with each puU Three
triais were coUected for each dispiacement.
4. The ND output was then converted h o force readings using the caiiiration equation
obtained in Part 1.
5. A series of force Iength a m e s were then pIotted to observe the effect of iacreasing
the rimer of resistive bands (Figure CI). The mean force value of the t h e trials was
used to plot the data
6. The force readings, Iengths aad number of resistive bands were used in a regression
amiysis to develop Equation (2) designeci to predict the amwnt of force required to
pedorm the leg extension (Table C2).
F (N) = 40.2 (#bands) + 92.5 (Length (m)) + 71.6 (# bmds)(Length) (2)
Tabk C 2. Statisticai results obtained 6om the regression analysis:
LenBth 925 19.3 4.8 0,000 S P ~ P 402 1.2 33.1. 0.000 Interaction 0.72 0.039 18.5 0.000
The intercept (-1.8) was not sipnincantiy diff&rent nom zero @ = 0.76) and thaefore was
removed h m the equation,
Figure C 1. Force Ieagth curve for eight m W N e bands. Number sîgn mfem to the # of rcsistivt bands,
7. The reüability of the three trials coiiected at each Iength was assessed using an intra
chss correlation coefficient (R *). Spe&cdy a G e n d Lmear Mode1 (GLM) was used
to assess the diffkrences between resistm bands, between lengihs and between repeated
measures.
Table C 3. Statisticd nsults fiom the GLM
k g t h (m) 28 4268474 4262418 152229 94.3 0,000 TMIflengh) 58 2953 2953 51 0.03 1 .O Etrot 563 909028 909028 1615
Both a s p ~ g a e c t and Iength effect w a e observeci @ = 0.00). No SigrUncast
ciiffierences were observed between npeated measures @ = 1.0). Ushg Equation (3), t6e
between repeated meauns.
Where MS e = Mean Sqpare Length MS = Mean Sqpare ( Trial ( Length )).
Part 3: Addition of four new bands to the exercise machine:
Wd the anticipation that eight bands wouid not be sufficiently taxing for some subjects
in terms of their maximum leg extension capabilities, four new bands were added to the
device. Caiiibration of the exercise machine with the twelve bands was compIeted
UnmediateIy after data collection.
Part 4: Caiibiotion of the force tirinsductt:
1. The force transducer was r&%rated by using known weigbts and record@ the
conesponding voitage output readings on an oscüloscope. From the values in Table C4,
the foff owing calibration Equation (4) was d e t d e d :
Y (N) = 78.78 X (volts) (4)
Table C 4. Calibration of the force transducer
Part S= Caiibration of the Shattie with twchft bands 1. Voltage output readings fbr the four new bands were recordeci in a smiilar xnanner as
outiïned in Part 2. One trial was collected et each dispIacemeat. A select number of
springs were cdbrated to assess day to day reiiabiiity.
2. T6e voltage outputs were then comimed into force readings using the &%ration
eqyatiou obtained in Part 4.
3. The force readings lengths and m b e r of resistive bands were used in a regression
aaaiysis to develop an equation designed to ptedict the amount of force required to
perform the Ieg extension.
A plot of the standardized residuals identined the presence of an outlier. This data
point rden to the Iast observation taken with tweive resistive bands. A standardized
residual of 3.3 was found. Aside fiom this influentid point, the residuais were
reasonably distnbuted about zero. The normal probability plot fkther substamiates
this hding (Figure C2). It was decided that at this point the system was strained and
diat the voltage output was a b n o d l y higher uian the preceding measures. A second
measure shouid have been taken although at this length, the resistive bands were
extremely taut and the sturdiness ofthe set up was a coacern
A second regression d y s i s without the outlier was perfomed on the data. Tables
CS and C6 present the statistical output for both regression equations.
Tabk C 5. Statisticai resuits fiom the regression andysis with the o u t k
Regiession Sta'stics Multiple R 0.97 R sq&e 0.94 Adjusted R Square 0.94 Standard E K O ~ 40.2 Ob savations 48
ANOVA Df SS MS F
Regression 3 1209062,S 403020.9 248.99 Residuai 44 71220.1 1618.6 Total 47 1280282.8
Coefficients Standard Error t Stat P-due bercePt -133.8 46.7 -2.86 0,006 S~ring 47.8 5.2 9.18 0.000
53.6 3 13 -7 0.17 0,865
Normal Probi bility Plot
8oo T
Figure C 2. Normal probabüity plot identirjling the outlier.
Table C 6. Statistical results from the regression andysis without the outlier
Reqgression Statistics Muitiple R 0.98 R Square 0.95 M@ed R Square 0.95 Standard Error 34.8 Observations 47
ANOVA d f SS MS F
Regression 3 IO67395 355798.2 294.87 Residual 43 51884.38 1206.6 Total 46 i 1 19279
Coefficient Standard Em>r t S&t P 4 u e Intercept -1 42.1 40.4 -3.518 0.001 S P M ~ 50.0 4.5 11.045 0.000 Le Wh 216.6 273.9 0.791 0.433 SpMg*Len@h 65.2 34,s 1.887 0,066
Without the ootlier, the r-sqyare and standard emr improved Hence, this mode1
was seiected since it was more acciaate in predicting the force required tu paform the I e g
In comrast to Equaton 2, length was no longer a signinamt fàctor in predicting
the amount offorœ required to pafonn the Ieg extension in Equation 5. One expIanation
for this unexpected fkduig relates to the variabaity in the predicted force d u e s between
consecutive rneasures at the higher tension levers (Figure C3). Specifically, as length
increased the force values did not increase in a systematic mamer- Instead consecutive
measures ffuctuated between higher and lower force values. This was partkulariy
evident when the number of resistive bands was eieven. Consequently both the Iength
and interaction term between resistive bands and Iength were no longer signincant in
Eqyation 5.
Force (N)= 50.0 1 (# of springs)-142.145
Figure C 3. Force -Length c u m Number sip refen to the P of mistive bu&.
P u t 6: Day ta Day Rdirbiüty
Figure C4 compares the resuits between days for four and eight resktÏve bands. Suice the
operathg raage ofthe sliding seat was at most 0.18 m durhg the streagth measurements,
the maximum displacement of the SIidÏng seat dunng the second calira;tiofi with the new
resistive bands was approxhately 0.25 m Table C7 contains the predicted forces using
the two regnssion equations devdoped in Part 2 and 5.
