Physical activity behavior in adults: trends for aging and disability

There is an abundance of evidence describing the rates of physical activity and inactivity among adults in the United States, and, although the rates vary based on the source of data and nature of the survey questions, the evidence is suggestive of a potential public health problem. The National Center for Health Statistics (NCHS) analyzed data on national estimates of physical activity (usual daily activity and leisure-time physical activity) among adults using the 2000 and 2005 National Health Interview Surveys (NHIS). One important observation was that of little change in the percentage of adults who reported engaging in usual daily activity and leisure-time physical activity between 2000 and 2005. The percentage of adults who reported spending most of the day sitting increased from 36.8% in 2000 to 39.9% in 2005, and the percentage of adults who engaged in no leisure-time physical activity increased from 38.5% in 2000 to 40.0% in 2005. The percentage of adults who engaged in regular leisure-time physical activity decreased from 31.2% in 2000 to 29.7% in 2005, and the percentage of adults who were never active increased from 9.4% in 2000 to 10.3% in 2005. The rates of physical activity/inactivity among adults are not much different based on an analysis by the Center for Disease Control (CDC) of Behavioral Risk Factor Surveillance System (BRFSS) data regarding the prevalence of regular, leisure-time, physical activity between 2001 and 2005. Regular physical activity was defined based on the Healthy People 2010 Objectives as 30 minutes or more per day of moderate-intensity activity on 5 days or more per week, or 20 minutes or more per day of vigorous-intensity activity on 3 days or more per week. The data indicated that between 2001 and 2005 the prevalence of regular physical activity increased 3.5% overall among men (from 48.0% to 49.7%) and 8.6% overall among women (from 43.0% to 46.7%). Nevertheless, fewer than 50% of adults in the United States reported engaging in recommended levels of physical activity, and the overall implication from the NCHS and CDC reports is one of a high rate of physical inactivity and low rate of regular physical activity among adults in the United States.

One noteworthy trend in the NHIS and BRFSS data sets is that of an association between age and the rates of physical activity and inactivity among adults in the United States. Both data sets document that physical activity levels reliably decrease and inactivity levels reliably increase as a function of increasing age. The NCHS reported that the percentage of adults who reported spending most of the day sitting in 2000 was 46.5% for those 65 years and older, whereas it was 38.4%, 33.3%, and 31.2% for those aged 45 to 64 years, 25 to 44 years, and 18 to 24 years. The percentage of adults who engaged in no leisure-time physical activity in 2000 was 51.8% for those 65 years and more, whereas it was 40.8%, 33.7%, and 30.6% for those aged 45 to 64 years, 25 to 44 years, and 18 to 24 years. Finally, the percentage of adults who were never active in 2000 was 22.2% for those aged 65 years and more, whereas it was 9.9%, 5.3%, and 4.3% for those aged 45 to 64 years, 25 to 44 years, and 18 to 24 years. The rates of physical activity/inactivity among older adults are not much different based on BRFSS data regarding the prevalence of no leisure-time physical activity between 1994 and 2004. No leisure-time physical activity was defined based on a “no” response to the question “During the past month, other than your regular job, did you participate in any physical activities or exercise, such as running, calisthenics, golf, gardening, or walking for exercise?” The data indicated that from 1994 to 2004 the prevalence of leisure-time physical inactivity decreased from 29.8% to 23.7% overall, but the rate of leisure-time physical inactivity was consistently higher in men and women aged 70 years or older. The overall implication from both data sets is one of a strong trend for late-life declines in physical activity and associated increases in the rate of physical inactivity.

Another important trend in the BRFSS data set is that of an association between disability and the rates of physical activity and inactivity among older adults in the United States. Indeed, the CDC analyzed data from the 2005 BRFSS on prevalence of physical activity and inactivity among adults with and without a disability. The percentage of adults with a disability who met national recommendations for physical activity in 2005 was 37.7%, whereas the percentage was 49.4% for adults without a disability. The percentage of adults with a disability who were physically inactive in 2005 was 25.6%, whereas the percentage was 12.8% for adults without a disability. The CDC further analyzed data from the 2003 BRFSS on prevalence of physical activity among adults with and without a disability who were 65 years of age and older. The percentage of older adults with a disability who reported engaging in recommended levels of physical activity in 2003 was 14.7%, whereas the percentage was 26.2% for older adults without a disability. Work from the authors’ laboratory further supports an inverse association between advancing age and physical activity as measured by a pedometer in persons with multiple sclerosis. Such data support the observation that there is an alarming rate of physical inactivity among adults who are aging with a disability and supports the importance of promoting physical activity among adults who are aging with a disability.

