Should you cycle sync your workouts?

This is an installment of Good Fit, a column about exercise.

The menstrual cycle has always had a PR problem when it comes to exercise and sport. The ancient Greeks and Romans thought physical activity would damage a woman's reproductive system. In the 19th century, the medical community believed that menstruation depleted women of "vital energy" and any activity during this weakened state would leave her incapable of bearing children. Even today, having a period is still a liability in sports, thanks to the persistent myth that losing your period is a good thing and a sign that you’re fit. (It's not.)

But social media influencers, period tracking apps, and even fitness companies are trying to flip this image. They’re rebranding the menstrual cycle, transforming it from a dreaded monthly visitor to an untapped superpower. To take advantage of it, the claim goes, anyone who gets a period should "cycle sync" their workouts, matching their activities with the phases of their menstrual cycle. For example, focus on high-intensity workouts during the first half of the cycle and shift to lower-intensity activities like yoga and walking during the second half. On TikTok, #cyclesyncingworkout has 12.6 million views and "cycle syncing workout" is a top trending search term.

But experts say there isn't enough evidence to support carefully cycle syncing your workouts—it's just not possible to harness your period for athletic benefits by following a simple prescription. Still, proponents of cycle syncing are drawing on real research. Even though the practice they tout doesn't stack up, they are onto something potentially powerful.

The menstrual cycle is the rhythmic rise and fall of hormones across two different phases, the follicular phase and the luteal phase; ovulation separates the two. While the primary job of hormones like estrogen and progesterone is to coordinate fertility, they also influence metabolism, muscle building, energy, recovery, and temperature regulation. These are all factors that can affect exercise and athletic performance.

Cycle syncing is designed to work with the body and its hormonal shifts. The idea is to adjust your workout—type, duration, and intensity—depending on whether you are in a high-hormone or low-hormone phase so you can take advantage of the naturally occurring ebb and flow of hormones. Evangelists of the method say it helps women see the best results from their time at the gym while also managing period-related symptoms.

The trend grew out of a shift in how women talk about menstruation. Olympians now chat openly about periods in post-race interviews. The U.S. Women's National Soccer Team discussed how they tracked their cycles in the lead-up to their historic fourth World Cup title in 2019. In February, the Orlando Pride, a team in the National Women's Soccer League, adopted dark-colored uniform shorts in response to player concerns about competing in white shorts while menstruating.

Openly talking about periods hasn't always been the norm—not at press conferences, and definitely not in the lab. Even though menstruation is a key part of a woman's physiology, it often isn't considered in the world of sports science. The vast majority of studies in the field are conducted with male participants. Women make up 34 percent of study participants, and only 6 percent of sports science studies focus exclusively on women. (These studies also don't account for transgender athletes, who are largely absent from the research literature.) We know so little about female physiology, especially when it comes to exercise and performance.

Male anatomy, physiology, and biology sets the standard for everything from athletic development and progression to training and nutrition guidelines to shoe, clothing, and gear design. Protocols that coaches and others rely on don't account for women's bodies or their lived experiences. What's more, women aren't taught about their body's unique physiology and how it may influence athletic development and long-term health. A 2019 survey found that 72 percent of women have never received any education about the intersection of exercise and their periods.

I’ve spent the past three years trying to understand the root cause of this gender data gap for my book Up to Speed: The Groundbreaking Science of Women Athletes. When I asked experts why women are not included in studies, they responded, "Women are complicated."

Scientists prefer simplicity. If their goal is to investigate a specific chemical or molecular mechanism, they want to eliminate as many external variables as possible. Women's bodies, and our hormonal environments, are the opposite of simple. A background of continuously fluctuating hormones adds "noise" to the data. It's cumbersome and expensive to control for this variability. It's easier to study men because of their steadier state bodies.

Opting for a streamlined study design isn't the only reason women are understudied. Money also plays a role. Major funders of sports science research include institutions like the National Football League and National Collegiate Athletics Association as well as companies like Gatorade. On the whole, these organizations prioritize men's sports because they’re more lucrative and thus allocate more resources to study male athletes.

While women athletes are breaking taboos, the field of biomedical research has started to move toward greater representation and inclusion through policy measures. More scientists and health care professionals recognize the need to study women. As they’ve turned their attention to women, they’ve homed in on the menstrual cycle and how it may affect exercise and performance. And they’re finding preliminary evidence of interesting trends.

