The idea that physical activity could be rewarding may seem counter-intuitive because many people find exercise aversive and would prefer to be inactive. Arguably one of the greatest health problems facing the United States today is inactivity, which is associated with obesity and metabolic syndrome, e.g., diabetes, heart disease, and stroke (Must et al., 1999). On the other hand, clearly, certain individual humans find at least some types of physical activity rewarding, as they choose to exercise multiple times per week and even report that they feel euphoria from exercise, as in the case of the runner’s high (Boecker et al., 2008). Moreover, many people who regularly exercise report withdrawal symptoms if they are unable to exercise, including irritability, anxiety, difficult time focusing, and bad mood (Mondin et al., 1996). Hence, in certain predisposed humans, it seems that physical activity can be rewarding and reinforcing to the extent that individuals choose to engage in the activities and show withdrawal when prevented from an exercise routine.