The Importance of the Menstrual Cycle on Training and Racing
Coaches, let me ask you a question. Do you talk with your athletes about their period? Can you even say the word "period" or "menstruation" without blushing and lowering your voice to an inaudible whisper? If not, there is a big f---ing problem and we need to change that, immediately. Athletes, this is important for you as well because your time of menstruation will have an enormous impact on your training, nutrition and performance, regardless of your level of fitness. Only recently have professional athletes begun to talk about menstruation in the public eye and it is unfortunately met with discomfort and we need to change that.
One of the first things that you are taught in scientific research is to use male subjects in experiments. When asking the reason for this, you are always given the same answer: the estrogen cycle causes too much variability in results. I get it. When looking for the smallest bit of statistically significant results, variability is your arch nemesis... but there is something so inherently wrong about this when nearly half of the worlds population is female. It is because of this "variability" that mostly all scientific research is directly applicable to the male athlete but only indirectly applicable to the female athlete. It has essentially been assumed that women are physiologically the same as men (albeit typically a little smaller in stature) even though their physiological differences were the reason they were excluded from the studies in the first place... Make sense to anyone else? Me either. Thankfully, the work of people like Dr. Stacy Sims is beginning to change all of that.
I have been reading Dr. Sims book, co-authored by Selene Yeager, titled: "ROAR: How to match your food and fitness to your unique female physiology for optimum performance, great health, and a strong, lean body for life" and would recommend it to any/every coach and female athlete. I will try to touch on a few important points here but this is an area of research that can take a lifetime, quite literally, to study. So please, dive into the research yourselves for a more in depth perspective.
*If you do not wish to learn about sex hormones and how they are produced, skip ahead to the BOLD TEXT for a TL;DR (too long; didn't read) and what you can do to be a stronger athlete.
To start, we need to understand hormones a little better. How the hell do we do that when we have no idea what they are in the first place. Believe it or not, it all starts from cholesterol. Yes, the thing you were made to believe is incredibly dangerous to your health is literally the building block (poor choice of term - cholesterol is actually being metabolized, aka broken down... The complete reverse of a building block but you get my point) of your hormonal health. Not to mention it's importance in molecular transporting, cell signaling, nerve conduction (allowing you to move those fingers of yours so precisely), etc... I digress. Cholesterol is a type of lipid, which is a fancy way of saying fat, that is made by all animals. It is a vital part of every single eukaryotic cell (every cell except the essential bacteria in your gut) in your body and makes up about 30% of the cell membrane (think of this as the skin of the cell) giving it it's fluidity. Essentially, if it weren't for cholesterol, we wouldn't be able to move and we definitely wouldn't be having this conversation.
Cholesterol also breaks down into pregnenolone. Pregnenolone is a neurosteroid ("neuro": relating to nerves or the nervous system and "steroid": a molecular compound primarily made of four carbon rings in a specific configuration... not necessary to know for this article). What this means is that pregnenolone can affect the function of neurons but it is also the precursor to molecules known as progesterone and Dehydroepiandrosterone (DHEA). Lets follow the progesterone pathway first, because you have probably heard of this molecule before.
Gonadal steroidal hormone development through the metabolism of cholesterol. Image from: Häggström M, Richfield D (2014). "Diagram of the pathways of human steroidogenesis". Wikiversity Journal of Medicine 1 (1). DOI:10.15347/wjm/2014.005. ISSN 20018762. - Self-made using bkchem and inkscape
Progesterone is another steroidal hormone that belongs to a class known as the progestogens. It is actually the only naturally occurring progestogen in humans. Progesterone is also a neurosteroid and is a vital precursor to corticosteroids, androgens and estrogens. You are likely familiar with cortisol, a corticosteroid that is released in response to stress and low blood glucose. Cortisol acts to increase blood sugar, aid in the metabolism of fat, protein and carbohydrates, and to suppress the immune system (a synthetic form is often used as a pharmaceutical). However, elevated and consistent levels of cortisol have been shown to have adverse side effects including a decrease in bone formation.
Progesterone can also be metabolized into androgens, which among other things, promote sex differentiation and enlargement of skeletal muscle. More specifically, progesterone is metabolized to androstenedione. DHEA, which was mentioned early as a metabolite (the product of metabolism) of pregnenolone, is also an androgen which can be converted into more androstenedione. The primary and most well known androgen is testosterone which is produced by the breakdown of androstenedione. Here is where things get interesting, to me at least. Testosterone is either converted into a molecule known as Dihydrotestosterone (DHT) which is 2-3 fold more potent than testosterone itself and is vital to the development of the penis, scrotum and prostate in the developing embryo (and may also be at the root of male pattern baldness) OR testosterone is converted into estradiol, the most common form of estrogen!
