How Menses Affects Athletic Performance

As athletes, we plan our training so that we peak at the right time. We pay close attention to our nutrition in order to perform well and avoid bonking. We invest loads of money into the right equipment. With all that prep, should women also be taking into consideration their menses cycle when planning races?

The answer is clearly yes. In order to recognize a few of the crucial players in the cycle, we must first understand the cycle itself.

  • The follicular phase: Occurs from days 1 to 14 of the cycle. During days 1 to 5 or 7 (on average), bleeding occurs.
  • The luteal phase: Occurs from days 14 or 15 to 28 on average. During this phase ovulation occurs as well as a sudden surge in estrogen. Several important changes occur during this dramatic increase in estrogen that could potentially negatively affect performance.

Most of us assume that a woman's performance is compromised because there is a major drop in her hemoglobin and hematocrit (iron) levels once the bleeding ends. Contrary to popular belief, studies show that for the majority of women (not including those who are heavy bleeders) there is not a significant enough decrease to affect performance. In fact, it is the thermoregulatory and metabolic changes that occur during the luteal phase which are more likely to affect performance.

Increased Carbs During Luteal Phase

The female body is trying to spare glycogen during the luteal phase. The surge in estrogen therefore stimulates the body to use fat more. What does this mean for the female athlete? If she is racing or training intensely during the luteal phase, she needs to be extra conscious to make sure she is taking in at least 40 grams of carbohydrate per hour, says Dr. Stacy Sims of Stanford University. There is less room for error than when she is in the follicular phase.

Slower Recovery Time

The second factor to consider if racing during the luteal phase is the drop in a woman's plasma volume. The blood becomes thicker when plasma volume drops and, as a result, blood moves more slowly between muscles which therefore results in slower recovery time (lactic acid build up and oxygen deficits).

Body Temperature

Along with a drop in plasma volume, comes a slower sweat rate. The body temperature therefore rises. A female racing or training in this phase should be extra concerned with overheating and should take precautionary measures to avoid becoming dehydrated. Consider slightly increasing your sodium-based pre-loading drink.

Cramps, bloating and negative attitude aside, studies suggest the best times to compete are the first couple days into one's period or immediately after bleeding has finished. It is during this time that estrogen and progesterone are at their lowest and less likely to create any menacing changes.

Another factor to consider is that a woman's weight is highest during the luteal phase as well and drops just after menses begin.   

Most importantly, women should keep a record of their cycle and track changes they make to their carb and sodium intake to see what works best. Try to recognize patterns within the different phases to plan (if possible) when to race. They should also get their ferritin tested when they are feeling at their best (not only at their worst!) to help set a standard.

Clearly, a woman's menses cycle is a crucial factor to consider when training for and racing in endurance events.

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Amanda McCracken has been racing triathlons competitively for 14 years and coaching athletes for 10 years. She resides in the mecca of triathlon, Boulder, Colorado, where the trails are her playground.

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