Table C 7. Predicted force caldations with 8 resistive bands
h g t h (m) Predided fmce ushg Predictedfbrce u&g Différence in scores Ecruatia (1) (5)
0.035 344.9 257-9 87.0 0,070 348.1 257.9 90.2 O- 105 35 1.4 257.9 93.5 O- 145 355- 1 257.9 97.2
In a clinical environment, certain tension setthgs on the Shuale 2000 wiil presumably be
used more fiequently than others and with the, the elasticity of the resistive bands will
be nduced as a result of Wear and tear. This was apparent by the different force
predictions caldateci using the two regression equations developed in part 2 and 5.
Based on these findings, day to day reliability is a factor to consider when attempting to
use the device for research purposes To mininiize Wear and tear, chnicians shouîd
aitemue betwee~~ the resistive bands for a partMar Ioad.
O O -1 O -2 O .3 O -4 O -5 O -6 Length (m)
Fyiue C 4. Conparima between days for four and eïght mistivt bands.
The equation deveIoped to predict the amount of force recpired to perform the leg
extension was based on the assumption that the inedai ioads were negligible during the
exercise. The foliowing section describes the procedures taken to ve* this assumption.
Part 1: cdibrition o f the accderometeiz 1. Prior to data collection, the accelerometer was zero bdmced ushg a wheatstone
bridge. This set zno volts to zero acceIeration
2. To obtain a calibration fàctor, voltage readings were recordecl with the sensitive axis
of the acceierometer placeci in tIiree different directions (Table D 1).
Tabk D 1. Voltage readings
Direction Voltage readhg + IG -0.475 OG -0.330 - 1G -0.203
From Table DI, the absoiute Merence between OG and + IG was 0.125 volts while it
was 0.145 volts between OG and -1G. Thus the voltage reading for 2G's was 0.270 volts.
Part 2= Data CoUection
1. One subject perfomed a &es of leg extensions at different speeds. SpecincdIy, the
subject complaed a slow, moderate and fhst leg extension at different Ievels ofresistance
(1 resistive band, 4 reshtive bands and 8 eight resistive bands).
2. The uniaxial 8cceIerometer was morneci on the siidhg apparatus ofthe Shuttie 2000.
The analog si@ ofthe acceierometer was connecteci a 12 bit AlD convata whereby it
was sampled at 200 hertz for 5 seconds.
3. For each triai, an average value of the amount of noise present in the signal was
determuid and subsequentiy removed. &.hg adjusted for the presence of mise the a/d
units were converted into G units using the foliowing conversion factor:
(AID unit )* (20 voltd4096 unit)*(2G's/0270 volts)
4. The peak acceIeration (G's) prior to impact with the foot plate was then determinecf
for each aiai (Table D2).
Table D 2. Acceleration observeci at each speed
Tnal name Maximum Acceleration Mean maximum Mean maximum pre impact(G units) acceleration in G unit's acceieration in m/s/s
pre impact. pre impact
F8 1.376 1 .O51 (0.324) 10.3 St slow spced; M= medium speed; F= Fast s p d Numerical number nfers to the number o f bands
5. Figure 0 1 ) is an exampIe of the accelerometer output for a slow, medium and fast trial*
As srpected the trials performed at a nist speed expenenced the greatest acceleration with
an average peak of 1.05 (s.324) G's. At the slow and medium speeds the average peak
accelaations were srnder, O. 175 (M.052) aad 0.334 (rt0.054) G's respectively.
Given the age of the populstiton under study, t was dcipated that aiî subjects wodd
perform the exercise at a sIow speed and therefore the iaertiai forces were neglected since
the meaa peaL acce1erations were smaii (1.7 mlsls). Furthennoie, a i i subjects were
verbally instructed to perfiom the Ieg extension sIowb-
Slow speed
-1 J Tîme (sec)
Ï Medium speed
Fast speed
Figure D 1. Efféct ofhcreasing the speed ofthe leg adension on the acceIeration oftée süding seat. Eight resistive bands were used
Table El. Suggcrrtcd Cut-~Cffrequencies obtained fron BIOMECH QD. The values wcre roundcd to the nearest integer Toe Heel Ankle Knee HP Shoulder
Trial Suegested Adual Suggesled Actual Suggested Adual Suggested Actual Suggested Adual Suggested Actual
rrr r w O V ) - C V * Q P ~ ~ ~ m b m r b o b œ h 1 - f l 0 0 ~ ~ * ~ * Y Y ? ~ R ~ Y ~ S = R ~ ~ ~ O O Q ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ N C Y C Y - C Y ~ C Y O O ~ t . c O O ~ t ~ r r O r r , ~ O m C Y ~ F t C 3 C Y N
Table FI. Chair height as a pemntage of kaee height for eacb gioup. Summary of the nsuitr obtained fmm the two siimpie t test asauming rinequai variance Low chair height GI GII t-Test Two-Samp(e Assurning Unequa1 Variances
