Increased Workload Enhances Force Output During
Pedaling Exercise in Persons With Poststroke Hemiplegia
D.A. Brown, PhD, PT; S.A. Kautz, PhD
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Background and Purpose—A principle of poststroke rehabilitation is that effort should be avoided since it leads to increased spasticity
and produces widespread associated abnormal reactions. Although weakness also contributes to movement dysfunction after a
stroke, it has been feared that heightened activity levels during strength training will further exacerbate the abnormal tone
imbalance present in spastic hemiplegia. The purpose of this study was to test this hypothesis by quantifying the effects of
increased workload on motor performance during different speeds of pedaling exercise in persons with poststroke hemiplegia.
Methods—Twelve healthy elderly subjects and 15 subjects with poststroke hemiplegia of greater than 6 months since onset were
tested. The experimental protocol consisted of having subjects pedal at 12 randomly ordered workload and cadence
combinations (45-J, 90-J, 135-J, and 180-J workloads at 25, 40, and 55 rpm). Pedal reaction forces were measured and used to
calculate work done by each leg, including net positive and negative components. An electromyogram was recorded from seven
leg muscles.
Results—The main finding was that net mechanical work done by the plegic leg increased as workload increased in 75 of 81
instances without increasing the percentage of inappropriate muscle activity.
Conclusions—This study provides evidence that persons with hemiplegia increase force output by their plegic limb when pedaling
against higher workloads without exacerbation of impaired motor control. Therefore, exertional pedaling exercise is a beneficial
intervention for achieving gains in muscular force output without worsening motor control impairments. (Stroke.
1998;29:598-606.)
Key Words: exercise n hemiplegia n motor activity n muscle spasticity
A
principle of poststroke rehabilitation, developed by Bobath1 and later continued by Neurodevelopmental Treatment practitioners, is that excessive effort in spastic conditions
reinforces the abnormal patterns of posture and movement and
increases spasticity. Accordingly, Bobath claimed that focusing
on strengthening spastic muscles is inappropriate.
This concept has been questioned.2,3 In particular, weakness has
been shown to contribute to the functional deficits observed after
stroke.4 – 6 In light of the documented deficits in persons with
hemiplegia, improving functional movement strength without
compromising motor performance should be a goal of the
physical therapist. Current research supports the appropriateness
of exercise for achieving this goal in persons with hemiplegia.
First, studies suggest that effortful isokinetic exercise is beneficial
for persons with hemiplegia.7–10 Second, studies have shown that
immediately after lower extremity isokinetic exercise there was no
motor performance decrement as measured by either gait parameters or an upper extremity tapping task.11 Third, no long-term
negative impact was found on motor performance (as measured
during a functional sit-to-stand task) after a 4-week lower extremity isokinetic exercise training program.12
Even though exertional exercise may have benefits both
immediately after exercise and after long-term training, no
published studies clearly demonstrate the changes in abnormal
muscle activity that might occur during exercise. An ideal
exercise would specifically target weaker muscles without
exacerbating abnormal muscle activity and would involve
multisegmental, complex movements that can be applied
within a functional context. Ergometer pedaling is an ideal
functional exercise and assessment tool for this research. The
movement is significantly complex to provide a functionally
relevant test for motor performance. Pedaling demands multisegmental coordination of bilateral, reciprocal, symmetrical
lower extremity movements in which the muscles go through
periods of activity and subsequent passive lengthening. Because
pedaling is functional, safe, and accessible to patients with a
wide range of ambulatory function, the bicycle ergometer has
been used to study bilateral movement patterns in several
patient populations, including stroke,13–20 and is commonly
used in rehabilitation. Studies in stroke rehabilitation suggest
that significant improvement in lower extremity function
might result from using cycling as a training medium.13–15,21
Mechanical measures of pedaling performance can characterize impairment in persons with hemiplegia.19,20 To pedal at
a given cadence and workload, the combined mechanical work
done by the two limbs must be sufficient to overcome the
resistive load. The net mechanical work done by the plegic leg
represents the net contribution of the plegic limb and can be
Received October 17, 1997; final revision received December 17, 1997; accepted December 17, 1997.
