PATHOLOGY

strokearticle3.pdf

Home >Applied Sciences homework help >PATHOLOGY

Muscle Impairments and Behavioral Factors Mediate Functional Limitations and Disability Following Stroke

Background and Purpose. Stroke remains the leading cause of disability in the United States. The purposes of this study were to examine whether quantita- tive measures of muscle strength and power in the involved lower extremity predict functional limitations and to evaluate the contributions of behavioral factors to mediating disability and quality of life in people who have survived a stroke. Subjects and Methods. A cross-sectional study design was used, and measurements of muscle impairment, lower-body function, disability, quality of life, and behavioral factors were obtained for 31 community-dwelling volunteers who had experienced a single ischemic stroke in the past 6 to 24 months. Results. Stepwise regression models including impairment and behav- ioral measures were strong predictors of function, disability, and quality of life. Involved-extremity muscle strength and power and self-efficacy were independently associated with function, whereas depression and self-efficacy were strong predictors of disability and quality of life. Discussion and Conclusion. The findings warrant future studies to determine whether inter- ventions that address muscle strength and power, depressive symptoms, and low self-efficacy effectively improve function, reduce disability, and enhance quality of life in people who have survived a stroke. [LeBrasseur NK, Sayers SP, Ouellette MM, Fielding RA. Muscle impairments and behavioral factors mediate functional limitations and disability following stroke. Phys Ther. 2006;86:1342–1350.]

Key Words: Cerebrovascular accident, Power, Quality of life, Self-efficacy, Strength.

Nathan K LeBrasseur, Stephen P Sayers, Michelle M Ouellette, Roger A Fielding

1342 Physical Therapy . Volume 86 . Number 10 . October 2006

Re se

ar ch

Re po

rt �

��

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

S troke presents a major public health concern in the United States, with more than 700,000 new or recurrent cases occurring each year.1 Despite a noteworthy reduction in mortality in the last

century,2 stroke remains the third leading cause of death. Moreover, morbidity in the approximately 4.8 million people who have survived a stroke is substantial, making stroke the foremost cause of serious, long-term disability in the United States.3

The impairments (abnormalities occurring in a specific organ or organ system4) resulting from stroke encom- pass motor, sensory, visual, affect, cognitive, and lan- guage systems. Of people who have survived a stroke in the long term, 50% demonstrate hemiparesis, 19% dem- onstrate aphasia, and 35% demonstrate clinical depres- sion. Stroke-related deficits are further manifested in functional limitations (limitations in performing func- tional tasks at the whole-body level4). Approximately 22% of people who have survived a stroke are unable to walk without assistance, and 26% are dependent in activities of daily living.5 The residual impairments and functional limitations in people who have survived a stroke in the long term represent a major cause of disability (limitations in performing a socially defined role in a physical or social environment4) in the popu- lation. Therefore, gaining a more thorough understand- ing of the relationships among impairments, functional limitations, and disability in people who have survived a stroke will provide a framework allowing rehabilitation professionals to identify strategies to better assist this population.

In previous work, various research groups investigated the relationships among age- and disease-associated motor impairments and limitations in physical function (ie, ability to walk, climb stairs, and rise from a chair) and disability. Specifically, muscle strength (maximum force-generating capacity) was demonstrated to have a positive association with measures of habitual walking speed,6 stair climbing,7 and chair rising8 in older adults. More recently, however, researchers observed that impairments in peak skeletal muscle power (the product of the force multiplied by the velocity of shortening) explain more of the variability in function and disability than does strength in older people.9 –11 Although previ- ous studies12–15 demonstrated that lower-extremity strength is correlated with gait quality and other mea- sures of function following stroke, impairments in mus- cle power and their association with function and dis- ability have not been well described.

In chronic and complex diseases such as stroke, disabil- ity and quality of life are related not only to physical impairments but also to behavioral, emotional, and psychological processes. Strategies to enable patients to improve their outlook and self-manage their chronic diseases so as to optimize health are fundamental.16 Self-efficacy is a psychological construct representing confidence in one’s ability to perform a task or specific behavior or to change a specific state, regardless of circumstances or contexts.17 Moreover, self-efficacy denotes the importance of an individual’s perception of his or her ability and capability to execute and achieve important and valued outcomes. Self-care self-efficacy

NK LeBrasseur, PT, PhD, was a doctoral candidate, Human Physiology Laboratory, Department of Health Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University, Boston, Mass, at the time of the study and is currently Assistant Professor of Medicine, Boston University School of Medicine, 670 Albany St, Rm 218, Boston, MA 02118 (USA). Address all correspondence to Dr LeBrasseur at: [email protected].

