During an (unsubtitled) interview after the 4x100m medley, in which the Chinese team placed fourth, she apologized to her teammates for her time, saying: "I didn't swim well enough this time. 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."
This is a particularly big deal because in China the subject of menstruation can be taboo, and many women are resistant to using tampons. Many Chinese women wondered on Twitter how Yuanhui could even be in the pool while on her period, because tampon use is so rare among women there. In 2013, only 2.5% of feminine hygiene products sold in China were tampons (they just started selling domestically-made tampons this year).
Most of the purchases were sanitary pads, which as any lady knows, don't make the best swimming gear, and sadly don't function as floaties.