Running performance and the menstrual cycle

One of the aspects of running that I love the most is understanding how our bodies work.  I have a biomedical engineering background in sports medicine, but I didn’t really start to run until several years after I finished my masters degree.  (Ironically, I simulated the Boston Marathon for my thesis waaaaay before I had ever run a marathon.)

One of the most complex and fascinating areas of science are the hormones that make us tick.  I never gave hormones their due respect until I got pregnant and realized within days that my body had completely changed as a result of a few hormones starting the cascade of signals to grow a baby.

I have been breastfeeding for 20 months now (check out a recent post on extended breastfeeding here), so my hormones are still a bit on the postpartum spectrum, but my period returned at 16 months postpartum and so far I’ve been regular every month.  With this, I’ve taken a new interest in understanding how different levels of hormones during the menstrual cycle affect running performance.

I was on birth control for as long as I can remember before my husband and I decided to have a family. With that, I do not feel like I experienced the same shift in hormones that I feel now that I am BC free.  Before you give a point to BC for eliminating noticeable shifts in how I felt, also note that I think that BC may have negatively affected my performance.  I have come back postpartum way faster than I was pre-pregnancy, and I don’t have as much body fat. (Little sidenote: Steph Rothstein Bruce did not use BC because of her suspicions that it could affect performance, and that is how she unexpectedly got pregnant with blessing #2.)

So back to the hormones:  There are two main phases: the follicular phase (days 1-14), in which you have your period and ovulate, and the luteal phase (days 15-28) when the body is preparing for a possible pregnancy.

Follicular Phase: First menstruation occurs at day 1, and then around day 5 or 6, estrogen starts to increase along with a hormone called the follicle-stimulating hormone (FSH).  Around day 12 the estrogen levels surge with the luteinizing hormone (LH), which causes ovulation and an egg is released.

Luteal Phase: After ovulation, estrogen dips for a brief time, only to rise again with progesterone, as the body prepares the lining of the uterus for possible implantation.  Estrogen and progesterone peak around 5 days before menstruation. If the egg isn’t fertilized and implanted, progesterone levels fall and the body returns to day one with menstrual bleeding.



How our hormones affect us: Our carbohydrate metabolism and recovery are more similar to men in the low hormone phase than the high hormone phase. During the high hormone phase, in which we have higher amounts of both estrogen and progesterone.  High estrogen makes us spare glycogen and utilize fat stores instead. This is not a great scenario for high intensity exercise when we need a fast source of fuel.  High progesterone delays the sweat response, turns up core temperature, increases sodium loss, and increases muscle breakdown.  The result in this shift to the high hormone phase can cause fluids to move into the cells, resulting in bloating, as well as a predisposition to central nervous system fatigue. (Yay! Tell me more!) Ok, so here’s more.  During the high hormone phase, your body is more likely to break down muscle but not re-grow more (low anabolism, high catabolism).

There is not a ton of research on the effects of the monthly cycle and performance, but it is recognized that generally, low hormone times are the best for performance, with actual menstruation being noted as one of the best times to compete.  This is of course, highly subjective, as everyone has a different experience with their cycles.  If you are planning to compete during a high hormone phase, be aware that cooling will be more difficult and that proper protein ingestion will help with muscle catabolism.

What Next: If you want to learn more, I highly recommend the book Roar by Stacy Sims. She goes into much greater detail how the system works and ways to mitigate some of the negative effects of our hormone shifts.  While some of the side effects of the hormonal shifts women experience can be frustrating, we need to celebrate the amazing mechanism taking place so that we can stay healthy and grow our families.  As with just about everything in life, the more we understand, the easier it is to navigate the things of life.

Do you notice a change in your running performance at a specific time of the month?

Do you plan your races around your menstrual cycle?