petrofsky1-vol5no2 6/1/05 9:20 pm page 345 training for...

The Journal of Applied Research • Vol. 5, No. 2, 2005 345

Abdominal and Lower BackTraining for People withDisabilities Using a 6 Second AbsMachine: Effect on Core MuscleStabilityJerrold S. Petrofsky, PhDEric G. Johnson, DPTScAshley HansonMaria Cuneo, DPTRussel Dial, DPTRyan Somers, BSGuillermo De La Torre, BSAlicia Martinez, BAMaritza McKenzie, DPTBonnie Forrester, DPTSc

Department of Physical Therapy, Loma Linda University, Loma Linda, CaliforniaDepartment of Physical Therapy, Azusa Pacific University, Azusa, California

platform, 13 control and 14 subjectswith spinal cord injury, stroke or multi-ple sclerosis were evaluated before andafter one month of training using threeabdominal exercises and one lowerback exercise accomplished from awheelchair.

Results: Improvement in reach andreductions in muscle tremor were asso-ciated with a core muscle-strengtheningprogram. Reach, which was less thanhalf that of control subjects, increased inthe following directions by 23% (for-ward), 91% (right), and 50% (left).

Conclusion: This program, which onlyrequired twenty minutes of daily exer-cise, should provide increased function-al abilities for people with disabilities.

KEY WO R D S : e x e r c i s e, e x e r t i o n ,r e h a b i l i t a t i o n , spinal cord injury, s t r o k e

ABSTRACTIntroduction: When people are confinedto a wheelchair, central neuropathiessuch as spinal cord injury and strokeusually reduce strength of core musclesand corresponding functional abilitiesfor standing or reaching. The presentinvestigation describes the effects of anexercise regime on reach and balance,accomplished with a low cost portabledevice, the 6 Second Abs machine.

Methods and Procedures: Using a modi-fication of the functional reach test(FRT) and assessment of balancethrough four load cells under a balance

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Vol. 5, No. 2, 2005 • The Journal of Applied Research346

INTRODUCTIONNumerous studies in the last one hun-dred years point to the advantage ofexercise training in providing positivebenefits for general health. Exercise candramatically increase oxidation of lipids;reduce body weight, low-density lipopro-tein (LDL) cholesterol, fasting glucose;and lower resting blood pressure.1-4

Lifting slowly against loads that fatiguemuscle in short periods of time, calledanaerobic exercise,5 causes muscleenzymes to be synthesized to favor gly-colysis and reduce oxidation of fattyacids. DNA is transcribed to build actinand myosin in muscle to increasestrength.5-9 This allows muscle to buildstrength and increase its ability to workwithout oxygen.10 In contrast, lightrepetitive work (aerobic exercise)requires high blood flows for energy andoxygen delivery. This causes the muscleto transcribe genomes on DNA, whichincreases the concentration of enzymesin the Krebs cycle. It ultimately resultsin the beta oxidation of fats, whichincreases the muscle’s ability to burnfats.7,11 Aerobic training also elicits anincrease in angiogenesis in capillaries,mitochondrial surface area, and densityto allow better oxygen and fuel deliveryto tissue for exercise.12 Aerobic trainingalso lowers triglycerides, inflammatorycytokines, C-reactive protein, andincreases collateral circulation in theheart.13 For people with diabetes, exer-cise is important because the increasednitric oxide production, from the mito-chondria and active skeletal muscle, acti-vates Glut-4 (without insulin as aco-factor) and thereby reduces circulat-ing glucose in the body.11 This is espe-cially pertinent because there is a highincidence of metabolic disorders, such asdia b e t e s, in people with motor paralysis.1 4

While cardio-respiratory condition-ing is important for people with disabili-ties, the most immediate concern issimply accomplishing the activities of

daily living (ADL). The activities ofdaily living are frequently limited due toweakness in core muscles (ie, the rectusabdominus, transverse abdominus, andthe internal and external obliques).15

