Participants with stroke were moderately impaired (Chedoke-McMaster Stroke Assessment [CMSA] leg score = 3-6/7, foot score = 2-6/7), had low aerobic capacity (8.1–11.1 mL/kg · min), slow preferred walking speeds (37–64 cm/sec) and mild to severe asymmetry during gait.8 EMG patterns varied across individuals, although cycle-cycle variability within a task and an individual was comparable to the variability observed across the healthy participants. Common to the participants with stroke was the observation of asymmetric activation favoring the nonparetic limb as well as phase-inappropriate activity and/or tonic activation and lack of modulation (Fig. 2). Individual case profiles are detailed below, followed by a summary of all results.
Patient 1 (P1)
P1 was a 51-year-old woman, two years post-stroke. A CMSA leg score of 6/7 indicated near-normal movement patterns where only faster or more complex movements were difficult, but the foot score was only 3/7, indicating marked spasticity and movement primarily within the synergy patterns. Accordingly, her gait speed was only 37 cm/sec, and she demonstrated severe temporal asymmetry favoring the nonparetic limb. EMG profiles during the control task clearly demonstrate minimal contributions from the paretic VL. P1 was not able to perform LLE at the prescribed intensity of four springs, and accordingly they were reduced to three springs and then to two springs in order to complete four minutes of pedaling. Although pedaling was discontinuous, Vo2 was increased 29% compared to the standard SR task. TA activity was increased in both limbs, and there were no observable increases in paretic VL activity. The EMG FB task was completed with a high RPE (RPE = 7). Despite a lack of increase in paretic VL activity, nonparetic VL was reduced and pedaling was more efficient (Vo2 reduced 28% compared to control task).
Patient 2 (P2)
P2 (male, five years post-stroke, 71 years old) had the lowest Vo2peak (8.1 mL/kg/min) but the highest level of recovery overall (CMSA leg = 5/7, foot = 6/7) and was also the fastest walker among the three patients. This individual demonstrated a high level of tonic activation during the control task, particularly in the paretic BF and MG, as well as phase-inappropriate activity in the paretic TA and nonparetic BF. The prescribed spring load was six springs, but P2 was only able to perform two minutes of LLE at one third of the prescribed load. Vo2 demonstrated a 17% decrease relative to the control task. EMG patterns during LLE showed little variation from the control task. In contrast, in the FB task paretic VL activation was slightly increased, along with corresponding decreases in nonparetic VL activity. This was associated with a 9% increase in Vo2 compared to the control task.
Patient 3 (P3)
P3 (54-year-old man, four years post-stroke) was the most impaired of the patients (CMSA leg = 3/7, foot = 2/7, spasticity present and no voluntary movement), with a high degree of asymmetry and phase-inappropriate activity in the paretic BF during the control task. Like the other patients with stroke, P3 was not able to pedal at his prescribed spring load (six springs), which was subsequently reduced to four springs. Of the three patients studied, P3 was the only individual to demonstrate increases in both VL muscles during LLE (although activity was still asymmetric). This change was associated with a large increase in Vo2 (46%) compared to the standard SR task. P3 decreased nonparetic VL activity during the FB task, but did not increase paretic activation. There were no differences in Vo2 compared to the control task.
None of the poststroke participants were able to pedal at 30% of body weight during LLE, and even with the reduction in tonic load applied through the springs, all three participants had difficulty maintaining a continuous, even rhythm for the duration of the four-minute testing session.Both cardiorespiratory and sensorimotor responses to LLE varied both across individuals and in comparison to the average of the healthy participants. In contrast, the EMG FB task was better tolerated. Although cardiorespiratory responses varied between individuals, all three patients were able to decrease VL activity in the nonparetic limb. However, it is noteworthy that this was not necessarily accompanied by an increase in paretic leg VL activation.
The purpose of this study was to examine the sensorimotor and cardiorespiratory characteristics of two modified pedaling tasks to evaluate the feasibility of increasing paretic limb activity during adapted aerobic pedaling after stroke. While only a small number of individuals with stroke were evaluated in this initial case series, the three participants are representative of the types of individuals who are likely to benefit from such an adapted program. Specifically, this subset of the stroke population would be unable to participate in a traditional aerobic walking program. The findings from the case series highlight the challenges faced in identifying aerobic training activities that may also target the primary sensorimotor impairments caused by stroke. Responses from a healthy control group were important to highlight expected variations between tasks and inform selection of a potential task for study with individuals after stroke. A number of observations were particularly noteworthy. Healthy participants and participants with stroke did not show the same adaptations to the modified pedaling tasks. The hypotheses were supported in the healthy participants, such that both tasks successfully increased target muscle activation with limited effects on other muscles and accordingly increased cardiorespiratory output and perceived exertion. However, these adaptations did not translate to the participants with stroke.
