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 award on the government’s physical fitness test by doing 10 pull-ups or chin-ups: for 14-year-old girls, it’s 2.

To find out just how meaningful a fitness measure the pull-up really is, exercise researchers from the University of Dayton found 17 normal-weight women who could not do a single overhand pull-up. Three days a week for three months, the women focused on exercises that would strengthen the biceps and the latissimus dorsi — the large back muscle that is activated during the exercise. They lifted weights and used an incline to practice a modified pull-up, raising themselves up to a bar, over and over, in hopes of strengthening the muscles they would use to perform the real thing. They also focused on aerobic training to lower body fat.

By the end of the training program, the women had increased their upper-body strength by 36 percent and lowered their body fat by 2 percent. But on test day, the researchers were stunned when only 4 of the 17 women succeeded in performing a single pull-up.

“We honestly thought we could get everyone to do one,” said Paul Vanderburgh, a professor of exercise physiology and associate provost and dean at the University of Dayton, and an author of the study. But Vanderburgh said the study and other research has shown that performing a pull-up requires more than simple upper-body strength. Men and women who can do them tend to have a combination of strength, low body fat and shorter stature. During training, because women have lower levels of testosterone, they typically develop less muscle than men, Vanderburgh explained. In addition, they can’t lose as much fat. Men can conceivably get to 4 percent body fat; women typically bottom out at more than 10 percent.

So no matter how fit they are, women typically fare worse on pull-up tests. But Vanderburgh notes that some men struggle, too, particularly those who are taller or bigger generally or have long arms. This is related to an interesting phenomenon: if you compare a smaller athlete to an athlete who has the same exact build but is 30 percent bigger, the bigger athlete will be only about 20 percent stronger, even though he has to carry about 30 percent more weight.

“We’re a combination of levers; that’s how we move,” Vanderburgh said. “Generally speaking, the longer the limb, the more of a disadvantage in being able to do a pull-up. I look at a volleyball player and wouldn’t expect her to be able to do a pull-up, but I know she’s fit.”