This results in an inability to reach any-thing that is not close to the wheelchair.Moving the trunk more than 5 or 10degrees from neutral can cause a loss ofbalance and falls from a wheelchair.16

Transfers, reach, and general balance areoften poor.17 Because of this poor bal-ance, bone fractures are common andthe most common fracture seen is at thehead of the femur, which results fromfalling out of the wheelchair onto theknee.18 These compression fracturesoccur in up to 10% of the population ofparaplegics and quadriplegics eachyear.32

Studies show that strengthening thecore muscles contributes to increasedfunctional abilities.19,20 Using exercisemachines in health clubs or rehabilita-tion centers strengthens the abdominaland lower back muscles and canincrease ADL’s and produce more effec-tive bowel and bladder function.17 Thisin turn leads to great psychological gainsby allowing a person to be more inde-pendent.

However, with ever-rising costs inrehabilitation and even health clubs, it isimportant to develop exercise tech-niques and devices that allow individualswho are disabled to exercise at home.21

One existing device is the 6 Second Absmachine. This machine provides a pro-gressive increase in resistance with abuilt-in timer so that individuals canexercise their abdominal muscles andlower back muscles from a wheelchair.22

In previous studies, we have shown thatthese devices offer a unique, more effec-tive way to build abdominal muscle toneand strength when compared to conven-tional sit ups.23 The purpose of thisinvestigation was to see if the devicewould help people with disabilities. This



device offers considerable advantage fordisabled people because it allows themto exercise in the seated position, asopposed to many of the other abdomi-nal machines, which require people tolay either horizontal or recline outsideof a wheelchair.

SUBJECTSFourteen people with disabilities and 13control subjects participated in the study.Seven of the participants with disabilitieshad paraplegia, three had multiple scle-r o s i s, and four had strokes. The generalcharacteristics of all of the subjects areshown in Table 1. The control subjectswere free of any physical disabilities, b u twere selected to create baseline data forreach and motor control, which wouldlater be compared with the data for peo-ple with disabilities. Control subjects per-formed all the exercises in wheelchairsexcept for the balance platform exercise.All subjects were free of cardiovasculardisease or orthopedic injuries that wouldlimit participation in an exercise pro-g r a m . Subjects with stroke were limitedto hemiplegia and had no cognitive loss.All protocols and procedures wereapproved by the committee on humanexperimentation at Loma LindaUniversity and all subjects signed a state-ment of informed consent.

METHODS6 Second Abs MachineThe 6 Second Abs machine was a com-mercial exercise device manufactured bySavvier LP in Carlsbad, Calif. The device

consisted of a rectangular plastic framewith rubber bands on the inside toadjust resistance. Resistance could beincreased in a number of different stagesso that it became increasingly more diffi-cult to compress the rectangle (Figure 1).

As the machine was compressed tothe first, second, and third click posi-tions, there was a linear increase in load.Muscles work concentrically, isometri-cally, and eccentrically. With 3 differentpairs of resistance bands, a total of 9 dif-ferent band settings could be selected.Both the upper and lower rectangleswere padded (Figure 1).

Measurement of Muscle StrengthMuscle strength was measured in theabdominal and back muscles. The sub-ject was in the seated position with theirback at 90 degrees in reference to thehips. A strap was placed around theirchest just below the axilla and connect-ed to a strain gauge force sensor (Figure2). Strength was then assessed for flex-ion and extension as the highest of 3maximal efforts in each muscle group; 1minute separated the contractions. Acomplete description is given below.22

Assessing BalanceBalance was assessed using a computer-ized dynamic posturography device thatwas built to accommodate wheelchairbound subjects. The basic frame of theplatform was constructed from twosheets of plywood and a ramp. The 1-inch plywood plates were separated byfour metal bars connected to strain

