I think we are in an age where the science around nutrition and excercise has led our athletes to the place where their ability to develop muscle far surpasses the human body's ability to develop the supporting structures around that muscle: ligaments, tendons and bones. This is why we are seeing large numbers of injuries even in a league that has put in place so many rules to protect the health of these athletes. A perfect example of this comes from my neck of the woods where in this video, two Australian NRL players have an arm wrestle on national TV, the result, one of them gets multiple fractures in his arm. Warning, this video is not for the feint of heart: