The menstrual cycle and running

For decades, physiologists tried to ignore it. They’d include only men in their studies, or they would test all female subjects at the same point in their menstrual cycle, in order to avoid the potentially confounding effects of widely varying levels of the hormones estrogen and progesterone. These days, it’s clear that these hormonal changes do inf luence athletic performance, and many sports scientists (not to mention coaches and athletes) are trying to understand exactly how and why.

There’s one problem, though: it’s complicated and highly individual. A major new meta-analysis in the journal Sports Medicine by a team of British researchers led by Kelly McNulty and Kirsty Elliot-Sale combined the results of 78 studies with a total of nearly 1,200 participants. The studies all tested athletic performances of various types – strength, endurance, power – at different stages of the nominally 28-day cycle to see if any phases were particularly good or bad.

In theory, they expected the best performances in either the mid-luteal phase (which occurs between ovulation and the start of menstruation, when both estrogen and progesterone are elevated), or around ovulation, when only estrogen is elevated. The worst performance, in contrast, would be expected in the early follicular phase ( between the start of menstruation and ovulation), when both hormones are low. In practice, though, they found virtually no differences between the phases. There was weak evidence that performance in the early follicular phase might be a little worse, but virtually no other overall differences between phases.

This doesn’t mean that the menstrual cycle doesn’t have any impact, but it suggests the effects are more nuanced than simply labelling parts of the cycle as “good” or “bad” for athletic performance. Some phases may be better for endurance, while others favour strength. Or it may be that individual differences in response overpower the broader patterns. The way forward, McNulty and Elliot-Sale suggest, is more research, but also more individual awareness among athletes: keep track of your cycle and your performances and look for patterns that help you determine when you’re at your best.