There is unanimous agreement that regular exercise is essential for optimal function of the human body. It is evident that extrinsic factors, such as diet and exercise habits, are reflected in the morbidity and mortality statistics, especially in aging. Aging is obligatorily associated with reduced maximal aerobic power and reduced muscle strength, ie, with reduced physical fitness. As a consequence of diminished exercise tolerance, a large and increasing number of elderly people will be living below, at, or just above "thresholds" of physical ability, needing only a minor intercurrent illness to render them completely dependent. Physical training can readily produce a profound improvement of functions also essential for physical fitness in old age. From a nutritional viewpoint one advantage of physical activity, and increased metabolic rate, is that a higher energy intake can better secure an adequate intake of essential nutrients.