I think you just always thought it was about your weight, but thin people have the same kinds of injuries - they are just less likely to attribute it to weight. And they are just as likely to gain a pot belly from overtraining. I've seen it a million times. I don't run long distances anymore but it's because of a nerve thing I inherited from my mother, not any injuries related to my weight. I mean, I was never athletic and don't have an athletic build at all. I know women who compete at very high weights and never develop an injury at all, in really strenuous things like Ironman triathlons. I do believe it's way more about an individual's physiology than carrying extra weight. In weightlifting, extra weight is rewarded, in fact, as in many other sports.