Here we are, estrogen. Estrogen is actually a group of steroidal hormones that stimulate female reproductive organs on top of numerous other processes. Technically there are 3 naturally occurring forms of estrogen (estrone, estradiol, estriol) and a fourth that is only produced during pregnancy (estetrol; produced by the fetal liver). For the sake of time, I will lump these three main forms of estrogen together however it is important to note that they all have different concentrations (and locations) with estradiol being the most abundant form in females of reproductive age.
All of the above are steroidal hormones, meaning that these molecules can easily pass through cell membranes and affect protein expression which can have a huge impact on the overall physiology of the athlete (or person). It is also important to note that these sex steroid hormones (gonadal hormones) can easily pass the blood brain barrier having an effect on emotional states and behavioral responses. Finally, and most importantly, all of these hormones are present in BOTH males and females, however it is the concentrations of which that is the difference.
**TL;DR
Cholesterol breaks down into pregnenolone, which can either break down into progesterone or androgens (testosterone). Progesterone further breaks down into corticosteroids (cortisol, the stress hormone) or more androgens. Androgens, break down into estrogens. Therefore, women are more complex and more evolved than men... Well, not really because all of these hormones are present in ALL healthy human beings, just at different concentrations.
Now for an introduction, or hopefully refresher, on the menstrual cycle. This is a "cyclic" fluctuation in hormones that prepare the ovaries and uterus for pregnancy. The average age of onset for menstruation is 12 years of age (and getting younger) and the average age of perimenopause and subsequently menopause (cessation of menstruation) is 51 years of age. For the purpose of this article, I will be discussing the ages between 12 and 51 when the menstrual cycle is applicable. I will also be ignoring hormone supplementation such as birth control.
The typical menstrual cycle (although there is nothing typical about it) is described as 28-29 days. I say that there is nothing typical about this because there is an incredible amount of variation in the length of a menstrual cycle between individuals. This is why being able to talk to your athlete is so important. For the purpose of this article, we will take the textbook average of 28 days. The menstrual cycle is typically broken down into two phases, each consisting of 14 days: 1) follicular phase where the ovaries are maturing the egg before ovulation (dropping of the egg) and 2) the luteal phase where the uterine lining is thickening and preparing for implantation of the egg. Day 1 marks the onset of menstruation or vaginal bleeding (which is actually the expulsion of the uterine wall) which can last anywhere from 2-7 days and can be mild, moderate or heavy. Ovulation typically occurs around day 14 or 15 (or the midpoint of the menstrual cycle). The final day (day 28 in our example) is immediately prior to vaginal bleeding. *Note: sometimes a third phase is included in the menstrual cycle and is known as the ovulation phase.
Now, lets look at our estrogen cycle diagram and at our progesterone cycle diagram to talk about why monitoring this rhythm is so important in the female athlete. Estrogen and Progesterone have been shown to affect temperature regulation, fluid regulation, carbohydrate vs fat metabolism and even fatigue and perceived effort due to the fact that they cross the blood brain barrier.
Estrogen concentration over the course of an average menstrual cycle. Image by: Häggström, Mikael (2014). "Reference ranges for estradiol, progesterone, luteinizing hormone and follicle-stimulating hormone during the menstrual cycle". Wikiversity Journal of Medicine 1 (1). DOI:10.15347/wjm/2014.001. ISSN 20018762
Progesterone concentration over the course of an average menstrual cycle. Image by: Häggström, Mikael (2014). "Reference ranges for estradiol, progesterone, luteinizing hormone and follicle-stimulating hormone during the menstrual cycle". Wikiversity Journal of Medicine 1 (1). DOI:10.15347/wjm/2014.001. ISSN 20018762. - Own work
During the follicular phase (aka the low hormone phase) estrogen and progesterone have dropped substantially signaling the uterine lining to be discarded. Early in the follicular phase is where men and women are the most similar in terms of the concentration of sex hormones circulating in their body. Some scientific research has even gone to the extent of including women in their research if they are in this phase of menstruation because of the lower variability resulting from low estrogen and progesterone levels. While in the follicular phase, women can follow most of the published data on endurance sports and training, minus significant fasting or a ketogenic diet, in my opinion. Women should have a baseline level of 130-140g carbs (still low carb) per day (520-560 Cal) for the proper function of biological systems (leave a comment below if you want me to explain why).
