Physical activity is a component of energy balance that is particularly important in the pathogenesis of obesity and in its treatment. The components of energy expenditure are resting (basal)-energy expenditure (REE) (eg, heat production for maintenance of body temperature, maintenance of ionic gradients across cells, and resting cardiac and respiratory function), diet-induced thermogenesis, and physical activity (figure 1) .
The optimal management of overweight and obesity starts with a combination of diet, exercise, and behavioral modification. In addition, some patients eventually require pharmacologic therapy or bariatric surgery. Physical exercise and activity are also important for maintaining long-term weight loss and can be beneficial in preserving lean body mass while dieting. A dose-response relationship has been demonstrated in overweight adult women between the amount of exercise and long-term weight loss maintenance .
This role of physical activity in the prevention and treatment of obesity will be reviewed here. Basal metabolic activities, thermogenesis, and other interventions in the management of obesity are reviewed separately. (See "Pathogenesis of obesity" and "Overview of therapy for obesity in adults" and "Behavioral strategies in the treatment of obesity" and "Dietary therapy for obesity".)
Obesity in children and adolescents is reviewed separately. (See "Definition; epidemiology; and etiology of obesity in children and adolescents" and "Management of childhood obesity in the primary care setting".)
MEASUREMENT OF PHYSICAL ACTIVITY
Accurate measurement of total daily energy expenditure (TEE) is possible using the doubly-labeled water technique . By subtracting energy expenditure (determined by measurement of resting energy expenditure [REE] and adding diet-induced thermogenesis, which accounts for 10 to 15 percent of the total) from TEE measured by doubly-labeled water technique, an estimate of energy expenditure as physical activity can be made. The physical activity level (PAL) can also be expressed as the ratio of total energy expenditure (TEE from doubly-labeled water) to resting energy expenditure (REE).