ABSTRACT
This chapter provides an overview of the physiology of physical activity (and inactivity). Where energy intake and expenditure are different we experience an energy imbalance. In cases where energy intake is greater than energy expenditure humans will tend to experience an increase in body mass and where energy intake is less than energy expenditure humans will tend to experience a decrease in body mass. When an individual engages in a sustained bout of physical activity (acute) and then if physical activity is engaged in with regularity (chronic) nearly all of the systems and organs in the human body are engaged in some form or another. Understanding these changes and the physiology of physical activity is a key component for effective research and practice in sport, exercise and health sciences. The second half of this chapter will then present information relating to the physiological changes that occur as a consequence of prolonged inactivity and the concept of Non-Exercise Activity Thermogenesis (NEAT).
