Menstrual Cycle and Athletic Performance

How you store and use carbohydrate depends on your cycle.

After British tennis star Heather Watson was knocked out of the Australian Open in the first round last month, she blamed her poor play on "girl things." That sparked a series of articles in the British press on a generally neglected topic: the effect of menstrual cycle on athletic performance. The BBC's take has some interesting details, like Paula Radcliffe's negative experiences with a drug called norethisterone that's sometimes used to delay periods, and the fact that she subsequently set her first marathon world record on the first day of her period (with no drugs).

I decided to take a look at this topic for my column in the Globe and Mail this week. There has actually been quite a bit of research on the effects of menstrual cycle on endurance performance, but with few definitive conclusions, in part because the effects seem to be highly individual. One key point: it's not just about the period itself – hormone levels vary throughout the cycle, with effects on various things like temperature regulation.

The most interesting detail to me was the effects of estrogen-to-progesterone ratio, which flips halfway through the cycle, on carbohydrate, protein, and fatmetabolism:

[Dr. Andrew] Bosch [of the University of Cape Town] and his colleague Dr. Tanja Oosthuyse of the University of the Witwatersrand in South Africa have found that these hormone fluctuations hamper pre-exercise carbohydrate storage during the first menstrual phase, and may compromise carbohydrate and protein availability during prolonged exercise during the second phase.

That means that carbohydrate loading the day before exercise is more important for female endurance athletes during the first phase, say Oosthuyse. During the second phase, it becomes more important to refuel during prolonged exercise, primarily with carbohydrates, but perhaps also with protein if you’re out for more than a few hours.

Moreoever, there may be a "sweet spot" a day or two before ovulation where a spike in estrogen leads to optimal endurance performance. Oosthuyse and Bosch found some hints of this effect in a cycling time trial study.

Here's my rough sketch of a figure (based on a graph Ooosthuyse sent me) showing how the hormones vary, and where the different performance effects take place (this figure didn't make it into the newspaper article, which is I'm including this highly artistic sketch):

By Alex Hutchinson

Article Reference: http://www.runnersworld.com/womens-running/menstrual-cycle-and-athletic-performance

Picture Reference: http://www.robertharding.com/