What's The Menstrual Cycle? Can It Effect Sports Performance? Elite Athletes Say YES!

The effect of the menstrual cycle on physical performance is being increasingly recognised as a key consideration for women’s sport, and rightly being called out as an important area for further research. This was further backed up by Dina Asher-Smith’s withdrawal from the 100m at the European championships due to menstrual issues’ and called for more studies to help female athletes fully understand their menstrual cycle, how it links to physical performance, and ultimately how can this information help them achieve their best athletic performance.  Females are different to Males if you hadn’t noticed….… yet the vast majority of sports science studies looking at physical performance and training have been carried out on men. Female sex hormone concentrations change throughout different phases of the menstrual cycle (MC), therefore, we shouldn’t expect the findings of these male dominated studies to extrapolate to females.  It’s not just Dina Asher-Smith who thinks this area needs more scientific attention, a study from 2019 noted that studying the impact of menstrual cycle phase on physical performance was one significant component needed to develop a female evidence base in sports science. Studies have shown that female athletes often subjectively perceive their performance to be relatively worse during the early follicular and late luteal phases.  Studies examining objective performance (using anaerobic, aerobic or strength-related tests) have not yet reported clear, consistent effects of the impact of menstrual cycle phase on physical performance. However, 10,000 meter runner Eilish McColgan has only ever failed to finish in two competitive races, the dreaded DNF as she called it. Both of these occasions were due to menstrual issues. In a recent article on BBC sport website she described her periods at times  ‘feeling like her legs have been replaced with concrete blocks, and a screwdriver is carving out the Taj Mahal around her ovaries.’  She stated that some months, it's manageable. Other months, it's unbearable. There's no telling how she was going to feel on any particular day. To try and run, or at least perform to the best of her ability, is an almost impossible task. We know that sport performance is as much psychological as physical, therefore, to optimise performance and management of female athletes who are menstruating, further research is needed to understand the impact of menstrual cycle phase on physical performance outcomes for each individual athlete.  But what do we know about the menstrual cycle and how it can potentially effect the body during exercise? Before doing some research I was pretty clueless. Let’s get the foundations set by answering the question: What is the menstrual cycle?  It’s a series of events that prepare the uterus for potential pregnancy. The Menstrual Cycle is separated into two distinct main phases, follicular and luteal, but we need to break that down further into sub-phases;  early follicular,  late follicular,  ovulatory,  early luteal,  mid luteal  late luteal. Oestrogen, progesterone, follicle stimulating hormone (FSH) and luteinising hormone (LH) are constantly fluctuating through these sub-phases as shown in this diagram on screen…   The early follicular phase begins with menstruation, which usually takes 4 to 6 days to complete; during this phase, female sex hormone concentrations (oestrogen, progesterone, Follicle Stimulating Hormone and Luteinising Hormone) are all relatively low and stable.  Oestrogen increases as the ovarian follicles (that each contain an egg) mature. When oestrogen rises to a certain level, we get a rapid increase in Luteinising Hormone (LH). The LH spike triggers ovulation (making this the ovulatory phase), here a mature ovarian follicle breaks open releasing the egg into the uterus.  After ovulation we have the early luteal phase; here we see a steady rise in the level of progesterone, and to a lesser extent oestrogen, coming from the ruptured ovarian follicle (now called the corpus luteum) that released the egg….. Progesterone peaks in the mid luteal phase and we also get a second, smaller peak in oestrogen that prepares the endometrium for the implantation of a fertilised egg. The luteal phase ends with pregnancy if a fertilised egg is implanted.  If the egg remains unfertilised, the corpus luteum will degrade, causing a decline in progesterone and estrogen during the late luteal phase as the cycle prepares to restart, with the uterine lining eventually detaching ready for menstruation to begin again.  The timings of each menstrual cycle phase shown in the diagram here are approximate figures, we know that everyone is different, therefore, the timing of ovulation, and the other menstrual cycle phases can vary greatly. So urinary tests that measure the hormone levels (oestrogen, Progesterone, FSH and LH) are used to more accurately identify the menstrual cycle phase the individual is in at that moment in time.  At least 2/3 elite female athletes are eumenorrheic and about half of eumenorrheic athletes don’t use Hormonal contraceptives that can help regulate their menstrual cycle. Eilish McColgan brought up a really interesting point in her article that the presence of menstruation can also be used as a barometer of whether the athlete is over training and under-fuelling. If the athlete is doing this then menstruation is often the first thing to disappear.’  Therefore, even though taking an OCP could help remove or reduce her problem, as much as it causes issues, it also gives useful objective feedback that her body is healthy and has enough surplus energy for menstruation to take place. If it was to disappear she can use this warning sign to alter her training program and/or her nutrition plan.  If you think this video was helpful please remember to subscribe to the channel and like the video. 1.2. Proposed Mechanisms behind Menstrual Cycle Based Changes in Performance It’s been assumed that Physical performance changes over the course of a menstrual cycle. Athletes like Dina and Eilish have voiced their experiences publicly, and that’s really useful as individual case studies. Because at the end of the day, as we said before, even if the current research says that the menstrual cycle doesn’t have any effect on sports performance we already have two elite athletes who feel and have experienced differently.  So what is the current research telling us? What do we know? (Or at least think we know).  We know that Oestrogen has a neuroexcitatory effect. This means it’s going to have a positive effect on movements require high level strength and power outcomes. On the other hand, progesterone inhibits cortical excitability, reducing force production. So there’s a potential tug of war between the two.  So let’s go back to our diagram running through the menstrual cycle and the fluctuations in the different hormones levels….  So, we could guess that greater strength and power outcomes would be produced when progesterone remains low during the follicular phase, and when oestrogen peaks during the late follicular phase. Lower strength outcomes would be expected to be produced in the luteal phase when progesterone levels are relatively higher.  Studies have looked at muscle and tendon stiffness to establish whether any particular MC phase means the athlete is more at risk for soft tissue injuries. Some studies concluded that stiffness is affected by MC phase.  Looking at a sprint athlete like Dina Asher-Smith it’s vital for her tendons and muscles to maintain a high level of stiffness for better storage and use of elastic energy during jumping, sprinting and hopping (all plyometric movements). Eilish McColgan said she made the mistake of pushing training too hard during a particular menstrual phase and tore her hamstring.  It has been suggested in research that the increased concentration of oestrogen in certain phases of the menstrual cycle may reduce tendon/muscle stiffness by decreasing collagen synthesis and therefore collagen density in those connective tissues, but as we speak this is yet to be proven. Results of studies are conflicting.  In one study it was concluded that any increase in oestrogen during the menstrual cycle is not great enough to result in a meaningful change in collagen synthesis and stiffness. Therefore, the effect of tissue stiffness may or may not vary throughout the menstrual cycle and meaningfully impact performance. We always have to allow for individual differences after all. Elevated progesterone during the luteal phase can shift the ‘thermoregulatory set point’. This could potentially negatively or positively impact performance depending on the activity duration. Increased body temperature is known to improve performance in short duration activities requiring speed and power. It’s a favourable environment for muscle contraction. Sprinters will always prefer to train and compete in warm conditions compared to cold conditions. (It would be interesting to see how many world records in sprint events have been set on cold days compared to warm days.)  Because of this it was proposed that the increased body temperature in the luteal phase could enhance short duration performance; however, studies found that if the athlete warmed up sufficiently it negated this difference.  In prolonged activities, like Eilish McColgan in the 10,000m the elevation in basal body temperature is suggested to impose greater thermoregulatory and cardiovascular strain, and potentially limit endurance performance...