From the Rehabilitation Research and Development Center, VA Palo Alto Health Care System (Calif).
Correspondence to David A. Brown, PhD, PT, Rehabilitation Research and Development Center (153), VA Palo Alto Health Care System, 3801
Miranda Ave, Palo Alto, CA 94306. E-mail [email protected]
© 1998 American Heart Association, Inc.
598
Brown and Kautz
BF
EMG
IEMG
MG
RF
SM
SO
TA
VM
599
sisting of healthy, elderly subjects with those from persons with
hemiplegia. It is generally believed that performance is degraded
and muscle activity patterns do not respond appropriately to
increased workload. Thus, if net mechanical work done by the
plegic leg does decrease because of greater relative amounts of
inappropriate muscle activity, then worsened performance is a
consequence of exertion and exertion should be avoided. However, if net mechanical work by the plegic leg actually increases
and performance improves, then strengthening exercises such as
high workload pedaling would be recommended as a potentially
effective training modality for reversing muscular weakness and
possibly improving motor performance.
Selected Abbreviations and Acronyms
5 biceps femoris
5 electromyogram, electromyographic
5 integrated electromyogram
5 medial gastrocnemius
5 rectus femoris
5 semimembranosus
5 soleus
5 tibialis anterior
5 vastus medialis
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positive (the limb assists crank propulsion), negative (the limb
resists crank propulsion), or zero. Since the total work provides
a net measure for a cyclic movement, and pedaling typically
includes periods of assistance and resistance,22 it is useful to
independently assess the assistance and resistance provided by
the leg. The net positive work done by the plegic leg
represents the component of the mechanical work that propels
the crank against the load and is principally the result of
muscular contributions in neurologically normal subjects.22
The net negative work done by the plegic leg represents the
component of the mechanical work that resists crank propulsion. Negative work occurs in the upstroke for neurologically
normal subjects and represents the combined effect of muscular
activity and gravity and inertial forces.22
The purpose of this study was to quantify the effects of
increased workload on motor performance during different speeds
of pedaling exercise in persons with poststroke hemiplegia. We
compared the motor performances of a control population con-
Subjects and Methods
Twelve healthy elderly subjects and 15 subjects with poststroke
hemiplegia of greater than 6 months since onset were tested (Table).
Subjects had sustained a single, unilateral cerebrovascular accident
with residual lower limb plegia; had no severe perceptual, cognitive,
or sensory deficits, no significant lower limb contractures, and no
significant cardiovascular impairments contraindicative to pedaling;
and could tolerate sitting on a bicycle seat for approximately 1 hour.
All subjects gave informed consent as approved by the internal review
board of the Stanford University School of Medicine. Patients
underwent the lower limb portion of the Fugl-Meyer test 23 for
assessment of global motor function. The reliability and validity of this
assessment have been documented for the poststroke hemiplegic
population.24 The healthy elderly subjects showed no signs or symptoms of neurological disease or lower limb orthopedic impairment.
The hemiplegic subjects in this study ranged in their walking ability
from mildly impaired to nonambulatory. They also varied in their
ability to perform movements outside of extensor/flexor synergy
patterns (eg, Reference 25) as assessed clinically by a portion of the
modified Fugl-Meyer assessment (see “Synergy Performance” in the
Subject Population Characteristics
Synergy
Performance*
Total Modified
Fugl-Meyer, %
Plegic Side
7
21
97
L
M
9
16
90
L
64
F
17
21
95
R
77
F
90
17
83
L
5
60
M
12
22
100
L
6
60
M
87
18
92
R
Subject
Age, y
Sex
1
58
M
2
63
3
4
Time After
Stroke, mo
7
64
M
38
9
72
R
8
69
M
32
16
88
L
9
74
F
46
7
71
L
10
64
M
119
21
93
L
11
65
M
132
18
88
R
12
63
M
15
19
86
L
13
69
M
8
20
91
R
14
72
M
15
16
85
L
15
Plegic (n515)
57
65.365.8
M
12 M
8
42.3643.1
3F
8
70
0–14, n53
86.768.7
15–18, n56
L
10 L
5R
19–22, n56
Control (n512)
69.568.4
7M
zzz
zzz
zzz
zzz
5F
*Synergy performance reflects the ability to move within (0–14), to combine (15–18), or to move outside of (19–22)
extensor/flexor synergy patterns as measured in a portion of the modified Fugl-Meyer assessment (maximum score522).
