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Historically, physiological research on female athletes has been limited in comparison to male athletes. The major contributing factor to this dearth of information is a belief that it’s simply “too complicated” to study women—their monthly menstrual cycle and resulting hormonal fluctuations skew otherwise straightforward results. The lack of research on this topic means data collected on males is extrapolated to females, and female athletes usually train based on recommendations made for male athletes.
But in the past few years, researchers have begun to dig deeper into sex differences in sports science. In doing so, they’ve discovered hormone fluctuations aren’t a complication; they’re actually key to understanding and optimizing athletic performance in women. Hormones like estrogen and progesterone rise and fall throughout a woman’s month-long menstrual cycle, influencing everything from how she performs in training or racing to how she recovers. Some studies have found hormones may affect ligament laxity, suggesting injury risk may increase at various stages of the cycle. There is also evidence that when hormones fluctuate, so too does a woman’s body’s ability to maintain proper hydration levels, metabolize nutrients, and regulate body temperature—unique factors critical to female athletic performance.
“With more women participating in sport and exercise, our understanding on how to optimize not only women’s performance, but health and well-being, must also increase,” said Kelly McNulty, sports physiology researcher, PhD candidate at Northumbria University, and founder of Period of the Period.
A growing body of evidence suggests that when female athletes adjust their training to fit with their menstrual cycles, they perform better. To align the two, most use period-tracking apps, which help women monitor where they are in their monthly cycles. Some apps even make recommendations on what kind of training to do (or avoid) and when. Though such apps can be enlightening for female athletes looking for insights on their individual physiology, McNulty and her colleagues warn that there currently isn’t enough research to make standard recommendations related to period tracking and sport performance. (Many of the non-sports-focused apps are also primarily aimed at fertility, not performance.)
“Whilst scheduling performance and training based on the menstrual cycle is an interesting concept, and to some degree very popular at the moment in the press, there is simply not enough published, high-quality evidence to suggest guidelines for practice,” McNulty warns. “Far more research needs to be done on this topic before such recommendations would be appropriate or warranted.”
That doesn’t mean that period tracking is a waste of time; only that experts aren’t at the point to confidently say “on X day of the cycle, women are best off doing Y workout and recovering with Z food.” McNulty says the information period-tracking apps give is often generic, and given the variety in menstrual cycle experiences among women, the information presented might not always be suited to the specific athlete.
While women wait for the scientific community to endorse a substantial body of evidence, there are still things athletes can do, McNulty said: ”If you are a female athlete or a coach/practitioner supporting a female athlete, then I recommend that you dive into the research and learn all you can about the potential effects hormones can have on women’s physiology. But do this with a critical eye.”
McNulty also says women can develop their own “bespoke athlete guidelines,” where each athlete uses her own expertise of her own body to identify patterns in performance. “When you learn more about your own menstrual cycle—what symptoms you experience and how you perform, train, and recover on certain days—you can use your knowledge and understanding to determine what bits of the research might apply to you and which don’t. From there you can begin to tweak and adjust things to maximize or manage performance/training depending where you are in your cycle,” she said.
It’s in these individual experiences of the menstrual cycle—not the advice of an app—where the biggest insights lie. “Every woman is different, and the research is only the beginning from which we can build our individualized content from,” McNulty said. “But this only happens if we understand our bodies first.”
Period Tracking for Athletes 101
Tracking the menstrual cycle can be as simple as circling a day on a paper calendar or marking an X in your smartphone on the first day of your menstrual flow, or period. The menstrual cycle is counted from the first day of one period up to the first day of your next period. The average menstrual cycle is 28 days long, but each woman is different. Some women’s periods are so regular that they can predict the day and time that the next one will start. Other women experience menstrual cycles that vary in length. Medically, periods are considered “regular” if they usually come every 24 to 38 days.
That menstrual cycle is further divided into four phases:
- Menstrual: Period “bleeding” begins when levels of the hormones estrogen and progesterone drop. Duration: 1-7 days.