SP Sayers, PhD, is Assistant Professor, Department of Physical Therapy, School of Health Professions, University of Missouri–Columbia, Columbia, Mo.

MM Ouellette, PT, MSPT, is Research Associate, Human Physiology Laboratory, Department of Health Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University.

RA Fielding, PhD, was Associate Professor and Director, Human Physiology Laboratory, Department of Health Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University, at the time of the study and is currently Director and Scientist I, Nutrition, Exercise Physiology and Sarcopenia Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, Boston, Mass.

Dr LeBrasseur and Dr Fielding provided concept/idea/research design. Dr LeBrasseur, Dr Sayers, and Dr Fielding provided writing. Dr LeBrasseur and Ms Ouellette provided data collection, and Dr LeBrasseur and Dr Sayers provided data analysis.

This study was approved by the Boston University Institutional Review Board.

This work was supported by grants to Dr LeBrasseur from the Boston University Roybal Center for the Enhancement of Late-Life Function (NIH/NIA AG11669) and to Dr Fielding from the Jacob and Valeria Langeloth Foundation. The Claude D Pepper Older Americans Independence Center (AG08112) provided assistance in subject recruitment.

This article was received May 17, 2005, and was accepted May 18, 2006.

DOI: 10.2522/ptj.20050162

Physical Therapy . Volume 86 . Number 10 . October 2006 LeBrasseur et al . 1343

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

has been shown to be highly correlated with quality-of- life measures at both 1 and 6 months following stroke.18 Therefore, high self-efficacy for one’s physical abilities may relate to improved function, reduced disability, and improved quality of life in people who have survived a stroke in the long term.

The purpose of this investigation was to quantify the relationships among impairments in lower-extremity strength and power, measures of lower-extremity func- tion, and global disability following stroke. Specifically, we examined whether quantitative measures of muscle strength and power in the involved lower extremity following stroke predict functional limitations and eval- uated the contributions of behavioral factors, such as self-efficacy and depression, to mediating disability and quality of life.

Method

Subjects Subjects were recruited through local newspaper adver- tisements, volunteer databases, and local stroke support networks. Inclusion criteria included age of 50 years or more; 6 to 24 months following a single, unilateral, ischemic, mild-to-moderate stroke (as classified with the Orpington Prognostic Scale19); community dwelling; independent ambulation with or without an assistive device; and willingness to attend the laboratory for 2 testing sessions. Stroke history was confirmed by medical records review. Exclusion criteria included myocardial infarction or fracture within the past 6 months, acute or terminal illness, symptomatic coronary artery disease or congestive heart failure, uncontrolled hypertension (�150/90 mm Hg), and a score 20 or less on the Mini-Mental State Examination (MMSE).20 All subjects provided written informed consent. All outcome mea- sures were obtained by 2 physical therapists. All study procedures were in accordance with institutional (Bos- ton University) guidelines.

Thirty-one community-dwelling subjects who had expe- rienced an ischemic stroke in the past 6 to 24 months and who met the inclusion criteria volunteered to par- ticipate in the study. The sample consisted of 23 men and 8 women (74.2% white, 22.6% black, and 3.2% American Indian). Sample and descriptive characteris- tics are shown in Table 1.

Impairment Measures The muscle strength and power of the involved and uninvolved lower extremities were quantified with previ- ously described methods21,22 that were demonstrated to have good-to-excellent reliability in people following stroke.23 Briefly, measurements of 1-repetition maxi- mum (1RM) and peak power were obtained for the knee

extensors (KEs) with computer-interfaced pneumatic resistance machines.* The 1RM is defined as the maxi- mum load that can be moved one time only through the full range of motion (ROM) while maintaining proper form. An ultrasonic system measuring position and therefore relative motion aided the examiner in estab- lishing a subject’s full ROM during performance of the measurement with minimal resistance. The examiner progressively increased the resistance for each successful repetition until the subject could no longer move the lever arm one time through the full ROM. The maxi- mum isometric strength of ankle plantar flexion and dorsiflexion was captured with an isokinetic dynamom- eter.† The 1RM and maximum isometric strength mea- surements were obtained twice, with the second evalua- tion occurring 3 to 7 days after the initial evaluation. The better of the 2 measurements was recorded as the 1RM and maximum isometric strength. In this sample, the intraclass correlation coefficients (ICC[3,1]) of repeated 1RM measures of involved and uninvolved KEs were both .88. For repeated maximum isometric strength measurements of the involved and uninvolved ankles in plantar flexion and dorsiflexion, the ICCs ranged from .69 to .84.