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Pedaling Exercise Enhances Force Output After Stroke
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Table). Subjects scoring 14 or less were only able to move within the
synergy patterns (n53), those scoring 15 to 18 were additionally able
to combine elements of the synergy patterns (n56), and the bestperforming subjects (scoring .18) were able to at least partially
perform a movement outside of the synergy patterns (n56). Therefore, although the group did not contain any subjects with severe
perceptual, cognitive, or sensory deficits, it was representative of a
range of rehabilitation candidates with motor impairment after stroke.
A standard ergometer with a frictionally loaded flywheel was
modified by including a backboard seating mechanism with shoulder
and lap harnesses to stabilize the subject and remove the need to
control balance. Further details concerning the apparatus are presented
elsewhere.26 Reaction forces oriented normal and fore-and-aft to the
pedal surfaces were measured by instrumented pedals.27 The feet were
firmly attached to foot plates on the pedal surface, which allowed the
subjects to create shear and vertical forces. Angular rotation of the
crank and pedals was measured by optical encoders.
The experimental protocol, conducted in an hour, consisted of
measurement of pedal forces, pedal and crank kinematics, and EMG
during pedaling at 12 randomly ordered workload and cadence
combinations (45-J [very low], 90-J [low], 135-J [medium], and 180-J
[high] workloads at speeds of 25 [slow], 40 [medium], and 55 [fast]
rpm). Crank angular velocity was displayed to the subjects, and they
were instructed to maintain a steady cadence while pedaling. Once a
steady cadence was achieved, 15 seconds of EMG, pedal force, and
encoder data were collected (1200 samples per second).
Surface EMG was recorded from tibialis anterior (TA), soleus (SO),
medial gastrocnemius (MG), rectus femoris (RF), vastus medialis
(VM), biceps femoris (BF), and semimembranosus (SM) of the right
leg in healthy subjects and of both legs in subjects with hemiplegia.
EMG (Ag-AgCl) electrodes (Therapeutics Unlimited) were positioned over the distal half of the muscle belly such that contact surfaces
were aligned longitudinally to the muscle fibers. Electrode sites were
prepared by cleaning the skin with isopropyl alcohol and shaving the
hair, when necessary, to ensure good contact. Electrodes (interelectrode distance522 mm, diameter58 mm) were attached with the use
of adhesive pads and electrode gel. Electrodes provided preamplification with a gain of 335. A common ground reference electrode was
placed on the distal end of the right tibia. Amplifier gain was selectable
from 3500 to 310 000 with a bandwidth of 20 to 4000 Hz. The
common mode rejection ratio was 87 dB at 60 Hz , and input
impedance was greater than 15 MV at 100 Hz.
Data Processing and Analysis
The net mechanical work done by each limb was calculated from the
kinematic and kinetic data and used as a measure of motor performance.
First, a third-order Butterworth low-pass filter was used to filter pedal
forces (20-Hz cutoff) and the crank and pedal angles (8-Hz cutoff). The
pedal force components oriented radial and tangential with respect to the
crank arm were calculated from the normal and shear forces. The
tangential component of the pedal force created a torque about the crank
center (referred to as the crank torque) that contributed to the angular
acceleration or deceleration of the crank. The crank torque was plotted
against crank angle, and the area under the resulting curve yielded the net
mechanical work done by the leg. The positive and negative areas were
also computed separately as measures of the positive (propulsive) and
negative (retarding) work done by the limb.
The total IEMG was calculated over the entire crank cycle and was
used to show any overall increases or decreases in total muscle activity
during higher workloads. Also, we developed a quantitative measure of
“inappropriate muscle activity” as a means for identifying increases or
decreases at higher workloads. Since muscle excitation cannot be consistently characterized by a single set of on-off times in persons with
hemiplegia, each EMG was quantified in terms of the relative percent
excitation present during four equal quadrants (90°) in the pedaling cycle.