88 83 76 82 Vananabk i VwabEe 81 80 Mean 81 I 79 79 Variance 26
82 Obsecvations 4 83 Hypothesized Mean Difference O 79 df 3
tstat -0.05 Pr-) onetan 0.48 t Cntical onetail 2-35 P('ïc=t) two-tail 0.96 t Critical twstail 3.18
GI GII Middle chair height 95 90
83 89 88 87 86 86
90 91 87
t-Test: TW-Sarnple Assuming Unequal Variances
VarCab4 f Vatf&& Mean 88 0 Variance 26 Obsewations 4 Hypotheslzed Mean DWerence O df 3 t Stat 4.22 Pr-) one-taiI 0.42 t Critical onetail 235 P(ï") twcbtail 0.84 t Critical two-tail 3-1 8
G1 GII High Chair height f03 98
89 97 95 9s 93 94
07 88 m
t-Test Twa-Sampie Assuming Unequa1 Variances
van-abhi variable Mean 95 9 Variance 34.7 Obsetvaîions 4 Hypothesized Mean Oifferenœ O df 3 tstat 4-38 Pr*) onetai1 0.37 t Critical one-taii 2-35 Pr-) tumtait 0.73 t Critlcal two-taQ 3-18
Table F Z S w n q of the ANOVAs oa the magnitude variabtes for the withh subject rrlipbüity
Sour~e DF A@SS AdjMS F P Rm
10 5.18 0.5179 22.58 0,000 0.99
Wkankle Sbj IO 0.118 0.0118 6.36 0.000 0.83
Cdn 2 0.002 0.001 0.53 0.593
Trial(%) 22 0.W3 0.00202 1-1 0.390
W k k Sbj IO 3X 0.325 12.4 0,000 0-93
Cdn 2 1.06 0.53 1 20.24 0.000
Trial.(Sbj!) 22 0.513 0.0233 0.89 0.606
Wk hip Sb! 10 8.03 0.803 10.72 0.000 0.90
Cda 2 0.217 0-108 1.15 0.245
Trial (Sb) 22 1-76 0.0800 1-07 0.412
Table F 3. Summary of the ANOVAs on the temporal variables €or nitbiwubject reliahiMy
Parameter Soorce DF AdjSS AdjMS F P R =
Phase t mi 10 2.23 0.223 32.85 0.000 O.%
CQi 2 0,021 0.0 10 1-52 0.231
Trial(SI# 22 0,183 0.00834 123 0.270
Table F 1 S m m a q of ANOVAs on ueh depend- m*abk
Factor Type Levels Values GrP fixed 2 1 2 c d n ( G r p ) fixed 6 1 2 3 1 2 3 sb j (Grp ) random 11 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for mhto, using Aâjusted SS fol: Tests
Source DF Seq SS Adj SS A d j M S F P G ~ P 1 O. 62428 0 ,71032 0,71032 3.01 O. 116 x cdn (Grp1 4 0,53891 0.55282 0.13821 5.31 0.006 sb j (G-1 9 2,22040 2-22040 0.24671 9.49 0.000 Error 16 0,41616 0,41616 0,02601 Total 30 3,79974
Gemnl Umar Modal with sub@cts as a fixad variable:
Factor Type Levels Values G ~ P f ixed 2 1 2 cdn (Grp ) fixed 6 1 2 3 1 2 3 sbj(G-) fixed 11 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for mhto, u s h g Adjusted SS f o r Tests
Source DF Seq SS Adj SS Adj MS F P G q 1 0,62428 0.71032 0.71032 27-31 0.000 cdn (Grp 4 0-53891 0.55282 0.13821 5.31 0,006 sb j (G-1 9 2,22040 2.22040 0,24671 9 - 4 9 0,000 Error 6 0.41616 0.41616 0.02601 Total 30 3.79974
âoafemoni S i i P l t a ~ o u s Test.: Al1 p a i m i s e comparisons among lavels of
Leveï Difference SE of (Grpl cdn of Means Difference 2 -0.3950 O, 1275 i 3 -0 1250 0 , 1275 2 1 -0,3343 O 1161 2 2 -0,5743 O. 1161 2 3 -0,5868 O, 1200
A d j usted Manuail y T-Value P-Vahe adj p-value -3.098 O. 1036 0.0414 -0,980 1.0000 0-4 -2,880 0 1631 N/A -4,948 0 - 0022 NIA -4.890 O. 0025 N/A
Level D i f f e r e n c e (Grp) cdn of Means 1 3 0,2700 2 1 O . 0607 2 2 -0.1793 2 3 . -0.1918
Level Di f ference ( G r p cdn of Keans 2 1 -0,2093 2 2 -0,4493 2 3 -0.4618
Level D i f f e r e n c e ( G r p 1 cdn of Means 2 2 -0,2400 2 3 -0.2525
Level D i f f erence (Grp) of Keans
SE of Di f ference
0 , 1140 0 * 1011, O * 1011, 0,1056
SE of Di fference
O , 10x1 O , 1011 0,1056
SE of Dif ference
0,08621 0.09143
SE of Difference
Adjusted P-Value O. 4626 1.0000 1,0000 2,0000
Adjusted P-Value O, 8243 O. 0061 O. 0071
Aàjusted P-Value O , 1991 0-2085
Adjusted P-Value
Manually adj p-value
0,185 N/A N/A N/A
Manually adj p-value
N/A N/A N/A
Kanuall y adj p-value
0,0796 O. O834
Manually adj p-value
0 .4
AndvJW ofVmIVIance for knee moment at thiph
Geneml Uneu Model with subjects as a mdom vukbk:
Factor Type Leveïs Values G ~ P fixed 2 1 2 cdn(Grp) fixed 6 1 2 3 1 2 3 sb J [ G-1 randorn 11 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance f o r rnkto, using Adjusted SS f o r T e s t s
S o ~ x c e Di? Seq SS A à j SS A d j MS F P G ~ P 1 0.61665 -0.66503 0,66503 3.79 0 . 0 8 3 ~ cda(Gsp) 4 O . 96273 O . 90280 O .22570 6.03 0.004 sbj(Grp) 9 1,64255 1.64255 0.18251 4.88 0,003 Error 16 0.59871 0.59671 0.03742 Total 30 3.82064
Genaral Linear Model with subjects as a med wiuiebîe:
Factor Type Leveïs Values Grp fixed 2 1 2 c&(Grp) fixed 6 1 2 3 1 2 3 sb j ( Grp ) fixed 1 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for mkto, using Aàjusted SS for Tests
Source DF Seq SS Adj SS Adj MS F P G ~ P 1 0.61665 0,66506 0,66503 17,77 0.001 cdn (G-1 4 0,96273 0-90280 0,22570 6.03 0,004 sbj (Grpl 9 1.64255 1,64255 0,18251 4 -80 0.003 E r r o r 16 0,59871 0.59871 0,03742 Total 30 3,82064