Peak skeletal muscle power is the product of the force and velocity of muscle shortening. Briefly, the power of the KEs was evaluated at 6 relative intensities (40%, 50%, 60%, 70%, 80%, and 90% the 1RM). Beginning with 40%, subjects performed 5 lifts at each established percentage of their 1RM (separated by 30 seconds) as quickly as possible through the full ROM. The software engineered for the testing equipment calculated power (in watts) between 5% and 95% of the concentric phase.

* Keiser Sports Health Equipment Inc, 2470 S Cherry Ave, Fresno, CA 93706. † Cybex International, 10 Trotter Dr, Medway, MA 02053.

Table 1. Descriptive Characteristics

Characteristic X SE

Age (y) 66.2 1.5 Time after stroke (mo) 17.5 1.2 Stroke severitya 2.9 0.2 Body mass index (kg/m2) 27.4 0.6 Comorbidities (N) 4.4 0.3 Prescribed medications (N) 6.1 0.6 Depression scoreb 10.7 1.4 Cognition scorec 26.6 0.9 Self-efficacy scored 27.0 2.5 Gait speed (m/s) 0.68 0.06 Stair-climbing time (s) 14.8 2.0 Chair rising time (s) 23.6 1.7

a Orpington Prognostic Scale (mild��3.2, moderate�3.2–5.2). b Geriatric Depression Scale (�9�depression of increasing severity). c Mini-Mental State Examination (0 –30). d Ewart Self-Efficacy Scale (0 –100).

1344 . LeBrasseur et al Physical Therapy . Volume 86 . Number 10 . October 2006

��

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

Peak power for ankle plantar flexion and dorsiflexion was measured with the Cybex isokinetic dynamometer. Subjects performed 5 repetitions at angular velocities of 60°, 120°, and 180°/s. For KEs and ankle plantar flexion and dorsiflexion, the highest power achieved during the 2 testing sessions was recorded as the peak muscle power. In this sample, the ICCs of repeated peak power measurements of the involved and uninvolved KEs were .86 and .87, respectively. For peak power of the involved and uninvolved ankles in plantar flexion, the ICCs were .83 and .87, respectively, and for peak power of the involved and uninvolved ankles in dorsiflexion, the ICCs were .79 and .84, respectively.

Measures of Function Habitual gait speed, stair climbing, and chair rising were measured as previously described.24 Briefly, habitual gait speed was assessed over a 10-m distance with an ultra- sonic gait speed monitor‡ and recorded as the average of 2 trials (ICC�.98). The time to climb a single flight of stairs (10 steps, 17.7 cm per step) was determined with a handheld timer, and the better of 2 measurements was used for analyses (ICC�.98). The time to perform 5 sit-to-stand sequences from a standard chair was mea- sured once. Repeated measures were not performed due to fatigue.

Disability Measure The limitation dimension of the Late-Life Function and Disability Instrument (LLFDI) was used to assess disabil- ity (inability to perform major life tasks and social roles). The limitation dimension of the LLFDI evaluates self- reported limitations (capabilities) in taking part in 16 major life tasks. The limitation dimension comprises 2 domains: the instrumental role and the management role. The instrumental role domain reflects limitations in the ability to perform activities in the home and in the community. The management role domain reflects lim- itations in the organization and management of socially defined tasks that involve minimal mobility or physical activity. The raw scores from each item response are transformed into linear scaled scores (0 –100) and sub- sequently summed to represent component and domain values.25 The test-retest reliability of data for the LLFDI domains has not been established in people following stroke; however, test-retest reliability of data for the LLFDI domains was previously determined in ethnically and racially diverse adults aged 60 years and older and was found to be moderate to high (ICC�.69 –.82).25

Quality-of-Life Measure The shortened version of the Sickness Impact Profile (SIP)26 was administered to evaluate 6 domains of health-related behavior (somatic autonomy, mobility

control, psychological autonomy and communication, social behavior, emotional stability, and mobility range), referred to as quality of life. In people who have had a stroke, the SIP exhibits reliability, validity, and responsiveness.27

Behavioral Measures The Geriatric Depression Scale was used to identify physical and nonphysical symptoms that are related to depression and that may have been present over the preceding week.28 The Geriatric Depression Scale is a reliable and valid self-rating depression screening scale for older people and people who have had a stroke.29 Cognitive impairment was assessed with the MMSE.

Self-Efficacy Measure The Ewart Self-Efficacy Scale measures self-perceived ability, or confidence, to perform a number of physical tasks (eg, walking and jogging various distances, climb- ing stairs, lifting objects of different weights). Scores are 0 to 100, with higher scores indicating higher self- efficacy.30 The Ewart Self-Efficacy Scale has been used extensively in studies of people who have coronary artery disease, but it has not been validated or reliability tested in people who have survived a stroke.

