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a Sargent College of Health and Rehabilitation Sciences, Boston University, Massachusetts
Alan M. Jette, Boston University, Sargent College of Health and Rehabilitation Sciences, 635 Commonwealth Avenue, Boston, MA 02215.
Decision Editor: John E. Morley, MB, BCh
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Abstract |
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Methods. A literature review was performed in Medline and Best Evidence databases for the years 1985 to 2000. Experimental and quasi-experimental aerobic and resistance exercise interventions were reviewed for impairment, function, and disability outcomes. The impact of exercise on specific impairments, functions, and disabilities was examined by summarizing the findings reported across all studies.
Results. Thirty-one studies were identified. Impairment and functional outcomes were reported in 97% and 81% of the studies, respectively; half of the studies examined disability outcomes. The most consistent positive effects of late-life exercise were observed in strength, aerobic capacity, flexibility, walking, and standing balance, with over half of the studies that examined these outcomes finding positive effects. Of the studies that examined physical, social, emotional, or overall disability outcomes, most found no improvements. In the five studies that reported reduced physical disability, the effect sizes ranged from .23 to .88.
Conclusions. Late-life exercise clearly improves strength, aerobic capacity, flexibility, and physical function. Existing scientific evidence, however, does not support a strong argument for late-life exercise as an effective means of reducing disability. This may be due, in part, to methodological limitations in studies that have examined disability outcomes. On the other hand, the theoretical basis of interventions aimed at reducing disability may need to extend beyond exercise and address behavioral and social factors.
Astrong link between exercise and improved health and well-being is widely accepted for individuals of all ages. In the older adult, exercise is known to reduce the risk of premature mortality in general (1)(2)(3)(4) and of coronary heart disease, hypertension, colon cancer, and diabetes mellitus in particular (5)(6)(7)(8)(9)(10). Exercise has been shown to be important for the health of muscles, bones, and joints, which is believed to be a major determinant of loss of function in late life (11)(12). The accumulation of scientific evidence led to the now landmark 1996 U.S. Surgeon General's recommendation that people of all ages include a minimum of 30 minutes of physical activity of moderate intensity (such as brisk walking) on most, if not all, days of the week (13). This report acknowledges that, for most people, greater health benefits can be obtained by engaging in physical activity of more vigorous intensity or of longer duration.
Whereas ample scientific evidence has accumulated on the positive effects of exercise on disease prevention, muscle strength, flexibility, and cardiovascular fitness in adults of all ages, it remains less clear as to the full range of functional benefits of exercise for the sedentary, deconditioned, and/or impaired, older adult. As the 1996 Surgeon General's report notes, whereas physical activity appears to improve physical functioning in persons compromised by poor health, the scientific evidence supporting this claim is less clear (14). Yet, increasing physical activity and/or formal exercise by the sedentary older population in the United States is widely promoted in the public health community as an effective means of improving physical function and reducing or preventing disability in late life (15)(16). Does the existing scientific evidence actually support the wide scope of positive claims, or have the public health recommendations extended beyond current scientific evidence? This review seeks to critically evaluate the existing scientific evidence on the wide range of purported functional benefits of exercise when performed by the older adult. More specifically, we examine the degree to which the scientific literature directly supports the assertion that exercise enhances the older adult's physical function, prevents the onset of disability, and/or restores daily activities that are already compromised in older adults. We examine if exercise is an effective means of preventing or reducing disability and a feasible means of promoting independence in late life.
To evaluate the accumulated scientific literature on the degree to which exercise is an established means of enhancing physical function and/or improving disability in late life, outcome measures must be organized around some conceptual framework. We have chosen to structure this review around a hierarchy of outcomes using Nagi's disablement model (17)(18), which has been widely used in the gerontologic literature. We examined the effects of exercise on measures of muscle strength, range of motion or flexibility, maximum oxygen uptake, body composition, and neuromuscular control, all examples of effects on physical impairments. Improvements of exercise on functional limitations were demonstrated by evaluating the effects of exercise on measures of gait function, chair transfers, stair climbing, general mobility skills, weighted-lift task, and/or standing balance. Finally, we evaluated the direct impact of exercise on disabilities as reflected in the individual's behavior across a range of activities of daily living (ADLs) and social activities. Following our review of the existing scientific evidence on the benefits of exercise in late life, we discuss several recommendations for future research on optimizing late-life physical function and ability.
