Women, Exercise, And The Menstrual Cycle

For a long time in science, the menstrual cycle’s effects on everything from response to drugs, food and exercise was largely ignored as an “inconvenience” rather than vital information. Thankfully that is changing and we are discovering how the different phases of the cycle affect women’s bodies and responses to the environment. I have been particularly intrigued in how tailoring your exercise regime to your cycle can maximise benefits while reducing risks. I first read about these effects in the book Roar by Stacy Sims, an excellent book on optimising performance in female athletes. While the menstrual fluctuations in exercise performance seem to be really small (and therefore perhaps only really applicable to athletes), I nevertheless found it really interesting and the information may help the average woman tweak her exercise routine (for example by seeing whether strength training during the follicular phase leads to greater strength gains, having motivation to work out during a period, and understanding why you might want to do yoga just before your period).

Here’s some of what we understand about the different phases of the menstrual cycle and how hormones may affect exercise performance…

  • During your Follicular phase (days 1-14, i.e your period and the days afterwards), your hormones are actually favourable for performance. Women make greater strength gains, and recover faster during this time. Your ability to utilise carbs is also improved. However chances of injury may be higher in this phase; this study showed reduced neuromuscular coordination and balance during the premenstrual and menstrual phase. Interestingly, those with PMS showed more variability in performance throughout the menstrual cycle. The risk of ACL tear is highest in women in the days leading up to ovulation.
  • Ovulatory phase – The study linked above showed improved neuromuscular coordination during the ovulatory phase. Resting blood pressure and heart rate are also highest during the ovulatory phase in this small study. Muscle strength may peak around ovulation.
  • Luteal phase (days 14-28) – the days after ovulation and before your period are characterised by high oestrogen and progesterone levels. This means it’s harder to build muscle, and workouts result in greater muscle breakdown. Endurance exercise may be harder during the mid luteal phase due to higher body temperatures and more cardiovascular strain, so it may be better to do gentle exercise during this phase.

What about non-cycling women?

Birth control – Obviously the above don’t apply if you are taking continuous hormonal birth control, as BC downregulates the hormones your body makes while providing external synthetic hormones in a continuous manner, thus eliminating your “cycle”. This may decrease exercise performance slightly compared to naturally menstruating women, but studies do vary. Oral contraceptives may decrease muscle gain but in the study this seemed to be related to higher cortisol and lower DHEA, DHEAS and IGF1 levels.

HRT – seems to improve muscle protein synthesis, so is something of a consideration post menopause, especially as muscle mass becomes ever more important with age.

Pregnancy/breastfeeding – The main special considerations for exercise that need to be taken into account during this time, are that core muscles can weaken, joints become more lax due to the hormone relaxin, and overheating can be a problem. Unfortunately, I couldn’t find much on how hormone levels during pregnancy and breastfeeding affect strength gains. I think during this time, it’s more important to just maintain muscle mass and fitness, rather than trying to beat personal records, as growing and feeding a baby is extremely energy intensive. At the same time, exercise prevents complications in the mother and baby.

PCOS – In polycystic ovarian syndrome, women often have irregular periods, high levels of androgens (testosterone and androstenedione) and insulin, and may not always ovulate. The hormonal effects on exercise therefore vary too widely to be known with any certainty. However, what we do know is that exercise can improve PCOS symptoms and balance hormones. A reminder that while hormones can affect exercise, it works in the reverse direction too!

Trans women – I don’t know much about hormone protocols for trans women, though the UCSF transgender care centre says it involves a combination of oestrogens and an androgen blocker, perhaps with progesterone. Similarly to hormonal birth control, there is a paucity of research on how this affects exercise performance, apart from a reduction in lean muscle mass.

In summary, there are ways women can work with their cycle to optimise performance and decrease injury risk. That said, physical activity at any time of the cycle is important and will have benefits!

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