Table 1. General Characteristics of Subjects

Subjects Age (years) Height (cm) Weight (kg)Spinal Cord Injury 35.3 ± 12.2 174.9 ± 12.8 75.9 ± 22.1Stroke 48.1 ± 25.5 169.4 ± 7.7 78.6 ± 19.6Multiple Sclerosis 49.6 ± 11.6 162.5 ± 9.6 75.1 ± 21.6Average of all subjects 43.3 ± 16.5 170.1 ± 10.1 77.7 ± 17.6

with disabilitiesControl 45.8 ± 14.1 171.5 ± 9.7 74.5 ± 17.1

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gages. Each bar was positioned at a 90˚angle with reference to the other bars.Strain gauges were placed at 0˚, 90˚, 180˚,and 270˚ angles. With the wheelchairplaced in the center of the platform,leaning in any direction was then trans-duced through strain gauges mountedon the metal bars to an electrical outputso that the deviation and center of gravi-ty could be assessed (Figure 3). The out-put of the strain gages was connected tofour strain gauge amplifiers (BiopacIncorporated, Santa Barbara, Calif) anddigitized with a sixteen-bit A/D convert-er (Biopac Incorporated, Santa Barbara,Calif). The digitized data was then sort-ed on an IBM computer for later analy-sis. A full description of the device isgiven later.24

Figure 2. Strength is measured in a wheel-chair bound subject during extension of theback muscles. In practice, the subject wouldbend 30 degrees forward and then try tostraighten up. An isometric strain gage trans-ducer was used to measure the strength.

Figure 3. A subject in a wheelchair on thebalance platform with eyes closed to meas-ure seating stability.

Figure 1. A subject exercising the rectusabdominus muscles using the 6 Second Absmachine.



ProceduresThe subjects exercised 3 days per weekfor 4 weeks. On any exercise day, a totalof 20 minutes of exercise was accom-plished. For each muscle group that wasexercised, 4 different exercises wereused; the load in the abdominal exercis-er was adjusted to fatigue the muscles in5 minutes. Exercise was accomplishedwith 3 seconds of flexion and 3 secondsof slow relaxation. If, on any one day, 5minutes of exercise was accomplished inany one exercise position, the workloadwas increased by 5 pounds, so that onthe next day, they fatigued within the 5-minute period. In this manner, then,over 30 days, the workload was progres-sively increased. Four different 5-minutebouts of exercise were accomplishedeach day. In the first bout, the subject satin the wheelchair facing forward to exer-cise the rectus abdominus muscles. To

exercise the external and internaloblique muscles, two other bouts ofexercise were accomplished with thesubject facing 45˚ to the left and 45˚ tothe right. Muscle use was verified byelectromyogram studies as describedpreviously.22,23 Finally, an additional 5minutes of work was done extending theback muscles. The 6 Second Absmachine was placed under the arms andthe torso was positioned at 30 degrees offlexion. By extending the back, the torsowas brought to the neutral positionagainst the load of the 6 Second Absmachine.

Pre and Post TestingBefore and after the 4-week exerciseperiod, functional reach, tremor, andmuscle strength was recorded. As statedabove, muscle strength was measuredfor the lower back and abdominal mus-cles. After strength was measured, amodified FRT was used.25 Each subjecteither sat in their wheelchair or stood inthe middle of the balance platform.Subjects remained as motionless as theycould with their eyes closed and thedirection and angle of any movementsfrom the center of gravity was deter-mined. Next, the subjects reached for-ward (Figure 4), left and right (Figure 5)as far as possible without losing their

Figure 4. A subject with MS standing on thebalance platform reaching forward to meas-ure the limits of stability in a forward direction.

Figure 5. A subject with a spinal cord injury ina wheelchair leaning to the right side at mini-mal reach to measure stability.



balance. Subjects held this position forapproximately 10 seconds and the move-ment at the center of gravity (COG) offof the base of support (BOS) was deter-mined. Subjects then repeated thismovement, at minimal reach (that is thearm extended but the back unbent), atmaximum reach without losing balance,and at half the distance between theminimal and maximum reach. Tremorwas assessed by acceleration at the wrist.The ability to displace the COG of theirbody away from their BOS was deter-mined in the forward, left, and rightdirections to see if they improved afterthe one-month core strengthening program.

