Prof. OIof Astrand, M.D, Ph .D., Dept of Physiology and Pharmacology, Karolinska Institute, Stockholm, Sweden.

There is a pronounced plasticity and adaptability in the structural and/or functional properties of cells, tissues, and organ systems in the human body when exposed to various stimuli. While there is unanimous agreement that regular physical activity is essential for optimal function of the human body, it is evident that extrinsic factors, such as diet, smoking, exercise habits, are reflected in the morbidity and mortality statistics, especially in the elderly. Aging is obligatorily associated with reduced maximal aerobic power and reduced muscle strength, i.e. with reduced physical fitness. As a consequence of diminished exercise tolerance, a large and increasing number of elderly persons will be living below, at, or just above "threshold" of physical ability, needing only a minor intercurrent illness to render them completely dependent. Physical training can readily produce a profound improvement of functions essential for physical fitness in old age. Adaptability to regular physical activity serves to cause less disruption of the cells' "milieu interior" and minimizes fatigue, thereby enhancing performance and the economy of energy output during physical demands of daily activities. Regular physical activity reduces the risk of 'premature mortality in general, and of coronary heart disease hypertension, colon cancer, and diabetes mellitus in particular. Physical activity also improves mental health and is important for the health and optimal function of muscles, bones, and joints. The most recent recommendations advise people of all ages to include a minimum of 30 mm of physical activity of moderate intensity, such as brisk walking, on most, if not all days of the week.