Chapter 3 Introduction

Physiologic Responses and Long-Term Adaptations to Exercise

When challenged with any physical task, the human body responds through a series of integrated changes in function that involve most, if not all, of its physiologic systems. Movement requires activation and control of the musculoskeletal system; the cardiovascular and respiratory systems provide the ability to sustain this movement over extended periods. When the body engages in exercise training several times a week or more frequently, each of these physiologic systems undergoes specific adaptations that increase the body’s efficiency and capacity. The magnitude of these changes depends largely on the intensity and duration of the training sessions, the force or load used in training, and the body’s initial level of fitness. Removal of the training stimulus, however, will result in loss of the efficiency and capacity that was gained through these training-induced adaptations; this loss is a process called detraining.

This chapter provides an overview of how the body responds to an episode of exercise and adapts to exercise training and detraining. The discussion focuses on aerobic or cardiorespiratory endurance exercise (e.g., walking, jogging, running, cycling, swimming, dancing, and in-line skating) and resistance exercise (e.g., strength-developing exercises). It does not address training for speed, agility, and flexibility. In discussing the multiple effects of exercise, this overview will orient the reader to the physiologic basis for the relationship of physical activity and health. Physiologic information pertinent to specific diseases is presented in the next chapter. For additional information, the reader is referred to the selected textbooks shown in the sidebar.