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CME Article

High Intensity Strength Training Improves Strength and Functional Performance After Stroke

Weiss, Angela MSPT; Suzuki, Toshimi MS; Bean, Jonathan MD; Fielding, Roger A. PhD

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American Journal of Physical Medicine & Rehabilitation: July 2000 - Volume 79 - Issue 4 - p 369-376
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Abstract

Objectives: Upon completion of this article, the reader should be able to: (1) understand the role of muscle weakness in the pathophysiology of stroke; (2) understand that progressive resistance training is effective in increasing muscle strength after stroke; (3) evaluate the implications of resistance training in rehabilitation after stroke.

Level: Advanced

Accreditation: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to sponsor continuing medical education for physicians.

The Association of Academic Physiatrists designates this continuing medical education activity for a maximum of one credit hour in Category 1 of Physician's Recognition Award of the American Medical Association. Each physician should claim only those hours of credit that he/she actually spent in the education activity.

Disclosure: Disclosure statements have been obtained regarding the authors' relationships with financial supporters of this activity. There is no apparent conflict of interest related to the context of participation of the authors of this article.

Stroke is the leading cause of physical disability in older men and women in the United States.1 Motor impairments including muscle weakness, decreased velocity and control of movement, and abnormal patterns of movement affect 60% to 78% of persons suffering a stroke and often result in decreased functional ability.2 The observed muscle weakness in the post-stroke population has been attributed to reduced muscle fiber size, decreased firing rate, atrophy of type II muscle fibers, increased fatigue, decreased motor unit numbers, and altered motor unit recruitment.3 In cross-sectional studies of stroke outcomes, voluntary muscle strength, particularly of the knee extensors, has been shown to be closely correlated with measures of gait quality,4-6 an important determinant of functional independence in this population.

Older stroke survivors, who number nearly 3 million, may have a continuing decline in mobility after stroke.7 Impairments in self care and mobility in all older adults during tasks such as walking, rising from a chair, and ascending stairs have been associated with a 2-fold greater risk for institutionalization and death.8, 9

Progressive resistance strength training exercise has been shown to increase muscle strength and size in healthy and frail older individuals (for review, see Fielding10). After stroke, few studies have addressed the effects of any type of strength or resistance training on changes in muscle strength.11-13 However, interpretation of these reports is complicated by several confounding factors including the timing of the intervention relative to stroke onset,12 the outcome measures used,11 and the type and intensity of the strengthening program implemented.11, 13

No studies have assessed the effects of progressive resistance training after stroke on changes in strength and the associated changes in functional outcome measures in community dwelling individuals after stroke. Traditionally, recovery of motor function after stroke has been thought to be nearly complete in the first 3 to 6 mo after onset.14, 15 Therefore, the present study was conducted to evaluate the effects of a high intensity resistance strength training intervention on bilateral lower limb strength, performance, and clinical outcome measures in older individuals at least 1 yr after stroke onset.

METHODS

Study Design

A time series clinical trial using progressive resistance training was conducted with baseline and postintervention measures of lower limb strength, functional performance, and functional outcome in a volunteer sample of post-stroke individuals.

Inclusion Criteria

Subjects were eligible for enrollment if they were living at home, older than age 60, at least 1 yr after stroke, not presently receiving any rehabilitation services, and unable to perform unilateral stance for more than 15 sec with the affected lower limb.

Recruitment

Participants were recruited from Local Easter Seals stroke support groups, Home Health Agencies, Rehabilitation Clinics, and an outreach letter via the National Stroke Association. Recruitment letters were sent to 75 prospective volunteers. Those who responded were screened on the phone and, if appropriate, began the recruitment process. Of the initial pool of 75 subjects, 12 responded to a mailing. All participants underwent further review with a medical history by their own primary care physician, which required a signed medical consent form. Persons scoring below an 18 on the Folstein Mini Mental examination were excluded. Three individuals were excluded who did not meet baseline criteria. Two dropped out after 3 wk for personal reasons. Of the original pool, seven participants met eligibility criteria and agreed to participate. A signed informed consent form was obtained. The protocol was approved by the Institutional Review Boards at Sargent College, Mt. Auburn Hospital, and Massachusetts General Hospital.

Exercise Training Protocol

Baseline measures of performance and strength were assessed twice, separated by 5 days to minimize testing effects.16 After the baseline testing, subjects began the exercise intervention.