Level Dif ference SE of (G-1 cdn of Means Difference 1 2 -0.2463 O. 1529 1 3 -0, 3538 O - 1529 2 1 -0-2516 O, 1392 2 2 -0 - 6159 O, 1392 2 3 -0.6763 O - 1439
O r p = 1 d a = 2 8tab-ard f=: Level Difference SE of (G-1 cdr; of Means Difference 3 -0.1075 0. 1368 2 1 -0, 0054 O. 1212 2 2 -0.3696 0 . 1212 2 3 -0,4300 O. 1266
Adjusted P-Value ~ * O O O O O. 5152 r*oooo O. O064 O ,0036
Adjusted P-value 1.0000 ~.OOOO 0-1149 0.0554
M;anually adj p-value
O, 4 0.206 NIA N/ A N/A
m u a l i y adj p-value
0.4 NIA NIA NIA
Level D i f ference SE of ( G r p ) cdn of Means Difference T-Value 2 1 O. 1021 0 , 1212 0,842 2 2 -0.2621 0 1212 -2.162 2 3 -0,3225 O. 1266 -2,547
Level Dif ference SE o f (Grp 1 cdn of Means D i f f erence T-Value 2 2 -0,3643 O. 1034 -3.523 2 3 -0,4246 O. 1097 -3.872
Level Di f ference SE of ( Grp ) cdn of M e a n s Difference T-Value 2 3 -0,06036 O, 1097 -0,5503
Adj usted P-Value ~ . O O O O O. 6916 0. 3232
Adjusted P-Value O , 0423 O, 0203
Adj usted P-Value i*ooo
Manually adj p-value
N/A N/ A N/ A
Manuaily adj p-value
O. 0169 O, O0812
Manuaiiy adj p-value
O. 4
Anaiivsis of Variance for ankk momtnt at thieb
GeneraI Lineu Modal with subjrctr as a nndom variable:
Factor Type Leveis Values G q fixed 2 1 2 c&(Grp) fïxed 6 1 2 3 1 2 3 sb j (Grp') random Il 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for mato, using Adjusted SS for Tests
Source DF S e q SS Adj SS Adj MS F P GrP 1 0.00633 0,00643 0.00643 0.03 0,867 x cdn (Grp ) 4 0.11639 O, 13534 O ,03383 3 0,215 sbj(G-1 9 2,03381 2,03381 0.22598 10.90 0,000 E r r o r L6 0.33171 O. 33171 0.02073 Total 30 2.48824
GenemI Linear Modrl with subjects as a fixed vuiabk:
Factor Type Levels Values GrP f ixed 2 1 2 cdn ( Grp 1 fixed 6 1 2 3 1 2 3 sbj (G-1 fixed II 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for mato, using Adjusted SS for Tests
Source DF Seq SS Aàj SS Adj MS F P GrP 1 0,00633 0.00643 0,00643 0.31 0.585 cdn(Grp) 4 0.11639 0.13534 0,03383 1.63 0,215 sbj ( G r p ) 9 2.03381 2,03381 0,22598 10-90 0.00o Error 6 0-33171 0.33171 0.02073 Total 30 2.48824
Anaivsis ofVrnWimce for Deak MD moment of force
General Linear Moûel with subjects as a random variabla:
Factor Type Levels Values G ~ P fixed 2 1 2 cdn(Grp1 fixed 6 1 2 3 1 2 3 sb j (Grp.) randorn 11 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for pkh, using Adjusted SS fo r T e s t s
Source Di? S e q SS Adj SS A d j MS F P G ~ P 1 0,55729 0,61759 0.61759 2-69 0,135 x cdn (G-) 4 0,53440 0.53192 0.13298 5.26 0,007 sbj (Grp l 9 2.16053 2,16053 0,24006 9-50 0,000 Error 6 0-40426 0.40426 0,02527 Total 30 3,65648
Gensral Linear Model with subjects as a fïxeâ variable:
Factor Type Levels Values GrP fixed 2 1 2 cdn(Grp) fixed 6 1 2 3 1 2 3 sbj(Grp) fixed 11 1 S 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for pkh, using Adjusted SS for Tests
Source DE' Seq SS Adj SS Adj MS F P G ~ P 1 0.55729 O. 61759 0.61759 24-44 0.000 cdn ( G r p ) 4 0,53440 O. 53192 0.13298 5-26 0.007 sbj ( G q ) 9 2,16053 2,16053 0,24006 9.50 0,000 Error 16 0,40426 0,40426 0102527 Total 30 3,65648
B o n f i Simuhaneous Tests: W @mise c o m p b n s ammg l e d s of ah(gp).
Level D i f ference SE of (Grp cdn of Means Difference 2 -0.3654 O, 1257 1 3 -0.1179 0, 1257 2 1 -0.2940 O. 1144 2 2 -0.5340 O , Tl44 2 3 -0.5648 0,1183
arp = 1 cdn = 2 subtraated foa: L e v e l D i f ference SE of (Grpl cdn of M e a n s Diffaence 1 3 O ,2475 O. 11240 2 1 O, 0714 O, 09963 2 2 -0.1686 O. 09963 2 3 -0, 1994 0. 10406
Adjusted P-Value O 1541 f.OOOO 0.3082 O, 0039 O.OO3l
Adjusted P-Value
O. 6402 1.0000 1.0000 1,0000
Manuall y adj p-value
O1O6l6 0-4 N/A N/A NIA
~ u ~ l y adj p-value
O ,256 N/A NIA N/A
Level D i f ference SE of (Grp l cdn o f Means Difference 2 1 -0.1761 0 09963 2 2 -0.4161 0 09963 2 3 -0.4469 O. 10406
Level Dif f erence SE of ( G r p cdn of Means Difference 2 2 -0,2400 O. 08496 2 3 -0 2708 0.09012
Level Di f f erence SE o f (Grp ) cdn of Means Difference 2 3 -0 03083 O. O9012
Adjusted P-Value 1.0000 O.OlOï 0. 0084
Arfjusted P-Value O. 1830 O , 1258
Adjusted P-Value
Manually adj p-value
N/A N/A N/A
Manually adj p-value
0.0732 0 0503
Maaually adj p-value
0.4
Aaaivsis of Variauce for rierk knae momeat offorce:
GeneraI Linear Model with subjucb as a nndom wiaôk:
Factor Type Levels Values G ~ P f ixed 2 1 2 cdn(Grp) fixed 6 1 2 3 1 2 3 sbj (G*) random 11 1 S 6 8 2 3 4 7 9 1 0 1 1
Analysis of Vasiance for pkk, using Adjusted SS f o r T e s t s
Source DF Seq SS Adj SS Adj MS F P G ~ P I 0,38303 0,43412 0,43412 3.10 0,112 x cdn(G-) 4 O . 16687 0.17701 0.04445 3.41 0.034 sbj(G-1 9 1.31015 1.31815 0,14646 11.24 0,000 Error 16 0.20844 O 20844 O, 01303 Total 30 2.07648
