A surprising new study published in 'Medicine & Science In Sports & Exercise' found that running can halve the risk of both osteoarthritis and hip replacement. Researchers looked at 74,752 runners over the course of seven years and 14,625 walkers for roughly six years and found that runners had about half the risk of osteoarthritis and hip replacement, thanks at least in part to their lower body mass index. "It was surprising," says Paul Williams, lead researcher of the National Runners' Health Study, which provided the data. "There is a documented risk factor for osteoarthritis, but it's due to injuries – mostly seen in elite athletes." The study also found that exercises like weightlifting and field sports increase the rate of hip replacement. "My take-home from this study is that running makes your bones and cartilage and everything else stronger," says Dr. Jordan Metzl, a sports-medicine physician at the Hospital for Special Surgery in New York City. "If you're running, I want you to run. If you're running and there's continuous pain, even after you've reworked your form, maybe you're not born to run."