Exercise physiology of normal development, sex differences, and aging.

The scientific study of human development has evolved from studies of children to studies of the full lifespan. Many physiological changes occur throughout the lifespan and unique changes occur during normal development compared to healthy aging. An enlarging body of data supports the idea that there exist critical periods of development during which physiological perturbations to the internal milieu (e.g., disease or physical activity) can alter the overall programming of developmental processes. Although different physiological functions decline with age with widely varying rates, the aging changes accumulated throughout the physiological systems reduce the capacity to cope with the stress and maintain homeostasis. The understanding of this process of development and aging is complicated by important physiologic sex differences with regard to nearly all physiological systems. Regular physical activity can favorably modulate this developmental and aging process and can have important health benefits. However, a physically inactive lifestyle can markedly impair normal development and lead to numerous diseases. Life-long physical activity is essential for preserving or delaying the onset of functional disability and chronic cardiovascular and metabolic diseases.