In the low hormone phase, women can access stored carbohydrate (glycogen) very well, their core body temperature is stable around 98.6°F (37°C), there is less central nervous system fatigue and the athlete is able to push high power and set PR's. The female marathon world record was actually set by Paula Radcliffe of the UK while she was suffering from menstrual cramps! It's important to note that the first 3 days of menstruation can be highly variable though, especially due to the severity of cramps. This can be mitigated slightly by a loading phase of fish oil (1g/day) or magnesium or white willow bark in the week leading up to menstruation. *Talk to a licensed doctor or nutritionist before trying this. Ovulation is preceded by a large surge of estrogen around 12-14 days (the ovulation phase if its included).
During the luteal phase (aka high hormone phase) the athlete is more prone to catabolize (breakdown) muscle and protein due to the hormone shifts, so having a more conscious approach to how you fuel an train is important (more information following). There is evidence that increases in estrogen and progesterone climb to highest levels 5-7 days before the period starts (this is a measure of combined hormone levels, not estrogen or progesterone alone). This peak is when most athletes have a lot of problems with bloating and fatigue due to fluid retention in the cells and central nervous system fatigue. Increasing estrogen and progesterone also leads to a drop in plasma volume by about 8%. Plasma is the water in your blood (also contains various hormones, minerals, proteins, etc.) that aids in sweat due to vasodilation of the capillary beds at the skins surface, diffusion of plasma through sweat glands and evaporation off the skin. This along with an increased sweat rate makes your blood thicker which can cause your heart to work a lot harder to produce the necessary cardiac output to support your working muscles. On top of the reduced blood plasma volume, your body kicks out more total body sodium which brings the athlete closer to hyponatremia (a dangerously low level of sodium in the blood). Females are already at risk for hyponatremia due to a smaller stature, so this is exceedingly important to monitor. It has also been shown that there is up to a 10% increase in metabolism during this high hormone phase. This coupled with the fact that estrogen spares carbohydrate (making glycogen more difficult to access forcing you to rely predominantly on fat as your primary source of fuel) and progesterone is highly catabolic (breaking down muscle) means that nutrition and recovery is paramount in this phase. This makes hitting those high intensity sessions much harder, even when ignoring the central nervous system fatigue associated with the high hormone period. Finally, the high hormone levels increase core body temperature up to 0.9°F (0.5°C). This means it is a shorter time to fatigue (often controlled by core body temperature and the reason cheetahs can only run very short periods of time) and makes it much more difficult to race in warm conditions.
So what do you do? It's actually pretty simple. In the high hormone phase, you should increase your carbohydrate and protein intake. Particularly around and during training sessions. Consider eating some protein and carbs an hour before your session and supplementing with carbs and BCAA's (particularly leucine because you need a minimum tissue level to stimulate muscle repair and adaptation) during your longer or higher intensity sessions. Be sure not to miss your recovery nutrition as well, which will stop the catabolism of muscle and restore any glycogen you did tap into (see the leucine comment above). Increase the amount of salt in your food and DO NOT drink just plain water while exercising. Make sure to hydrate adequately with cold beverages as much as possible during training and racing to offset the increased core body temperature and delay your time to fatigue. Most importantly, it may not seem like it but your menstruation week is prime time when it comes to performing, so hit those intensities and hopefully your races fall in that time frame as well. If not, don't fret and follow the advice above and you will likely still hit those PR's.
Finally, a comment on amenorrhea (the abnormal absence of menstruation). Short but to the point. This should never happen and if it does, seek help IMMEDIATELY. This is another reason it is absolutely imperative that you are able to talk with your coach/athlete about this. This can be the result of so many factors including under eating, stress leading to the pregnenolone steal, or a whole host of other reasons. The key is, don't wait. Your PR is not worth sacrificing health! Hope you found this article insightful but most importantly, thank-you to Dr. Sims who is helping pioneer the work in the field.
- Tom
* I am not a physician, I am a molecular biologist, and this is not meant to diagnose or imply treating abnormalities yourself. If you notice problems with your menstrual cycle, please seek professional help.
Did we find a cheat sheet on how to delay muscular fatigue in endurance sports? Find out here!
Additional Resources:
Effects of Female Reproductive Hormones on Sports Performance