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 brown{at}roses.stanford.edu
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.
This concept has been questioned.2 3 In
particular, weakness has been shown to contribute to the functional
deficits observed after stroke.4 5 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 8 9 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 14 15 16 17 18 19 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 14 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 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 consisting 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.
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 2525 ) as assessed clinically by a portion of the
modified Fugl-Meyer assessment (see "Synergy Performance"
in the Table
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
distance=22 mm, diameter=8 mm) were attached with the use of
adhesive pads and electrode gel. Electrodes provided preamplification
with a gain of x35. A common ground reference electrode was placed on
the distal end of the right tibia. Amplifier gain was selectable from
x500 to x10 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 M
Data Processing and Analysis
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
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.
The following results contain analysis of those trials in which
subjects successfully completed the task of pedaling (n=128, 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
Control subjects demonstrated typical kinetic responses to increased
workload (Fig 3
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 (n=14), 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
Muscle Activation Responses to Increased Workload and
Speed
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
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
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).
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 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 transitions. 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 31 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.
Received October 17, 1997;
revision received December 17, 1997;
accepted December 17, 1997.
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© 1998 American Heart Association, Inc.
Original Contributions
Increased Workload Enhances Force Output During Pedaling Exercise in Persons With Poststroke Hemiplegia
Abstract
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
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.
Key Words: exercise • hemiplegia • motor activity • muscle spasticity
Introduction
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
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.
Subjects and Methods
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
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
test23 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.
View this table:
[in a new window]
Table 1. Subject Population Characteristics 
). Subjects scoring 14 or less were only able to move
within the synergy patterns (n=3), those scoring 15 to 18 were
additionally able to combine elements of the synergy patterns (n=6),
and the best-performing subjects (scoring >18) were able to at least
partially perform a movement outside of the synergy patterns (n=6).
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. 
at 100 Hz.
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. ). 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 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
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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).
Results
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
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 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 ±5 rpm of a specified
target speed category measure (20 of 24 combinations were
recategorized).
Subjects with hemiplegia performed less net mechanical work with
the plegic leg than control subjects with the nonpreferred leg
(22.1±21.8 J versus 68.3±8.0 J at the 135-J workload level;
P<.0001) and produced a very large range of work values
(-19.8 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 (48.8±13.3 J versus 70.0±4.8 J; P<.0001) and
more net negative work (-26.7±14.0 J versus -6.3±4.6 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).
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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. ). Subjects showed
increased net mechanical work done by each leg as workload increased at
all speeds (P<.0001). This resulted from a combination of
increased net positive work (P<.0001) and decreased net
negative work (P<.0001).
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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 (n=15). 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. ). 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.
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Figure 4. Net mechanical work differences from two
contiguous workload levels from the plegic leg of each subject with
hemiplegia (n=14; 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 mean±2 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.
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).
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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. ).
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.
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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.
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%
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.
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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.
Discussion
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
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.
Selected Abbreviations and Acronyms
BF
=
biceps femoris
EMG
=
electromyogram, electromyographic
IEMG
=
integrated electromyogram
MG
=
medial gastrocnemius
RF
=
rectus femoris
SM
=
semimembranosus
SO
=
soleus
TA
=
tibialis anterior
VM
=
vastus medialis
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.
References
Top
Abstract
Introduction
Subjects and Methods
Results
Discussion
References
1.
Bobath B. Adult Hemiplegia: Evaluation and
Treatment. 2nd ed. London, England: William Heinemann Medical
Books; 1978.
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