Energy expenditure and aging: effects of physical activity.

Aging is associated with a decline in daily energy expenditure that is disproportionately greater than the decline in daily energy intake. Collectively, these events can create a "positive" energy balance, secondary gains in central and total body fat, and a subsequently higher risk of morbidity and mortality. Participation in regular physical activity is a logical strategy to attenuate the decline in energy expenditure with aging, as physical activity can comprise between 10-50% of an older person's daily energy expenditure. Understanding the influence of regular physical activity on energy expenditure with advancing age is clinically relevant, particularly since estimates predict that nearly 25% of the population will be > or = 65 years of age by the year 2030. This brief review will focus on the current state of aging, energy expenditure, and physical activity literature. Topics to be addressed include: (a) measurement of physical activity in older adults; (b) aging and physical inactivity; and (c) influence of regular aerobic exercise on resting metabolic rate (RMR), thermic effect of food (TEF), and non-exercising physical activity.