How your menstrual cycle affects performance in sport
The issue of periods and women's menstrual cycle affecting sports performance was raised in 2015 when British number one Heather Watson lost in the first round of the Australian Open tennis tournament.
She reported dizziness, nausea, low energy levels and light-headedness, and told the BBC: "I think it's just one of these things that I have, girl things."
A former British tennis number one, Annabel Croft, sympathised with Heather at the time, saying periods were the "last taboo" for women in sport, who tend to "suffer in silence".
What are the facts on periods affecting a woman's sporting performance?
Periods and sport
In theory, hormone changes during a woman's menstrual cycle could have a physical and psychological effect on performance in sport. However, there's a lack of good quality evidence on the exact effects. Those potential effects are also likely to differ from woman to woman.
Measuring sports performance can be straightforward for researchers, with timings, distance and scores, but measuring symptoms linked to the menstrual cycle, such as fatigue, bloating and lethargy are more difficult to quantify. It is harder still to work out whether those symptoms might be the cause, or some other factor affecting sport, such as psychological effects and infections.
Some studies have looked at variations during a woman's cycle of plasma, electrolytes, sodium, potassium, chloride, bicarbonate, blood sugar levels, breathing rates and temperature. An Italian study found female footballers were more likely to have injuries before and during their periods.
However, overall, researchers have not found conclusive evidence of a cause-and-effect between sporting success, or failure, and the menstrual cycle.
The chief medical officer for Netball Australia, Dr Susan White, looked at the evidence and concluded that world standard sporting performances have been seen at all stages of female athletes' menstrual cycles, including pre-menstrual and menstrual phases.
This doesn't mean that periods don't make a difference to individual women in sport, but that science hasn't found a general tendency.
Regulating periods for sports fixtures
If the menstrual cycle is having an impact on a woman's sports performance, some experts say using oral contraceptives may help stabilise hormones for important training and competitions. However, this should only be done after taking medical advice.