Gemral Unear Moâel mth subjects as a fixed vuiibîe:
Factor Type L e v e l s Values G ~ P fixed 2 1 2 cdn(Grp1 fixed 6 1 2 3 1 2 3 sbj(Grp1 fixed 1 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for pkk, using Adjusted SS f o r T e s t s
Source DF Seq SS A d j SS Adj MS F P -P 1 0,38303 0.43412 0.43412 33.32 0.000 cdn(Grp1 4 0,16687 0.17781 0,04445 3-41 0.034 s b j ( G - 1 9 1.31815 1,31815 0.14646 11.24 0,000 Ekror 16 0,20044 O ,20844 0,01303 Total 30 2,07648
O r p = I lrdn = 1 8 t l b ~ a c t d froni:
L e v d Dif f trence SE of Grp 1 cdn of Means D i f ferencc 1 2 -0,0925 0,09023 1 3 -0.1475 O, 09023 2 1 -0.2246 O 08214 2 2 -0,3404 O , 08214 2 3 -0,4375 0,08492
L e v e ï Difference SE of (Grpl c h of Means Difference 1 3 -0.0550 O ,08071 2 1 -0.1321 0.07154 2 2 -0.2479 O, 07154 2 3 -0.3450 O. 07472
Adj usted P-Value L*0000 1,0000 0. 2202 0.0114 O , 0014
Adj usted P-Value ~.OOOO r,oooo O ,0479 O, 0043
Manually adj p-value
O. 4 O. 4 N/A N/ A NIA
m u a l l y adj p-value
O , 4 N/A N/A N I A
Level Di f ference SE of (Grp l cdn of Means Dif ference 2 L -0,0771 0 , 07154 2 2 -0.1929 O , 07154 2 3 -0.2900 O. 07472
Level D i f ference SE of (Grp ) cdn of Means Difference 2 2 -0.1157 0 06101 2 3 -0 -2129 O, 06471
Level D i f f erence SE of ( G r p ) cdn of Means D i f ference 2 3 -0.09714 O. 06471
Adjusted P-Value ~ , O O O O 0.2386 0.0199
b u a l l y adj p-value
N/A N/A N/A
Manually adj p-value
0.4 O, 0277
ManuaUy adj p-value
0-4
Anaiv& O€ Varbce for m& ankk moment offorce:
Factor Type Levels Values G ~ P fixed 2 1 2 cdn(Grp) fixed 6 1 2 3 1 2 3 sb j (Grp-) random II 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance f o r pka, usinq Adjusted SS for T e s t s
Source DE' Seq SS Adj SS Adj MS F P G ~ P 1 0.01508 0,03989 0.03989 0.67 0 . 4 3 4 ~ cdn(Grp) 4 0,03745 0.07654 0,01914 1.00 0.437 sbj(Grp) 9 0, 55484 0.55404 0.06165 3.22 0.020 Error 16 0,30663 0.30663 0.01916 Total 30 0,91399
Factor Type Levels Values GrP fixed 2 1 2 c d n ( G r p ) fixed 6 1 2 3 1 2 3 sbj (Grp) fixed 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for pka, using Adjusted SS for T e s t s
Souxce DF Seq SS Ad j SS Adj MS F P G ~ P 1 0,01508 0,03989 0,03989 2,08 0,168 c&(Grp) 4 0.03745 0.07654 0,01914 1.00 0.437 sbj (Grpl 9 0.55484 0,55484 0,06165 3.22 0,020 Error 16 0,30663 0.30663 0,01916 Total 30 0,91399
* No significant diffemce for for cdn (grp)
Anrilvsb of Vdonce for work done at the h i ~ :
Genenl U n w Modal with subjects as a nndom wiable:
Factor Type Levels Values GrP fixed 2 1 2 cdn ( Grp 1 fixed 6 1 2 3 1 2 3 sb j (GEP.) random Il 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for workh, using Adjusted SS for Tests
Source DE' S e q SS Adj SS A d j MS F P GrP 1 0-45851 0.39395 0,39395 1-22 0 . 2 9 7 ~ cdn(Grp) 4 0,09349 0.09102 0,02275 0-41 0.799 sbj(Grp1 9 3.02977 3,02977 0,33664 6 0 6 0.001 Error 16 0,88938 0,88938 O. 05559 Total 30 4.47115
Generai Unear Model with subhcts as a fixed vrirbk:
Factor Type Levels Values GrP fixed 2 1 2 cdn (Grp ) fixed 6 1 2 3 1 2 3 sbj(G-) fixed Il 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Vadance for workh, using Adjusted SS f o r T e s t s
Source DF S e q SS Adj SS Adj MS F P GrP 1 0.45851 0.39395 0,39395 7.09 0,017 cdn(Grp) 4 0.09349 0.09102 0.02275 0.41 0.799 sbj ( G r p ) 9 3.02977 3.02977 0,33664 6.06 0.001 Error 16 0,88938 0.88938 O, 05559 Total 30 4,47115
100 m i g n i f î c a n t diff-c~s u u e fouad for câa ( grp).
Aaalvsis ofVmiance for work donc at the hee:
General Lïnear Modef wim subjects as a mndom vriabk:
Factor Type Levels Values G ~ P fixed 2 1 2 cdn ( G r p ) fixed 6 1 2 3 1 2 3 sb j (Grp.) random il 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Va~iance for work k, using Adjusted SS for Tests
Source Di? Seq SS Adj SS AdjMS F P G q 1 0,10840 O, 16619 O ,16619 1-34 0.277 x cdn(Grp) 4 0.48970 0,52478 0.13120 10-42 0.000 sbj (Grpl 9 1. 17170 1.17170 0,13019 10-34 0,000 E r r o r 16 0,20138 0,20138 O , 01259 Total 30 1.97119
General Linear Mode1 with subjects as a fixed variah:
Factor Type Levels Values G r p fixed 2 1 2 cdn ( G r p ) fixed 6 1 2 3 1 2 3 sb j (Grp) fixed 11 L 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for work k, using Aàjusted SS f o r Tests Source DF Seq SS Aàj SS Adj MS F P GrP 1 0,10840 0,16619 0.16619 13-20 0.002 cdn(Grp) 4 0,68970 0,52478 0,13120 10,42 0,000 sbj Grp) 9 1.17170 1,17170 0.13019 10.34 O.OOO Error 6 0,20130 0,20138 O 01259 To ta1 30 1,97119
B o n f i $' '- Tests: M p i in r i r raipuiroar am- 6 m b dcdn(gp).
