The endogenous circadian system (i.e., an internal biological rhythm) plays an important role in regulating blood glucose, blood pressure, and energy expenditure. Physical activity improves health and reduces the risk for cardiovascular diseases and type 2 diabetes. The goal of this study is to understand the interaction between the circadian system and physical activity. We aim to test whether such relationship between the circadian system and physical activity can be used to enhance the health benefits of physical activity.