Arent said that what is considered "old" changes from sport to sport. While athletes' bodies may change in predictable ways, he said, their performance also depends on the unique demands of the game. Maximum heart rate also falls as people age, and training may take an extra toll on muscles, joints, and ligaments. Maximum oxygen consumption takes a hit. For women especially, bone density may drop after age 30. Genetics may also play a role in athletic performance. In one analysis of the ages when athletes reach their peak performance in different sports, researchers found two separate trends: For sprint-like events that demand bursts of power, the longer the event, the younger the age at which athletes peak. For endurance events, athletes peaked later for longer events.