Physical activity and exercise affect many dimensions of health. This book presents an up-to-date and wide ranging account of the key issues of the biology of physical activity and health. The context is set by considering the comparative and temporal aspects of activity in humans. There follows an examination of the concepts and methodological issues associated with activity, exercise, health, and fitness, as well as their interrelationships. Particular attention is given to activity in children, adolescents and the elderly, activity and weight maintenance, and the psychological effects of activity. The book ends with an overview of current and future leisure life styles.