G l p = L cda = 1 subtrrctmd frorn: Level Difference SE of (Grp) cdn of Means Difference 1 2 -0.0925 O, 08869 3 -0 2975 O, 08869 2 1 -0 , 1171 O. 08073 2 2 -0.2857 O , 08073 2 3 -0 ,4589 O, 08347
Leveï Difference SE of Grp) cda of Means D i f f e r e n c e 1 3 -0,2050 O. 07933 2 1 -0,0246 O. 07032 2 2 -0 1932 O, 03032 2 3 -0.3664 O. 07345
Adj usted P-Value ~.OOOO O. 0605 1.0000 0,0409 0.0007
Adjusted P-Value
O ,2996 L O O 0 0 O ,2145 0.0020
ManualZi y adj p-value
0-4 O. 0242 N/A N/A N/A
Manually adj p-value
O. 120 N/A N/A NIA
Level Di f ference SE of (G-1 cdn of Means Difference 2 1 0. 1804 O. 07032 2 2 O. 0118 O. 07032 2 3 . -O, 1614 O. 07345
Leva Difference SE of ( G r p l cdn of Means D i f ference 2 2 -0.1686 O. 05997 2 3 -0,3418 0.06361
Level Dif ference SE of ( Grp 1 cdn of Means Difference 2 3 -0,1732 O. 06361,
Adj usted P-Value 0,3115 1.0000 O , 6453
Adjusted P-Value O. 1883 O, 0009
Adjusted P-Value
O. 2256
Manually adj p-value
NIA NIA N/A
Manually adj p-value
O . 0753 o. O00
Manually adj p-value
O. 0902
Aaaivsis of Variance for work doue at tbe ankk
General Linear Mo&l witti subbctr as a random variabla:
Factor Type Levels Values G ~ P fixed 2 1 2 cdniGrp) fhed 6 1 2 3 1 2 3 sbj (Grp) random 11 1 5 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance for worka, u s h g Adjusted SS for T e s t s
Source DF S e q SS Adj SS Adj MS F P GrP 1 0,0094076 0:0137162 0,0137162 4,61 0.060 x cdn (G-1 4 0,0056371 0.0058935 0,0014734 2-21 0,115 sb J (G-1 9 0,0278589 0,0278589 0.0030954 4.63 0-004 E r r o r 16 0,0106899 0.0106899 0,0006681 Tata1 30 0,0535935
General Linear Model with subjects as a fixeâ m*abîe:
Factor Type Levels Values GLP fixed 2 1 2 cdn ( G r p ) fixed 6 1 2 3 1 2 3 sb j (Grp ) fixed 1 1 S 6 8 2 3 4 7 9 1 0 1 1
Analysis of Variance f o r worka, using Adjusted SS f o r Tests
Source DE' S e q SS Adj SS Adj MS F P GrP 1 0,0094076 0.0137162 0.0137162 20.53 0-000 c d n ( G r p ) 4 0,0056371 0.0058935 0,0014734 2.21 0.115 sbj Grp) 9 0,0278589 0.0278589 0,0030954 4-63 0.004 Exxor 16 0.0106899 0-0106899 0,0006681 Total 30 0,0535935
NORMAL PROBABILITY PLOT OF TEIE PEAK ANKLE MOMENT
Peak adde momrt at the anfde
NORMAL PROBABILSrY PLOT OF THE PEXK KNEE MOMENT
peak knee moment
NORMAL PROBABJUTY PLOT OF TEE PEAK HIP MOMENT
Peak hip moment
W 4 e t for Normiaty R: OM81 P-Valu. (rppaw): . O*?000
NORMAL PROBABIUIY PLOT OF TEE TOTAL AMOUNT OF WORKDONE AT TEE HP
Work done a€ the tip
NORMAL PROBABILlTY PLOT OF THE M T . AMOUNT OF WORK DONE AT TBE KNEE
NORMAL PROBABITY PLûT OF THE TOTAL AMOUNT OF WORK DONE AT THE ANKLE
Work done at the anide
NORMAL PROBABaSrY PLOT OF THE MEAN ANEaE MOMENT
Mem moment at the anlde
NORMAL PROBABILFFY PLOT OF TEE MEAN KNEE MOMENT
Mean moment a€ fie knee
NORMAL PROBABaSrYPLOT OF THE MEAN KNEE MOMENT lB@'L-
mean knee moment
NO- PROBABILJTY PLOT OF THE MEAN EIP MOMENT
Mean moment at the tip
NORMAL PROBABILITY PLOT OF THE MEAN HIP AND KNEE MOMENTS
Mean rnomgit f a sum of hip and knee
NORMAL PROBABUI'Y PLOT OFTHE MEAN AMC[LE AND KNEE MOMENTS
Mean moment for sum of k m and ankk
Ankle moment at thigh off
Knee moment at thigh off
W-test tor N o m al iy R : O. 8@34 P-Value [ipprax): > O . t O O 0
Hip moment at thigh off
Knee m m n t
Low Chair Height Croup 1 (Sabjeets A, F, 1)
Hip Moment
% exhnsion phase
Knee momnt
Middle Chair Hcigbt Croup 1 (Subjecfs A, F, G, 1)
Hip Moment
Hlp ponmr
%extension p i m e
Low C h u Height ( Subjects A, F, I)
Knee ponnr
Middle Chair Height Croup1 (Subjects A, F, G ,I )
Hip power
5.0 7
%extension phase
Knee powr
t r i
Ankle moment
HlGH CHAIR HEIGHT CROUP II (Subjects B,C,D,H,I<,W)
Htp power
HlGH CHAlR aElGHT CROUP 1 (B,C,D,H,K,W)
Ankh power
Mem momenb QF the ankl@ (Ma), knee (Mk) , hip (Mb), hip and knee (H& K) and kna and ankle (A&K) rt tbc low chair height Cor crch. Group l and II
Subjed a n Ma (we) Mk(eve) Mh (me) H&K A&K 1 1 0,443 0,344 0,795 1,138 0,787 2 4 0,261 055 1 1.677 0,81 3 1 0,513 0,887 0,604 1 ,56 1.38 4 1 0,601 033 1.125 1,285 1,13 5 1 0,454 1,24 0,521 1,785 1,695 7 t 0,318 0.802 0,855 1 ,88 1,12 8 1 0,263 0,629 0,842 1.47 0,895 O 1 0,388 0,642 1,OQ 1,733 1,033
10 1 0.23 0,745 1 ,W 1,70 0,893
Group Il Subjecî cdn Ma (ave) Mk (ave) Mh (ave) H&K A&K
2 2 0,087 0,532 0,880 1,42 0.61 9 3 2 0,331 0,744 0,732 1,473 1,073 4 2 0,307 0,483 0,746 1.2283 0,788 7 2 0,255 0,593 1 .O4 1,64 0,847 9 2 0,297 0,569 0.98 1.547 0,865
I O 2 0,4'î2 0.57 1 ,Il l l,68 0,983
sd 0,105 0,082 0,142 0,152 0,144 covariance hk 0,0039 14.5% var 0,OI 1 O, 007 0.020 0,023 0,021 covariance ak w0,0030 -1 6,0%
moup II Subjed odn Ma (me) Mk (eve) Mh (ave) H&K A&K
2 3 0,247 0.488 0,771 1.26 0.74 3 3 0,132 0,607 0,672 1.277 0,739 4 3 0,51)7 0,365 0,798 1,165 0,877 7 3 0,156 0,571 0,934 1,503 0,728
I O 3 0,083 0,472 1, 347 1,753 0,488 II 3 , 0,i 87 0,216 1 ,16 1,372 0,403
mean 0,220 0,453 0,047 1,388 0,683 W O, 155 0,144 0,259 0.212 0,179 covariance hk variarice 0,024 0.021 0,067 0.045 0,032 covariance ak
Alexander, N., Koester, D. & Gninadî, J.A (1996). Chair Design M i s How OIder Addts Rise fiom a Chair. Journal ofthe Amencan Genatrics Society 44,356-362.