RESULTSIn a one-month period, the averageincrease in workload was similar for therectus abdominus, right and left oblique,and back extensor muscle exercises. Forexample, Figure 6 shows the averageincrease in the workload for exercises ofthe rectus abdominus muscles. The ini-tial workload started at less than 9 kg onthe first day of the first week. However,it gradually increased and the weeklyaverage for the first week was 10.8 ±4.11 kg. For the fourth week, the average

load was 16.0 ± 7.6 kg. The range ofworkload was large. In some subjects thefinal workload was 9 kg, while in othersubjects the workload increased to over31 kg. For example, in one subject withMS, the work in the first week was 9 kg,and in the third week was 15.1 kg,whereas the average workload in thelast week was 31.19 kg. Thus, individualshad either a smaller or a larger increasein workload depending on their motiva-tional level and the ability of muscles totrain due to their paralysis. The samepattern was seen for the oblique mus-cles. For the right oblique, the averageworkload increased from 11.9 ± 4.3 kgto 15.72 ± 7.1 kg in the last week. Theleft oblique muscle exercises workloadsincreased from 11.9 ± 4.4 kg to 15.7 ± 7kg in the last week. For the back exten-sion exercise, workloads generally start-ed higher at the beginning of theone-month exercise period with loadsset at 18.0 ± 15 kg and increased to 23.0± 13 kg in the final week.

Overall compliance for accomplish-ing the exercise for the group was 97.8%± 5.4%. Compliance was calculated bydividing the actual number of days sub-jects exercised in the month by the totalnumber of days that participants were

Figure 6. The increase in load in the AB machine each week for exercise of the rectus abdomi-nus muscles. Each bar is the mean of the group (± the appropriate standard deviations).



told to exercise. However, since subjectshad severe disabilities and limited mus-cle function, workloads for many sub-jects could only be increased marginallythroughout the exercise period, but allsubjects did increase their workload.More importantly, the large standarddeviation seen in these experiments issimply due to the fact that subjects withgreater paralysis simply could not exer-cise at a greater workload.

The results of the measurements ofmuscle strength for the abdominal andparaspinal muscles are shown in Figure6. The average strength of the abdomi-nal muscles increased from 70.46 ± 32.54lbs (31.96 ± 14.76 kg) before the exer-cise program to an average of 121.08 ±33.62 lbs (54.92 ± 15.25 kg) after theone-month program. This correspondedto a 72% increase in muscle strength.The increase was significant (P < 0.01).In the back muscles, strength increasedfrom 75.62 ± 28.42 lbs (34.32 ± 12.89 kg)to 122.54 ± 34.90 lbs (55.58 ± 15.83 kg)after the exercise program, an increase

of 62%. This increase was also signifi-cant (P < 0.01).

A corresponding increase in theFRT was associated with this increase inmuscle strength, as shown in Figure 7.Figure 8 shows the results of the FRTbefore and after the one-month trainingprogram in the forward, right side, andleft side directions. Functional reach inthe forward direction increased from22.3 inches (56.6 cm) to 28.4 inches (72.1cm), an increase of 23.9%. Reach to theright increased from 15.5 inches (38.2cm) to 29.4 inches (74.8cm), an increaseof 91% and, reach in the left directionincreased from 15.4 inches (39.1 cm) to23.2 inches (58.8 cm) and increase of50.4%. These increases in reach were allstatistically significant (P < 0.01) whencomparing pre- to post-conditioningdata. There was no consistent differencein the gain in reach or strength in any ofthe three subgroups of people with dis-abilities examined here (P > 0.05).

