The Mechanics of the Pull-Up (and Why Women Can Absolutely Do Them)

Posted: March 14, 2013 by JonoShmono "SykOse. Live. Extreme." in Climbing
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As a former rock climbing instructor, I have seen many contorted struggles to raise a chin over a bar. The pull-up for many is a sort of “test piece” of fitness—an indicator of athletic prowess—that is a cornerstone of a good workout (or a good showing-off). Most either never try a pull-up after they leave high school gym class, or fail, but many succeed, especially women.

Long-time rock climber Sarah Brengosz pulls hard.

Long-time rock climber Sarah Brengosz pulls hard.

You can do yoga all day, you can run or bike or swim, but a pull-up will still be hard. It’s not that you have to be a juiced-up “lunk” to do one; it’s a matter of physics. In physics, as in a pull-up, you need to do work to affect one system or another. Work is described as the energy needed to move some mass over some distance. For a pull-up, the work that your arms and back need to do is a function of your mass and how far you need to move it upwards to get your chin over the bar.

The equation below describes the struggle:

A few things pop right out of the equation. If you have more mass fighting Earth’s gravity, or if you have further to move, the work you need to do quickly increases. But for its simplicity, the equation also reveals a few things about why pull-ups are so hard for so many people.

A lanky individual myself, I happen to have a decent balance between mass and arm length.

A lanky individual myself, I happen to have a decent balance between mass and arm length.

First, muscle men tend to flounder with the pull-up because of their mass. The heavier you are, the more work is required to move that bulk. I have seen many first-dates come to a screeching halt at the climbing gym after the would-be impresser fails to pull himself up six inches. Though rippled with muscle, they “have nothing to do with all their strength,” as the Joker would say.

Second, arm length matters. 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.

Lastly, gravity is important for the pull-up. I’d guess that no one will do a pull-up on another planet for at least a few decades, but suffice to say that a pull-up on Mars—with only 38% of Earth’s gravity—would be much easier.

So there is a trade-off. Especially in rock climbing, you want to be light enough to move gracefully yet powerful enough to handle the hard stuff. Being larger with shorter arms works, as does lanky and light. Both combinations fit most of the professional rock climbers that you will see, or the people at the local gym proud enough to pull-up.

Through this whole discussion, I’d bet that your mental image was of a man doing a pull-up; I want to change that.

Why Women Can Do Pull-Ups, A Lot of Them

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. She then generalized the study out to all women, citing grade school fitness tests to keep would-be pull-uppers on the ground.

Tell Sarah that she can’t do a pull-up, I dare you.

Tell Sarah that she can’t do a pull-up, I dare you.

Two immediate problems with the study are time and number. The study trained 17 women over three months to get the result reported in the Well. Any science writer will tell you that generalizing to half the world’s population from 17 individuals is a no-no. But more importantly, three months is simply not enough time for everyone. As I said before, and as the Well apparently knows, pull-ups are hard. In my experience as a rock climbing instructor, I have known men and women alike who couldn’t do a pull-up after a whole year of training who have eventually pulled one off.

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. That is a perfectly reasonable conclusion, but I see no logical way to get from that to “women cannot do pull-ups.” And my guess is that if their sample included more athletic women, like Sarah featured in the photos above, their results would be different. Sarah isn’t a “freak” bucking the trend; she’s a dedicated woman climber (who has never specifically trained to do pull-ups) and the exception that disproves the rule. It’s not that women can’t do pull-ups, it’s that almost nobody can consistently do one without training, the required musculature, or that careful balance between mass and arm length.

Some will argue that women have lower centers of gravity (because women tend to store more fat around the buttocks and hips), and therefore are at some disadvantage. Again, physics tells us otherwise. Unless that woman has a significantly different mass or arm length to make a pull-up more difficult, her center of gravity moves the same distance vertically regardless of where it is. This is another attack on the female form that falls flat.

Despite the criticisms, it does seem like it is easier for men to do pull-ups than it is for women. Indeed, if we put the average heights and weights of American men and women into our equation, women have less physical work to do than men. So if it’s not because of center of gravity or arm length or weight, what is it?

It comes down to musculature. Men do in fact tend to have more muscle in their upper bodies ripe for the bulging. More muscle makes the work easier. But this advantage over women is fleeting. It may take a woman more time to develop the musculature required, but once developed, those muscles function like any males’. Overcoming this steep curve is no easy task. I suspect that because few among us have the time or effort available to significantly change our musculature, our bias against women doing pull-ups is not because they actually can’t do them, but because of men’s fortunate physiology.

Concluding that women can’t do pull-ups has a more sinister effect. I have trained many women who outright refuse to even try one. Women already believe that a pull-up is out of reach before their hands touch the bar. How many able women are discriminated against by this cultural truism?

Pealing back the bias, to me it’s obvious: if a woman isn’t culturally dissuaded from trying, she is absolutely able to pull up and hit her head against the glass ceiling, smashing through it.

It is easy to buy into the cultural stereotype of “the gentle sex,” but it simply isn’t true. If you put a woman in a situation where she has to effectively do pull-ups all the time, as in rock climbing, she will learn to do one. Of course I am biased here, but rock climbing is the perfect counterpoint to the “women can’t do pull-ups” truism. The same kind of glass ceiling is present in the sciences, where a significant bias against women festers. Imagine how many women could excel in science if not for the pernicious myth that science and math are a man’s game. Likewise, fitness isn’t defined by the Arnold Schwarzeneggers of the world. If you give women a chance to pull past the bias and the bullshit, they often do.

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