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Methods |
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Of the studies meeting our criteria, we reviewed each article for (i) type of intervention program, (ii) length of intervention and follow-up assessment, (iii) sample size, and (iv) the intervention effects on impairment, function, and physical, social, emotional, and overall disability. Impairment outcomes included strength (e.g., isokinetic dynamometry, hand held dynamometry, strain gauge load cell, and single repetition maximal lift), range of motion or flexibility (e.g., goniometry measurements and sit and reach tests), aerobic capacity (e.g., blood pressure, heart rate, and maximum oxygen uptake), body composition (e.g., weight and muscle mass), and symptoms. Functional outcomes included walking (e.g., endurance, distance, speed, and gait characteristics), chair rise (e.g., sit-to-stand transfers with or without a short walk and repeated chair stands), weighted lift task (e.g., lift and place a weighted object and repeated lifts of a weighted object), general mobility skills (e.g., mobility assessments, obstacle courses, complex stand-to-floor movements), stair climbing, and balance (standing unilateral or bilateral balance tests, functional reach tests, or walking on balance beams).
To capture the multi-domain nature of disability, we examined the outcomes associated with exercise in four areas: (i) physical disability, (ii) social disability, (iii) emotional disability, and (iv) overall disability. Assessments of physical disability included the physical disability subscales of the Sickness Impact Profile (SIP) (21)(22), Short-Form-36 Health Survey (SF-36) (23), the Arthritis Impact Measurement Scale (24)(25), and other assessments of ADLs and/or instrumental activities of daily living (IADLs), such as the Barthel Index (26). The SF-36 social role subscale was used to examine social disability outcomes. Assessments of emotional disability included instruments tapping depressive or anxiety symptoms and affect, such as the Center for Epidemiological Studies-Depression Scale (27), the Geriatric Depression Scale (28), the SF-36 emotional subscale (23), the Philadelphia Geriatric Center Morale Scale (29), the Affect Balance Scale (30), the State-Trait Anxiety Inventory (31), and the Profile of Moods (32). Overall disability was assessed by using measures that capture summary scores of physical, social, and emotional disability, such as the SF-36 and SIP. Finally, for the studies that reported significant effects of exercise on physical disability, we report effect sizes. Effect sizes for emotional, social, and overall disability were not calculated because either few studies explored these outcomes (i.e., social and overall disability) or the outcome measures used were inconsistent (i.e., emotional disability).
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Exercise Effects on Impairment, Functional Limitation, and Disability Outcomes
In most of the studies, impairment and functional outcomes were reported. Ninety-seven percent of the studies examined the effects of exercise on at least one impairment-level factor. Eighty-one percent of the studies examined the effects of exercise on at least one functional activity-related factor. Disabilities were the least assessed outcome, with half of the studies reporting exercise effects on physical, social, emotional, or overall disability.
The most consistent beneficial exercise effect was found in strength, aerobic capacity, and range of motion or flexibility (Table 1 ). Of the studies in which strength effects were assessed, 88% of the studies showed that subjects who exercised achieved improved strength over control subjects. Similar findings occurred with aerobic conditioning outcomes: 70% of the studies reported that intervention subjects improved their aerobic capacity. Of the studies in which range of motion effects were examined, 63% of the studies found that exercise subjects improved range of motion or flexibility compared with control subjects. Exercise effects on body composition, neuromuscular control, and symptoms were examined in only a few studies, and the findings were inconsistent.
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Discussion |
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Several potential methodological explanations can be offered to account for the lack of clear evidence of the positive effects of exercise on disability outcomes. These include variations in sample characteristics, differences in the type and length of the exercise intervention, inadequate sample size and power, and shortcomings in the measures of disability used by investigators.
The samples used in the five studies that reported improvements in disability with exercise consisted mainly of older adults with preexisting functional limitations, measurable physical disability (37)(38)(39), or chronic arthritis, which is a major risk factor for physical disability (33)(34). Therefore, it might be reasoned that the beneficial effects of strengthening and aerobic exercises on disability outcomes might only be observed among elderly subjects with existing functional deficits where the potential for measurable improvement in disability levels existed, as suggested by Chandler and colleagues (42). On the other hand, such an explanation would not account for the several well-conducted studies in our review with samples of older adults with functional limitations and/or disabilities that found no improvements in physical disability (42)(43)(44)(45). Another possible explanation of the findings may be that adults who have disability caused by chronic arthritis respond particularly well to exercise interventions: three of the five studies that found beneficial impacts of exercise on function and disability used a sample of people with arthritis.
