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Research ReportA Comparison of Oxygen Consumption DuringWalking Between Children With and WithoutBelow-Knee Amputations

Background and Purpose. Dzferences, if any, in ermgv costs during walkingof children with below-knee amputations ( B a )and those of children withoutamputations have not been quantzjied. The purpose of this investigation was tocompare measures of heart rate and oxygen consumption during walking (1)between children with BkX and long residual limbs and children with BkX andshort residual limbs and (2)between children with BK4s and children without am-putations. Susjects. Twenty-fourchildren volunteered to partinpate in this investi-gation. Ten of the children, aged 6 to 18years, had BkX, and 14 children, aged 6to 17 years, were without amputations.Methods . The subjects walked for 2 min-utes at each of the following four speeds: (1) chosen walking speed (CWS),(2)20%below CWS, (3)20% above CWS, and (4)fied speed of 1.2m/x Heart rate anda?cygen uptake were measured at each speed.Results. The results indicated (1) thatthere were no signzjicant dzferences between children with long residual limbs andthose with short resiUual limbs; (2) hat oxygen consumption was 15% greater forchildren with BkAs compared with children witbout amputations;(3) hat there wereno dzfferences in heart rates between children without amputations and those withBkAs or within c h i h with BkX; and (4)that children with BkX did not choosespeeds dzffwentjbm their peers without amputations, regardless of stump length.ConcZuston and Discussion. The results indicated that children with BkAs hadhigher energy needs or walking than children who had no amputation. Whetherthe increased enetgv needs prevent or inhibit children with B k X f i m having alifstyle comparable to that of children without amputations is currently unknownand warrants urther research. [HerbertW.l,Engsberg JR , TedfordKG, Grimston SKA comparison of q g e n consumption during walking between children with andwithout below-knee amputations. Pbys Ther. 19%; 74:943-950.1Key Words: Below-knee amputation, Children, Energy cost, Heart rate, Oxygenconsumption.

LM Herbe:rt, is Graduate Student, Human Performance laboratory, University of Calgary, Calgary,Alberta, Canada T2N 1N4.JR Engsbe:rg, PhD, is Biomechanist and Director, Motion Analysis laboratory, St Louis Children'sHospital, One Childrens' Place, St Louis, MO 63110-1077 (USA). Address all correspondence to DrEngsberg.KG Tedford, RPT, s Physiotherapist, Alberta Children's Hospital. Calgary, Alberta Canada T2T 5C7.SK Grimston, PhD, is Human Biologist, Division of Endocrinology and Metabolism, WashingtonUniversity Medical Center, 216 S Kingshighway, St Louis, MO 63178.This study was approved by the Institutional Review Board of the University of Calgary.This research was supported by the Alberta Children's Hospital Foundation, the Alberta HeritageFoundation for Medical Research, and the Variety Club of Southern Alberta Tent 61.This article was submitted November 27, 1992, and wa r accepted May 17, 1934.

Lisa M HerbertJack R EngsbergKathl G TedfordSusan K Grimston

It has been previously reported thatthe kinematics and kinetics of chil-dren with below-knee amputations(BKAs) are significantly different dur-ing ambulation when compared withthose of children without arnputa-tions.14 These differences have beenattributed to prosthetic limb mechani-cal deficiencies-5 Although quantify-ing mechanical differences providesinformation useful for the improve-ment of prosthetic limbs, it does notaddress how the mechanical differ-

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MethodTable 1. Characteristics of Children W ith Below-Knee Amputati ons (n =I O) Subjects

Chosen LengthBody Walking of

Age Height Mass Speed Termlnal Suspenslon Resldual(y) (cm) (kg) (mls) Gender Devlce Method Llmba

