Bloating, cramping, headaches and crankiness — most of us dread “that time of the month.” We don’t feel our best, and putting on tight lycra to go out and ride or race is perhaps the last thing you want to be doing. Others however credit their period and their “racing ovaries” for good performances, citing lower hormone levels during the start of the cycle.

But what does research say? Does your menstrual cycle have an effect on athletic performance? Should you consider your menstrual cycle in planning your training or racing schedule?

We turned to exercise physiology and sports nutrition expert, Dr. Stacy Sims, for advice.

Background: What exactly happens during the menstrual cycle?

The typical menstrual cycle is 28 days long, with the first day of menses (bleeding) considered Day 1.

Start of Menstrual Cycle: first day of bleeding

Day 1 until ovulation is called the follicular phase, and during this time the ovarian follicles mature.

Day 5 -7: menstruation completed. Mucosal lining, called endometrium, of uterus begins to build up
again in preparation for an egg.

Day 14-15: ovulation.

Day 15-28: The phase between ovulation and the day before menses is called the luteal phase. During this phase, the lining of your uterus thickens preparing for possible pregnancy.

A note about contraceptive pills: With a triphasic oral contraceptive pill, the first active hormone pill is taken on Day 1, with low hormone levels lasting from Day 1-5, moderate levels lasting from Day 6 – 10, and the highest hormone levels lasting from Day 11 -21, with a sugar pill or no pill taken for Day 22 – 28, allowing for breakthrough bleeding to mimic a period. Due to the varying hormone concentrations with OCP, there is not a follicular or a luteal phase, just low and high hormone phases.

Does being on your period affect physical and psychological performance?

Is there a time during the menstrual cycle that an athlete would be physiologically primed for competition?

Dr. Sims: Yes. A woman is physiologically primed for performance during the first 7-10 days of the menstrual cycle, with Day 1 being the first day of bleeding. The caveat here is however, is that some women feel better the day after their period starts. The cramping and the fact that the hormones are still dropping can physiologically and psychologically reduce performance potential.

‘Primed’ how?

Dr. Sims: Women are more like men in the follicular/low hormone phase — what I mean by that is during that time, we can access carbohydrate, hit intensities, have greater muscle contractile strength and power, and less central nervous system fatigue than during any other phase.

Knowing that, during this phase (the first two weeks of your cycle), it’s great to do high intensity work , try to set PRs, push yourself harder for increased power/strength/top end fitness gains.

“My legs feel ‘flat’”

Dr. Sims: Women often feel “flat” around ovulation, due to the upsurge of estrogen. Estrogen “spares” glycogen/carbohydrate in the muscle and liver, increasing the reliance of fatty acids for fuel. This translates, performance-wise, into women feeling stronger doing more steady, endurance efforts and not so much high intensity interval training (HIIT).

The worst time of the month…

…is not during menses. It is during the mid to late luteal phase (5-7 days before your period starts), when women feel progressively worse. Progesterone and estrogen interplay to cause a bit of metabolic mayhem:

– A woman’s core temperature is elevated ~0.5’C (decreasing heat tolerance)
– Sweating happens later. This means a woman gets hotter before she starts to sweat, which is why hot yoga can feel harder right before the period starts
– she can’t access stored carbohydrate well, which makes it harder to hit intensity workouts well
– estrogen and progesterone cross the blood-brain barrier, and increase central nervous system fatigue. This results in a loss of “mojo” and feelings of moodiness – a.k.a PMS..

In this phase, it’s better to do more steady state/endurance focused work, bodyweight or lighter resistance training work (e.g. higher reps, lower weight).

Recovery needs more attention during this phase:
With elevated progesterone, it is harder to recover because progesterone is catabolic and signals muscle tissue breakdown. So a woman needs to increase her intake of whole protein, inparticular good sources of leucine.

For endurance athletes (marathoners, long-distance triathletes)- the high hormone phase also predisposes a woman to hyponatremia because progesterone increases total body sodium loss, and there is a shift in baseline plasma osmolality to a lower setpoint (bringing a woman closer to clinical hyponatremia before she even starts to exercise).

Sleep is affected as well. With elevated progesterone, a woman may find it is harder to fall and stay asleep the few nights before her period starts. This is because her body can’t drop to the right temperature to induce optimal sleep and she may wake up with night sweats as well. Remember that sleep is critical for recovery and metabolic health, so a simple fix to this is to drink 4-6 oz of cold, tart cherry juice about 30 minutes before bed. The cold drops internal temperature, and the tart cherry juice enhances the body’s own production of melatonin.

Should an athlete take into account her menstrual cycle when setting a training plan?

Dr Sims: It depends on what the woman is trying to gain from her workout routine. If she’s trying to set PRs and gain strength or power, then yes, paying attention to how the sex hormones affect your physiology can benefit, but if it is general fitness or basetraining she’s after, then it’s not critical. Just be aware that it is your physiology, not your fitness, that can affect your performance across the monthly cycle.