Photo Credit: Presca Sportswear
Ten minutes into your session and you feel low in energy, a bit lethargic. You did the same session the week before at ease and felt like you were flying! You had the same amount of sleep, the same breakfast, felt hydrated, have no changes in your mental health… so what’s the difference? It may simply lie with your unique female physiology. As a woman your hormones fluctuate throughout your menstrual cycle. During the first two weeks, the follicular phase of your cycle, oestrogen dominates. Whilst during the second two weeks, the luteal phase of your cycle, progesterone dominates. In general, most women will feel ‘better’ when it comes to training during the follicular phase when oestrogen is high.
Let’s think about physiological changes
Muscle activation, how our bodies burn carbohydrates and fats, and thermoregulation are a few of many physiological factors that are altered by our menstrual cycle, but are they altered enough to affect our physical performance? Oestrogen can enhance force production whilst progesterone can impair it, meaning you might be stronger and more powerful during the follicular phase when progesterone is low and oestrogen is high. Substrate availability (i.e. your energy sources, carbs and fats) and metabolism may also be affected by the menstrual cycle, as oestrogen is proposed to enhance lipid availability in muscle, whilst progesterone limits the burning (“oxidation”) of lipids for energy. An enhanced rate of lipid oxidation could lead to the sparing of muscle glycogen stores and may ultimately delay fatigue.
In relation to thermoregulation, increases in basal body temperature (normal body temperature at rest), such as those seen during the luteal phase, could positively affect performance in activities requiring speed or power (e.g. sprinting, lifting weights). But as some of you are endurance athletes, what about the prolonged activities?
Elevated body temperature during the luteal phase may actually impair performance due to greater thermoregulatory and cardiovascular “strain”, whilst your cooling mechanisms (e.g. sweat rate) are unchanged between phases. There is evidence that during this phase you will also have greater total body water though, which could act as a compensatory mechanism.
Overall, it is clear that your menstrual cycle causes many physiological changes throughout the cycle, depending on the ratio of the hormones oestrogen and progesterone, and these have positive and negative effects. But will any of these changes be large enough to affect performance?
What about if you’re on your period on race day?
This is something most female athletes would not want, but how bad is it to be on your period on race day in reality?
Menstrual symptoms (e.g. bleeding) occur in the late-luteal and early-follicular phases of your cycle, times at which both oestrogen and progesterone are relatively low. Mentally this may affect us (discussed in more detail below), but physiologically is it such a bad thing?
Famously, Paula Radcliffe broke the world record for the fastest marathon in Chicago in 2002 whilst having menstrual cramps! In a study of 16 female runners (of which only 8 had regular menstrual cycle) there was no effect of cycle phase on aerobic performance. A review article also concluded that performance may not actually be affected by menstruation other than the potential adverse effect of the luteal phase on endurance performance due to the increase in core body temperature, which can be prepared for.
Performance isn’t just about your physical performance though… what about psychological performance?
Psychological changes during the menstrual cycle
Your mental state is a key part of being able to train and perform well in endurance sports - especially ultra-endurance sports. Many athletes perceive that their performance fluctuates with the menstrual cycle. It seems that in the early-follicular phase and late-luteal phase, women feel they perform worse, which coincides with menstrual symptoms. Common reasons for this perceived impairment in performance include fatigue or lethargy, as well as distraction by concerns about bleeding. Interestingly, this perception of fatigue may be due to changes in levels of a neurochemical names serotonin. Serotonin has many effects, including stabilisation of your mood. Oestrogen may increase serotonin signalling in the brain, so during the late luteal phase, when oestrogen is lower, lower serotonin levels may contribute to fatigue and lethargy.
For many reasons, people are interested in ways of boosting serotonin, with exercise, bright light therapy and diet all being examined. So it will be interesting to see whether such strategies could be used in relation to phases of the menstrual cycle.
Can you use your hormones to your advantage?
Over the past few years there has been a surge of interest in using the menstrual cycle to our advantage, as well as in differences between men and women in general. As Dr Stacy Sims, author of ‘Roar’ and ‘Eat, Race, Win’, points out, “women are not small men”… so why should we train like men?
If oestrogen is high during your follicular phase and force production is supposedly greater too, should we endurance athletes focus on high-intensity interval training, strength and/or plyometric work at this time? Then use the lower hormone phase, the luteal phase, to focus on more endurance-based work?
This approach could be very powerful, basically using your hormones as your very own performance-enhancing aid, though it is also important to consider the practicality of this strategy.
As females, our cycles vary in length, so there isn’t really a one-size-fits-all approach that could be used. And how we can actually know our hormone levels (i.e. the ratio of oestrogen:progesterone) without blood analysis?
If as a female endurance athlete you are in tune with your menstrual cycle, you could attempt to apply such principles to your training by estimating your cycle phase. Tracking your menstrual cycles could be key to understanding how your hormones may affect your mentality and physical performance. Apps such as Fitrwoman and Garmin Connect allow menstrual tracking, which may help us gain this insight, though it’s important to note that, unless actually menstruating, all of these apps will just be estimating your cycle and hormone levels - without blood analysis you cannot know for sure. Maybe it’s time platforms such as Training Peaks added a menstrual-tracking function so athletes can communicate effectively with their coaches. However, this also requires us to work on the culture change in our (in)ability as a society to discuss periods!
Finally, if as a female, you are not currently menstruating, it is worth speaking to a medical professional. For more on this, check out our recent article on RED-S.
Take home messages
- Hormones vary throughout the menstrual cycle. This may affect your physical and mental performance in both positive and negative ways.
- Having your period on race day is not necessarily a bad thing! But mentally you may feel distracted or uncomfortable, so it may be worth preparing for this.
- Tracking your menstrual cycle could help you understand how your hormones affect you at different parts of your cycle.