ACSM Position Stand on Exercise and Physical Activity for Older Adults. Med. Sci. Sports. Exerc., Vol. 30, No. 6, pp. 992-1008, 1998. By the year 2030, the number of individuals 65 yr and over will reach 70 million in the United States alone; persons 85 yr and older will be the fastest growing segment of the population. As more individuals live longer, it is imperative to determine the extent and mechanisms by which exercise and physical activity can improve health, functional capacity, quality of life, and independence in this population. Aging is a complex process involving many variables (e.g., genetics, lifestyle factors, chronic diseases) that interact with one another, greatly influencing the manner in which we age. Participation in regular physical activity (both aerobic and strength exercises) elicits a number of favorable responses that contribute to healthy aging. Much has been learned recently regarding the adaptability of various biological systems, as well as the ways that regular exercise can influence them. Participation in a regular exercise program is an effective intervention/ modality to reduce/prevent a number of functional declines associated with aging. Further, the trainability of older individuals (including octo- and nonagenarians) is evidenced by their ability to adapt and respond to both endurance and strength training. Endurance training can help maintain and improve various aspects of cardiovascular function (as measured by maximal VO2, cardiac output, and arteriovenous O2 difference), as well as enhance submaximal performance. Importantly, reductions in risk factors associated with disease states (heart disease, diabetes, etc.) improve health status and contribute to an increase in life expectancy. Strength training helps offset the loss in muscle mass and strength typically associated with normal aging. Additional benefits from regular exercise include improved bone health and, thus, reduction in risk for osteoporosis; improved postural stability, thereby reducing the risk of falling and associated injuries and fractures; and increased flexibility and range of motion. While not as abundant, the evidence also suggests that involvement in regular exercise can also provide a number of psychological benefits related to preserved cognitive function, alleviation of depression symptoms and behavior, and an improved concept of personal control and self-efficacy. It is important to note that while participation in physical activity may not always elicit increases in the traditional markers of physiological performance and fitness (e.g., VO2max, mitochondrial oxidative capacity, body composition) in older adults, it does improve health (reduction in disease risk factors) and functional capacity. Thus, the benefits associated with regular exercise and physical activity contribute to a more healthy, independent lifestyle, greatly improving the functional capacity and quality of life in this population.