Data Analysis Descriptive statistics were calculated for all subjects. Paired sample t tests were calculated for all KE and ankle plantar-flexion and dorsiflexion muscle strength and power measurements to determine differences between the involved and uninvolved limbs. A Bonferroni test- wise correction adjusted the P value to �.008 (.05/6). Pearson correlations were calculated to examine the relationships between potential adjustment variables and dependent variables. Prior to regression modeling, the normality of the dependent variables was deter- mined with the Shapiro-Wilk test (sample size under 50). If the Shapiro-Wilk test was significant (P�.05), then the data were considered nonnormal and the dependent variable was log transformed. For each regression model, linearity was checked by adding a quadratic term to each model. If the quadratic term was significant, then the independent variable was log transformed to achieve linearity and then was used in the regression model.

The relationships of impairment with function, disabil- ity, and quality of life for both the involved and un- involved limbs were examined by stepwise regression modeling. The relationships of our strength and power impairment measures (KEs and ankle plantar flexion and dorsiflexion) with function and disability were very similar. In this report, we have presented KE strength and power analyses, given the fundamental role of the involved musculature in the performance of lower- extremity physical functions and the previously reported

‡ OCPB Electronics, G11 6 NT, Glasgow, United Kingdom.

Physical Therapy . Volume 86 . Number 10 . October 2006 LeBrasseur et al . 1345

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

excellent reliability of strength and power measure- ments.23 Thus, we fit 2 regression models for each of the 3 measures of function (habitual gait speed, chair rising time, and stair-climbing time), the disability index (lim- itation dimension of the LLFDI), and the quality-of-life measure (SIP) by using the KE power of the involved and uninvolved limbs. The covariates of cognition, depression, and self-efficacy were chosen because of their significant associations with dependent variables (P�.05) and their potential effect on the relationships of impairment with function and disability. The statistical significance for all multivariate regression models was accepted at P�.05. All data were analyzed with SPSS statistical software.§

Results

Impairments in Muscle Strength and Power Paired sample t tests indicated signifi- cant differences between the involved and uninvolved limbs for all KE and ankle plantar-flexion and dorsiflexion strength and power measurements (P�.004 for all measurements). Mea- surements and comparisons of muscle strength and power for the involved side versus the uninvolved side are shown in the Figure.

Relationships Between Impairments and Function Stair-climbing times (Shapiro-Wilk test: P�.006) and chair rising times (Shapiro-Wilk test: P�.001) were non- normal, and log transformations were performed. As shown in Table 2, regression model 1 (strength) and model 2 (power) were significantly associated with habitual gait speed, stair-climbing time, and chair rising time (P�.001 for all measurements). The strength of the relationships between the 2 models and the mea- sures of function ranged from R2�.43 to R2�.78. The KE strength and power in the involved limb were significantly associated with habitual gait speed (P�.05) and explained similar degrees of variability (R2�.13 and R2�.12, respectively). In addition, self-efficacy and sex were associated with habitual gait speed in both regression model 1 and model 2 (P�.05) but explained

less of the variability than either KE strength or power in the 2 models. Analysis of stair-climbing time revealed that KE power in the involved limb explained more of the variability in performance than KE strength (R2�.24 versus R2�.11). The KE power in the uninvolved limb also was significantly associated with stair-climbing time. The relationship between self-efficacy and stair-climbing time also was significant and proved stronger in the strength model (R2�.11) than in the power model (R2�.07). In contrast to the other measures of function, neither KE strength nor power of the involved or uninvolved limb was associated with chair rising time (not retained in the stepwise model; P�.05). Self- efficacy, however, demonstrated a strong relationship with this measure in both models (R2�.43). As shown in Table 2, the KE strength in the uninvolved limb, cogni- tion, and depression all failed to explain a significant

§ SPSS Inc, 233 S Wacker Dr, Chicago, IL 60606.

Figure. Muscle strength and power are significantly impaired in the involved lower extremity of people who have survived a stroke. Quantification of knee extension and ankle plantar-flexion and dorsiflexion maximum strength (A) and peak power (B) in uninvolved (black bars) and involved (hatched bars) lower extremities is shown (n�31 for all analyses; P values were �.004 [asterisks] and �.001 [daggers], respectively).

1346 . LeBrasseur et al Physical Therapy . Volume 86 . Number 10 . October 2006

��

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

portion of the variability in the stepwise regression models for measures of function (P�.05 for all measurements).