The type and duration of the exercise intervention might also account for some of the paucity of positive effects of late-life exercise on disability outcomes. Generally, the interventions employed in the studies we reviewed consisted of standard exercise programs performed at least two to three times per week for a relatively short period of 8 to 12 weeks. Interventions of longer duration may be required to translate changes in impairments and functional limitations into change in the daily life activities of older adults. Whereas 8 to 12 weeks may be sufficient to demonstrate physiological and functional improvement, it may take longer to achieve measurable behavioral change. In this vein, it is interesting to note the extended duration of the Ettinger and colleagues (39) study in which physical disability improvements were achieved in subjects with chronic arthritis. In the Ettinger intervention, the longest intervention period of all the studies we reviewed, the first 12 weeks of the program consisted of a group exercise program with a final 15 months of the intervention involving a home-based program with occasional contact by health professionals to address questions, progress the training program, and encourage participation. Beneficial effects of exercise were reported at the completion of the study (i.e., after the 18-month intervention). Whereas it may be that longer intervention durations are desirable to best capture beneficial improvements in disability, it is clear that they are not required to demonstrate behavioral improvements. In the other four studies that we reviewed, the duration of the exercise programs that achieved disability improvements (33)(34)(37)(38) ranged from 2 to 6 months, similar in duration to most of the studies that did not achieve behavioral change. Furthermore, no improvements in disability were found in the study by King and colleagues (46), which included a 12-month intervention period.
With respect to the type of intervention studied, most studies used standard exercise programs performed by participants engaging in individual and/or group strength training or aerobic exercise routines. There were some exceptions, however, where the intervention program included structured cognitive/behavioral components designed to maximize exercise adherence and maintain behavioral change among the participants. Jette and colleagues (38), for example, used a social-cognitive theoretically driven intervention to increase exercise adoption and enhance adherence change over a 6-month intervention period. A physical therapist delivered the exercise intervention in the subjects' homes where specific cognitive and behavioral strategies were employed to enhance subjects' attitudes toward exercise. Therapists used ongoing behavioral incentives and subsequent telephone contacts during the 6-month intervention to help subjects progress and maintain their exercise program. Similarly, Kovar and colleagues' (34) intervention was theoretically based to enhance exercise adherence. The combination of exercise intervention plus a behavioral science component may have resulted in cognitive and behavioral changes among participants that, in turn, enhanced the impact of the exercise intervention on disability behavior (47). On the other hand, King and colleagues (46) also used a theoretically driven intervention and found no improvements in physical disability.
An inadequate sample size, in part, might explain some of the lack of impact of exercise on disability outcomes. Several of the studies that examined disability outcomes had small sample sizes, which may have resulted in inadequate statistical power for finding significant disability effects (36)(43)(45)(48)(49)(50). Disability outcome "trends" may have been significant if more subjects were included in the study; thus the beneficial effects of exercise reported in this review may be underestimated. Four of the five studies that reported significant improvements in physical disability included samples of 100 participants or more. The studies by Ettinger and colleagues (39) and Jette and colleagues (38), for example, had larger samples compared to most studies included in this review.
A final methodological reason for the disability findings in this review may be inadequacies in the disability outcome measures used in these clinical trials. Physical disability was the outcome examined most frequently, and the instruments used assessed ADL and/or IADL abilities. The lack of responsiveness of existing disability measures to detect important changes resulting from ceiling or floor effects, however, is a shortcoming of these measurements that limits the thorough evaluation of interventions directed toward reducing disability. These effects occur if the instrument content lacks sufficient breadth or if the increments of item ratings are too global. Whereas more responsive measurements of disability might have resulted in more consistent findings, our present measures are somewhat limited in this capacity because they were not designed primarily for use in controlled trials. For effective use in trials such as those we reviewed, there exists an ongoing need for disability instruments to be developed with the explicit purpose of detecting change (51)(52).
