There have been lots of crazy challenges on the Internet, especially when it comes to fitness and body image. The Belly Button Challenge and the Reverse Prayer Body Challenge are just some of what trended last year, and you can lump the new A4 Waist Challenge in the same category.

Women in China are holding a piece of A4 size paper in front of their body to determine if they are thin enough. If the paper can hide their waist, they take a photo of themselves in front of the mirror and share proof of their slim body online using the hashtag #A4waist.

A4 size is 8.5 inches by 11 inches and the idea behind the challenge is that if your body is "fat" and spilling out of the paper's dimensions, you could be at risk of developing health issues like obesity, high blood, heart disease and diabetes. This is not something you'll find in the CDC guidelines for assessing weight, nor is it in any of the policies supported by the Obesity Society.

However, young people - especially women - are participating in this latest "fitness" challenge, which already has millions of posts since February. It started on the Chinese social site, Weibo, but it's also spreading across Twitter and Instagram.

#a4waist #challenge Lol..

A photo posted by Elzawan (@elzawan) on Mar 15, 2016 at 11:02pm PDT

Meanwhile, the unrealistic body image challenge is receiving criticism from netizens, and in fact, it has spawned a #stopa4waist trend. Some women took the #A4waist challenge just express their displeasure for the craziness.

One Instagram user shared: "This kinda stuff is ridiculous. Essentially measuring your worth based on whether your waist is smaller than a piece of paper." She used her graduation certificate to hold up against her torso. "I'm worth more than a measurement against a piece of paper, that piece of paper is an achievement in itself."

A plus-size women's magazine editor also denounced the social media fad. "The A4 challenge does nothing to promote health and fitness but instead encourages young girls to evaluate themselves by their measurements and appearance," SLiNK editor Rivkie Baum said. "Being the size of an A4 piece of paper is not an accurate way to depict or assess health and perhaps it is time for social media to crack down on these types of irreverent campaigns that harm the young women that are so hooked on them."

No one actually wins in these "challenges," but the ones who eagerly participate use the platform to #humblebrag about their bodies, according to some observers.