Alexander, N., Schultz, A & Warwick, D. (199 1). Rishg From a Chair Effects of Age and Functionai Ability on Performance Biomechanics. Journal ofGeromo1o~v 46(3), M91-98.
Andrews, J.G. (1983). Biomechanid Meames of M u d a r mort. Medicine and Science in S~orts and Exercise 15 [3L 199-207.
Baer, GD. & Ashburn, AM. (1995). Trunk Movements in Older Subjects hiring Sit-to- stand. Archives of PhvsicaI Medicine and Rehabüitation 76,844849.
Bassey, E.J., Fiatarone, M., OWe& E., Kelly, M., Evans, W. & Lipsitz, L A (1992). Leg Extensor Power and Functiod Performance in Very Old and Men. ClinicaI Science 82 321.327. _+
BIOMECH @ Motion AnaIysis System, copyn*ght Kinesiology Department, University of Waterloo, ontano, Canada
Burd* R, Habasench, R, Pisciotta, J. & Simon, S. (1985). BiomechanicaI Cornparison of Rishg nom Two Types of Chairs. Ph~sicaI Therapv 65(8), 1177-1 183.
Brown, M, Sinacore, D.R. & Host, H.H. (1995). The Relationship ofstrength to Fuaction in the OIder Adult. The J o d s of GerontoIop SerÏes A 5 0 4 55-59.
Cm, JH. & Gentile, A M (1994). The EEiect of Arm Movement on the Biomechanics of Standing Up. Human Movement Science 13,175493.
Co- S.S & McFadyen, B.J. (1994). Transfier Strategies Used to Rise From a Chair in Normal and Low Back Pain Subjects. Clinical Biomechanics 9,85-92.
Chapman, AE. (1985). The Mechanical Propdes of Human Muscle. Exercise and S~ort Sciences Review 13,443-501.
Crosbie, I., Herbert,R.D. & J.T. Bridson (1997). Intersegmental Dynamics o f Standing fiom Sitting. Clinid Biomechanics 12o.227-235.
Doorenbosch, CA, H a r k , J., RoebroecIq M, Lankhorst, J. (1994). Two Strategies of T r a u s f d g fiom Sit-to-Stand; The Activation ofMonoartiCUIar and Biarticular Muscles. Journal Of Biornechanics 27,12994307.
mes, DR, Judge, J.O. & Gunnarsson, O.T. (1997). Powa as a Redictor of Functional AbiIity in Community Dweliing Oldei Persans (Abstract). Journal of the American Coiiege of Soorts Medicine 29 îsu~~lement 52 S 1 1.
Ellis, M.I., Seedhom, BB., Amis, AA, Dowson, D. & Wrigh~ V. (1979). Forces in the Knee Joint Whiist Rising fiom Nomial and Motorized Chairs. Engineain~ in Medicine 8 a 3340.
ais , M.& Seedhom, BB. & Wright, V. (1984). Forces in the Knee Joint WhiIst Rising h m a Seaîed Position. J o u d of Biomedicd Enaineerhn 6, 113-120.
Fiatarone, M, Marks, E., Ryan, N., Meredith, C., Lipsitz, L.A & Evans,W.(I990) HÏgh Intensity Strength Training in Nonagenarians. Journal ofthe American Medicd Association 263,3029-3034.
Fiatarone, M., O'Neill, E., Doyle Ryan, N., Clernents, K, Solares, G., Nelson, M., Roberts* S., Kehayias, LI., Lipsitz, L A & E m 9 W . (1994). Exercise Training and Nutritionai SuppIementation For Physicai FraiIty in very EIderIy People. The New Endand J o d of Medicine 33M29.1769-1775.
Fieckemein, S., Knby, RL. & MacLeod, O. (1988). E f f i ofLimited Knee-Fiexion Range on Peak Hip Moments ofForce While T d i g h m Sitting to Standingg J o d of Biomechanics 2I(I I), 915-918.
Hanke* T., Pai, Y-C. & Rogers, M (1995). Reliabiiity of Measurements ofBody Center 0f-s Mornemm during Sit-to-Stand niHWby Aduits. Pwcai 118.
Hughes, M, Weiner, DIC, Schenkrnan, M.L., Long, RU & Studenski, S.A (1994). Chair Rise Strategis in the EIderly. CIinicaf Biomechânics 9, 187492.
Hughes, M A , Myers, B.S. & Schenkmaa, ML. (1996). The Rde ofstrength in Rising fiom a Chair in the F u n c t i o ~ y Impaired Elderly. Journal of Biomechanics 29(12), 1509-1513.
Hughes, M.A. & Schenkman, ML. (1996). Ch& Rise Strategy in the Fundonaiiy Impaired Elderly. Joumal of Rehabüitation Researcb and Development 33(4), 409412.
Ikeda, E., Schenkmaa, M, Riley, P .O. & Hodge, W. A (199 1). Influence of Age on Dynamics of Rising fiom a Chair. Phvsical Theraov 71(61,473-48 1.
Jeng SE, Schenkman, M., O Rüey, P. & Lin S. (1990). Reliability of a Clinicai Kinematic Assessrnent of the Sit-to-Stand Movement. Phyicai Theratgr 70(Q 5 1 1-520.
Kelley, DL., Dainis, A & Wood, GK (1976). Mechanics and Musailar Dynamics of Rising fiom a Seated Position. In: Komi, P.V., ed. Biomechaaics V-B. Bahimore, MD: University Park Press, 127-134.
Kotake, T., Dohi, Ney Kajiwara, T., Sumi, N., Koyama, Y. & Mïun, T. (1993). An Analysis of sit-testand Movements. Archives of Phvsicai Medicine and Rehabilitation &109S- 1099.
Lexeil, J., Taylor, C. & Sjostrom, M. (1988). What is the Cause of the Aging Attopfiy* Journal of the NeuroIogicai Sciences 84,275-294.