Relationships Between Impairments and Disability and Between Impairments and Quality of Life Regression model 1 and model 2 were significantly associated with the limita- tion dimension, the instrumental role domain, and the management role domain (P�.001 for all measurements) of the LLFDI. The strength of the rela- tionships between the 2 models and the 3 dimensions of disability ranged from R2�.43 to R2�.70. For the limitation dimension, self-efficacy demonstrated a strong association (R2�.55, P�.001), and depression also was significant (P�.05) but explained a much smaller degree of variability (R2�.09) in both model 1 and model 2. Self-efficacy was the only variable associated with the instrumental role domain (P�.001) and explained 63% of the variability in this measure in both models. Both self- efficacy (P�.01) and depression (P�.01) were significantly associated with the management role domain and explained similar degrees of variability in this measure (R2�.23 and R2�.24, respectively). Neither KE strength (model 1) nor power (model 2) in the involved or uninvolved limb, cognition, or sex was significantly associated with disability in either model (P�.05). These relationships are shown in Table 3.

Similar to the results for disability, regression model 1 and model 2 were significantly associated with health- related quality of life, as measured by the SIP (P�.001). The strength of the relationships of both models with qual- ity of life was R2�.69. Depression and self-efficacy in model 1 and model 2 were significantly associated with qual- ity of life (P�.001). In contrast, KE strength and KE power of both the involved and uninvolved limbs, cogni- tion, and sex were not associated with quality of life (P�.05 for all measure- ments). These relationships are shown in Table 4.

Table 2. Associations Among Impairments, Behavioral Factors, and Functions, as Determined by Stepwise Regression Modelinga

Parameter � SE Partial R2 R2 P

Habitual gait Model 1 .71 �.001

KE strength (In) 0.33 0.10 .13 .002 Self-efficacy 1.10 0.37 .10 .007 Sex 0.25 0.10 .08 .014

Model 2 .70 �.001 KE power (In) 0.21 0.06 .12 .003 Self-efficacy 1.16 0.37 .11 .005 Sex 0.21 0.09 .06 .029

Stair climbing Model 1 .66 �.001

Ke strength (In) �0.23 0.08 .11 .006 Self-efficacy �0.95 0.32 .11 .006

Model 2 .78 �.001 KE power (In) �0.25 0.05 .24 �.001 KE power (Un) 0.00 0.00 .04 .008 Self-efficacy �0.75 0.26 .07 .005

Chair rising Model 1 .43 �.001

Self-efficacy �0.74 0.17 .43 �.001

Model 2 .43 �.001 Self-efficacy �0.74 0.17 .43 �.001

a All stepwise models included sex, cognition, depression, self-efficacy, and either knee extensor (KE) strength (model 1) or KE power (model 2) of both the involved (In) and the uninvolved (Un) limbs.

Table 3. Associations Among Impairments, Behavioral Factors, and Disability, as Determined by Stepwise Regression Modelinga

Parameter � SE Partial R2 R2 P

Limitation dimension Model 1 .70 �.001

Self-efficacy 53.70 8.58 .55 �.001 Depression �0.42 0.17 .09 .020

Model 2 .70 �.001 Self-efficacy 53.70 8.58 .55 �.001 Depression �0.42 0.17 .09 .020

Instrumental domain Model 1 .63 �.001

Self-efficacy 72.50 11.85 .63 �.001

Model 2 ‘ .63 �.001 Self-efficacy 72.50 11.85 .63 �.001

Management domain Model 1 .53 �.001

Self-efficacy 36.90 11.56 .23 .004 Depression 0.74 0.23 .24 .004

Model 2 .43 �.001 Self-efficacy 36.90 11.56 .23 .004 Depression 0.74 0.23 .24 .004

a All stepwise models included sex, cognition, depression, self-efficacy, and either knee extensor (SE) strength (model 1) or KE power (model 2) of both involved and uninvolved limbs. The limitation dimension and instrumental and management role domains are from the Late-Life Function and Disability Instrument.

Physical Therapy . Volume 86 . Number 10 . October 2006 LeBrasseur et al . 1347

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

Discussion and Conclusions In the United States, both stroke prevalence and survi- vorship continue to heighten3 and have made evident the need to attenuate stroke-related disability and opti- mize quality of life. In this report, we examined the disablement process in community-dwelling people 6 to 24 months following ischemic stroke. We observed a strong association between residual impairments in skel- etal muscle strength and power on the involved side and performance on measures of gait speed and stair- climbing time. Moreover, we demonstrated that behav- ioral factors, including depression and self-efficacy, more than physical impairments, are significantly related to disability in socially defined life tasks and quality of life in people who have survived a stroke. These findings have important implications for the design of both clinical interventions and future research initiatives aiming to optimize rehabilitation following stroke.