The exercise training was performed for 12 wk (2× per wk). Subjects performed standing hip flexion, abduction, and extension using a stack weight training machine (California Gym Apollo, Pomona, CA). Sitting knee extension and leg press were performed on Keiser Pneumatic training equipment (Keiser Sports Health Equipment, Fresno, CA). Each of these exercises was performed unilaterally on both the affected and intact side. All participants were able to do knee extension on the hemiparetic side through part of their range of motion. All subjects worked up to three sets of 8 to 10 repetitions at 70% of the 1 repetition maximum (1 RM). All training and testing was supervised by a physical therapist.

1 RM Muscle Strength

Muscle strength testing was performed on all the muscle groups undergoing training and on the same equipment on which the subjects trained. Strength testing in stroke populations has been shown to be reliable and valid as an outcome measure in clinical trials.5 When support in stance was needed, an assistive device such as a cane or walker was used along with occasional physical contact by the therapist. Subjects were allowed several trials of exercise as warm-up. The weight was then progressively increased with a minimum of 30-sec rest between each trial. The 1 RM was used to measure muscle strength. This is defined as the maximum weight that could be lifted correctly for one repetition within 5% of the full range of motion. In general, three to five progressive weight increases were required before 1 RM was found. The 1 RM test was measured at baseline and every 2 wk during the training period. At baseline, the highest of the two measurements was established as the baseline 1 RM and used to determine the initial training intensity.17

Gait Velocity

Habitual gait velocity was measured to the nearest 0.01 as the mean of two trials by an ultrasonic gait speed monitor (OCPB Electronics, Glasgow, Scotland). The apparatus was applied around the waist and the subject was asked to begin walking at their comfortable walking speed along a level corridor for approximately 6 m. The use of assistive devices was noted. Reliability estimates for habitual gait velocity at baseline were determined by calculating the single test intraclass correlation coefficient (ICC = 0.924).

Chair Rise Time

Repeated chair rise time included five full sit-to-stand sequences. Subjects were instructed to rise from the standard firm seat and use their arms only if necessary. Chair rise time was measured from initiation to full stance and timed to the nearest 0.1 sec. This test was only performed once at each evaluation session. The reliability of this test determined at baseline is excellent (ICC = 0.933).

Stair Climb

Subjects were asked to climb a single flight of stairs (11 steps) with rails on both sides. Subjects were instructed to ascend and descend as quickly as possible. The test was repeated twice with the average time taken for analysis. Time for ascent and descent was recorded as well as use of rails and stepping pattern. Reliability for this test was good (ICC = 0.756).

Unilateral Leg Stance

The time was measured as a participant was asked to stand on each leg without upper limb support. The inability of a subject to stand unilaterally was recorded as 0.00 sec. Three trials were performed for each leg with the average time recorded at each session.

All functional performance measures were assessed at baseline, 4, 8, and 12 wk.

Motor Assessment Scale

All subjects were asked to perform the first five items, which test domains of lower limb function, of the Motor Assessment Scale (MAS) at baseline and 12 wk. The MAS uses a 7-point ordinal scale to rate motor function for eight everyday tasks, including gait12. It has been shown to be a valid and reliable baseline indicator of motor function after stroke.18

Balance

Static and dynamic balance were tested by using the Berg Balance scale at baseline and 12 wk. It includes 14 items of functional reach, sitting and standing balance, transfers, turning, and tandem walk.19

Self-Reported Measures of Functional Status and Activity

The physical function subscale of the Medical Outcome Survey (36 item short form) health survey (MOS-36) was administered at baseline and 12 wk.20 Levels of voluntary physical activity were monitored by using the Harvard Alumni Questionnaire,21 which has been validated in postmenopausal women,22 and the Physical Activity Scale for the Elderly.23 The Barthel Index was also determined at baseline because it has been used as a good overall measure of disability in randomized controlled studies.24-26 The Barthel Index has been tested for both validity and reliability in assessing disability in the stroke population.2

Depression Index

The Geriatric Depression Scale was administered with an interviewer to assess a clinical marker of depression.27 This is a 30-question instrument that asks questions related to depressive symptoms. Marked depressive symptoms have been noted in 21% to 22% of the stroke population 1 yr after stroke.25 Previous studies have shown progressive resistance exercise to improve depressive symptoms in depressed elders.28 The test was administered at baseline and 12 wk. The Geriatric Depression Scale represents a reliable and valid self-rating depression screening scale for the older population.27 A score of 14 indicates an 80% sensitivity rate for classifying depression.

