When it comes to athletic performance, everyone wants to gain an edge. That might mean taking supplements or trying out a new sneaker that promises to make you lighter on your feet. But what if, instead of external help, you could hack your body’s internal systems to optimize your health and fitness?

When 26-year-old weightlifter Monica Knowlton tried adjusting the intensity of her training to her menstrual cycle two years ago, she noticed improvements in both her physical performance and mental toughness. She scheduled her highest intensity days to coincide with her follicular phase, when she felt strongest, and timed her deload week (a drop in volume and intensity at the end of one training program and before starting the next) to coincide with the days when she was prone to premenstrual symptoms.

“It makes me feel better mentally because I know when to accelerate and when to brake,” she says.

Knowlton is cautious, however, not to attribute the sole responsibility for this change to her hormone levels. “Although I made improvements in performance, I can’t say whether that was due to cycle synchronization,” she said.

Cycle syncing involves matching exercise intensity, nutrition and recovery to the phases of the menstrual cycle. Proponents believe the hormonal highs and lows can help determine when to aim for a personal best and when to slow down. So how does it work?

The basics of cycle synchronization

Most people who have a natural menstrual cycle go through four phases: menstruation, follicular phase, ovulation and luteal phase. During each phase, hormone levels rise and fall, which for some can cause bouts of fatigue, mood swings, bloating, headaches and cramps.

To adjust your workout accordingly, this could include low-intensity activities such as walking or yoga during menstruation when energy levels may be lower; cardio-based and high-intensity workouts such as running and weight lifting when energy levels increase in the follicular and ovulatory phases; and strength training or moderate-intensity exercise during the luteal phase before menstruation.

Why is it so popular?

“Many women seriously feel that they have been neglected by fitness, science and health for a long time,” says sports scientist Dr. Alyssa Olenick.

Between 2014 and 2020, only 6 percent of studies in sports and science journals focused exclusively on women, writes Christine Yu, author of Up to date: The groundbreaking science on female athletes. Therefore, it is understandable that a practice based exclusively on sport and the female reproductive system seems attractive.

Although you can now hire a trainer or buy a program to help you tailor your workouts to your cycle, there is still not much research to support the idea of ​​tailoring your workouts to typical—but by no means universal—cycle lengths and symptoms.

But does it work? Yes and no.

The average cycle is 28 days, but can range from 21 to 35 days for some people. no contraceptive, with the number of days in each phase varying from person to person. Likewise, symptoms such as fatigue and cramps are typical but not a given, meaning that not everyone will get the same benefits from a week’s rest, just as not everyone will achieve a personal record just because they are in a certain phase of their cycle.

For women who take birth control, the structured form of cycle synchronization may also not be suitable because they do not experience the typical hormonal fluctuations. This can make it difficult to stick to a one-size-fits-all program.

Lauren Colenso-Semple, PhD, and her colleagues at McMaster University evaluated a number of meta-analyses and systematic reviews on the influence of the menstrual cycle on athletic performance and strength performance. They concluded that “coaches and athletes should create an individualized training plan because there is no high-quality evidence to support the development of strength training programs based on the phase of the menstrual cycle.”

More reports on cycle synchronization, including a 2020 meta-analysis of 78 studies based on endurance and strength results, have come to similar conclusions.

When it comes to adjusting a workout due to menstrual cramps, Colenso-Semple says listening to your body can be powerful. “But that’s very different than saying, ‘This two weeks you should do yoga and this two weeks you should do strength training,'” she says. “Because those kinds of recommendations go against everything we know about solid exercise programs.”

The advice to Forcing yourself to rest can also feel a bit archaic, as a preset program may not match the sensations in your own body.

“When we’re given the advice, ‘Don’t do any intense exercise, just sit there and abstain from anything intense or heavy for between seven and 14 days a month,’ that becomes demeaning and reinforces the narrative of women’s fragility that I think we’ve worked really hard to overcome,” Olenick says.

So you can decide for yourself

Sonya Romanowski, a 33-year-old strength athlete, doesn’t experience hormone fluctuations during her cycle that would require her to change her entire training program, but like Knowlton, she tries to time her relief to the start of her period.

“I take the training a little slower with higher percentages and try not to break any personal records during this time,” she says.

If you’re curious about what it would feel like to consider your cycle when planning your workouts, Olenick recommends letting your own body be your guide.

“I encourage people to track their cycle for three to six months to find out their true pattern and see where things sometimes shift or change,” says Olenick. She suggests assessing your perceived effort rate – how hard you think you are trying when you exercise – on a scale of one to ten, and can be used to adjust the intensity of your workout. Exercisers should remember that things like nutrition, hydration, stress and fatigue – not just your hormone levels – all affect your workout.

“Adapting training to your individual responses and needs is not cycle synchronization,” Olenick adds. “It’s just good training.”