Hemiparesis is a hallmark of acute stroke and a persis- tent burden in people who have survived a stroke in the long term.5,31 In this study, we observed significant deficits in lower-extremity muscle strength (�30%) and lower-extremity muscle power (�40%) for the involved side compared with the uninvolved side 6 to 24 months following the onset of stroke. Residual impairments in skeletal muscle strength in people who have survived a stroke previously were correlated with gait capacity and other measures of function.12–15 In this study, we con- firmed these findings and demonstrated, for the first time, the significant contribution of stroke-related defi- cits in muscle power to measures of function, namely, habitual gait speed and ability to climb a standard flight of stairs. Muscle power was the strongest predictor of stair climbing time and explained nearly twice the variability as muscle strength. These observations suggest that measures of function that require a lower percent- age of maximum strength to perform (eg, gait speed on level surfaces and stairs) may be more sensitive to the velocity of movement. Thus, efforts to optimize the power of the involved musculature may confer improve-

ments on the performance of lower- extremity physical functions following stroke. In contrast to gait speed and stair-climbing time, KE muscle strength and power failed to demonstrate an association with chair rising time. This finding may be attributed to the task relying more heavily on muscle groups (eg, core musculature), coordinated movement patterns, balance, endur- ance, or motor planning not assessed in this study.

Despite the associations between motor impairments and measures of function,

we failed to demonstrate an association between muscle power and disability in statistical models that also included sex, depression, and self-efficacy. However, when these 3 variables were removed from our regres- sion model, both KE strength and KE power of the involved limb were significantly associated with the lim- itation dimension of the LLFDI (P�.04 for both mea- sures; data not shown). Thus, although various investi- gators have demonstrated the efficacy of progressive resistance training in improving skeletal muscle strength23,32,33 and, more recently, power23 in the involved lower extremity of people who have survived a stroke in the long term, the effectiveness of this strategy in improving function and reducing disability indepen- dently remains ambiguous. Therefore, future studies are warranted.

The Nagi model of physical disability outlines the pro- gression of active pathology to impairment, impairment to functional limitation, and functional limitation to disability.34 Modifications of this scheme include the addition of internal and external factors that may aug- ment or attenuate the disablement process.4 Relevant to stroke, we have examined the influence of cognitive impairments and depression. At 3 months and at 1, 2, and 3 years following stroke, the prevalences of cognitive impairments (MMSE score of �24) have been reported to be 39%, 35%, 30%, and 32%, respectively,35 and associated with institutionalization 4 years following stroke.36 The fact that we did not detect an association between cognitive impairments and disability may be attributable to the relatively low level of these impair- ments in our study volunteers. In contrast, we did observe a relatively high prevalence of depression in our study participants. This finding is in agreement with a recent prospective epidemiological study that reported a high occurrence of depression in people who have survived a stroke in the long term (odds ratio�3.5, 95% confidence interval�1.4 – 8.3).37 In our statistical model, depression was not associated with measures of function; however, it was strongly correlated with disability and

Table 4. Associations Among Impairments, Behavioral Factors, and Quality of Life, as Determined by Stepwise Regression Modelinga

Sickness Impact Profile � SE Partial R2 R2 P

Model 1 .69 �.001 Self-efficacy �60.70 14.20 .21 �.001 Depression 1.65 0.332 .46 .001

Model 2 .69 �.001 Self-efficacy �60.70 14.20 .21 �.001 Depression 1.65 0.332 .46 .001

a All stepwise models included sex, cognition, depression, self-efficacy, and either knee extensor (KE) strength (model 1) or KE power (model 2) of both involved and uninvolved limbs.

1348 . LeBrasseur et al Physical Therapy . Volume 86 . Number 10 . October 2006

��

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

quality of life. The contribution of depression to disabil- ity was particularly evident in tasks that involved more socially defined roles, such as organization and manage- ment of social activities that have little reliance on an individual’s physical capacities. These findings corrobo- rate those of previous investigations38,39 and underscore the importance of early detection and treatment of stroke-related depression in attenuating the disablement process and improving the quality of life.

Self-efficacy, the perception of one’s ability, has been described as an intraindividual factor modifying the disablement process4 and recently was proposed to be a component of the disability pathway that directly influ- ences functional limitations.40 In this study of people who have survived a stroke, self-efficacy, akin to muscle power, emerged as a strong predictor of measured functions. Moreover, self-efficacy was the only indepen- dent variable associated with all dimensions of self- reported disability and, in accord with a previous report,18 was related to quality of life. These findings strongly suggest that the perception of one’s ability may be as important as objective physical impairments in mediating the disablement process. Given the social- environmental context of disability and the compensa- tory mechanisms used by people who have survived a stroke to cope with new challenges, strategies to improve self-efficacy may have a direct and beneficial influence on multiple components of the disability pathway and quality of life.

