Female Runner In Park.
According to experts, understanding how women experience the menstrual cycle is fundamental to sports and performance. (Photo: Ivan Gener/Stocksy)

Everything You Need to Know About Period Tracking

A handful of apps are rebranding the menstrual cycle as a female athlete's untapped superpower. Here's what you need to know about them.

Female Runner In Park.
Ivan Gener/Stocksy(Photo)

Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

“Track your period and train smarter.” That was the promise of FitrWoman, an app I downloaded on my phone last fall. I’d decided to try it out because my fitness level seemed to drop off precipitously last year. Even though I was healthy and there were no major changes in my training, my endurance tanked. My joints and muscles were unrelentingly tight and brittle. My body didn’t seem to recover—ever. I’d have one or two good weeks followed by a lackluster one where I could barely rally to run more than three miles and do some physical therapy exercises. The cycle repeated over and over.

All year, I tried every trick in the book to get back on track, but blindly following the advice of the latest fitness articles and sports research papers felt like a crapshoot (and not a very smart strategy). I was desperate for some concrete guidance. When nothing else seemed to help, I wondered if I should pay more attention to my hormones and menstrual cycle. Honestly, even though I’ve written about the myriad ways that women’s cycles can impact health and performance, I don’t regularly think about it in the context of my own life. I don’t compete at a high level, and I wasn’t training for a goal race. I like to run, swim, practice yoga, and play outside as much as possible, and I wasn’t sure my period really mattered. But I’m in my early forties, and recently my period started acting finicky when it used to run like clockwork.

To the extent that I did think about my period, I considered it a liability when it came to sports—a nuisance at best, and a barrier to peak race-day results at worst. And I’m not alone. A 2016 study in the journal PLOS One found that 55.4 percent of female athletes felt that their monthly cycle impacted their training or performance. However, menstruation is usually a taboo and embarrassing topic to discuss with friends, coaches, and teammates—so most women are left with few strategies to mitigate the effects of their cycle on their workouts except to grin and bear it. In fact, according to a 2019 analysis of responses from over 14,000 female Strava users, 72 percent said they have received no education about exercise and their periods.

Yet according to experts, understanding how women experience the menstrual cycle is fundamental to sports and performance. “Women’s physiology changes dramatically across the whole cycle,” says Emma Ross, the former head of physiology for the English Institute of Sport, which supports British Olympic and Paralympic athletes. Hormones like estrogen and progesterone ebb and flow throughout the month, influencing everything from how women respond to training, metabolize nutrients, and regulate body temperature and hydration levels. In other words, my fueling needs and ability to recover from workouts may change depending on whether I’m in a low-hormone phase or a high-hormone phase.

In an attempt to get to the bottom of why my fitness was stuck in the doldrums, I tracked my period for two months using two apps: Clue and FitrWoman.

According to experts, understanding how women experience the menstrual cycle is fundamental to sports and performance.

Let’s back up for a minute. You may remember from biology class that there are two phases of the menstrual cycle. The first phase is the follicular phase, which kicks off when a woman starts her period: the body prepares to release an egg from an ovary and begins to rebuild the uterine lining. Generally, hormones are low during this period but start to rise. Ovulation occurs mid-cycle, when the egg is released. This marks the end of the follicular phase and the beginning of the luteal phase, when hormone levels are generally high and the body prepares to either accept a fertilized egg and support a pregnancy, or the body gets ready to shed the uterine lining.

In the past few years, researchers have begun to dig deeper into sex differences in sports science, with a particular focus on the impact of the menstrual cycle. There is mounting anecdotal evidence that when you adjust training protocols to the specifics of female physiology, athletes perform better. The biggest endorsement for period tracking came last summer, when it was revealed that the U.S. Women’s National Soccer Team—who won a historic fourth World Cup last July—tracked their cycles leading up to and during the tournament. The team implemented training, nutrition, recovery, and sleep strategies based on where each player was in their cycle. Chelsea F.C. Women (a women’s soccer club based in England), the Brisbane Lions Women’s team (an Australian Football League women’s team), and others have also followed suit.

While recognizing monthly fluctuations can be useful, period tracking isn’t a silver bullet. There isn’t enough high-quality research to create evidence-based guidelines, especially given women’s highly variable experiences with their period. In a Twitter thread, Kirsty Elliot-Sale, an associate professor at Nottingham Trent University and a researcher on female physiology, cautioned: “We, the scientific community, have not yet reached a consensus on the direction or magnitude of changes that occur during the menstrual cycle and as such it is impossible for us to guide women’s sport on this basis.” (In July of this year, Elliott-Sale and her colleagues published a meta-analysis of the research on the menstrual cycle and exercise performance in the journal Sports Medicine, and called for further investigation because of the inconclusive results.)

