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Men take the ability to lift their entire body weight so their chin is above a bar for granted. But for a woman to do even a single chin-up, she needs to work for it, said Boston strength and conditioning coach Tony Gentilcore.

And the work, he added, is worth it.

"I consider it an important fitness goal for women," he said. The training helps sculpt muscles in a way many find appealing, and "weight loss can be part of the discussion because it's less weight to pull up over the bar."

Once his clients have mastered a chin-up, it's a skill they don't want to lose, he said. Instead, they want to go for two chin-ups. Then more.

Why is it women need to work so hard to achieve even a single chin-up?

"It's not the quality of the muscle, it's the total amount," said Cassandra Forsythe, an assistant professor of exercise science at Central Connecticut State University and co-author of "The New Rules of Lifting for Women." "With men, puberty provides an enhancement in testosterone, which creates greater muscle mass. There is a large difference in the amount of upper-body muscle between men and women."

So what kind of training does it take?

"You need to train four to five times a week," Gentilcore said. "Planks, pushups, core strength. Building total body stability starting on the floor is important, so when they're hanging from the bar they can hold a good position."

He then has his clients practice hanging from the bar, adding in flexed arm hangs and hanging leg raises. When they're ready, he has them "build the pattern" by mimicking the chin-up while having clients stand on elastic bands attached to the bar to help lift them up. Over time, those elastic bands get thinner and the clients do more of the work, until they can do the entire exercise on their own.

The chin-up had long escaped Michelle Kania, a 37-year-old athletic trainer in Oswego, Ill., but she made it her mission to learn. She followed Gentilcore's program via online coaching and is currently able to do five chin-ups.

Kania said she once impressed a group of Marines with her ability to do chin-ups.

"I like doing it in public, so people look at me," she said. "I get a kick out of that."