FRT data in the disabled group iscompared to that of the control subjects

Figure 7. The strength of the abdominal and back extensor muscles during testing before (pre)and after (post) of a one-month exercise program using the 6 Second Abs machine. The meanresponse of the entire group (± the appropriate standard deviation) is shown.



in Figure 8. The forward reach for thesubjects with disabilities averaged 22.3inches (56.6 cm) compared to the con-trols in a seated position who had anaverage forward reach of 37.9 inches(96.1 cm). For the right reach, subjectswith disabilities had a reach of 15.5 inch-es (39.4 cm), whereas control subjectshad a reach of 37.9 inches (96.1 cm). Thedifferences for the right and left reach,and forward reach between control sub-jects and subjects with disabilities weresignificant (P < 0.01).

After the one-month exercise pro-gram, the functional reach had increasedto 28.4 (forward), 22.9 (right), and 23.2inches (left). In subjects with disabilities,there was still a statistical difference inthe forward reach and left reach, whencompared to control subjects (P < 0.05)(Figure 9).

The results of the determination ofbalance and movement of the COG andlimits of stability (LOS) are shown inTables 2, 3, and 4. Table 2 shows the datafor control subjects. Table 3 shows datafor the subjects before the one-monthexercise program and Table 4 shows the

data after the one-month exercise pro-gram. The data for reaching in the for-ward direction, to the right, and to theleft and includes the magnitude of theshift in the COG while lifting the arm inthat direction (minimal reach, maximumreach, and a point halfway between thetwo) is shown in Tables 1, 2, and 3. Thestandard deviations are for the changein COG. Whereas the standard deviationshows a measure of variation within thegroup, the average peak-to-peak varia-tion in the COG during that maneuveris also shown. Peak-to-peak is useful inthat it shows tremor or wobble duringsitting or extension of the arms. If thearm is held steady, then there is very lit-tle variation in the COG on the plat-form, on the other hand if the subjectmoves a great deal, there would be alarge peak-to-peak variation in theCOG. These tables also show the direc-tion of the angle of movement and thestandard deviation of the angle of move-ment of the subject on the platform.Finally, the LOS in degrees was also cal-culated for the movement of the bodyaway from neutral.

Figure 8. The reach distance from the neutral position to the furthest reach in inches for reach-ing in the forward direction and to the right and left before (pre) and after (post) of one-monthexercise program. Each point is shown with the appropriate standard deviation representing themean for the entire group.



For the control subjects, the averageshift in the COG for maximum reachwas approximately 30 kg. For example,movement in the front direction forminimal reach, which required simplyextending the arm forward withoutbending the trunk, the shift in the COGaveraged 8.9 kg. There was an increaseof 18.3 kg for mid reach, and 29.7 kg forthe furthest extended reach. Duringeither minimal or maximal reach, thestandard deviation of the COG wassmall, averaging only 4.7 kg for minimalreach and 7.5 kg for maximal reach. Thisis reflected in peak-to-peak movement.The average tremor or variation in theCOG was 0.9 kg peak-to-peak for mini-mal reach and 2.2 kg for maximal reach.The calculated angular LOS showed thatthe furthest extent that the subjectscould reach without losing their balancewas a 23.5˚ shift in the angle of the bodyin the front reach direction compared to22.1˚ for the right reach and 19.5˚ for theleft reach. The angular LOS in the threepositions was statistically different fromeach other (P > 0.05).

The average data for the subjects

with disabilities is shown in Table 3.There was a significant differencebetween this group and the controlgroup of subjects. For example, lookingat the shift in the COG during minimal,mid, and maximal reaches, subjects withdisabilities could not reach as far asshown above for control subjects andthey could not shift their COG as wellas the control subjects. For example,looking at maximum reach, the shift inthe COG was 16.8 ± 7.5 (front reach),14.4 ± 4.9 (right reach), and 15.0 ± 10.2kg (left reach) in the subjects with dis-abilities (Table 3); whereas the shift inthe COG was 29.7 ± 7.5 (front reach),33.6 ± 9.1 (right reach), and 33.3 ± 8.9 kg(left reach) in the control subjects(Table 2). The differences for each direc-tion were statistically significant (P < 0.01). Even at less reach, the peak-to-peak variation in the COG was muchhigher in subjects with disabilities. Forthe control subjects, the front reach atmaximal excursion peak-to-peak varia-tion was 2.2 kg compared to 4.2 kg forsubjects with disabilities. For controlsubjects, this amounted to a variation of

