I usually don't participate in these discussions because it's all too easy to commit the typical mind fallacy. The implicit assumption seems to be that working out and lifting weights must be uncomfortable for most people. I offer myself as a person for whom this is not true: I take pleasure out of lifting weights in a way that I haven't yet experienced from most other sports. As for 'toughness', well it's true that if you start experiencing extreme pain you should stop doing what you're doing, but any kind of medium-intensity exercise is always going to come with some mild discomfort. Some people tend to exaggerate this discomfort. Just because something is uncomfortable doesn't mean it's an 'evolved safety signal.' You could just as easily argue that it's the body merely trying to conserve energy because in the past energy was hard to come by. Evolutionary explanations don't hold water here.