Participants with stroke were not able to pedal at the same spring load as healthy participants during the LLE task. This is an issue of inappropriate exercise prescription and a reflection of a lack of any published, standardized guidelines for establishing exercise intensity in a new and previously untested paradigm. Accordingly, we adjusted the spring load for participants with stroke as necessary to allow them to complete the task at a lower intensity. Interestingly, even at reduced spring loads, sensorimotor and cardiorespiratory adaptations did not match those of the control group. This could be due to the differences in load between populations and/or due to the dyscontrol experienced by the individuals with stroke. Moreover, on the whole, these patients were unable to increase paretic limb activation during the LLE task. It appears that even at reduced spring loads, the LLE task was excessively challenging for these individuals. This issue may be addressed in future studies by identifying appropriate spring loads. It is also possible that limb-loaded ergometry may be more appropriate for higher functioning patients as an adjunct to walking exercise. While these case studies provide preliminary insights for guiding development of LLE prescription, clearly more study is required in a broader and larger sample to determine which subset of the stroke population may be most appropriate for limb-loaded training.
Similarly, pedaling with EMG FB induced different adaptations in each of the groups. Healthy participants successfully used EMG FB to increase VL activation with minimal compensations in other muscles. In contrast, although the EMG FB task was better tolerated than LLE task in participants with stroke, they were unsuccessful in increasing paretic limb involvement. One possibility for this is that FB may have been provided too infrequently for participants with stroke to sustain adaptations. FB was generated from cumulative EMG activity, updated every 30 seconds. While this time frame was selected to allow participants adequate time to process the information and make conscious adjustments in pedaling strategies and was effective in the healthy group, participants with stroke may have benefited from increased frequency of FB. Interestingly, although the participants with stroke did not increase paretic leg activity with EMG FB as hypothesized, nonparetic muscle activation was reduced. While the functional implications of such a change are not clear, it indicates that participants were attempting to perform the task. Like LLE, use of EMG FB warrants further study before being recommended for practice. That said, the EMG FB was well tolerated, and, in light of moderate successes with EMG FB in other paradigms, such as the improvement in gait quality with FB-based gait training,17,18 it may be more relevant than LLE for future application in stroke rehabilitation. However, such trials need to have sufficient power and standard assessments to appropriately assess the effectiveness of EMG FB.18
Our results highlight the challenges experienced when adapting traditional exercise models for enhanced training. The current emphasis on SR ergometry was due to (1) the availability of such equipment in clinical facilities and (2) the limited ability of many people with stroke to perform walking-based aerobic training. Selection of an appropriate adapted training activity may not necessarily require both limbs to work equally as long as the paretic limb participates. In fact, differential loading would likely be ideal, particularly if the degree of loading could be varied as the patients’ abilities improved. Both of the proposed models allow patient-specific needs to be addressed during training, such as modification limb loading or of the muscles targeted for FB.
We recognize that the small number of participants with stroke limit the conclusions that can be drawn from this study. However, our examination of feasibility of adapted training has revealed the need for further study of enhanced-use training tasks. For example, while the present encouraged-use strategies did not induce the desired changes in motor control, modifications to both adapted paradigms (such as decreased loading and more frequent FB) may yield more positive results. The current work was limited to evaluation over a short-term interval. The insights gained from the present study are warranted before embarking on future long-term training programs to explore the influence on learning and neurological change.
The development of adapted training modalities to address both sensorimotor and cardiorespiratory deficits after stroke is important for several reasons. First, many existing approaches do not encourage paretic limb use during aerobic training, and there is a lost opportunity to attempt to concurrently improve sensorimotor control. Furthermore, development of such activities could improve efficiency of rehabilitation sessions and may optimize functional recovery. This feasibility case series represents an important first step and highlights the challenges involved in adapting training activities. The tasks selected in the present study, which have the potential to generate the desired effects, require more refinement and study in a broader group of participants before being recommended on a larger scale. Alternative adapted training paradigms (such as recumbent stepping or force-based FB) also warrant attention.
We thank Mark Bayley, MD, Sandra Black, MD, Valerie Closson, and John Esposito for assistance with medical screening, patient referral, recruitment, and data collection.
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Keywords:© 2008 Neurology Section, APTA
paresis; cerebrovascular accident; cardiovascular deconditioning; exercise; rehabilitation