- Follicular phase: The time between the first day of the period and ovulation. Estrogen rises as an egg prepares to be released. Duration: 10-22 days.
- Ovulation phase: The release of the egg from the ovary, mid-cycle. Estrogen peaks just beforehand, and then drops shortly afterwards. Duration: 12-24 hours.
- Luteal phase: The time between ovulation and before the start of menstruation. Progesterone is produced, peaks, and then drops. Duration: 9-16 days.
The length of each phase can differ from woman to woman, and it can change over time. The way each woman responds to these hormone fluctuations in each cycle can vary as well; some feel a pronounced effect on their endurance or energy levels, while others notice very little.
If you want to track your period and performance, then, addition to recording the start dates of each menstrual cycle, you may want to track additional data that will help you identify patterns. In an athletic context, a training log may be the best place for this information, as it will allow the user to more clearly see parallels between where she is in her cycle and how she performed:
- How many days your period lasted: Was your period shorter or longer than the month before?
- Daily changes in vaginal discharge: clear/white, thick/think, sticky/slippery
- Workout performance: What did you do? Did you hit your goals for the workout? Did it feel harder or easier than when you have done this workout before?
- Recovery: Soreness, new injuries or flare-ups of pre-existing injuries
- Hunger and thirst: What did you eat after your workout? Was this satisfying? Were you more thirsty than usual?
- Premenstrual syndrome (PMS) symptoms: cramping, headaches, moodiness, forgetfulness, bloating, breast tenderness
You can also download apps (sometimes for free) to track periods. While many period-tracking apps are focused on ovulation and fertility, a growing number (like Clue and Flo) allow women to log exercise and energy levels. Several activity trackers (including Garmin and Fitbit) have also added period-tracking functions to their logs.
There are also specialized fitness apps targeted specifically to active women popping up more recently. FitrWoman syncs with Strava, allowing the user to see daily activities alongside menstrual cycle data. Coach management software AthleteMonitoring is designed to help coaches plan light or heavy workloads according to each athlete’s individual cycle in order to maximize performance while minimizing the risk of injury. It also detects and flags irregular cycles and potential medical issues, offering proactive recommendations for users and coaches.
Whether you go the pencil-and-paper route or download a tracking app, the premise is the same: record the same information every day, and patterns will begin to emerge with time. “No matter your method of tracking, I would encourage athletes to track for at least three months to allow meaningful conclusions about their cycle patterns to be made,” McNulty said. “Collect your own data, look for patterns, and make reasonable adjustments, using the evidence base to inform your decisions.
A Note on Birth Control
There is very little research on various oral contraceptives (ie. the pill) and its effects on performance, training, and recovery. There’s even less on other contraception methods, such as IUDs. Even though these methods can regulate a woman’s cycle (or even eliminate a period altogether), they don’t make the hormones that come with your period disappear. “I think it’s just as important, if not more important, for female athletes on hormonal contraception to take control and track,” McNulty said. “My advice is to track what symptoms you experience and how you perform, train, and recover at different points during your pill cycle or whichever hormonal contraceptive ‘cycle’ you are on.”
This is especially true when switching from one hormonal contraceptive to another, or transitioning on or off hormonal contraceptives. “This will give you the best personalized information,” McNulty said. “This will enable you to make a plan and advocate for yourself when talking to your doctor or support team about your choice of hormonal contraception to make sure you are taking the one that suits you best.”
Red Flags in Period Tracking
Talk to your doctor or nurse if you have menstrual cycles that are longer than 38 days or shorter than 24 days. In addition, consult your health care provider if:
- Your periods suddenly stop for more than 90 days (and you’re not pregnant)
- Your periods become erratic after having been regular
- You bleed for more than seven days
- You bleed between periods (also known as “spotting”)
- You develop severe pain during your period
- You experience extreme mood changes during your cycle
Want more information about the research (or lack of research) on female athletes? Check out this Endurance Geeks’ deep dive.