Overall, the age-related trends in the rates of physical activity and inactivity among adults with and without a disability are alarming considering that physical activity is associated with reduced risks of many chronic disease conditions and premature mortality. Physical activity might be associated with beneficial effects on functional limitations, disability, and QOL in older adults, and represents a primary component of healthy and successful aging. The following sections focus on the role of physical activity in mitigating the progression of functional limitations and disability and improving QOL among adults who are progressing through advanced years of age.

Functional limitations, disability, and physical activity among older adults

As previously noted, there is an unprecedented growth in the older adult population of the United States, and the additional years of life are likely to be associated with chronic disease conditions and the onset of functional limitations and disability. There is considerable evidence that the aging process is associated with declines in function that result in increased risk of disablement. For example, the prevalence of mobility disability was 18.8% and 13.3% for women and men, respectively, aged 65 to 69 years, and the prevalence was 83.3% and 63.4% for women and men, respectively, aged 90 to 95 years. Furthermore, 51.8% of adults more than 65 years of age reported limitations in one or more domains of functioning such as walking, grasping, carrying, or pushing and the prevalence of disability doubled in successive age groups. One final observation is that nearly one-fifth of adults aged 65 years or older reported limitations with basic activities of daily living such as dressing and bathing. The prevalence of functional limitations and disability among older adults supports an examination of factors such as physical activity behavior within the process of disablement.

Theoretically, the process of disablement with advancing age and the role of physical activity can be understood by considering Nagi’s Disablement Model. The authors acknowledge the value and innovation offered by the World Health Organization’s International Classification of Functioning, Disability, and Health, but opt against this model in favor of Nagi’s model for several reasons as recently articulated by Guralnik and Ferrucci. The Disablement Model includes 4 interrelated components. The first component is active pathology. Active pathology describes the interruption of normal cellular processes based on degenerative disease processes, injury/trauma, and infection. The second component of the model is impairment and this involves structural abnormalities and dysfunction in specific body systems. The third component is functional limitations. Functional limitations describe restrictions in basic physical and mental actions (eg, walking 1 mile). Disability is the fourth component and involves the expression of physical or mental limitations in a social context (eg, difficulty doing activities of daily living that are required for one’s employment, personal care, and recreation). The 4 aspects of the Disablement Model are interrelated such that activity pathology results in impairment, impairment results in functional limitations, and functional limitations lead to disability. Those basic components have been extended to include personal (eg, lifestyle behaviors and psychosocial attributes) and sociocultural (eg, physical and social environments) variables as core influences of the disablement process. Physical activity has been identified as a biobehavioral, intraindividual determinant of disablement in older adults and is considered a primary determinant of functional limitations. To that end, physical activity is a behavior that has a distinct entry point in the process of disablement through its influence on functional limitations in older adults. The authors direct readers to a series of articles on physical activity and disablement in older adults based on Nagi’s Disablement Model that are published in a supplement of the American Journal of Preventive Medicine .

There is emerging evidence regarding physical activity and its association with functional limitations and disability in older adults. Physical inactivity or sedentary behavior seemingly exacerbates the impairments in physiologic and structural systems that occur with the aging process. Those impairments in physiologic and structural systems will likely result in the accumulation of functional limitations and disability over time. By extension, interventions that promote or maintain physical activity behavior among older adults might represent an effective strategy for attenuating functional decline and reducing the risk of disability in older adults.

