Obesity is the result of an inability to maintain energy balance, and changes in energy balance can also be important contributing factors in the etiology of diabetes and other metabolic diseases. A major goal of Core D is to provide investigators with the services necessary to accurately measure the major components of energy balance (energy intake, energy expenditure, body composition, nutrient digestibility) in their mouse models. Core D also provides tests that allow investigators to examine physiological factors that may influence food intake or energy expenditure. A second focus of Core D is to understand the contribution of physical activity to energy balance as well as the beneficial effects of voluntary exercise or treadmill training on metabolism. Behavior is the third component of Core D, with an array of tests for cognitive and behavioral assessment. Core D investigators have complementary expertise in energy metabolism and exercise/muscle biology to provide clients with assistance in all steps of the research process, from designing experiments to analyzing and interpreting data. In addition to offering standard services in our catalog, Core D also works with investigators to design custom tests or develop new tests to meet their research needs.