In all 4,658 men, 20-79 years of age, with no prior myocardial infarction, attended two examinations. Jogging status was self-reported based on the question "Are you a jogger?" The study shows that regular jogging is not associated with increased mortality in men, as the joggers had significantly lower mortality than non-joggers. The lower mortality of joggers could be an effect of the physical training, but it could also be due to selection or a combination of both. On the other hand, numerous studies within the fields of epidemiology, work-physiology, psychology and biochemistry have all pointed toward a beneficial effect of physical activity on health, but the optimal intensity, frequency and duration of physical activity has yet to be established.