Cutting Through the Confusion of Cycle-Sync Style TrainingApr 06, 2023
Tracking and training with your menstrual cycle helps you dial in your fitness with your physiology.
It’s well known that I advocate tracking and when appropriate adjusting training and nutrition to align with the physiology of the menstrual cycle and the individual’s responses to her hormones. I came to that position over a decade ago from working with elite and professional athletes, and have been refining it ever since based on a wide array of female physiology research findings.
For example, did you realize your immune system has a significant shift at ovulation, moving to a pro-inflammatory response state, and the autonomic nervous system is affected by progesterone, increasing a woman’s sympathetic drive? Both of these decrease stress resilience after ovulation, in particular during the late luteal phase. From a training point of view, it would not be advantageous to push hard/over reach that stress resilience and expect positive adaptations. This is the prevailing pattern I have found during my years of working with elite and professional athletes (and being an athlete myself) and by looking outside of sport science research. I have been refining this style of training as science evolves and more women are open to discussing how their cycles affect them (physically and psychologically).
Research evolves as it always does (which is great!) and some recent research has some questioning the worth of tracking and training with the menstrual cycle. Before I dive into that, I want to highlight that there is an important difference between performance and training. Because I never tell a woman to rearrange her race or competition schedule according to her menstrual cycle. She’ll be fine (barring some extreme episodes we’ll get to in a minute) on any day.
When you have to perform—whether it’s the Boston Marathon, CrossFit Games, or when, say, there’s a team of scientists gathered around you in a laboratory setting—your sympathetic nervous system kicks in causing blood pressure, heart rate, and respiratory frequency to rise and performance capacity to improve. We’ve all had the experience of travel delays, poor nutrition, lousy sleep, and maybe even a little illness before an A event, but once the gun goes off, so do we. This isn’t new news. Remember Paula Radcliffe publicly broke the world record for the fastest marathon in Chicago in 2002 while she had menstrual cramps!
But what if you were trying to train against your physiology as a matter of routine? You could of course. But is it optimal? I don’t believe it is. That’s why I recommend getting to know your cycle and training with it, so you take advantage of your physiological strengths at every phase and, importantly, learn how to mitigate any physiological effects that may make peak performance harder to hit.
This includes nutritional adaptations, which get overlooked in this conversation. For instance, during the high hormone phase, your body is busy building the uterine lining, so your metabolic rate comes up, your protein needs increase by about 12% (building tissue here!) and you need more calories to support this. Estrogen and progesterone work to shift your reliance on carbohydrate and shuttle it to the uterine lining to have rich glycogen stores for a fertilized egg, while increasing fat-burning and fatty acid availability. This is great for endurance activities, but you’ll need to eat more carbs for high-intensity activity to keep carbohydrate available for the muscles’ hard work. Your body also does not use or store carbohydrates as effectively in the luteal phase as in the follicular phase. Adjusting your training and/or nutrition just makes sense to get the most out of those sessions.
There’s more, of course. The natural fluctuations of these powerful biochemical messengers impact your exercise metabolism, the fuels that you burn and spare, your plasma volume levels (which are needed to sweat), how well you tolerate heat, your moods, your reaction time and neuromuscular coordination, blood sugar levels, breathing rates, muscle cell turnover and protein synthesis, and more.
So while research shows that key performance indicators such as max VO2 and lactate threshold remain constant throughout your cycle, so you can still score a personal best even with PMS in endurance sports, the story doesn’t stop there. There’s more we can do to understand and optimize our performance. That’s why you’re seeing menstrual cycle tracking working for elite athletes like the U.S. Women’s National Soccer team, who have found that it helps them connect what they’re feeling–poor sleep, food cravings, mood changes–during parts of their cycle to concrete steps to work with their physiology and maintain elite level performance.
What About Conflicting Findings?
Okay, so what about recent research that some argue shows the menstrual cycle has no meaningful effect on performance and/or that there’s no evidence to merit tracking and training with your cycle?
The first paper has a conclusion I agree with: that the menstrual cycle shouldn’t disqualify women from exercise research. Amen to that. We are in need of more women in exercise studies. (I will add that they should be included and the phases of their menstrual cycles should also be noted.) Some have interpreted it to mean that we shouldn’t take it into consideration in our training, which to reiterate what I said earlier, training is different from performance.
In this study, researchers put seven women and 10 men through a series of three ramped cycling tests to failure. They had them pedal at 85 to 95 revolutions per minute on electronically braked cycle ergometers. They started at 50 watts and the resistance went up by 1 W every 3 seconds until their cadence fell for more than 5 seconds despite strong verbal encouragement.
The women performed this test at three points during their menstrual cycle as confirmed through blood draws and ovulation tests. The men performed them at 10 day intervals. As the participants performed the trials, researchers measured heart and respiratory rates to assess performance.