Makndes, L. & Carnpagna, P. (1992). Elde&: A Guide to Exercise for seniors. Dalhousie University, Halifi Canada.
Miller, MC. (1990). Biomechanics ofRishg fiom a Chair or Bed. PhD Disseeon Ann Arbor: The UniversiCy ofMicbigaa
Munro, B.I., SteeIe, IR, BWord, GM, Ryaa, M & Britten, N. (1998). A Kinematic and Kiaetic Analysis ofthe Sot-testand T d e r uskg an Ejector Chair. hpIications for ElâerIy R6eumaîoid Arthitic Patients. J o d ofBiomechanics 31,263-271.
National Tsometnc M u d e Strength (NIMS) Database Consortium (1996). MuscuIar Weakness Assessment: Use ofNormal Isometric Strength Data Archives in Phvsicai Medicine and Rehabilitation 77,125 1-1255.
Pai, Y-C, & Rogers, M. (1990). Control of Body Mass Transfer as a Function of Speed of Ascent in Sit-to-Stand. Medicine and Science in S~orts and Exercise 2X3). 378-384.
Peak Performance Technologies Inc. 2D Motion Measurement System 0 (version %O), CoIorado, United States.
Podsiadlo, D. & Richardson, S. (1991). The Timed " Up & Go": A Test ofBasic Functionai MobiiÎty for Frd Elderly Persoas. Journal of Amerban Gerïatrics Society 39. 142-148.
Read, A (1998). A Detailed Analysis of the Temporal Phases ofthe Timed 'TJp and Go" Test. Master's thesis. Dalhousie University.
Riley, P.O., Schenkman, ML, Manri. RW. & Hodge, A (1991). Mechanics of a Conmained Chair-Rise. Journal of Biomechanics 24111 77-85.
Rodosky, M.W., Andriacchi, TP. & Andersson, GB. (1989). The Muence of Chair Height on Lowa Limb Mechanics During Rising. Journal of Orthopaedic Research 7, 266-271.
Roebroeck ME., Doorenbsch, C U . , HarIaar, J., Jacobq R 8t Lankhorst, G.J. (1994). Biomechanics and M d a r Durhg Sit-to-Stand Tran&er. C h i d BiomechmCcs 9.235-244.
Rosedd, R & R O ~ O W ~ R (1991). Models ofQuasi-Experhentai Desigiis, In Essentials of Behaviod Research: Methods and Data W v s i s Im. 92-1 091 New York McGraw-Hill.
Schenkmnii, U, Berge& RiieyS.0, MiuqR-W. & Hodge, WA(1990). WhoteBody Movements huing Rising to Standing fiom Sitting. PfysicaI Therabv* -101 636648.
Schenkman, M, Rüey, P.O. & Pieper, C. (1996). Sit-to-stand fkom Progressively Lower Seat Heights - AIterations in Angular VeIocity. Clinical Biomechanics 1 1-2 153-1 58.
Schuitq A, Alexander, N. & Ashton-Miller, J.(1992). Biomechanical Analyses of Rising Eoom a Chair. Journal of Biomechanics 25(12), 1383-1391.
Schultz, A(1995). Muscle Fmction and Mobility Biomechaaics in the Hderly: An OvervrCew of Sorne Recent Researcb (1995). The IoumaIs of Gerontolog Senes A 5 0 4 60-63.
Seedhom, BB. & Terayama, K (1976). Knee Forces During The Activity of Getthg Out Ofa Chair Wth and Without the Aid of Arms. Biomedicd Enaineering, 278-282.
Shepherd, RB. & Koh, W. (1993). Biomechanical Consepuences of Varying Foot Placement În Standing Up. Ihtemationai Society of Biomechaaics XIV Conmess, Abstracts II @p. 1240-1241). Paris: Imprimerie Laballery.
Singleton, R, Straits, B. & Straits, M.(2 ed.) (1993). &proaches to Sociai Reseetch. Mord: Mord University Press.
SkeIton, DA, Gr% C . 4 Danes, 3.M. & Young, A (1994). Streagth, Power and Relateci FmctrConaI Abiiity ofHdthy People Aged 65-89 Years. Ane and Aaeinq, 23, 371-377,
Tippett, SK Pushing tbrough Successf*ur Rehab with the Shuttie. Advance Rehabiiitation February I994,47.
Thomas, I. & NeIson, 1.(2 ed) (1990). Research Methods in Ph-id Activity IUinois: Human KinetlLcs.
Weiner, DK, Long, R7 Hughes, M-A, Chandler, 3. & Studemki, S.(I993). When Older Adults Face the Chair Rise ChalIenge. J o d ofthe Amerkan Watr ïc Society 41.6- 10-
Whore, J E & C o d , DL. (1994). PhvsioIow of S~ort and Exetcisee Uied States: Human Kinetics.
Wmtter, D.A (1978). Caicdation and lnterpretation of Mechanid Energy of Movement. Exercise and Sprîs Science Review 6,183-20 1.
Winier, D.A (1980). Overaii Principle of Lower Limb Support Duriag Stance Phase of Gait. Journal of Biomechanics 13.923-927.
Winter, D.A (1984). Kinematic and Kinetic Patterns in Human Gait: Variability and Compensating Effects. Human Movement Science 3,s 1-76.
Winter, D.A (1989). Biomechanics ofNormal and PathoIogical Gait: Implications for Understanding Human Locomotor Contro1. Joumal of Motor Behavior 2 1(4), 337-355.
winter, D.A. (2 ed). (1990). 0 New York John Wiley & Sons Inc.
Wmter, D.A, Patla, AE., F e I.S. & Wait, SE. (1990). Biomechaaicai Walkixig Pattem Changes in the Fit and Healthy EIder1y. Phvsical Therapv 70(6b 340-347.
Wmter, D.A. (199 1). The Biomechanics and Motor Control of Human Gait: Nord, EiderIy and PathoIomcai (2 m. Ontario, Cana& University ofwaterioo Press.
Winter, DA(1995). AB.C.(Anatomy, Biomechomics and ControI) ofBalance during Standing and Walking. Omsno, C h : University of Waterfoo.
Woffin, L., Judge, J., Whipple, R & King, M (1995). Strengîh is a Major factor in Balance, Ga&, and the Occurrence ofFalis. The Iournals of Gerontolopv Series A. SO& 64-67.
Yan& J E & Wmter, D. (1983). Electrornyography Reliabihty in Uaximal and Submaximai Isometric Contractions- Arcbiws of Phvsicai Medicine md Rehabilitation 64 417420. d