According to WebMD, while running has been linked to weight control, stress reduction, better blood pressures and improved cholesterol, research indicates that running for more than two to three hours per week is linked to shorter life spans. Alex Hutchinson of Runner's World supports these findings to a certain extent, with the addendum that some studies have discovered a link between running and increased arterial plaque.
Hutchinson avers that these studies demonstrating that too much running leads to poorer health are flawed, with poor data collection and bias affecting results. He points out that none of these studies indicate that running causes poorer health, only that runners cannot reverse poor eating habits and family history of heart disease.
Runners who jog 2.5 hours per week at a moderate pace see the greatest amount of health benefits, and athletes who run long distances put too much strain and stress on their bodies, leading to a restructuring of the heart.
Bill Bradley of GQ debunks the myth that too much running damages the knees and leads to osteoporosis and arthritis. When running form is correct, the leg remains fairly linear. Over time, the body learns to adapt and the constant impact promotes cartilage thickening rather than thinning.