SeattleSeattleSeattleDynamicSeattleGreissengerSeattleFlexSachSeattle

CondylarCondylarlsleeveCondylarCondylarSleeveSleeveSleeveSleeveSleeveCondylar

LongShortLongLongLongShortShortShortLongLong

"Long residual limb=greater than 67% of intact limb length (note: all children with a long residuallimb had a congenital defect); short residual limb=less than 67% but greater than 33% of intactlimb length (note: all children with a short residual limb had a traumatic amputation).'Subject walked at each speed only once.ences affect ene rgy costs in ch ildrenwith BKAs.Studies comparing the ene rgy costsduring w alking in adults with BKAshave shown that they have the sameenergy costs as adults without ampu-t a t i ~ n s . ~ l Ohis similarity wasachieved, however, because the per-sons with amputations walked atslower speeds. When the adults withBKAs walked at the same sp eed asadults without amputations, theirenergy costs were approximately 32%greater.Wonzalez et a17 found thatadults with BKAs and lo ng residuallimbs (greater that 8% of total bodyheight) had a 10% increase in oxygenconsumption (iro,) com par ed withadults without amputations, whereasadults with BKAs and s hort residuallimbs (less than 6% of total bodyheight) had a 40% increase when thegroup s performed the sa me activities.

It is currently unknown whether it ispossible to generalize these differ-ences in en ergy costs between adultswith and without BKAs to children. Apreliminary study conducted in ou rlaboratory indicated that children withBKAs (n=3) consumed 10% mo reoxygen than did children withoutamputations (n= 2) wh en walking atthe same speeds.1 Du e to the smallnum bers in each gro up, it was notpossible to generalize these trends tothe larger populations of childrenwith BKAs.The p urpose of ou r investigation wasto co mp are physiological measures ofheart rate and VO, during w alking (1)between children with BKAs and longresidual limb s and children with BKAsand short residual limbs and (2) b e-tween children with BKAs and chil-dr en w ithout am putations.

'Quinton Instruments, 2121 Terry Ave, Seattle, WA 98121.'Sensormedics Corp, 1630 S State College Blvd, Anaheim, CA 92806.

Ten children (1 female, 9 male) withBKAs and 14 children (8 female, 6male) without amputations volun-teered as subjects for this study. De-scriptive measures for the childrenwith BKAs and the children withoutamputations are given in Tables 1 and2 , respectively. All children with BKAshad a prosthes is for at least 4 yearsand said they we re comfortable withthe fit of the prosthesis. To comparechildren with different residual limblengths, the children w ith BKAs wereplaced into two groups by a physicaltherapist according to the interna-tional classification of amputations.On e group consisted children withBKAs and residual limbs of less thantwo thirds of intact limb length. Theothe r grou p consisted of those chil-dren w ho had a stump length equalto o r greater than two thirds of intactlimb length. These groups were con-sidered short- and long-limbed, re-spectively, and we re similar to thegrouping of G on za la et aL7 Medicalhistories indicated that, excep t for theamputation in the children with BKAs,all children were in good health andhad no known medical problems.Subjects and parents w ere familiar-ized with the testing procedures andequipment prior to signing humanconsent forms.ProcedureOxygen uptake (in milliliters perkilogram pe r minute) was measuredusing a Quinton Instruments Model2 4 7 2 Treadmill System* and a Hori-zon Metabolic Measurement CartSystem.+Th e gas analyzers were cali-brated be fore an d after each test.Volume and temperature were cali-brated prior to each test. Heart rate(in beats pe r minute) w as monitoredduring testing using a Polar SportTester PE 30 00 .~ he Sport Testersystem consists of a transmitter that isattached to a n electrod e belt. Theelectrode belt was secured aroundthe subject's chest at the level of thefifih intercostal s pac e be low th e left

*polar USA Inc, 470 West Ave, Stamford, CT 06902. nipple. The Sp ort Tester system per-52 / 944 Physical Thera py/V olum e 74, Number 10/0ctober 1994


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-able 2. Characteristics of C hildren Withou t Am putation s (n=14)

