The economics of intense exercise.

Despite the well-known benefits of exercise, the time required for exercise is widely understood as a major reason for low levels of exercise in the US. Intensity of exercise can change the time required for a given amount of total exercise but has never been studied from an economic perspective. We present a simple model of exercise behavior which suggests that the intensity of exercise should increase relative to time spent exercising as wages increase, holding other determinants of exercise constant. Our empirical results identify an association between income and exercise intensity that is consistent with the hypothesis that people respond to increased time costs of exercise by increasing intensity. More generally, our results suggest that time costs may be an important determinant of exercise patterns and that factors that can influence the time costs of exercise, such as intensity, may be important concerns in designing interventions to promote exercise.