It is fairly settled in the scientific community, barring the odd few objections here and there, that regular moderate exercise improves health in the long term, relative to a sedentary lifestyle. When it comes to the details of the dose-response curve for exercise, however, the scientists of the field are still somewhere in the midst of a slow and grand debate that has lasted decades and seems likely to last for decades more. Extracting solid conclusions from human epidemiological data is a challenging endeavor at the best of times. The papers noted below are illustrative of a score or more similar efforts published every year, as researchers add ever more analysis to the existing mountain of thought on exercise and health.
Present evidence is leaning in the direction of a big leap in benefits in the transition from no exercise and minimal physical activity. Benefits increase thereafter up to the point of an hour or so a day, and then may or may not decline with further increases. Clearly there is a point at which too much exertion is harmful, but does that occur prior to the level of exercise undertaken by profession athletes? If so,