However, menstrual cycle tracking can be an opportunity to empower women to appreciate their own physiology, says Dr. Ellen Casey, associate attending physiatrist in the Women’s Sports Medicine Center at the Hospital for Special Surgery in New York City. “If it’s really true that risk of injury and performance fluctuates across the menstrual cycle, we can either say, ‘That sucks,’ and not deal with it, or we can say, ‘This is fascinating. Are there things we can learn from this? Can we harness these changes and train in certain ways at certain times?’”

In the past, most women have relied on pen and paper to keep tabs on their periods, if they did at all. Today there is no shortage of apps to help women understand their bodies better. It’s all part of the booming “femtech” market, broadly defined as products, apps, and digital services centered around women’s health and well-being. The category is projected to be worth $50 billion by 2025, according to Frost and Sullivan, a marketing consulting firm.

While most period-tracking apps are geared toward ovulation and fertility, a growing number like Clue and Flo allow women to log exercise and energy levels as well as more traditional symptoms like cramps and cravings. Garmin and Fitbit also offer period-tracking functions, so women can make notes on their cycle alongside their runs, bikes, and swims. MyFlo suggests different physical activities that may be more suited to the current phase of your cycle. The app then sorts through your data and looks for patterns and trends.

FitrWoman, which is targeted specifically to active women, takes things a step further: in addition to menstrual cycle and activity tracking, it provides educational snippets on what’s happening in your body based on your current menstrual cycle phase, and offers strategies to mitigate those effects. On the home screen, you can swipe through a few slides and read how hormonal fluctuations may affect your physiology, training, and nutrition. There’s a link to recipes, too, which are tailored to support training and recovery for the phase you’re in.

Each day, I opened the apps, clicked on the calendar (the main hub in both apps), and reported any symptoms I experienced that day. In FitrWoman, I scrolled a single page and chose from 20 different symptoms.

Clue, on the other hand, groups symptoms into nine categories (bleeding, pain, emotions, sleep, energy, cravings, digestion, mental, and exercise). Each category has four options: like cramps, headache, ovulation, and tender breasts for pain; or happy, sensitive, sad, or PMS for emotions. Just swipe and tap to log the relevant symptoms. I also have the option to create custom tags. Each month, I noted when my period started, its flow, and how long it lasted. The apps then predicted when my next period would start.

At first, chronicling daily symptoms was like starting a brand-new puzzle. I was excited to dig in and figure out what all the pieces would reveal about my physiology. For example, I noticed that I typically feel great in the follicular days between the end of my period and ovulation, when my hormone levels are relatively low. I’m happy. I have plenty of energy. And I feel strong during my runs and strength sessions, so I can push myself harder.

On the flip side, during the luteal phase I tend to feel flat, battle daily headaches, and have less energy and motivation to work out. This makes sense, since estrogen and progesterone levels are high, which can lead to bloating and fatigue. I also want to eat all the sweet and salty foods I can get my hands on during this time. “We know that cravings are likely caused by increased insulin resistance in this phase,” says Georgie Bruinvels, an exercise physiologist and the creator of FitrWoman. This can make blood-sugar levels more unstable. Instead of criticizing myself for being lazy and giving into my cravings, I was more proactive about fueling throughout the day to keep my blood sugar stable and switched up harder workouts for yoga, swimming, or a rest day during this phase.

Both apps also let women share information with their real-life coach. FitrWoman uses FitrCoach, a separate fee-based platform on which coaches can see where an athlete is in her menstrual cycle and which symptoms they’ve logged. It also sends a notification if an athlete hasn’t logged a period, which may be a sign of amenorrhea, the absence of menstruation. Amenorrhea can have a long-term impact on a woman’s health and signal the presence of a larger issue like the female athlete triad, or relative energy deficiency in sport (RED-S).

Since many women don’t talk openly about their menstrual cycle, this setup can be a way to facilitate these private conversations, says Adam St. Pierre, an ultrarunning coach based in Boulder, Colorado. Previously, athletes would send him a text or email, or leave a note in their training log when they started their period or if they experienced troublesome symptoms. “It wasn’t super scientific,” he says. “FitrCoach allows for more tracking, letting me make sure things are going well.” The equivalent setup for Clue is called Clue Connect: you can invite others to view your cycle, such as a coach, partner, family member, or friend. The app will show them the dates for your past, current, and predicted periods, fertile windows, and PMS. Other symptoms remain private.

While logging symptoms and collecting data about my cycle was easy, figuring out what it all meant and how I could apply it to my life wasn’t so simple. Both apps provide educational information about menstruation and common symptoms, but the information is generic. I had to triangulate between FitrWoman, exercise physiologist and nutrition scientist Stacy Sims’s book Roar (the go-to training and nutrition guide for female athletes), and my own experience to determine which adjustments I could make and when.