Statistical Analysis

All data are reported as mean ± SEM values. Differences before, during, and after training were analyzed by analysis of variance for repeated measures. Measurements determined at 0 and 12 wk were compared by using a paired t test. Relationships between variables of interest were determined by using least-squares linear regression. Significance was established at P < 0.05.

RESULTS

Descriptive Characteristics

The clinical characteristics of the seven subjects enrolled in the intervention are presented in Table 1. The mean Barthel score at baseline was 96/100, which indicates a high independence level of the group. In five subjects, their stroke occurred in the left hemisphere and, in two, it occurred in the right. In addition, three of seven subjects had some degree of sensory loss.

TABLE 1
TABLE 1:
Descriptive characteristics

Intervention Compliance

All seven subjects successfully completed the training protocol. The attendance rate was 90% for the 12-wk program. All participants were able to perform the exercises as planned. Two subjects infrequently experienced minor back discomfort during exercise, and one subject experienced some knee discomfort on her intact side with knee extension. None of the participants required analgesic medication or missed sessions because of discomfort.

Baseline Muscle Function

At baseline, strength of the knee and hip extensors of the affected side was reduced by 53% (P < 0.0002) and 62% (P < 0.01), respectively. Muscle strength for all other muscle groups tested was not different between affected and intact side.

Functional performance measures were also related to the 1 RM of several muscle groups evaluated. Repeated chair stand strongly correlated with affected knee extension 1 RM (r = −0.788; P<0.035) (Fig. 1). In addition, affected leg press (r = −0.827; P < 0.022), affected hip flexion (r = −0.824; P < 0.023), and intact hip extension (r = −0.857; P < 0.014) were also associated with repeated chair stand time. Associations were also found between the Berg Balance Scale and affected side leg press (r = 0.875; P < 0.002). The MAS also was strongly associated with affected side leg press (r = 0.776; P < 0.068).

Figure 1
Figure 1:
Plot of initial muscle strength and functional performance. Repeated chair stand time vs. affected side knee extension strength (r = −0.788; P < 0.035).

Gait velocity at baseline was associated with affected hip flexion strength (r = 0.814; P < 0.026). Single leg stance time of the affected side was most strongly correlated with hip abduction strength at baseline (r = 0.879; P < 0.01) and affected side leg press (r = 0.867; P < 0.011).

Strength Training Effects

Absolute improvements in muscle strength gains occurred over the 12-wk period for all muscle groups trained with the exception of the hip extensors using the leg press (Table 2). The time course of strength gains revealed that nearly all of the improvements in strength were accomplished by the eighth wk of training. Relative gains in muscle strength were similar on the intact and affected side and averaged 48% and 68%, respectively (Fig. 2).

TABLE 2
TABLE 2:
Muscle strength (Mean ± SE)
Figure 2
Figure 2:
Plot of relative changes in muscle strength for all muscle groups trained on the affected (open bars) and intact side (filled bars) n = 7.

Functional Performance

Repeated chair stand time decreased 21% (P < 0.02) by week 12 of the training intervention. There also was a trend for stair climb time to decrease 11% (P < 0.07) (Table 3). Although stair climb time did not improve significantly, in the four of seven subjects with a step-to-step stair climb pattern, their stair climb quality improved to a step-over-step pattern. Gait velocity and leg stance (affected and intact) were not affected by the exercise intervention.

TABLE 3
TABLE 3:
Functional performance measures (mean ± SE)

Clinically Based Functional Assessments

Evaluation of function by using the lower limb subset of the MAS revealed a 12% (P < 0.02) improvement after the intervention (Table 4). In addition, the walking subscale of the MAS also improved significantly when analyzed separately (P < 0.03). Static and dynamic balance, as measured by the Berg Balance Scale, improved 12% (P < 0.003).

TABLE 4
TABLE 4:
Functional assessment measures (mean ± SE)

Self-Reported Functional Status

The physical function subscale of the MOS improved 17% (P < 0.03) from baseline to week 12. The Geriatric Depression Scale score, the Physical Activity Scale for the Elderly, and Harvard Alumni Questionnaire were not significantly improved over time (Table 5).