Many individual studies have examined physical activity and its association with impairment, function, and disability outcomes in older adults and this literature has been summarized in 2 extensive literature reviews. Keysor and Jette performed a literature review of research examining physical activity behavior as a means of improving function and preventing or decreasing disability in older adults. The review included 31 studies published between 1985 and 2000 that examined the effects of aerobic and resistance exercise interventions using experimental and quasi-experimental designs on impairment, function, and disability outcomes in older adults. The effects of exercise on impairment and functional outcomes were reported in 97% and 81% of the studies, respectively, whereas only 50% of the studies reported effects on physical, social, emotional, or overall disability. The most consistent observation was that more than half of the studies reported improvements in strength, aerobic capacity, flexibility, standing balance, and walking after exercise training in older adults. The effects of exercise on physical, social, emotional, and overall disability were less clear with most studies reporting no improvement, and the 5 studies that reported reduced physical disability yielded variable effect sizes ranging between 0.23 and 0.88. Such findings result in ambiguous conclusions regarding physical activity effects on disability in later life, but this might be linked with methodological shortcomings that include variable sample characteristics and exercise parameters, small sample sizes and low power, and inadequate measures of disability as noted by Keysor and Jette. An additional observation of this review was that few studies have actually targeted disability as a primary outcome of physical activity. This literature review and its findings were consistent with those of earlier reviews, including one by Chandler and Hadley.

Keysor later provided another excellent review of the scientific evidence underlying physical activity as an important component for preventing and minimizing functional limitations and disability among older adults. This review used a best-evidence framework and included meta-analyses and systematic reviews of randomized controlled trails (RCTs), individual RCTs, and longitudinal observational studies. The synthesis of the scientific literature clearly supported that exercise, particularly walking, was associated with improvements in strength, aerobic capacity, and function. By comparison, there was again conflicting evidence regarding physical activity and disability outcomes, with minimal evidence that exercise or physical activity prevents or minimizes physical disability from RCTs but stronger evidence from prospective studies of an inverse association between physical activity and disability. One major recommendation of this review for strengthening the scientific evidence on physical activity, function, and disability was a focus on understanding the mechanisms of action. The improved understanding of how physical activity and exercise result in beneficial effects on function and disability would seemingly result in the design of more effective interventions. Such interventions could target exercise behavior plus the presumed mediator variables as a means of maximizing beneficial effects on function and disability in older adults.

To that end, one group of researchers has adopted a social cognitive perspective for examining self-efficacy and physical function performance as possible mediators in the association between physical activity and functional limitations among older adults. The first study included a sample of older Black and White women who completed measures of physical activity, self-efficacy, physical function performance, and functional limitations as part of the baseline assessment of an ongoing longitudinal, observational study. The analyses indicated that physical activity was associated with self-efficacy for exercise, efficacy for gait and balance, and physical function performance; measures of self-efficacy and physical functional performance were associated with functional limitations. Those relationships were independent of demographic and health status variables. Such findings support that physical activity, self-efficacy, and physical functional may all be associated with reducing functional limitations, and perhaps disability, in older adults. The findings further suggest that self-efficacy might be an important mediator of physical activity and its association with functional limitations.

This same group of researchers later examined the possibility that changes in self-efficacy and physical functional performance mediated the relationship between changes in physical activity and functional limitations over time. This study used a prospective observational design whereby community-dwelling, older Black and White women completed measures of self-reported physical activity, self-efficacy for exercise and balance, and functional limitations and underwent 4 measures of physical function performance on 2 occasions that were separated by 24 months. The results indicated that a change in physical activity over time was associated with residual changes in exercise and balance self-efficacy. Changes in exercise and balance self-efficacy were, in turn, associated with residual change in physical function performance. Most importantly, changes in self-efficacy for exercise and balance and physical function performance were associated with residual change in functional limitations. This supports that self-efficacy and physical function performance mediated the association between physical activity and functional limitations. The findings further support self-efficacy and physical function performance as possible mediators in the relationship between changes in physical activity and functional limitations in older women.

Overall, there has been an increased interest in the study of physical activity and its role in the process of disablement among older adults. The available evidence supports that exercise is associated with improvements in strength, aerobic capacity, and function, but there is less clear, and perhaps conflicting, evidence regarding physical activity and disability outcomes. Recent work has highlighted the role of self-efficacy in the pathway between physical activity and functional limitations, and such findings suggest that researchers integrate strategies for promoting change in self-efficacy along with physical activity interventions for maximizing improvements in disability outcomes among older adults. Indeed, self-efficacy is a modifiable factor and should be a central component of physical activity programs designed for preventing and minimizing functional limitations and disability in older adults.