Increasing physical activity: alterations in body mass and composition.

I provide an overview of the role of physical activity in the prevention of overweight and obesity and in the treatment of overweight and obese individuals. A secondary focus of this paper is on the potential mechanisms responsible for changes in body composition consequent to physical activity. The use of the term "physical activity" is preferred to the term "exercise" to better reflect a broader scope of movement, not limited to formal exercise regimes. A brief review of prospective studies that investigated alterations in body composition consequent to physical activity alone is presented, along with a discussion of the influence of genetics, macronutrients in the diet, and characteristics of exercise programs on the magnitude of change observed in these studies. This is followed by a review of the specific role of chronic physical activity on energy intake, resting metabolic rate, the thermic effect of feeding, and the thermic effect of activity. Finally, I discuss the role physical activity plays in preventing overweight and obesity and the most appropriate use of exercise in the management of overweight.