TABLE 5
TABLE 5:
Functional status and habitual physical activity (mean ± SE)

DISCUSSION

In the present study, measures of muscle strength were associated with several measures of functional performance at baseline. Previous studies have also found strong associations between paretic knee extension torque and locomotion.5, 6, 29 In addition, power generated by the hip flexors and the ankle plantarflexors of the paretic lower limb has been shown to be a strong predictor of walking speed in individuals after stroke.30 Associations between knee extensor strength and gait velocity have also been observed in older frail institutionalized individuals.31 Because of the observed relationship between strength and function in our population, we tested the hypothesis that progressive resistance training would improve muscle strength and subsequently improve measures of functional performance.

The major finding of the present study was that progressive resistance training improved affected and intact side muscle strength in individuals at least 1 yr after stroke onset. Previous studies have attempted to train solely the involved lower limb by using strengthening exercises. Studies have used "step-up" exercise and leg extension weight training on the involved side during acute post-stroke rehabilitation,11, 12 and, more recently, 6 wk of isokinetic training of the affected side knee extensors in long-term stroke survivors improved peak torque at all velocities examined.13 It is interesting that, in the present study, the relative improvements in muscle strength on the intact and affected side were similar and represented a greater relative improvement in strength than has been observed in previous studies after stroke. In addition, examination of changes in the 1 RM in the present study suggests that the gains in strength were achieved progressively through week 8 of the 12-wk training program. This rate of improvement is consistent with previously reported gains in strength in healthy and frail older individuals undergoing similar resistance training interventions.31, 32

Despite the nearly universal improvements in strength for all muscle groups trained, functional performance measures were only improved for the repeated chair stand time and there was a trend for improvement in stair climb time. Gait velocity and leg stance time were unaffected by the intervention. In other studies where the relationships between strength gains and functional performance changes have been evaluated, the results have been conflicting.28, 33-37 Generally, in more frail or disabled individuals, improvements in functional performance have been associated with the observed improvements in muscle strength.28, 33, 35, 37 After stroke, Sharp and Brouwer13 found a significant improvement in gait velocity but not chair stand performance or stair climb with isokinetic training of the hemiparetic knee. Recently, Duncan et al.38 reported improvements in gait velocity in individuals with mild-to-moderate stroke after an 8-wk home-based endurance strength and balance training program. The specific differences in functional performance improvements from the present study and other reports may be related to differences in baseline function of subjects and/or specific differences in the type and length of the exercise training protocol. The present study together with previous reports does suggest some association between restoring strength and enhancing functional performance after stroke.

Improvements in clinical measures of function and balance were consistent with the observed improvements in functional performance. The MAS has been used as a clinical marker of function after stroke and was modestly improved in our subjects after the training intervention.18 Although gait velocity did not change in our intervention, the quality of gait changed enough to significantly improve scores on the gait subscale of the MAS. This improvement in the gait subscale of the MAS is accounted for by changes in the use of assistive devices and/or changes in the ability to pick up an object while walking. The observed improvements in static and dynamic balance were consistent with some reports of improved balance with exercise training in frail or disabled elderly.35, 39, 40 Duncan et al.38 reported no effect of a home-based exercise intervention on balance in individuals with mild-to-moderate stroke. It is possible that the supervised high intensity exercise intervention used in the present study may have been responsible for the reported gains in static and dynamic balance. Improvements in balance in individuals with stroke may be an important outcome specifically in relation to reducing the risk of falls.

Both measures of habitual physical activity remained unchanged and revealed a low level of habitual activity. Measurement of physical function, however, using the MOS SF36 physical function subscale, did improve over the intervention. This is consistent with two other studies of exercise in stroke.13, 38 Improvements using this scale (MOS) may have been more sensitive to changes in performance of activities of daily living compared with the other indices of recreational or habitual activity (Harvard Alumnae, Physical Activity Scale for the Elderly).

CONCLUSION

The motor impairments coupled with the continuing loss of muscle mass and strength in long-term stroke survivors potently accelerate the progression of disability in this population. The results of the present study challenge the concept that functional recovery after stroke is greatest in the first 3 to 6 mo after stroke onset. Although the limited number of subjects enrolled in the present study may limit the generalizability of these findings, the present results show that strength training can profoundly improve strength and result in modest improvements in function late in the course of stroke recovery. Future studies should address the role of rehabilitation strategies using resistance training to maintain independence and prevent further progression of disability after stroke.

ACKNOWLEDGMENT

We acknowledge Keiser Sports Health Equipment for use of their strength training equipment.

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Keywords:

Exercise; CVA; Rehabilitation; Function

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