Although the female participants often reported that their menstrual cycles affected how they felt during exercise and how well they expected to perform, there was no measurable change in performance. They didn’t see a decrease in performance regardless of phase, despite what is known about how hormones like estrogen influence endothelial function and how blood flows to the muscles.
Again, here I’d point to the differences between training and performance outcomes. Also, this study (and others I’ve seen) rule out women with menstrual cycle dysfunction or disorders. By definition disorders can include PMS (premenstrual syndrome), menorrhagia (heavy bleeding) or dysmenorrhea (painful cramps), which can impact 35 to 40 percent of women, maybe more. That percent of this population may especially benefit from tracking and training—and their performance may be more profoundly impacted, as we’ve seen in professional sports.
Also important to note, this study did find meaningful sex differences with regard to performance, even after normalizing for body composition, and they conclude that male-only data within the literature may not apply to females.
The second study is a research review that includes 5 systematic reviews and meta-analysis looking at menstrual cycle phase-based resistance exercise training outcomes in young, healthy eumenorrheic women with no known menstrual cycle dysfunctions. After addressing the literature showing that estrogen signaling may influence some pathways and processes that influence resistance training muscular adaptations, including protein turnover, myosin function, and satellite cell activity, and acknowledging that a long-term decline in hormonal levels (as in menopause) is likely detrimental, they questioned whether short term hormonal fluctuations throughout the menstrual cycle that occur over several days so profound that fluctuations influence acute performance and long-term muscular adaptations to resistance training?
What did they find? A fair amount of subpar research with conflicting outcomes, leading them to conclude:
“In the absence of high-quality evidence to support designing resistance training programs based on menstrual cycle phase, coaches and athletes should tailor an exercise plan to the individual. The influence of the menstrual cycle could be a factor to consider in program design, along with a host of other factors: nutrition, fatigue, sleep quality, stress, injury, motivation, and program enjoyment. We acknowledge that menstrual symptoms can influence exercise performance in some women, and thus it would be helpful to document this for reviewing long-term progress and adjusting a program. When reviewing the evidence as a whole—and the methodological shortcomings therein—we propose it is highly premature to conclude that short-term fluctuations in ovarian hormones appreciably influence acute exercise performance or longer-term adaptations to resistance training. Thus, the development of RET [resistance exercise training] prescriptions based on cyclical hormonal changes is not an evidence-based approach.”
Am I surprised by this conclusion? No. Not at all. When we look at sport science literature as a whole, you’re pulling from a historically male-dominated body of literature, meaning that often the studies are underpowered in the moment. So, post-hoc analyses are employed to look for differences in studies that were not designed to investigate differences (e.g. the study designs are usually designed from a male model and applied to women).
So, a lack of cohesive, strong evidence from sport science literature does not mean “no evidence,” but rather that the statistical analyses used did not pick up strong effects. Because the number of participants in sport science studies are often small, the finer nuances that would be a real effect in large randomized control trials are often lost or not detected (again, the studies do not have adequate power). The meta analyses and systematic reviews do not include case studies and case scenarios, which often give longitudinal data on elite populations. I suggest looking outside the field and at emerging research across cell biology, fertility/endocrinology, and computational biomechanics, as well as reading case studies and case series reports in sport and exercise medicine (note to self, get on to publishing the case series data that I have accumulated over the years!).
Importantly again, like others, this analysis specifically excludes any women with “known menstrual cycle dysfunctions.” I would want more clarity on that, as some studies specify “dysfunction” (i.e. a lack of regular menstrual cycles) while others specify “dysfunction or disorders”. That’s a huge pool of women if we’re excluding women with PMS, heavy bleeding, and/or cramps. A 2022 study from 1,086 athletes from 57 sports at different performance levels found that menstrual cycle-related symptoms were common across all athlete levels, particularly dysmenorrhea, or painful cramps associated with menstruation (74%, n = 300) and premenstrual symptoms (78%, n = 318), which also influenced perceived performance of aerobic fitness, muscle strength, mental sharpness, balance, and sleep quality. That’s important!
Finally, I am aware that studies such as these may be choke points for those who are looking for published studies on which to base their training and coaching. I understand this, as I would be the same if I did not fully understand the way these reviews are conducted and how mass media jumps on a singular concept while missing the nuance, or the larger picture.
There is no question that the human body–including the female human body–is not an algorithm, and there are individual differences that should be the cornerstone of any training. There is also no question that millions of women feel real, measureable, meaningful impacts of their menstrual cycle. They are empowered by the emerging sports culture that acknowledges the impact the menstrual cycle can have and by understanding, talking about, and working with their cycles. There are women of all levels, including the most elite, who thrive on the current protocols designed for women by women to acknowledge sex and hormone differences.
Science is never “settled.” It evolves. We will continue to learn. We are in need of gold standard, robust randomized controlled trials to get baselines for all women. Those may be a long time coming. In the meantime, I encourage you to know your own body as completely as possible, and to track your cycles and know how your hormones affect you on an individual basis, and to continue to follow emerging research, especially that which is adequately powered around female physiology.
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