The four quadrants were defined by axes parallel and perpendicular to the
seat tube (Fig 1). Quadrants I and II coincided with limb extension (foot
moving away from pelvis), and quadrants III and IV coincided with limb
flexion. Alternatively, contiguous quadrants IV and I (foot moving
anteriorly with respect to the trunk/pelvis axis) or II and III (foot moving
posteriorly) coincided with limb “transitions” (ie, the switch from limb
Figure 1. Experimental setup shows the ergometer, subject,
and variables recorded. Inset shows orientation of the four
phases of the pedaling cycle that were used to analyze EMG
activity (see text for further explanation).
flexion to extension or vice versa). For each quadrant, the excitation,
quantified by integrating the rectified EMG (IEMG), was expressed as the
percentage of IEMG over the entire cycle. The relative IEMG in a
quadrant provided a measure to quantitatively test whether the plegic
EMG was inappropriately timed (ie, excitation in a quadrant where
excitation does not occur in control subjects). This technique has been
reported elsewhere and has been used to identify one quadrant for each
muscle group where inappropriate activity can occur (ie, SO3, MG1,
VM3, RF3, BF1, SM1).19,20 Inappropriately timed activity occurs during
periods in the pedaling cycle when muscles are lengthening and hence
doing negative work.28
We visually examined individual, nonaveraged crank kinematics,
kinetics, and EMG activity for general trends. Then we calculated the
total positive, total negative, and net mechanical work and percent
IEMG in the “inappropriate” quadrant for each revolution and
averaged to get the mean values for the plegic limb in each trial.
Differences between the control subjects and the hemiplegic subjects
were evaluated with a two-tailed Student’s t test (P,.05). The
differences in net mechanical, positive, and negative work were
calculated between each pair of contiguous workload conditions (eg,
very low to low; low to medium; medium to high) within each actual
speed. In the absence of a contiguous pair of workloads, the next
highest workload was used for comparison. Because of the large
intersubject variability among hemiplegic subjects,29 the individual
subject data are also presented wherever possible to demonstrate the
robustness of findings within the hemiplegic population.
Results
Success With Pedaling at Specified Workloads
and Speeds
Although all subjects were able to pedal the ergometer at some
speed-workload combination, problems related to completing the
task occurred in almost all subjects with hemiplegia. In all, there
were 180 speed-workload combinations possible for the 15
subjects with hemiplegia (12 combinations per subject times 15
subjects). Only 2 of 15 hemiplegic subjects were able to successfully pedal at all 12 speed and workload combinations. Of the 180
combinations, pedaling performance fell under the following four
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Figure 2. Crank torque versus crank angle for plegic limb of subject 5 and the control leg of a representative control subject. Net positive work is reduced and net negative work is increased for subject 5, resulting in decreased net mechanical work.
categories: (1) successfully able to pedal at the specified workload
and speed (108 combinations in all subjects); (2) unable to push
the crank against the specified load (ie, no cranking motion
achieved) (48 combinations in 6 subjects); (3) pedaled slower than
the target speed (16 combinations in 8 subjects); and (4) pedaled
faster than the target speed (8 combinations in 7 subjects). Those
combinations that were performed either faster or slower than the
target speeds were recategorized at the level of actual speed if they
fell within 65 rpm of a specified target speed category measure
(20 of 24 combinations were recategorized).
The following results contain analysis of those trials in which
subjects successfully completed the task of pedaling (n5128, or
180 total combinations minus 48 nonpedaling and 4 noncategorized speed combinations). Most subjects with hemiplegia
were able to pedal against at least two workloads at the fastest
target speed (55 rpm). Ten of 15 subjects with hemiplegia
successfully pedaled at the highest workload, and 14 were able
to hit the fastest target speed. In contrast, all control subjects
were able to pedal at the highest workload and at the fastest
target speed (although not all subjects when the highest speed
and workload were combined). Of the healthy, elderly control
subjects, 9 of 12 subjects were able to successfully pedal at all
12 conditions. Of the 3 remaining subjects, 2 were unable to
push against some specified load, and all 3 pedaled slower than
the fastest target speed at the highest workload.
