Exercise and the menstrual cycle
This article was authored by Meg Doohan, PHD candidate & SOF internship alumni.
Alright Ladies and Gents, it’s time to talk about the menstrual cycle.
That’s right boys, this is important for you to know about as well. The menstrual cycle is a physiologically amazing process, and an incredibly important function for survival, health status, psychological well being, cognitive performance, and for our specific focus - exercise performance.
We’ve recently realised that a lot of the women we train with, or spend time around, don’t know a whole lot about what effect the menstrual cycle can have on their exercise performance. So, using what we do know, we’re here to debunk a few of the myths that coincide with the proposed effects the menstrual cycle can have on exercise performance.
First thing’s first. Let’s take a quick re-cap of the basic mechanisms of the menstrual cycle. Bearing in mind that the days noted in this explanation are typical of a 28-day cycle. We recognise that many, many women, do not experience strict 28-day cycles, or use differing forms of contraception to regulate their menstrual cycle, so take this explanation as your textbook definition.
The follicular phase:
This phase begins on the first day of the period. During this phase, the body sheds the outer linings of the uterus to expel the unfertilised egg from the body, and prepare the body for the start of the next cycle. Generally, levels of progesterone and oestrogen in the body are pretty low at this point, with the lowest point of hormonal concentrations occurring at around day three. The follicular phase covers the entire of the menstruation stage and beyond – lasting for between seven and twelve days on average.
Next comes the ovulation phase:
This occurs straight after the follicular phase, lasts only a few days, and generally occurs right in the middle of the cycle. During this phase, oestrogen levels are high, as the ovaries work to release the egg into the uterus, while progesterone levels stay low.
Finally, we have the luteal phase:
The luteal phase is generally the longest of the phases, and lasts until the end of the cycle – just before the period begins again – so can stretch for a few weeks at a time. During this phase, both progesterone and oestrogen levels reach their peaks at around day 21, and attempt to support a potential pregnancy. If the egg remains unfertilised, then the process begins all over again.
During this time, oestrogen plays an essential role in the regulation of female sex hormones and reproductive function, while progesterone works to thicken the lining of the uterus, in preparation for either shedding it, or protecting a foetus in the event of the pregnancy. It’s important to note here, that both men and women have these hormones freely floating around in the bloodstream, so they are used for a range of additional physiological processes – it’s just that women have larger concentrations of these hormones to help protect and regulate reproductive processes.
Seems pretty simple, right?
The constantly changing concentrations of hormones can induce a series of physiological and psychological changes within the body, outside of the functions of the reproductive system, all of which may have implications for exercise performance and beyond.
So what else do these hormones do?
A lot, actually.
Oestrogen for example, is exceptionally important in skeletal bone health. This is what makes resistance training in post-menopausal women so vital to continued mobility and performance of activities of daily living. Once a woman hits menopause, the body slows down it’s oestrogen production.
This means that bone matter is not built up as quickly if it doesn’t have mechanical stress placed upon it (i.e.: strength training), so bone health starts deteriorating, and women can experience more fragile bones, and a greater risk of falls and fractures, if left too long. Oestrogen however, is also thought to improve muscle glycogen storage and fat use, while progesterone appears to elicit anti-oestrogenic effects.
This means that it is likely that the two hormones play a game of to-and-fro. As the levels between the two fluctuate, they can independently work to counter-balance the effects of the other.
However, the levels of these two hormones do not always completely work in tandem, meaning that the effects of high levels of one, and low levels of the other, and vice versa, are likely to have a range of effects of a number of physiological processes which can influence exercise performance.
While we don’t yet know everything that coincides with exercising at differing phases of the menstrual cycle, we do have a few important pieces of information to share.
The menstrual cycle does elicit constant changes in internal body temperature. Remember how we said there was a low point in hormone concentration at around day 3 of the cycle?
Well, this also typically coincides with the lowest core body temperature of the cycle – the ‘coolest’ a woman will be. This point typically sits around 36.7 °C, however, can change from person to person. At the other end, at the peak of the hormone concentration, we have the highest core body temperature. This can be around to 37.2 °C – which is an average 0.5 °C change in core body temperature across the cycle. While this might not sound like a whole lot, remember that the human body functions under a strict range of internal environments.
So, even if the body can function at differing core temperatures, when a person exercises – these fluctuations can elicit very different physiological responses.
Think about this, as an example.
You’re an elite marathon runner. You’re racing in 30 °C heat, and you’re currently in the hottest part of your cycle. You’re starting the race 0.5 °C hotter than the woman next to you. You have run similar times for the past few months, but all of a sudden, she has a natural advantage over you. That competitor is starting off with a cooler internal temperature than you. She may not get as hot as you, or as quickly, her sweat response may be slightly delayed, and her respiratory system may not be under as much stress as yours, as it attempts to inhale oxygen, pass it to the working muscles and increase blood flow to the skin surface to allow heat removal from the body.