In addition to the methodological explanations discussed above, another reason for the inconsistent findings on the relationship between exercise and disability might be an oversimplified theoretical rationale for the hypothesized impact of late-life exercise on the severity of disability. The disablement model provides a framework for examining the rationale behind exercise interventions designed to have an impact on physical disability. The disablement model posits that the main pathway by which chronic disease or pathology leads to subsequent physical disability is through its impact on intervening impairments and functional limitations. We can use a simple clinical example to illustrate the disablement process linking a chronic pathology with subsequent disability. A woman aged 75 with osteoarthritis (pathology) may have a weak grip and restricted finger range of motion (musculoskeletal impairments). These impairments may cause difficulty in grasping and holding objects (a functional limitation), which leads to difficulty or restriction in getting dressed and cooking her meals (physical disabilities). From a disablement model perspective, an exercise intervention designed to improve this woman's dressing and cooking disability would achieve its impact by reducing her musculoskeletal impairments and functional limitations. Improvements in these areas would be hypothesized to reduce the difficulty she experienced in performing ADLs and IADLs.
Many have criticized the main pathways of the original disablement process as overly medical and too simplistic, which has led to modifications of Nagi's original formulation taking into account the psycho-social and medical aspects of disability in late life (18)(53)(54). A sociomedical model of disablement may be useful in designing interventions beyond exercise that might be more effective in decreasing late-life disability. The progression from initial pathology to impairment to functional limitation, although viewed as a necessary pathway to disability, may not be sufficient to result in subsequent disability or its reduction. Interventions designed to reduce disability may need to look beyond the main disablement pathways. Broader personal risk factors, such as beliefs, emotions, social norms, coping strategies, and even demographic background, might be important predisposing factors that may have an impact on the process of becoming disabled. In other words, the impact of pathology, impairment, and functional limitations might be mediated by an individual's beliefs, emotions, and behaviors, and thus influence the disablement process. Furthermore, the older individual faced with underlying pathology, impairments, and loss of function lives within a physical and social environment that can also have an impact on disability behavior.
Disability is operationalized by Nagi as the inability or limitation in performing socially defined roles expected of individuals within a social and physical environment (17) and is conceptualized as the product of the person-environment interaction—the "gap between a person's capabilities and the demands of the environment" ((54), p. 81). Disability is, therefore, an interaction of an individual within his or her environment and may be viewed as a behavior; potential intervention targets need to address this interaction. Disability, therefore, may be viewed as an intricate interplay of biological factors that occur within a socio-medical context consisting of the individuals' beliefs, background, and personal behaviors as well as their physical and social context. Perhaps, in employing exercise interventions to reduce disability, effects are diminished because the intervention fails to address broader risk factors such as the individual's beliefs, emotions, coping strategies, and physical and social environments (55)(56).
Viewing disability from such a socio-medical perspective suggests a need for interventions beyond or in addition to those designed to reduce impairments and limitations in function, if the ultimate aim is a reduction in disability. For example, we may need to implement specific interventions designed to reduce fear, frustration, and other emotions that may limit an older person's personal and/or social role behaviors. Other intervention targets may involve improving self-efficacy—older persons' perceptions of their ability to utilize their level of functional ability—or interventions designed to enhance readiness to change and problem-solving and coping skills, so that older persons with disabilities are able to adapt to and/or modify their environment and behaviors to optimize their participation in personal and social roles. Still other areas of intervention include enhancing the ability of social and physical environments to support and encourage elderly people in their personal and social-role participation.
If, as this review and the work of others suggests (41), resistance training and aerobic conditioning alone may have little, if any, effect on disability, then we need to be clear and not overstate the known beneficial effects of exercise. The growing literature on late-life exercise supports the notion that late-life exercise improves function. However, we need to be cognizant of the potential lack of beneficial effects of exercise on disability or at least of the lack of present scientific evidence that shows late-life exercise decreases disability.
These findings have methodological as well as theoretical implications for future research on late-life exercise and disability outcomes. If our expressed aim is to use exercise to decrease late-life disability, investigators must carefully consider the target sample, the type and duration of the exercise intervention, the statistical power needed to detect disability outcomes, and the specific disability outcomes to be targeted, and how they will be assessed to maximize the likelihood of detecting positive effects if they occur. Also, the theoretical basis of programs should be considered so that stronger, theoretically driven interventions designed to have an impact on disability may be developed and evaluated. Perhaps in addressing disability we need to target directly the person-environment interaction. Therefore, more research is needed to examine the mediating and moderating role of beliefs, emotions, coping strategies, and physical and social environments so that we can develop and evaluate interventions to enhance behavior and reduce late-life disability.
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Acknowledgments |
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Received January 26, 2001
Accepted January 29, 2001
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