Exercise

In most physiologic systems, there is considerable evidence that the normal aging processes do not result in significant impairment or dysfunction in the absence of pathology, and under resting conditions. However, in response to a stress, the age-related reduction in physiologic reserves causes a loss of regulatory or homeostatic balance. This process has been termed "homeostenosis" (a lessened capacity for fine-tuning of the system). Thus, subtle changes in physical activity patterns over the adult life span cause most people not engaged in athletic pursuits to lose a very large proportion of their physical work capacity before they notice that something is wrong or find that they have crossed a threshold of disability. The second consequence of age-related changes in physiologic capacity is the increased perception of effort associated with submaximal work. Thus a vicious cycle is set up: "usual" aging leading to decreasing exercise capacity, resulting in an elevated perception of effort, subsequently causing avoidance of activity, and finally feeding back to exacerbation of the age-related declines secondary to disuse.

One of the major goals of gerontological research over the past several decades has been to separate the true physiologic changes of aging from changes due to disease or environmental factors, including disuse or underuse of body systems. Numerous studies point out the superior physical condition of those who exercise regularly compared to their more sedentary peers, even in the tenth decade of life. On the other hand, research indicates that years of physiologic aging of diverse organ systems and metabolic functions can be mimicked by short periods of enforced inactivity, such as bed rest, wearing a cast, denervation, or absence of gravitational forces. These two types of studies have led to a theory of disuse and aging which suggests that aging as it is known in modern society is, in many ways, an exercise deficiency syndrome. This implies that people may have far more control over the rate and extent of the aging process than was previously thought.