Potential limitations of the present study also must be considered. First, we focused on selected impairments on the basis of our expertise and experience. Admit- tedly, the population studied has a multitude of impair- ments not evaluated here (eg, in sensory and language systems) that undoubtedly further contribute to the disablement process. Moreover, in a comparable sample of people that had survived a stroke (3–9 months), Nichols-Larsen et al41 determined that individual char- acteristics (ie, age, race, and comorbidities) also may have a significant influence on the physical domain of health-related quality of life and are worthy of further investigation. Second, the sample size was relatively small, and the sample consisted of people 6 to 24 months following mild-to-moderate stroke, a time frame that we selected on the basis of our objective to examine residual impairments that persist despite acute rehabilitation efforts. Although the sample that we studied was repre- sentative of the population that has had a stroke on the basis of age and health status (eg, stroke severity, age, comorbidities, medication use), a larger and more func- tionally diverse sample would have allowed further eval- uation of the impairment-function-disability relation- ships across various magnitudes of the chosen measures.

Collectively, these data reflect the complexity of the disablement process initiated by stroke. On the basis of the work of our group and others, future studies are warranted and necessary to determine whether interven- tions that address residual impairments in muscle strength and power improve function and whether strat- egies to address depressive symptoms and low self- efficacy help attenuate functional limitations and disabil- ity and optimize quality of life in people who have survived a stroke.

References 1 Heart Disease and Stroke Statistics: 2004 Update. Dallas, Tex: American Heart Association; 2003:13–16.

2 Whisnant JP. The decline of stroke. Stroke. 1984;15:160 –168.

3 Muntner P, Garrett E, Klag MJ, Coresh J. Trends in stroke prevalence between 1973 and 1991 in the US population 25 to 74 years of age. Stroke. 2002;33:1209 –1213.

4 Verbrugge LM, Jette AM. The disablement process. Soc Sci Med. 1994;38:1–14.

5 Helgason CM, Wolf PA. American Heart Association Prevention Conference IV: prevention and rehabilitation of stroke— executive summary. Circulation. 1997;96:701–707.

6 Rantanen T, Guralnik JM, Ferrucci L, et al. Coimpairments: strength and balance as predictors of severe walking disability. J Gerontol A Biol Sci Med Sci. 1999;54:M172–M176.

7 Salem GJ, Wang MY, Young JT, et al. Knee strength and lower- and higher-intensity functional performance in older adults. Med Sci Sports Exerc. 2000;32:1679 –1684.

8 Skelton DA, Greig CA, Davies JM, Young A. Strength, power and related functional ability of healthy people aged 65– 89 years. Age Ageing. 1994;23:371–377.

9 Bean JF, Kiely DK, Herman S, et al. The relationship between leg power and physical performance in mobility-limited older people. J Am Geriatr Soc. 2002;50:461– 467.

10 Foldvari M, Clark M, Laviolette LC, et al. Association of muscle power with functional status in community-dwelling elderly women. J Gerontol A Biol Sci Med Sci. 2000;55:M192–M199.

11 Cuoco A, Callahan DM, Sayers S, et al. Impact of muscle power and force on gait speed in disabled older men and women. J Gerontol A Biol Sci Med Sci. 2004;59:1200 –1206.

12 Nadeau S, Arsenault AB, Gravel D, Bourbonnais D. Analysis of the clinical factors determining natural and maximal gait speeds in adults with a stroke. Am J Phys Med Rehabil. 1999;78:123–130.

13 Bohannon RW, Walsh S. Nature, reliability, and predictive value of muscle performance measures in patients with hemiparesis following stroke. Arch Phys Med Rehabil. 1992;73:721–725.

14 Olney SJ, Griffin MP, Monga TN, McBride ID. Work and power in gait of stroke patients. Arch Phys Med Rehabil. 1991;72:309 –314.

15 Patel AT, Duncan PW, Lai SM, Studenski S. The relation between impairments and functional outcomes poststroke. Arch Phys Med Reha- bil. 2000;81:1357–1363.

16 Marks R, Allegrante JP, Lorig K. A review and synthesis of research evidence for self-efficacy-enhancing interventions for reducing chronic disability: implications for health education practice (part i). Health Promot Pract. 2005;6:37– 43.

Physical Therapy . Volume 86 . Number 10 . October 2006 LeBrasseur et al . 1349

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021

17 Bandura A. Self-efficacy: toward a unifying theory of behavioral change. Psychol Rev. 1977;84:191–215.

18 Robinson-Smith G, Johnston MV, Allen J. Self-care self-efficacy, quality of life, and depression after stroke. Arch Phys Med Rehabil. 2000;81:460 – 464.