Body ChosenHeight Mass Walking SpeedAge (Y) (cm) (kg) (mls) Gender

"Subject walked at each speed only once.mitted continuous monitoring ofheart rate.Subjects we re familiarized with thetreadm ill (approx imately 3-5 min-utes) and then asked to select theirfreely chosen walking spee d (CWS).The CWS for each subject was deter-mined by increasing and decreasingthe speed of the treadmill until thesubject verbally communicatedwhich spee d was the most comfort-able and approximated the speedthe subject would likely choose if heo r she were walking about dur ingan average day. The CWS plus 20%and CWS minus 20% were then calcu-lated. Sul~jec ts ere fitted with a head-gear apparatus and then familiarizedwith each of the three speeds whilewearing the headgear. In addition, afixed speed of 1.2 m/s was also testedbecause it had been used in relatedinvestigations.l-3 The subjects thenrested until their heart rate return edto the pre-warm-up state.The headgear system, designed tosecure the mouthpiece to the expiredair hose, was conne cted to a meta-

bolic cart and was fi t onto eachchild's head along with the mouth-piece a nd a noseclip. To record pre-test heart rates, the subjects w ereasked to stand in a relaxed man nerfor 2 minutes prior to starting the test.They then walked for 2 minutes ateach of the four speeds in a randomlyassigned ord er . No rest was givenbetween speeds, and changes to th enew speeds were made with the sub-jects on the treadmill. In this way, thesubjects were permitted to graduallyadapt to new speeds . All tests we rerepeated, with the exception of thefixed-speed test, which ea ch subjectcompleted only once. For somesmaller subjects (Tabs. 1 and 2), thetreadmill protocol was modified suchthat they were only tested onc e ateach s pee d. After the treadmill testswere com pleted, each subject wasseated in a chair and heart rate wasagain mon itored fo r 2 minutes. Heartrate and VO, were measured every 30seconds, but only the final 30 secondsin each of the 2-minute intervals wasused for calculations. Rose et all1determined that the VO, measuredduring the final 30 seconds of a

2-minute test fo r a group of 18 chil-dren without known impairments andfor a grou p of 13 children w ith cere-bral palsy reflected a steady-statelevel. This result was confirmed in apilot investigation1 con duc ted p rior tothis study. Finally, to assess the repeat-ability of the measures, 2 childrenwithout amputations who w ere notinvolved in the study were retested 1week after the initial testing session(Tab. 3).Data Reduction and AnalysisOxygen consumption relative to dis-tance (SVO,) (in milliliters per kilo-gram per meter) and heart rate at the2-minute marks along with the corre-spond ing walking spe ed and physicalcharacteristics for each subject we reentered into a computer file for statis-tical analysis.A physiological costindex (PC9 was derived using thefollowing equation:(1) PC1= hw - hr)/swhere "hw" is heart rate while walk-ing (in beats per minute), "rhr" isheart rate at rest (in beats perminute), and "s" is average walkingspeed (in meters per minute).lz Per-centage of maximum heart rate(%MHR) was deriv ed for each w alk-ing spee d using the followingequation:(2) %MH R=sshr/age h rx 100where "sshr" is the steady-state exer-cise heart rate (in beats per minute)and "age hr" is the age-predictedmaximum heart rate (220-age) (inbeats pe r m i n ~ t e ) . ~ata for the twotrials at the sam e spee ds were aver-aged fo r each subject.Tw o m ultivariate analyses of variance(MANOVAs) were used to determinesignificant differences i n physiologicalmeasures between children with BKAsand long residual limbs and childrenwith BKAs and sh ort residual limbsand between children with BKAs an dthose without amputations. Thewithin-g roup factor was walkingspeed. The MANOVAs were necessarybecause the depen dent variables (ie,

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-able3. Mean Physiological M e a s u m t s f i m Retesting Trvo Subjecfi heart rate, PCI, %MHR, S V O ~ erecorrelated. Statistical significance werebased on a probability level of < 05.The post hoc test used in this investi-Speed gation was an F test.20% 20%Physlologlcal Below Above Because the population density inMeasure Day CWSa CWS CWS Flxed the region wher e the study wasconducted was low, the number ofsubjects with amputations availableSubject 1 for this study was limited. A test toHRb (blmin) 1 102 102 104 98 determine the power associated2 102 99 104 104 with the investigation was thereforeSVO,~mL performed.12kg-' rn-') 1 0.2538 0.2861 0.2344 0.1431