There is currently no easy way to step back and get a macro-level view of my cycle and symptoms alongside my training log in either app. While FitrWoman syncs with Strava, I can only see that information for an individual day, not on a weekly or monthly basis. My basic activity stats (distance, pace, time, calories, elevation gain, etc.) automatically feed into my FitrWoman calendar and appear alongside symptoms I’ve logged for that day. The data isn’t pushed to my Strava feed. Plus, I normally use TrainingPeaks, not Strava, to track my workouts, and right now the app doesn’t sync with TrainingPeaks. So I had to manually jump back and forth between all the apps, making it harder to see trends and process the overall picture of my health and performance. Bruinvels says FitrWoman plans to develop a higher-level view of the data over a longer time period and overlay it with training information. It may also move toward predicting when symptoms are likely to occur based on previous cycles. (The timeline for these developments is unclear.)

For its part, Clue does begin to analyze your reported data after you complete two cycles. It plots recurrent symptoms across each recorded cycle and predicts when you’re likely to experience them based on past cycles. It also presents an overview: the average length of a cycle, the average length of a period, and the typical cycle length variation. Clue’s cycle analysis starts to get at the macro-level insights I crave and provides the data points to start piecing together the puzzle.

Admittedly, I wanted period tracking to be a fix, and to offer me a prescriptive path back to better fitness and strength. But it’s never that easy. I’m still in the process of parsing out the data and testing different adjustments to get back on track.

Still, the simple act of noticing how I felt each day gave me a framework to interpret the signals my body was sending. Instead of berating myself for a bad run or lack of energy during strength workouts, I can put those workouts into context: Where am I in my cycle? What’s going on with my body that may make me feel this way? Should I expect to feel good today? Now I have a plausible explanation for how I feel, putting a stop to some of the second-guessing going on in my head.

“There’s no part of the cycle that’s negative,” Sim says. “It’s about gaining awareness of how you are across your cycle” and learning to work with that.

If you want to take a peek under the hood and understand your menstrual cycle and how it affects you, here are some tips to get you started.

How to Start Tracking Your Period

Demystify Your Cycle

Whether you use an app, a fitness tracker, or pen and paper, the first step is to commit to tracking your menstrual cycle and determine its length. “Not every woman’s period is a textbook 28 days,” Sims says. Cycle length can vary greatly from woman to woman, and even fluctuate from month to month. Even women at the same phase of their cycles can have vastly different experiences and symptoms, so it’s important to understand the influence of hormones in your own body.

Sims also recommends using an at-home ovulation predictor kit to determine when you’re ovulating, especially if your app doesn’t provide this information. (Clue does. FitrWoman doesn’t.) This will tell you more precisely when you’re entering the higher-hormone luteal phase of your cycle.

If you’re taking hormonal birth control, it’s a little more complicated. For IUD users, you still experience natural hormonal fluctuations, even if you don’t get a period, and can track your cycle and find your monthly patterns. However, if you’re on combined hormonal birth control, you don’t experience the same high- and low-hormone phases, since the contraceptive provides stable levels of estrogen and progesterone for three weeks out of every month. “You can track, but you’re not going to have the same benefit as if you were using your natural cycle,” Sims says. While you may identify days when you feel good and bad, the whole concept of employing specific strategies for high-hormone versus low-hormone phases doesn’t apply.

Note Patterns and Trends

Sims recommends tracking your cycle for at least three months. This will begin to give you enough data so that you can start to see trends. “If you track for one or two months, what you experience may just be an off day,” she says. “But if it happens three times, then you know there may be a real pattern.” Overlay this information with your training log to spot connections between the menstrual cycle and workouts and races.

While the research isn’t quite strong enough yet to make general recommendations, simply increasing your body literacy is beneficial. Ross, the UK-based physiologist, says that when you’re in tune with the physical and emotional experience of your cycle, you may be more confident in planning your training, nutrition, and recovery, which can eliminate a lot of anxiety.

Adjust, Adjust, Adjust

Once you notice patterns, begin to dial in your training and nutrition. “It doesn’t have to be prescriptive like, ‘I’m in a low-hormone phase so I’m going to do high-intensity training this day, this day, and this day,’” Sims says. Instead, use those patterns as signals for when to ramp up activities or take things down a notch.

For example, during the high-hormone phase when women are likely to feel flat physiologically, it’s not the best time to work hard. Instead, focus on technique like running drills. “With drills, you get the neuromuscular stimulus when the body is tired. Then, when you do the same drills when hormones are more optimal, you’ll perform that much better,” says Sims.

While “listen to your body” feels like cliché advice, it’s still a good mantra. Every woman’s experience is different across her cycle, and there’s no one-size-fits-all template. Pay attention to what’s happening and make reasonable adjustments based on your personal experience.