19 Kalra L, Crome P. The role of prognostic scores in targeting stroke rehabilitation in elderly patients. J Am Geriatr Soc. 1993;41:396 – 400.

20 Folstein MF, Folstein SE, McHugh PR. “Mini-mental state”: a practical method for grading the cognitive state of patients for the clinician. J Psychiatr Res. 1975;12:189 –198.

21 Fielding RA, LeBrasseur NK, Cuoco A, et al. High-velocity resistance training increases skeletal muscle peak power in older women. J Am Geriatr Soc. 2002;50:655– 662.

22 Suzuki T, Bean JF, Fielding RA. Muscle power of the ankle flexors predicts functional performance in community-dwelling older women. J Am Geriatr Soc. 2001;49:1161–1167.

23 Ouellette MM, LeBrasseur NK, Bean JF, et al. High-intensity resis- tance training improves muscle strength, self-reported function, and disability in long-term stroke survivors. Stroke. 2004;35:1404 –1409.

24 Sayers SP, Bean J, Cuoco A, et al. Changes in function and disability after resistance training: does velocity matter? A pilot study. Am J Phys Med Rehabil. 2003;82:605– 613.

25 Jette AM, Haley SM, Coster WJ, et al. Late life function and disability instrument, I: development and evaluation of the disability compo- nent. J Gerontol A Biol Sci Med Sci. 2002;57:M209 –M216.

26 de Bruin AF, Buys M, de Witte LP, Diederiks JP. The Sickness Impact Profile: SIP68, a short generic version: first evaluation of the reliability and reproducibility. J Clin Epidemiol. 1994;47:863– 871.

27 Buck D, Jacoby A, Massey A, Ford G. Evaluation of measures used to assess quality of life after stroke. Stroke. 2000;31:2004 –2010.

28 Yesavage JA, Brink TL, Rose TL, et al. Development and validation of a geriatric depression screening scale: a preliminary report. J Psychiatr Res. 1982;17:37– 49.

29 Johnson G, Burvill PW, Anderson CS, et al. Screening instruments for depression and anxiety following stroke: experience in the Perth community stroke study. Acta Psychiatr Scand. 1995;91:252–257.

30 Ewart CK, Stewart KJ, Gillilan RE, Kelemen MH. Self-efficacy mediates strength gains during circuit weight training in men with coronary artery disease. Med Sci Sports Exerc. 1986;18:531–540.

31 Sommerfeld DK, Eek EU, Svensson AK, et al. Spasticity after stroke: its occurrence and association with motor impairments and activity limitations. Stroke. 2004;35:134 –139.

32 Weiss A, Suzuki T, Bean J, Fielding RA. High intensity strength training improves strength and functional performance after stroke. Am J Phys Med Rehabil. 2000;79:369 –376.

33 Teixeira-Salmela LF, Olney SJ, Nadeau S, Brouwer B. Muscle strengthening and physical conditioning to reduce impairment and disability in chronic stroke survivors. Arch Phys Med Rehabil. 1999;80: 1211–1218.

34 Nagi SZ. Some conceptual issues in disability and rehabilitation. In: Susman MB, ed. Sociology and Rehabilitation. Washington, DC: American Sociological Association; 1965:100 –113.

35 Patel MD, Coshall C, Rudd AG, Wolfe CD. Natural history of cognitive impairment after stroke and factors associated with its recovery. Clin Rehabil. 2003;17:158 –166.

36 Patel MD, Coshall C, Rudd AG, Wolfe CD. Cognitive impairment after stroke: clinical determinants and its associations with long-term stroke outcomes. J Am Geriatr Soc. 2002;50:700 –706.

37 Whyte EM, Mulsant BH, Vanderbilt J, et al. Depression after stroke: a prospective epidemiological study. J Am Geriatr Soc. 2004;52:774 –778.

38 Parikh RM, Robinson RG, Lipsey JR, et al. The impact of poststroke depression on recovery in activities of daily living over a 2-year follow-up. Arch Neurol. 1990;47:785–789.

39 King RB. Quality of life after stroke. Stroke. 1996;27:1467–1472.

40 Rejeski WJ, Focht BC. Aging and physical disability: on integrating group and individual counseling with the promotion of physical activity. Exerc Sport Sci Rev. 2002;30:166 –170.

41 Nichols-Larsen DS, Clark PC, Zeringue A, et al. Factors influencing stroke survivors’ quality of life during subacute recovery. Stroke. 2005; 36:1480 –1484.

1350 . LeBrasseur et al Physical Therapy . Volume 86 . Number 10 . October 2006

��

D ow

nloaded from https://academ

ic.oup.com /ptj/article/86/10/1342/2805211 by guest on 10 M

arch 2021