2 0.2910 0.2852 0.2490 722 ResultsPCld (blm) 1 0.5128 0.4892 0.4583 0.22222

MHRe(%) 12

Subject 2HR (blmin) 12

SVO, (mLkg-' .m-') 12

PC1 (blm) 12

MHR (%) 12

Comparison W ithin ChildrenWlth Below-Knee AmputationsThere were n o differences betweenthe children with BKAs and long resid-ual limbs and the children with BKAsand short residual limbs with regard topersonal characteristics (ie, CWS, rest-ing heart rate, age, height, body mass,and gender) (Tab. 1). In addition,there were no differences between thetwo groups of children with an ampu-tation with respect to the physiologicalcharacteristics (ie, heart rate, SVO,,PCI, %MHR) (Tab. 4). -"CWS=chosen walking speed. d~ ~~ =p hy si ol og ic alost index.

hean an rate. eMHR=maximum hean rate.C~~o ,=o x y g enonsumption relative to distance.

Comparison Between ChildrenWith Below-Knee Amputationsand Those Without Amputations- There were no differences betweenTable 4. Means (?Standard Ewors) for Four Physiological Measures ~ u r i n gour the children with BKAs and the chil-Walking Speeds for Children With Below-Knee Amputations With Long and Short dren without amputations for age,Residual Limbs (n height, and weight. Only one femalechild with a BKA was available forSpeed testing. There were also no differ-Physiological Resldual ences between groups for VO, as aMeasureb Llmb 20% Below CWS c CWS 20% Above CWS Flxed function of age.

HR LongShort

SVo, LongShort

PC1 LongShort

MHR LongShort

"No significant difference existed between groups.'see Tab. 3 footnotes for description of abbreviations.CCWS=chosenwalking speed.

The means and standard errors forthe four physiological measures forthe children with BKAs and the chil-dren without amputations are illus-trated in Figures 1 through 4. Thetwo-way repeated-measures MANOVA(groups [subjects with BKAs and sub-jects without amputations], walkingspeeds 120% below CWS, CWS, 20%above CWS, and fixed]) conducted forthe physiological measures (heartrate, SVO,, PCI, and %MHR) providedvarying results. The multivariate main

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20% BELOW CWS CWS 20%ABOVE CWS FIXEDWALKING SPEED

Figure 1. Means and standard errors for heart rate of children with below-kneeamputations ( B m ) (n=10) and for children without BMs (n=14). No dzrerencesa-isted between the groups. (CSW=chosen walking speed.)- *20% BELOW CWS CWS 20%ABOVE CWS FIXED

WALKING SPEED

Figure 2. Means and standard errors for oxygen consumption relative to distancefor children with below-knee amputations ( B a ) (n=IO) and for children withoutamputations (n=14). Asterisks (*) indicate that children with B m onsumed signzji-cantly greater amounts of oxygen (P


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same magnitude as the differencesbetween groups. Because only 2 chil-

**

20% BELOW CWS CWS 20% ABOVE CWS FIXEDWALKING SPEED

- .dren were retested, it is impossible todetermine how the day-to-day effectwould have influenced the groupeffect. Finally, the age range of thechildren was 6 to 18 years. Astrandand Rodah114 have reponed that VO,in boys and girls is about the sameuntil about year 14 .At that time, VO,increases at a greater rate in boysthan in girls. In our investigation, 6 ofthe 7 children aged 14 years or olderwere boys. Of these 6 boys, 4 werechildren with amputations and 2 hadno amputations. No difference wasfound between groups as a functionof age. If an influence of age hadexisted, however, it would probablyhave moved the results for the groupof children with BKAs closer to thoseof the group of children withoutamputations.Physiological measures of effort have

Figure3. Means and standard m r s or physiological cost index (PC4 for children been documented for adults withwith below-knee amputations ( B m) (n=IO) and for ch ildm without amputations BKAs. There is a paucity of available(n= 14). Asteri'sks (*) indicate that chi- with BXtls had a signijicantly greater PC1 value information, however, fo r children(P


