<p>While the pull-up has been used by everyone from middle-school gym teachers to Marine drill instructors to measure fitness, the fact is that many fit people, particularly women, can't do even one. To perform a pull-up, you place your hands on a raised bar using an overhand grip, arms fully extended and feet off the floor. (The same exercise, performed with an underhand grip, is often called a chin-up.) Using the muscles in your arms and back, you pull yourself up until your chin passes the bar. Then the body is lowered until the arms are straight, and the exercise is repeated. The Marines say a male recruit should be able to do at least 3 pull-ups or chin-ups, but women are not required to do them. In school, 14-year-old boys can earn the highest...</p>