Individual lifestyle was held accountable for health and disease throughout much of American history. Since the advent of the germ theory of disease, the focus on the etiology of disease has shifted to factors beyond individual control. But in the past two decades, there has been a resurgence of interest in the role of personal habits in producing sickness. This paper examines the history of one facet of the health promotion movement--aerobic exercise, primarily jogging. Initially, concepts in exercise physiology were adapted from non-medical fields--such as competitive sports and the military--for use in cardiac rehabilitation. Subsequently, a few physicians generalized their experience with cardiac patients to the general population, concluding that aerobic exercise could prevent heart attacks. This idea of exercise as a prophylaxis was seized upon by the public, who were receptive because of the political climate of the sixties. Once the popular movement was underway, researchers began studying the role of exercise in preventing coronary heart disease, confirming that exercise does confer some benefit. In the seventies, exercise attracted a new, wider audience--not because of the justification for its use provided by the scientific community, but because of the appeal of upright living as a means to personal and social redemption. The case of aerobic exercise provides an instructive example to social scientists and policymakers seeking to understand or to encourage widespread behavioral change.