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both groups of children easily fellbelow the anaerobic threshold valuereported by Cooper et al.ls Whetherthis dfierence prevents children withBKAs from performing all the activi-ties of children without amputationsduring a typical day is impossible todetermine from our investigation.This issue, however, warrants furtherinvestigation.The CWSs and heart rates recorded inour investigation are comparable tothose previously attained on adultswith BKAs. Nielsen et al%nd Pagli-arulo et a19 reported a CWS of 1.1 m/s(SD=1.3) for adults with BKAs,whereas in our investigation the CWSof the children with BKAs averaged1.05 m/s (SD=0.22). The heart raterecorded for CWS by Pagliarulo et a19was 106 b/min (SD= lo), whereas theheart rate recorded in our investiga-tion was slightly higher at 114.9 b/min(SD= 13.8) (Fig. 1). This differencewas likely due to the higher restingheart rate in children compared withadults. 6We recorded an increase of 15% inSVO, for children with BKAs as com-pared with children without amputa-tions at their CWS (Fig. 2). In studiesof adults, the general consensus wasan approximate 32% increase in VO,,as reflected in SVO, at the CWS.XThehigher increase seen in the studies ofadults may be a result of the signifi-cantly slower walking speed for adultswith BKAs, which would result in anincrease in SVO, (noting that at aslower speed it would take longer towalk the same distance). The lowerSVO, values with the higher speeds inour study agree with the results foradult subjects reported by NielsenetThe PC1 was studied by Butler et all7for children without amputations(n=72, age range=3-12 years). Theyreported a mean PC1 of 0.4 (SD=0.12). They also stated that PC1 isindependent of age, height, and gen-der, but may be affected by puberty.There appear, however, to be nostudies reporting the effects of stageof puberty on PCI. In our study, werecorded PCIs of 0.37 (SD=0.03) for

children with BKAs and 0.25(SD=O.Ol) for children without am-putations at CWS (Fig. 3). Stage ofpuberty was not assessed, however, sothe possibility of differences in stageof puberty between groups could notbe determined. The lower PC1 valuesfor children without amputations maybe a reflection of the higher restingheart rate for that group. The differ-ences in resting heart rate, however,were not significant between the twogroups of children.Nielsen et a18 suggested that %MHRwas a good indicator of the relativeexercise intensity, and they found a%MHR of approximately 65% forCWS. In our study, we found a %MHRof approximately 55% for childrenwith and without BKAs. Nielsen et all8recommended, as a general guideline,that %MHR should be below 80%.The results of our study, therefore,indicate that the children with BKAsand those without amputations werewell within their physiological limitswhile walking (Fig. 4).We found no difference in CWS in thesubjects with BKAs when grouped byresidual limb lengths. In contrast,Gonzalez et a17 and Waters et all0found a higher CWS for adult subjectswith a short residual limb BKA com-pared with adult subjects with alonger residual limb. Gonzalez et a17suggested that this finding may bedue to age, duration of amputation,general physical condition, complicat-ing illnesses, and prosthetic type andfit. The difference between the investi-gations with adults and children withBKAs warrants further scrutiny. Thisdifference, however, could be relatedto the percentage of maximum oxy-gen consumption at which the groupsfeel comfortable during walking.Other resear~h~.3 ~5as shown biome-chanical differences between childrenwith BKAs and children without am-putations. The results of our studysupport the notion that a relationshipbetween biomechanical differencespreviously reported between the twogroups could have a significant effecton physiological function. Althoughnot the focus of this investigation, it

would seem reasonable to hypothe-size that the reported differencesbetween the two groups of childrenare a result of the lack of function ofthe prosthesis and the prostheticlimb. Thus, if the goal is to enablechildren with BKAs to walk like chil-dren without amputations, then re-search should be directed towarddeveloping prostheses that permit theprosthetic limb to function more likean intact limb. Such a prosthesiswould probably permit dorsiflexionand plantar-flexion movements andprovide propulsive forces similar tothose generated by children withoutamputations.SummaryThe results of this study indicate (1)that children with BKAs chose walkingspeeds similar to those of childrenwithout amputations, regardless ofresidual limb length; (2) that no dif-ferences existed in heart rates be-tween children with BKAs and chil-dren without amputations o r withinchildren with BKAs with respect toresidual limb length; and (3) that anincrease in VO, existed for childrenwith BKAs.Children with BKAs had higher en-ergy needs for walking than childrenwithout amputations. Whether theincreased energy needs prevent orinhibit children with BKAs from hav-ing a lifestyle comparable to that ofchildren without amputations is cur-rently unknown and warrants furtherresearch.

