But it's not just in the movies. Increasing numbers of real-life women are now sporting stronger looking shoulders and upper arms - and it's a result of a shift in how we train to get fit, says Sydney-based strength coach Michelle Drielsma​.

"In the past the main focus for women was on training the lower body and using cardio for fat burning. But with the influence of CrossFit, Acroyoga, calisthenics and Olympic lifting, there's now a more whole-body approach to training and a by-product of this is that women are getting stronger in the upper body - and once they start training they like the way their arms look," she says.

"But it's not just about looking strong. I think more women want to be strong - and more women are interested in competing in events such as Tough Mudder​ and CrossFit events and holding acrobatic-style yoga poses."  

Only 10 years ago, a woman in the weights room of a gym was a rare sight, and the words "women" and "chin up" would never have been included in the same sentence. Now more women are training in the weights room, gravitating to the battle ropes (which work out shoulders, arms and core muscles) and even trying the chin-up bar, says Drielsma, although she admits that chin ups and pull ups are harder for women.

"Although women's lower-body strength is more closely matched to men's, women generally have only half the upper-body strength of men. The reason is mostly biological in that men can build more strength because they have more testosterone, and also tend to have a higher proportion of their muscle concentrated in their upper body," she says.

"I have a solid 10 years of strength training behind me and although I could out-squat some of my male friends it's still hard to beat them in a chin up or an arm wrestle - even when they're untrained."

Still, more women are giving chin-ups and pull-ups a go, she says, explaining that of the two, the chin up is more do-able. It involves gripping a bar with palms facing you and pulling your body up until your chin is over the bar. The fact that you use your biceps as well as back and chest muscles makes this easier. The pull-up is a similar movement but with a wider grip and less involvement of the biceps, Drielsma explains.

But before you attempt either a chin-up or a pull-up it's important to build stability and strength in the upper body, she stresses. That is achieved through traditional strength exercises like bench or overhead presses, but also from a range of movements that can include pushing, pulling and crawling, and which are now built into many gym classes.  

"We've learned that the body likes change; if you stick to the same movements for too long you get diminishing returns," she says.

When you've built a stronger upper body, the benefits go beyond looking good in a tank top.

"Things that involve lifting and carrying and any sport or activity that includes throwing, pushing, pulling, batting or climbing become easier," Drielsma says. "Even movements with weights that strengthen the lower body like a dead lift or a squat are easier when your upper body is strong," she says. "There are also the health benefits that come with building more muscle, like a faster metabolic rate that burns more kilojoules, better bone density and healthier blood sugar levels."