Image copyright Reuters Image caption Fu Yuanhui won a bronze medal in the Women's 100m Backstroke

Competing in the Olympics is stressful at the best of times - but imagine doing so while having your period.

Fu Yuanhui, one of China's swimming stars, became an overnight social media sensation thanks to her frank post-race interviews and exaggerated expressions.

Now, she's become a talking point online again - for breaking a sporting taboo by talking about her period.

China missed out on a medal in the women's 4x100m medley relay on Sunday, coming fourth.

After the match, team-mates Lu Ying, Shi Jinglin and Zhu Menghui were interviewed by a reporter - but Fu was initially nowhere to be found.

It turns out she was crouched behind a board, doubled over in pain.

Image copyright AFP Image caption Social media users have expressed support for Fu

When the journalist asked her (in Chinese) if she was OK, Fu said: "I didn't swim well enough this time," and apologised to her team-mates.

"It's because my period came yesterday, so I felt particularly tired - but this isn't a reason, I still didn't swim well enough."

It was a poignant moment for many Chinese viewers, who took to social media to express their support for her.

"I really admire Fu Yuanhui, for swimming while she was on her period - women can be affected during their periods, especially with period pain... she felt guilty for coming fourth, but Fu Yuanhui we're still very proud of you," user TAO wrote on Sina Weibo.

Tampons are relatively unknown in China

It's also sparked a discussion about tampons - which are not widely used in China.

According to one industry survey, only 2% of women in China use tampons - compared to 42% of US women.

Image copyright AFP

Many women weren't familiar with how to use them, or had not heard of them before, the survey by Cotton Inc said.

"Someone accused Fu of lying, asking how she could have gone in the water on her period," weibo user Dvingnew wrote. "Chinese people have prejudices about tampons - women in their 30s around me are ignorant about tampons, and full of fear about tampons."

And there may also be cultural factors at play too - some Chinese women have been told to avoid using tampons because it could stop them from being virgins, despite health experts pointing out that the two things are unrelated.

One poster defending tampons wrote: "Who told you virgins can't use tampons?...Come on, it's the 21st Century."

According to reports, China's first domestic tampon brand may be launched soon - which may encourage more women to swim while on their periods.

So can menstrual cycles affect sporting performance?

The subject of competing while menstruating is "definitely a taboo", Georgie Bruinvels, a sports scientist, tells the BBC.

"A lot of [elite] sport coaches are men, and that makes it harder for women, who don't want to say 'I'm on my menstrual cycle'.

"We need incidents like this to raise the issue" and encourage more research, she says.

Image copyright PA Image caption GB tennis player Heather Watson has previously described the impact of periods on her energy levels

Ms Bruinvels surveyed over 1,800 sportswomen as part of her work as a researcher at the Female Athlete Health Group - a collaborative project between St Mary's University and University College London.

"More than half the sportswomen I surveyed said they felt their menstrual cycle affected their performance."

While there is not enough research into the impact of periods on sport, Ms Bruinvels says, one potential factor she was researching was iron deficiency.

"Menstruation is the leading cause of iron deficiency in the developed world, but many women are not aware they have it.

"There could be an impact on the amount of time you can exercise, and the maximum amount of oxygen" an athlete can use, and she recommends that sportswomen who feel they've been affected get their iron levels tested.