You're lean. You're strong. You're in good physical condition. So why can't you perform a single pull-up?

Relax. Scientists at the University of Dayton in Ohio have found that even fit women struggle to do the exercise manoeuvre, which involves gripping a bar overhead and pulling your body off the ground using upper-body strength.

According to The New York Times, the researchers wanted to test whether pull-ups (also known as chin-ups) are a good measure of physical fitness. It turns out they are not.

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The Dayton researchers recruited 17 women of normal weight who were unable to perform a single pull-up. They then trained them for three months, prescribing exercises to strengthen their upper bodies, improve their aerobic fitness and lower their body fat.

All that training produced results: the women's upper-body strength increased by 36 per cent and their body fat was reduced by 2 per cent. But they failed to produce the main result researchers were looking for: only four of the 17 women were able to perform a pull-up.

"We honestly thought we could get everyone to do one," study author Paul Vanderburgh told the Times.

One reason women have greater difficulty doing pull-ups than men is because women develop less muscle and typically have more body fat. But tall, long-limbed individuals are also at a greater disadvantage, regardless of gender.

"Generally speaking, the longer the limb, the more of a disadvantage in being able to do a pull-up," Vanderburg said. "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."

Even the Canadian Armed Forces do not use pull-ups as part of their official fitness evaluation.

Try telling that to your bootcamp class instructor.