Kinetic Responses to Increased Workload
Subjects with hemiplegia performed less net mechanical work
with the plegic leg than control subjects with the nonpreferred
leg (22.1621.8 J versus 68.368.0 J at the 135-J workload
level; P,.0001) and produced a very large range of work
values (219.8 J to 54.3 J at the 135-J workload level).
Compared with control subjects, single leg crank torque
trajectory was characterized by less net positive (48.8613.3 J
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Pedaling Exercise Enhances Force Output After Stroke
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Figure 3. Averaged data of kinetic measures of pedaling performance at increasing workload levels at each of three speeds (slow,
medium, and fast) from all control subjects (n515). Net mechanical work and net positive work are shown to linearly increase, while net
negative work is shown to linearly decrease. Error bars represent SEM.
versus 70.064.8 J; P,.0001) and more net negative work
(226.7614.0 J versus 26.364.6 J at the 135-J workload level;
P,.0001) in the plegic leg. As a consequence, the nonplegic
leg must necessarily generate compensatory forces to overcome
the higher negative work (by increasing downstroke work) and
lesser positive work (by generating positive work during the
upstroke) generated by the plegic leg. The performance deficit
in persons with hemiplegia can be characterized as reduced
force output during the downstroke phase and increased
resistive force output during the upstroke phase (Fig 2).
Control subjects demonstrated typical kinetic responses to
increased workload (Fig 3). Subjects showed increased net
mechanical work done by each leg as workload increased at all
speeds (P,.0001). This resulted from a combination of in-
Figure 4. Net mechanical work differences from two contiguous workload levels from the plegic leg of each subject with hemiplegia (n514;
subject 9 was unable to pedal at two workloads for any one speed level) at three speeds of pedaling. A total of 81 workload pairs are presented. Dashed lines represent the mean62 SDs of the differences measured in control subjects. Values are expressed as a percentage of
the total work increase that occurred. Values greater than 50% indicate that the plegic leg contributed the majority of net mechanical work
for the increased workload. Values less than zero indicate a decrease in net mechanical work done by the plegic leg at a higher workload level.
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Figure 5. Averaged data of total IEMG values from seven muscles at increasing workload levels at each of three speeds from control
subjects and subjects with hemiplegia. All muscles in control subjects and subjects with hemiplegia are shown, on average, to increase
across the workload levels.
creased net positive work (P,.0001) and decreased net negative work (P,.0001).
Subjects with hemiplegia appropriately increased the net
mechanical work done by the plegic leg as workload increased
at all speeds. This occurred even though the nonplegic leg is
capable of generating all of the extra work output at higher
workloads because the coupled cranks allow it to compensate
for deficits in the plegic leg. Of those subjects with hemiplegia
who were able to complete at least two levels of workload
(n514), there was rarely individual evidence for further
impaired kinetic performance as a result of increased workload.
With no exceptions, subjects showed increased net positive
work done by the plegic leg. The net mechanical work done
by the plegic leg, with only six exceptions of 81 workload pairs
(subject 2 [medium and fast speeds, twice in each], subject 11
[fast speed], and subject 15 [medium speed]), always increased
when the workload increased (Fig 4). The plegic leg contributed significantly less than 50% of the increase in workload (53
workload pairs). However, in 12 workload pairs (in subjects 1,
2, 3, 5, 8, and 12), the net mechanical work contributed by the
plegic leg actually equaled or exceeded 50% of the mean
contribution from the nonplegic leg.
Muscle Activation Responses to Increased
Workload and Speed
Control subjects and subjects with hemiplegia showed increased IEMG by the plegic leg as workload increased at all
speeds (P,.05 for all seven muscles and at all speeds). Nonplegic muscles, on average, also showed increased IEMG at higher
workloads (P,.001), similar to control legs (Fig 5).
Plegic leg total IEMG increased without a disproportionate
increase in the percentage of activity occurring during inappropriate quadrants of the pedaling cycle. In all inappropriate muscle
activity quadrants (ie, SO3, MG1, VM3, RF3, BF1, SM1), the
percent muscle activity occurring remained unchanged (P..05
for all six muscles and at all speeds) (Fig 6). Although the plegic
muscles showed greater percentages of muscle activity during
these quadrants when compared with control subjects (at least
P,.05 for all muscles except BF), this overactivity was not
exacerbated by increased workload demands. In both the control
muscles (Fig 6) and muscles of the nonplegic leg (not shown),
inappropriate activity was low and therefore showed no significant
increase with higher workloads.