Figure 9. Results of the functional reach testing the forward direction and to the right and leftside while sitting in a wheelchair in the subjects with disabilities before engaging in the onemonth exercise program (PRE) compared to control subjects doing a similar test. Each bar rep-resents the mean response of the appropriate group (± the standard deviating of the group).



plus or minus 7.74% at maximum reach.However, since their maximum reachwas twice the distance of the controlsubjects, the more correct comparison

would be to compare the mid reach datawhere the reach distances are the same.The mid reach data, peak-to-peak varia-tion was 1.4 kg against a movement of

Table 2. Data for Control Subjects*

Center of SD Center` Peak- Angle of SD angle Limits ofGravity (kg) of Gravity to-peak Movement of Stability

(degrees) Movement (degrees)Front

min 8.9 4.7 0.9 15.3 33.4 7.2mid 18.3 7.2 1.4 -37.2 23.6 13.6max 29.7 7.5 2.2 18 21.6 23.5

Rightmin 6.6 3.6 0.7 -42 18.4 3.8mid 18.6 5.4 1.3 -11.7 21.8 13.2max 33.6 9.1 1.9 4.9 9.9 22.1

Leftmin 6.1 3.2 0.7 15.2 14.9 4.2mid 16.7 5.5 1.3 -10.4 17.2 14.1max 33.3 8.9 1.8 3.9 21.3 19.5

*Displacement of the center of gravity (vector and angle), variation of the force vector over a 4 second period (SDvector and peak-to-peak excursion) and the variance in vector angle (SD of the angle), and Limits of Stability (LOS)during reach in the group of control subjects. Min indicates minimal reach; Max, maximum reach; Mid, a point halfwaybetween the two; and SD, standard deviation.

Table 3. Data for Subjects with Disabilities Before the One-month Exercise Program*

Center of SD Center Peak- Angle of SD angle Limits of Gravity (kg) of Gravity to-Peak Movement of Stability


min 4.8 2.3 2.6 33.0 24.5 3.8mid 9.8 5.7 3.1 14.0 57.2 7.4max 16.8 7.5 4.2 17.7 53.7 12.9

Rightmin 4.5 1.7 2.8 33.9 28.4 3.5mid 12.0 7.9 3.6 -0.5 38.9 8.6max 14.4 4.9 4.1 -2.5 56.8 10.3

Leftmin 3.9 1.4 2.1 28.6 46.1 3.1mid 9.3 5.0 3.0 17.1 43.3 7.1max 15.0 10.2 4.0 8.1 52.8 11.2

*Displacement of the center of gravity (vector and angle), variation of the force vector over a 4 second period (SDvector and peak-to-peak excursion) and the variance in vector angle (SD of the angle), displacement of the center ofgravity and Limits of Stability (LOS) during reach in the group of disabled subjects before 1 month of exercise. Minindicates minimal reach; Max, maximum reach; and Mid, a point halfway between the two.



18.3 kg or 7.6%. For the subjects withdisabilities, as shown in Table 3, a maxi-mum reach (the same reach distance asmid reach on the control subjects), thevariation was 4.2 kg during peak-to-peakmovement or against the total shift of16.8 kg, 25% of the shift in weight. Inother words, the subjects with disabilitieshad approximately four times thetremor in holding their hand at maxi-mum reach or even at mid reach thanwas seen for the control subjects.

Not only were the tremor, reach,and shift in COG less in subjects withdisabilities, the LOS angle was also less.The control subjects were able to shifttheir COG by an angle of 23.5˚, 22.1˚,and 19.5˚ for front, right, and left reach-es, respectively. In contrast, for maxi-mum reaches for the subjects withdisabilities, the average change in bodyangle was 12.9˚ (front), 10.3˚ (right), and11.2˚ (left).

