Running is a great form of cardiovascular exercise and great way to maintain physical fitness levels. There are some who are concerned that running causes arthritis, particularly in the hips and knees. A systematic review of 25 studies, covering 125k people found that "recreational" runners (<57miles/wk) had a lower frequency of arthritis, 3.5%, compared to "non-runners" @ 10.2%. Interestingly, "competitive" runners, (>57miles/wk) had a 13.3% chance of developing arthritis. Over-training can overload joints and not allow cartilage [...]