How Your Cycle Affects Your Running

We’ve all shown up to a long run and had a friend groan, “I started my period today.”  We’ve likely all done the same thing ourselves. While I’m all about equality among the sexes, there really are some certain biological things that separate us – and one of them is our menstrual cycle. Our menstrual cycle is full of hormone changes and these hormone changes DO affect our running.

Oddly enough, I went through most of my life (I’m assuming most of you did too) knowing NOTHING about what my body was going through every 28 ish days. I thought of my menstrual cycle 100% in terms of my period and nothing else. If they did teach me some form of it in my sex education class, I was too embarrassed to listen and absorb any of it. Well, once I got older and I got into running, and eventually started thinking about starting a family, I started getting curious about how the female menstrual cycle works.

While training for CIM back in 2014, I read the book “Taking Charge of Your Fertility” which a friend highly recommend and lent to me. I was planning to run the marathon in December and then try for our first baby immediately after, and I wanted to be informed. While reading the book and simultaneously logging long runs, tempo runs and speed work, I started wondering more and more about how the changes going on throughout the month might affect my running. I ended up down a rabbit hole of research that led me to the conclusion that: you run better during certain times of the month than others. 

How Your Menstrual Cycle Affects Your Running

To start, the menstrual cycle is made up of two phases: the follicular phase and the luteal phase. The follicular phase is generally the first half of the cycle, beginning on the day you start your period and ending on the day you ovulate, which is stereotypically day 14. The luteal phase is the time between ovulation and the day before your next period. The “typical” cycle is 28 days or 4 weeks, but we all know that’s not always true (mine is generally 26 days for example – in case you were dying to know!!!).

Running in the Follicular Phase

You may be surprised to find out that running in the first half of your cycle, or the follicular phase, is WHERE IT’S AT. In fact, if you could magically position yourself to race your A game race the day before you ovulate (around day 13), you’d get a serious biological advantage!!! Estrogen levels are at an all time low during this phase and your body can more easily break down glycogen and turn it into fuel – this translates you being able to run faster and further. This also may explain why sometimes you have those “I felt like I was flying” workout where everything falls together -next time you do, think about where you are in your cycle – it may be related to your hormones (or all that hard work you put in….).

But what about the heaviness and general craziness you feel while on your period? Multiple studies have shown that the average drop in a woman’s hemoglobin and hematocrit (iron) levels while on her period is not significant enough to affect performance (source). Although it’s not ideal to race the first day of your period, you’re actually more likely to perform better that day than had you raced the day before. Additionally, we tend to weigh the most during the PMS phase due to water retention and weigh the least around day 4 of our cycle – and we all know a couple of pounds, even if it is water weight, can actually make a difference over the course of a 26.2 mile race.

Running in the Luteal Phase

Here’s the bad news. The luteal phase affects your body in a lot of ways that lead to not optimal running performance. The good news is that there are a few ways you can combat these negative changes if you’re aware of them.

During the second phase of your cycle, peaking in the final days before your period (aka PMS), your body is flooded with hormones  your progesterone levels increase by the day, leading to your period. Your estrogen level is higher in this phase but is level. The higher levels of estrogen promote fat utilization rather than glycogen. This could be good news for the marathoner, who wants her body to use fat, but could be bad news for those short intervals or 5k runners who are relying on glycogen.

You will also have lower blood sugar during this phase, which unfortunately results in lower lactate thresholds. The good news is, lactate threshold is largely determined by your training, not your hormones, so the impact isn’t severe. You can definitely make up for racing during your luteal phase by simply being well prepared for your race.

Your core body temperature increases in the luteal phase as well and remains that way until your period. This means that it’ll be harder to cool yourself down, especially in higher temperates. A woman’s plasma blood volume decreases on average by 8% during this phase, which means you will be slower to start to sweat and cool yourself down. If you’re racing or doing a hard workout in this phase, you’ll want to pre-load your workout with a sodium rich drink to combat dehydration.

Running on Birth Control

This could be a whole separate article (and I found one here if you want to read on). The truth is, no clinical studies have been done on birth control’s impact on running. However, research suggests that birth control use may have small negative effects on things like strength gains, Vo2 max, and aerobic capacity in elite athletes (source). Some researchers don’t believe it negatively impacts running at all. Professional runner Steph Bruce has been quoted saying she’s never been on birth control because she does believe it affects her running. To sum it up, I don’t think we can really say whether or not the pill is going to truly affect your running but if you are simply a recreational runner, I’m pretty sure the benefits of your contraceptive method of choice far outweighs the potential downside.

I should note that if you are on the pill, everything I mentioned above about the phases of your cycle affecting your running doesn’t matter becuase your hormone levels remain the same throughout the month.

Running While Pregnant

Again, another article that could be written separately, but I will note that all of the downsides of the luteal phase that I mentioned are amplified in pregnant women, who essentially remain in an amped up luteal phase for 9 months. I remember feeling a significant impact on my running soon after getting pregnant.

What To Do With This Information

There are a few things you can do with this information. You can start tracking your cycles using various apps (I use Fertility Friend Tracker) and then alter your training and expectations depending on where you are in your cycle. During the first half of your cycle, ride the high! During the second half, be sure to get in extra electrolytes, extra fluids, wear cooler clothing, eat extra carbs, and perhaps give yourself a break if your paces aren’t where you usually see them. Recognize that you are more likely to overtrain and under-recover in the second half of your cycle so give yourself extra rest time.  And most importantly, don’t give up on a race just because it’s going to happen in the luteal phase or while you’re on your period! Your training is a FAR better predictor of your success than your hormone levels.

Do you take your menstrual cycle into consideration when running and racing? Have you ever done any research yourself on this topic? Ever had a great race while on your period?