However, after the one-month exer-cise program, as cited above, functionalreach increased significantly (Figure 10).Associated with this increase in func-tional reach was an increase in the abili-

ties of their bodies to shift their COGwithout losing balance. For example, forthe following reaches the shift in theCOG was 26.4 ± 6.3 kg (front), 26.6 ±9.6 kg (right), and 25.3 ± 8.6 kg (left)(Table 4). These shifts in the COG werestatistically greater than seen in thesame subjects (related t test) before theone-month of exercise (P < 0.01).Tremor was also reduced. For example,looking at the furthest extent of thereach for front reach, the peak-to-peakvariation was 3.1 kg. With the shift of26.4 kg of body weight, this amounted toan 11.7% variation in COG during thereach. Thus, tremor was reduced by50%. However, the furthest reach wassubstantially longer, away from the cen-tral core of the body, after training thanbefore training. The correct comparisonwould be comparing mid reach wherethe variation was only 2.1 kg in a for-ward direction. Here, the variation wasonly 12%. Thus, tremor was reduced byover half, even though reach increasedby almost double after core training.These differences were significant (P < 0.01).

Figure 10. The results of the functional reach test in the forward right and left directions while sit-ting in a wheelchair in subjects with disability after a one month exercise program (post) com-pared to control subjects. Each point is the mean response of the appropriate group (± thestandard deviation).



Finally, with regard to the angle atthe LOS, the maximum angular move-ment before the subjects lost their bal-ance also significantly improved (P <0.01) after training. For example, lookingat the maximum reach in the forwarddirection, the maximum angle that thesubjects could lean before losing theirbalance went from 12.9˚ to 17.9˚.Whereas the LOS angle for either front,right, or left reach was still significantlyless than control subjects (P < 0.05), thiswas still a significant improvement inthe reach of the subjects.

DISCUSSIONThere are many benefits of daily exer-cise. These include reducing LDL cho-lesterol, increasing oxidation of lipids,and increasing overall aerobic capacity.1-

3,5 Further, the overall benefit of exerciseon building strength and endurance iswell established.10 But for people withdisabilities there may be the addedadvantage of strengthening core mus-cles. Theoretically at least, this shouldincrease functional ability by allowing

individuals to move the COG away fromtheir BOS without falling19,20 The coremuscles (the erector spinae, transverseabdominus, and rectus abdominus mus-cles) stabilize the upper body. Increasedreach (movement of the COG awayfrom the BOS) translates into morefunctional independence.17 Therefore,the practical role of rehabilitation,increasing functional independence,could be accomplished with a goodstrengthening program for the core mus-cles. However, because of the inaccessi-bility of most health clubs, individualswho are disabled generally prefer toexercise at home.21 One recent option, adevice called the 6 Second Abs machine,provides a progressive increase in resist-ance to exercise the abdominal musclesand could be used quite practically froma wheelchair.22 These devices are com-monly marketed in most sports stores inthe United States, but up until this point,have not been tested on people with dis-abilities. While it is easy to establish atraining program using a machine suchas the 6 Second Abs machine, it is more

Table 4. Data for Subjects with Disabilities After the One-month Exercise Program*

Center of SD Center Peak- Angle of SD angle Limits of Gravity (kg) of Gravity to-Peak Movement of Stability


min 8.3 6.1 1.6 19.6 71.2 6.3mid 16.3 6.4 2.1 -29.1 78.5 10.2max 26.4 6.3 3.1 15.9 80.9 20.4

Rightmin 7.1 4.2 1.3 -36.5 65.1 4.3mid 15.1 6.2 2.9 -8.5 21.6 10.5max 26.6 9.6 3.2 3.1 11.3 19.7

Leftmin 4.2 4.0 1.3 19.3 61.7 3.2mid 14.3 6.2 2.1 -12.3 14.6 9.8max 25.3 8.6 3.0 -2.0 14.7 18.3