While this is an extreme example, it is important to note that at the hottest point in the cycle (the mid-luteal phase) women may be more susceptible to heat related injuries or illnesses than at any other point in the cycle. As their internal body temperature is higher, their likelihood of reaching a point at which heat can no longer be removed from the body at the same rate at which it is gained is increased.
This makes it more likely that they will, in these hot environments (such as playing sport in summer), experience heat-induced cramps, stress, or stroke. So practically, what does this mean? While we can’t know exactly what day a woman is at her peak core temperature, there are some things you can do to reduce the risk of dehydration and other heat-induced complications, as a result of intense or prolonged exercise.
This peak is likely to occur 1-2 weeks before the period begins. So, if we can acknowledge that a woman is approaching her potential peak, we can put some practices in place to reduce the risk of heat stress. For example, ensuring adequate hydration is a must, particularly with longer duration exercise. Even in the gym, on those super hot nights of a Primal session – tracking fluid and electrolyte intake can be the difference between a massive dehydration migraine, and bouncing straight back into life the next day.
This doesn’t mean you should be sucking on water and Powerade all day long, but it does mean ensuring the fluid intake is matching how much you’re sweating out, and taking in some salts to replace those lost in sweat.
Now we’re heading into the wishy-washy stuff.
Over the course of the menstrual cycle, some women may feel more fatigued, or sore, or get serious PMS symptoms that make it harder to train consistently during that week. This isn’t just during the period phase, this can be all throughout the cycle, and it’s real. However, to date, there’s not a whole lot of evidence that can say, without a shred a doubt, that, yep – it’s day 14, you’re X% more susceptible to soft-tissue injuries than you were yesterday, or that this week you won’t be able to train near as hard as last week because of where you are in your cycle. And that is simply as a result of the different experiences women have regarding their cycles. Some experience no change, some know that on a particular day, they’re going to feel like they’re getting stabbed repeatedly in the womb, and that’s okay. What we do know, is that as a result of consistently changing hormone concentrations throughout the cycle, different levels of these hormones between each individual, and variations in menstrual flow, there are no clear-cut answers.
Even a recent (2020) meta-analysis of exercise performance across the course of naturally menstruating women with a regular cycle, failed to come up with strong conclusions about explicit deficits or performance improves with menstrual phases; stating that exercise performance (strength, speed, endurance, power) might only be trivially reduced during the early follicular phase of the menstrual cycle (when a woman first gets her period.
This doesn’t really give you that much to go on, does it?
Now we do realise that, and unfortunately there’s not a large amount of literature in this space yet. However, science is pressing forward in leaps and bounds, and we’re positive that in the next few years, we’re going to be seeing more and more in this field – that can help to accurately program exercise sessions around the most vulnerable points in time in the menstrual cycle. So watch this space!
What we do recommend though, is to track your cycle.
Not just days between periods, but how you feel as well. Feeling as though your body is really fatigued?
Note it down.
Note it down next time it happens, and the time after that too.
You might notice a pattern. And if you notice a pattern, this can help you plan the most appropriate exercise regimes around it.
If you know you’re going to be struggling to get to the gym four times in a given week, because you’re feeling fatigued, or more sore than normal, then swap one of those killer conditioning sets for a lighter session instead. It might feel like you’re copping out on your training, but in reality you’re giving yourself more opportunity to recover from the last session, and adapt to the constant physical demands you’re placing on yourself.
The point we’re trying to get across, is ladies: Be kind to yourselves.
The pain you experience during a period, is real.
The excessive fatigue you might be experiencing, is real.
The increased heat and sweating you felt during your last session, is real.
The mood swings you’re copping today, are real.
These are all real experiences by women, as a function of the menstrual cycle, and they can be influencing your exercise performance more than you may think. Stop beating yourself up because you couldn’t lift as heavy today as you did last week. Instead, try working your schedule around the days you know you won’t be feeling your best, as a result of your menstrual cycle. And be open to your trainers and coaches about it. If you don’t let them know what’s happening, they can’t work with you to get the best out of you.
What we need is more coaches and trainers to be on board with the variability of working with female athletes and clients, if science is ever going to be able to inform how we conduct training sessions and competition conditions.
Want to learn more about how individualising training program’s to suit each woman's needs? Take a look at this article regarding how personalising training programs for the USA women’s soccer World Cup Team, was a major influencing factor in their World Cup Win in 2019: https://www.telegraph.co.uk/world-cup/2019/07/13/revealed-next-frontier-sports-science-usas-secret-weapon-womens/amp/?__twitter_impression=true
Also, if you wish to read more on the large-scale effect of exercise performance as a result of the menstrual cycle, take a look at the following link: https://link.springer.com/article/10.1007/s40279-020-01319-3
Let’s end the taboo on talking about periods. Period.