For instance, since estrogen plays a role in muscle synthesis, research suggests that women may build more muscle if they focus on strength training during the late follicular phase, when estrogen levels are high. During the luteal phase, the body conserves carbohydrates and relies on fat as fuel. This phase may be more ideal for steady-state cardio activities compared with high-intensity or power-based activities, which require access to quick bursts of energy typically offered by carbohydrates. Recovery from exercise might be slower during this phase too. Since there are estrogen receptors in bone and connective tissue, injury risk may also fluctuate across the cycle. Research suggests that estrogen can make ligaments weaker, and there's evidence that the knee becomes more lax around ovulation when estrogen surges. This could potentially contribute to the greater prevalence of ACL injuries seen in women.

The excitement about the menstrual cycle and how hormones may benefit fitness and performance is warranted. People are hungry for more and better information, and cycle syncing offers strategies for what type of exercise to do and when. But the trend has gotten ahead of the research by positioning hormones as the key to women's fitness. "The message right now is that we’re defined entirely by our menstrual cycle or hormonal status," says Alyssa Olenick, an exercise physiologist at the University of Colorado, as if that's the only factor that matters when it comes to exercise. "But we’re more than just periods and hormones." There are, for example, many things that can go into making you feel sluggish, and a little less able to complete a HIIT workout.

What's more, the picture of how hormones affect our muscles and our stamina is only starting to come into view. Scientists still don't know how much certain associations matter, whether, in some cases, they make a certain time of the month ideal for avoiding or leaning into a particular kind of workout. Although the selection of studies mentioned in the paragraph above sound promising, they are often small and conflict with other research into the matter, making the overall picture muddy. The conclusion of any single research paper cannot be taken as a prescription.

On balance, evidence does not support modulating exercise or training programs according to the menstrual cycle. A 2020 meta-analysis of 51 studies found that phases of the menstrual cycle don't affect overall performance outcomes related to endurance and strength. A 2023 study came to a similar conclusion with regard to strength training.

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"Menstrual cycle training has become gimmicky," says Megan Roche, research lead for the Stanford Female Athlete Science and Translational Research (FASTR) Program as well as an ultrarunning coach. From her perspective, the research doesn't capture the nuances she sees in the individual athletes she works with. Studies report on the average effect observed across the cohort of participants. But no two people have the same hormonal profile, and individual response to hormones and their influence on exercise can be subjective. Even if the broader effects of menstrual cycles on training were well understood, some people would be more sensitive to fluctuations in hormones than others, who may feel no effect at all. "Every athlete is their own case study of one," Roche says. What's more, it's difficult to be your own lab rat: Most people with periods don't have a textbook 28-day cycle, with ovulation falling on Day 14. Without a blood or urine test to confirm ovulation, cycle syncing is, on top of everything else, a bit of a guessing game. More research—and more tech—would be needed to follow your cycle and see benefits.

While it's not (yet) possible to fine-tune your performance to your cycle, it could still be worth paying attention to it—particularly if you feel as if your period is holding you back. The biggest impact of the menstrual cycle on exercise may actually be the side effects that accompany one's cycle, like abdominal cramps, headaches, breast pain, fatigue, and mood changes. Studies have found that more than 80 percent of exercising women report at least one symptom, and some will change or skip a workout because of these issues. Helping women identify strategies to mitigate these symptoms may have a more direct impact on fitness and performance than any phase-to-phase hormonal fluctuations.

To mitigate unpleasant menstrual symptoms and reduce their effects on movement, experts suggest tracking your cycle for several months, which can help uncover your individual pattern of symptoms. Olenick advises paying attention to the basics first, before adjusting your workouts: Are you eating enough to support your physical activity? How's your sleep? How's your stress? These areas all influence training adaptation, performance, exercise adherence, and hormones. People may find that if they eat or sleep more, symptoms go away and workouts improve.

When it comes to exercise, Olenick recommends using the rate of perceived exertion, a scale from 0 to 10 to measure effort level, to calibrate workouts. If you feel terrible right before your period, adjust the weight used in your strength-training session to maintain the same relative intensity originally planned. Or front-load higher-intensity workouts during a time of the month when you know you’ll have more energy. But the idea is not to put several weeks’ worth of cycle-specific workouts on the calendar, switching activities along with phases. "You’re not changing what you’re doing," Olenick says. "You’re listening to your body."

Scientists are just getting started learning how the menstrual cycle may or may not affect exercise and sports performance. "With every year that we spend time doing this research, we learn even more about what questions to ask," Roche says, and that could potentially lead to better guidance down the road.

While cycle syncing may not be the solution, it has opened the doors to discussing menstrual cycles outside of whispers in the bathroom. It's encouraging women to pay attention and listen to their bodies. And by observing their own patterns and needs, they can make more informed decisions about workouts so they can feel their best and train consistently.