References1 Engsberg JR, Macintosh BR, Harder JA. Com-parison of effort between below-knee-amputeechildren and normal children.Journal of theAssociation of Children's Prosthetic-OrthoticClinics. 1991;26(2):4652.2 Engsberg JR, Lee AG, Tedford KG. Norma-tive ground reaction force data for able-bodiedand below-knee-amputee children duringwalking.J Pedian Ombop. 1993;13:169-173.3 Engsberg JR, Tedford KG, Harder JA. Centerof mass location and segment angular orienta-tion of below-knee-amputee and able-bodiedchildren during walking. Arch PLys Med Reba-bil. 1992;73:1163-1168.4 Lewallen R, Dyck G, Quanbury M, et al. Gaitkinematics in below-knee child amputees: a

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Force-plate analysis.J Pediatr Orthop. 1986;6:291-298.5 Engsberg JR, Ted ford KG, Harder JA, ClynchG. Timing changes for stance, swing and do u-ble support in a recent child below the kneeamputee. Pediatric Exercise Science. 1990;2:255-262.6 Ganguli S, Datta SR, Chatterjee BE, Roy BN.Metabolic cost of walking at different speedswith patellar tendon-bearing prosthesis. J ApplPhysiol. 1974;36:44C443.7 Gonzalez EG, Corcoran PJ, Reyes RL. Energyexpenditure in below-knee amp utees: correla-tion with stump length. Arch Phys Med Rehubil.1974;55:111-119.8 Nielsen DH, S hurr D G, Golden JC, Meier K.Comparison of energy cost and gait efficiencyduring ambulation in below-knee amputeesusing different prosthetic feet: a preliminaryreport.Journal of Prosthetics and Orthotics.1989;1(1):2431.9 Pagliarulo MA, Waters RL, Hislop HJ. Energycost of walking of below-knee amputees hav-

ing n o vascular disease. Phys Ther. 1979;59:5 3 ~ 5 3 4 .10 Waters RL, Pen y J, Antonelli D, Hislop H.Energy cost of walking of amputees: the influ-ence of level of amputation. J Bone Joint SUT.1976;58:4246.11 Rose J, Gamb le JG, Medeiros J, et al. En-ergy cost of walking in normal children and inthose with cerebral palsy: comparison of heartrate and oxygen uptake. J Pediatr Orthop.1989;9:276279.1 2 MacGregor J. The objective measurementof physical perform ance with long-term amb u-latory physiological surveillance equipment(LAPSE). In: Scoot FC, Raftery EB, Goulding L,eds. Proceedings of the Third InternationalSymposium on Ambulatoy Monitoring. Lon-do n, England: Academic Press Inc (London)Ltd; 1979:29-39.13 Lieber RL. Statistical significance and statis-tical power in hypothesis testing.J Orthop Res.1990;8:304-309.

14 Astrand PO, Rodahl K. Textbook of WorkPhysiologp Physiological Buses of Exercise.New York, NY: McGraw-Hill Book Co; 1977:319.15 Coop er DM, Berry C, Lamarra N, Wasser-ma n K. Kinetics of oxygen uptake at the onsetof exercise as a Function of growth in children.J Applied Physiol. 1985;59:211-2 17 .16 Moss AJ. Indirect methods of blood pres-sure measurement. Pediatr Clin North Am.1978;25:34.17 Butler P, Engelbrecht M, Major RE, et al.Physiological cost index of walking for normalchildren and its use as an indicator of physicalhandicap. Dev Med ChiM Neurol. 1984;26:607-612.18 Nielsen DH, Amundsen LR.Fxercise physi-ology: an overview with emph asis on aerobiccapacity and energy cost. In: Amundsen LR, ed.Cardiac Rehabilitation. New York, h Y Chur-chill Livingstone Inc; 1981:ll-28.

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ped le amputee o2 consumption-1994

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