Since three subjects (subjects 2, 11, and 15) showed a
significant decrease in net mechanical work as a result of
increased workload, we examined the change in inappropriate
muscle activity for the major power muscles (ie, RF, VM, BF,
and SM). These muscles would be expected to contribute
significant inappropriate activity and hence do greater negative
work at higher workloads. Fig 7 shows that for subject 2 at the
medium-speed condition (when less mechanical work was
done at the low versus very low workload), there is a large
increase in RF3 activity (24% to 35%) and VM3 activity (19%
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Pedaling Exercise Enhances Force Output After Stroke
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Figure 6. Averaged data of percentage of activity during inappropriate quadrants for six muscles at increasing workload levels of three
speeds from control subjects and subjects with hemiplegia. Percent inappropriate activity in control muscles is relatively low, and percent inappropriate activity in plegic muscles is generally higher. However, no significant linear increases in this activity occur at higher
workloads in the plegic muscles.
to 31%) in the plegic leg. In contrast, for the slow-speed
condition (when net mechanical work actually increased), the
percentage of both inappropriate plegic RF3 activity and
plegic VM3 activity remained unchanged. The activity in these
muscles is shown to proportionately increase during the
appropriate as well as the inappropriate quadrants. Therefore,
although both inappropriate activity and appropriate activity
increase in absolute terms with increased workload, the majority of enhanced muscle activity occurs during the appropriate quadrants, leading to the increased net positive work done
by muscles. This increase in appropriate activity offsets any
increase in net negative work. As a result, increased net
mechanical work is done at higher workloads.
No subject reported any negative or positive effects on gait
quality from the exercise resulting from participating in the
2-hour session of this study. Subjects did report a significant
amount of fatigue after the experimental session ended, but all
ambulatory subjects were able to leave the facility under their
own volition. In addition, upper extremity postural tone
typically increased as a result of extra effort during the
experiment. In all cases, any increased postural tone returned
to its usual state before the subject left the premises (within one
half hour of the session end).
Discussion
The main finding from this study was that force output by the
plegic leg, although impaired, was enhanced at higher pedaling
workloads without exacerbating inappropriate muscle activity.
This contradicts the principle of worsened motor performance
and exacerbated spastic muscle activity at higher exertional
levels. If this principle were supported, we would have
observed that a disproportionately larger amount of inappropriate muscle activity would have occurred at higher workloads and lesser amounts of mechanical work would have been
generated by the plegic leg. Although this did occur in rare
cases (6 of 81 workload pairs), the majority of cases showed
increased appropriate and inappropriate activity resulting in
increased mechanical work output.
This study provides evidence that persons with hemiplegia
can increase the positive work done by their hemiplegic limb
during pedaling when working against higher workloads. Our
results showed that when subjects with hemiplegia pedal
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Figure 7. Two representative groups of averaged muscle activity profiles (rectified) from subject 2 showing VM, RF, and BF muscle
activity patterns from two workload pairs. Asterisks indicate phases of inappropriate muscle activity. In the top group of workload pairs,
at the low versus very low workload level (where net mechanical work decreased), the inappropriate activity of the VM and RF muscles
showed substantially increased activity relative to the appropriate activity at the higher workload. In the bottom group of workload
pairs, at the high versus medium workload level (where the net mechanical work increased), the inappropriate activity of the VM, RF,
and BF muscles showed increases in inappropriate activity that were proportional to the appropriate activity.
against a low workload, they generate relatively low levels of
muscular force. When higher workloads are encountered, the
level of the muscular output is heightened so that greater
positive work can be produced. These results are consistent
with a previous study by Benecke et al,17 who also used
ergometer pedaling to evaluate spastic movement dysfunction.
