A new Internet challenge — to show how slender your figure is by touching your belly button by reaching behind your back and around your waist — has taken China by storm.

Popular among young females online, the craze has already led thousands of people to post selfies on the web, including Chinese celebrities like Yang Mi, Huo Siyan and Zhang Jiani and even men with beer bellies.

The "belly button challenge" has received 170 million hits as of Thursday since its launch on Wednesday, and the hashtag translated as "reaching your belly button from behind to show you have a good figure" is among the top three trending topics on Weibo, China's Twitter.

"It's just showing off of their slim figures, as well as an expression of competitiveness and insecurity," said Shao Yu, a Chinese Weibo user, told China Daily.

"Especially when the challenge is supported by US scientists, and now they are authenticated by the US scientific community as being in good shape."

According to Weibo, the challenge originated from research by US scientists suggesting women who could achieve the challenge are of good figure. The referenced research, however, is nowhere identified.

In addition to women's tiny waists, a photo uploaded by a male blogger touching his beer belly from behind his back has also lit up the blogosphere.

As of this writing, his post had been forwarded more than 8,612 times and gotten 2,420 comments since June 9 when he posted the selfie on his Weibo account.

Whether being able to touch your bellybutton from behind proves you are in good shape has caused some debate and experts say don't despair if you come nowhere near reaching your bellybutton.

"Being able to complete the challenge does not necessarily mean you have a fit body," said Zhang Shitian, a fitness instructor at a gym in Beijing who is obviously fit enough yet still unable to touch his own bellybutton from behind.

"It requires a slim figure, small waist, long arms, as well as good flexibility," said Zhang, "and those who work out regularly with six-packs would fail it too."

"A good figure and the ability to touch your bellybutton from behind do not have too much correlation," he added. "You have to work out regularly and scientifically to stay in good shape."

Many girls who can complete the challenge are too slim and are not of a healthy shape and figure at all, he said. The bellybutton challenge might be confusing a healthy shape with being thin as a rail.

Some experts also suggest that China's new bellybutton trend might lead to — or at least promote — eating disorders.

Wang Shuo, a private tutor at a gym in Shanghai, agreed.

"For many Chinese, the way to stay slim is to eat less or not at all and many worry going to the gym might gain them muscle," he said.

"The pictures are fun to see but they can also reinforce the idea that being overly slim is the only standard of beauty for girls."

zhengxin@chinadaily.com.cn