Age is a primary risk factor for developing chronic diseases such as CVD, type 2 diabetes, obesity, as well as degenerative musculoskeletal conditions such as osteoporosis, arthritis, and sarcopenia. Fortunately, despite the long list of systems that are adversely affected by aging, increased physical activity or exercise can either slow the decline seen with aging, or even improve the health of these systems. Studies have shown a statistically significant decrease in the relative risk of cardiovascular and all-cause mortality among persons who are highly fit/active, as compared with those who are normally fit/active or low fit/sedentary.46

Regular physical activity increases average life expectancy through its influence on chronic disease development (via reduction of secondary aging effects). A graded, inverse relationship between total physical activity and mortality has been identified. Physical activity, even when initiated later in life, can lessen morbidity and improve mortality rates, while postponing the onset of disability. This concept has been termed “disability threshold”; which is when the person goes from independent to disabled. This can be modified in a positive way with muscle strengthening and increased mass, and can also be affected by environmental changes such as home modifications or assistive devices. These changes can influence the age at which a person becomes disabled (Figure 6.1).

In an analysis of more than 10,000 older adults in the Established Populations for Epidemiologic Studies of the Elderly, there was an almost twofold increased likelihood of dying without disability

How the disability threshold changes with age, muscle mass, and environment

FIGURE 6.1 How the disability threshold changes with age, muscle mass, and environment.

among those most physically active compared with those who were sedentary.47 The largest increment in mortality beneht is seen when comparing sedentary adults with those in the next highest physical activity level.46 The DHHS report “Physical Activity Guidelines Advisory Committee Report” provides a comprehensive summary of the evidence linking lower levels of physical activity with a higher risk of developing and dying from a variety of different conditions.3

Physical activity can also limit the impact of secondary aging through restoration of functional capacity in older adults who have previously been sedentary. However, helping older adults beneht from increased physical activity can be difficult. Older adult populations not only have a reduction in overall amounts of physical activity, but also the intensity of physical activity may be less. The most popular activities in older adults tend to be of lower intensity such as walking, gardening, golf, and low-impact aerobic activities, compared to activities such as running, sports, and high-impact aerobic activities preferred by younger adults.

Healthy sedentary older adults have the same physiological responses to submaximal aerobic exercise as do younger adults, although not always to the same degree. This response includes the control of arterial blood pressure and vital organ perfusion, augmentation of oxygen and substrate delivery and utilization within the active muscle, maintenance of arterial blood homeostasis, and dissipation of heat.48 Healthy older adults are also able to demonstrate normal cardiovascular and neuromuscular responses to RET. Thus, the normal age-associated changes in physiologic function should not preclude participation in physical activity. Although absolute improvements tend to be less in older adults versus their younger counterparts, there are similar relative increases from baseline in VO2max, submaximal metabolic responses, and exercise tolerance with AET and limb muscle strength, endurance, and muscle size in response to RET.49-51 However, older adults may take longer to achieve these improvements with exercise, and often have reduced exercise tolerance with heat or cold stress. In addition, cessation of AET in older adults leads to rapid loss of cardiovascular and metabolic htness, just as it does in younger populations.

It is important to note that improvement in physiological parameters does not always translate into functional gains. Studies have demonstrated that endurance exercise alone with minimal resistance training is less likely to have a signihcant effect on function, but does improve cardiovascular health. There is also a threshold of strength where frail adults can have a marked improvement in function with minimal change in strength, whereas healthy older adults may not have as much of a beneht with the same percent increase in strength.52 53 Above the functional threshold, additional reduction in physical impairments will add to the strength reserves, which serves to protect against future functional decline.

Longevity and “successful” aging are associated with characteristic behaviors including exercising regularly, maintaining a social network, and having a positive outlook on life.54,55 Physiological characteristics of these older adults include lower blood pressure, lower body mass index and central adiposity, preserved glucose tolerance (low plasma glucose and insulin concentrations), and a favorable blood lipid prohle (low triglycerides and LDL-C and high HDL-C concentrations).55,56 Regular physical activity seems to be the only lifestyle behavior identihed to date which can favorably influence a broad range of physiological systems and chronic disease risk factors.4

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