The Mechanics of a Pull-Up

By Wesley Fenlon

The not-so-secret secret to being able to do pull-ups? Properly developed muscles. Long arms and too much mass can make pull-ups impossible, however.

"The Mechanics of the Pull-Up (and Why Women Can Absolutely Do Them)" is a Scientific America story that delves into the physics behind that most awkward of elementary school P.E. exercises. The parenthetical in the title seems like a "duh" statement at first--of course women can do pull-ups!--but it's actually a response to a study that claimed the exact opposite.

"Last year, in an article titled “Why Women Can’t Do Pull-Ups,” Tara Parker-Pope at the Well blog commented on a study which found that after training regular women three days a week for three months, almost none of the women could complete a pull-up," writes Scientific American's Kyle Hill. "She then generalized the study out to all women, citing grade school fitness tests to keep would-be pull-uppers on the ground...So, the only thing that the study really says is that these women needed more than three months of training to do a pull-up."

Photo Credit: USMC Flickr via Creative Commons

Hill discounts the argument that women have trouble with pull-ups due to lower centers of gravity. That's not a problem, he writes. Being able to do a pull-up comes down to mass and arm length. Bodybuilders with hugely developed arms may not be able to do pull-ups because that mass is working against you. And the longer your arms are, the harder it is to lift your body:

"Take two people of the same mass, say 100 kilograms. If one person has to contract half a meter of arm to complete a pull-up, he or she is exerting 490 Joules of energy. If the other person, quite a lanky individual, has to pull through one full meter, he or she exerts 981 Joules of energy—the same amount released by a quarter gram of TNT. With just a moderate variability in arm length among us, pull-ups become harder or easier."

Women are at a disadvantage when performing pull-ups, but the task is hardly impossible. Hill writes that men do, naturally, have more muscles in their bodies, but women can make up the difference with proper training. Long-armed men and women alike, though, may be out of luck.