One part of their study calculated the net mechanical work
asymmetry between limbs as the workload increased from 1 to
5 kilopond-m (kpm) in nine subjects with hemiplegia pedaling
at 40 rpm. It was found that the percentage of work done by
the nonplegic limb increased from approximately 60% to 68%
as the workload increased from 1 to 3 kpm and then remained
essentially constant at 68% as the workload increased from 3 to
5 kpm. For the percentage to stay constant as the workload
increased from 3 to 5 kpm, the net mechanical work done by
the plegic limb had to increase with increased workload.
We found in this study and in other studies related to pedaling
in persons with hemiplegia that the nonplegic leg performs the
majority of net mechanical work, working to overcome the
increased negative work produced by the plegic limb.17,19,20
Therefore, increases in pedaling workload will consequently place
greater demands on nonplegic leg muscles. Our work has shown
that the nonplegic leg is usually capable of responding to the
increased demands because the timing of muscle activity patterns
is similar to that of control leg muscles and does not change with
increased workload. However, one unintended consequence of
this type of exercise may be a further asymmetry in muscle
strength between the two legs. However, persons with hemiplegia often attempt to perform tasks that require strong compensation by the nonplegic limb to accomplish the task, and therefore
the increased force capabilities of the nonplegic leg may be useful
in functional tasks.
It is important to recognize the several unique aspects of
pedaling exercise before attempting to generalize these results to
all exertional leg exercise modalities. First, pedaling is a bilateral
task that allows the nonplegic leg to compensate for functional
impairments of the plegic leg (through coupling of the cranks).
Thus, successful pedaling can occur even if the motor deficits are
profound. Second, pedaling allows stabilization of abnormal trunk
postures so that, although abnormal trunk and upper extremity
postural responses were observed, the functional output of the leg
muscles could still increase. Third, the trajectory of the feet is
constrained to move in a circle, which reduces sudden changes in
direction of movement and allows relatively smooth phase tran-
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Pedaling Exercise Enhances Force Output After Stroke
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sitions. As a consequence, the transition periods, usually a difficult
portion of any reciprocal movement, are rendered less consequential. Finally, loading occurs at the pedal/crank interface, which
differs from upper extremity tasks that usually involve increased
manipulative skills in order to deal with heavier workloads. In
contrast to pedaling, in arm exercises in which handgrip is essential
or when limbs are weighted, the added control demands can
significantly reduce the person’s capability to respond to the load.
Studies have shown the physiological benefits of aerobic
ergometer exercise.13,21 Potempa et al21 trained 21 subjects with
hemiparesis over a 10-week period, three times a week, on a
bicycle ergometer. Significant improvements in maximal oxygen consumption, workload, and exercise time were measured, as well as lowering of systolic blood pressure during a
submaximal exercise test. Our study implies that exertional
pedaling exercise may also be a beneficial intervention for
achieving gains in muscular force output. An exercise program
can be designed to increase aerobic capacity and functional
muscle strength by simply varying the workload and pedaling
rates without undue harm to motor performance. Our study
showed that plegic muscle activity is appropriately increased to
meet the demands of increased workload during pedaling
without further exacerbation of impaired performance. Although the muscular work done by plegic muscles may be
small at low workloads, the increased muscular work done
during repetitive cycles at higher loads may serve as a stimulus
to muscle hypertrophy and to reduce the muscle atrophy
commonly associated with disuse.30 –32 With appropriate
screening and monitoring of vital cardiovascular signs, a person
with hemiplegia could exercise on a bicycle ergometer using
low repetitions (10 to 15 cycles) of exertional (high workload)
pedaling and expect to find increased motor output in the
plegic leg. Such a long-term, high-exertional pedaling program would be expected to result in chronic strength gains in
otherwise weakened muscles.
Acknowledgments
This study was funded in part by the Foundation for Physical Therapy
and Department of Veterans Affairs, Rehabilitation Research and
Development Division. The authors wish to acknowledge Christine
Dairaghi for technical assistance and Drs Felix E. Zajac and Kevin
Mcgill for their editorial contributions to this article.
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Increased Workload Enhances Force Output During Pedaling Exercise in Persons With
Poststroke Hemiplegia
D. A. Brown and S. A. Kautz
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Stroke. 1998;29:598-606
doi: 10.1161/01.STR.29.3.598
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