*Displacement of the center of gravity (vector and angle), variation of the force vector over a 4 second period (SDvector and peak-to-peak excursion) and the variance in vector angle (angle of the SD), and Limits of Stability (LOS)during reach in the group of disabled subjects after 1 month of exercise. Min indicates minimal reach; Max, maximumreach; Mid, a point halfway between the two; and SD, standard deviation.



difficult to evaluate changes in the abili-ty to reach. In a recent publication,Nichols26 divided balance into threeaspects, steadiness, symmetry, anddynamic stability. The neurologicalmechanism causing the loss of balancecan be complex involving the vestibularsystem, visual cues, and loss of sensoryand motor pathways.27,28 For motor dis-abilities, the usual deficit is the strengthof the core muscles. Evaluating the abili-ty to balance, especially while sitting in awheelchair is conventionally accom-plished with a test called the FRT.Duncan and colleagues25 published theFRT for people in wheelchairs. Duncanpresented evidence that the FRT was ahighly reliable tool for measuringdynamic balance. But while the FRTshowed a good correlation to forward-back movement, it did not correlate aswell for assessing side-to-side move-ment.29 This is a problem especiallybecause individuals usually fall whenreaching to the side.29 Newton29 modi-fied the FRT into two different planesand found a high correlation to multidi-rectional experience with falls. ButJonsson30 found a low correlationbetween reach distance and the actualdisplacement to the COG of the body.And therefore, Jonsson30 suggestedmeasuring the actual displacement ofthe COG and not just the actual reach,since reach can be accomplished by anumber of different strategies involvingshifting of the body frame. In the pres-ent investigation, therefore, the FRT wasmodified to measure not only the reach,but also the actual displacement of theCOG of the body, measuring the angle,magnitude, and error in maintaining sta-bility on the balance platform. In thepresent investigation, there was a signifi-cant improvement after 30 days of exer-cise in the ability to reach. Both thedistance that could be reached in theforward and side-to-side directions andthe ability to move the COG away from

the BOS improved. Further, the tremoror error in controlling movement evenat the furthest reach was dramaticallyimproved after core strengthening withthe 6 Second Abs machine.

It is important to distinguish the useof the LOS test and the LOS. Often, theLOS test has been used to assess bal-ance. However, functional reach meas-ures performance irrespective of angle.A recent paper has stated that the LOStest in some cases does not correlatewell with the FRT.31 In this study, therewas a good correlation. This may be dueto the fact that sitting in a wheelchairlimits the strategy that can be used toreach. While standing, movement can beachieved at the hips, knees, ankles orshoulders to achieve a strategy for agiven reach. Therefore, good reach canbe achieved with or without the sameshift in LOS angle depending on howthe reach was achieved. Sitting in awheelchair, the strategies are muchmore limited and therefore, the two testscorrelated well. Further, from the per-spective of a therapist, the FRT dictateshow independent someone can be. Howthey get there (eg, shifting their bodyweight) is inconsequential. Therapy istherefore outcome driven and not driv-en by academic measurements of howsomeone is able to move. As such, theFRT becomes more important than thebalance analysis.

For individuals with disabilities,there was better reach with less tremorand less motor error after strengtheningthe core muscles. Often, in rehabilita-tion, the cost outweighs the benefits.Here, however, with the low cost of amachine such as the 6 Second Absmachine (less than $75 US), exercise wasperformed safely and efficiently at hometo increase independence in activities ofdaily living with nominal expense.

Anecdotally, patients have remarkedthat they have “never felt so stable in awheelchair” and they “are able to



accomplish more at home” than beforeexercising with the 6 Second Absmachine. The improvement in reachafter only 30 days of exercise to near thereach of the control subjects, and thereduction in tremor seen here is highlysignificant for any type of exercise.Perhaps there is no type of exercise thatcan bring the group with disabilities tothe performance level of the controlgroup sitting in wheelchairs, but thepresent exercise regime was remarkablyeffective toward the benchmark reachand tremor of the controls.

In the present investigation, ourgoals were realized in that subjectsincreased their activities of daily livingand functional independence with a sim-ple home-exercise strengthening pro-gram.

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