What if there was a better way to exercise—one that took advantage of your menstrual cycle? It’s a question asked by elite athletes and casual gymgoers alike, who want to know how their body’s natural hormone fluctuations might be affecting their workouts.
You can see it on TikTok, where some influencers swear by lifting heavy weights in the early weeks of their cycle for better muscle gains. You can also find it in traditional media from The Guardian to Women’s Health, which offer guides for syncing your workout routine with the phases of your cycle.
But is there any scientific evidence to bolster this idea?
“The really short answer is: not yet,” says Xanne Janse de Jonge, an exercise physiologist at Macquarie University in Sydney, Australia. “It's important to realize that research on women in sport is still so young.”
In fact, what little evidence we do have suggests that the menstrual cycle has no effect on athletic performance, says Jayson Gifford, an exercise physiology professor at Brigham Young University, who recently co-authored a study showing just that. “I think the trend is probably very premature, and not based on science.”
Here’s why—and what experts say you can do to make your workouts better throughout your cycle.
Do you really know your menstrual cycle?
The first problem with syncing your workouts to your menstrual cycle is that it’s really hard to know for sure when you’re in each phase—and what your hormones are up to.
Each cycle generally lasts anywhere from 21 to 35 days, depending on the individual, and there are four phases within a cycle.
The first phase is menses, or bleeding, which can last for several days as the body sheds its uterine lining. Then in the follicular phase, estrogen begins rising and an egg develops in one of the ovaries. That ovary releases the egg in the third phase, ovulation. Finally, in the luteal phase the body releases a surge of progesterone to thicken the lining of the uterus for pregnancy. If pregnancy doesn’t occur, estrogen and progesterone levels drop, and the cycle begins again.
Hormones released during these phases have physical and mental effects on the body, says Kathryn Ackerman, director of the female athlete program at Boston Children’s Hospital. They might, for example, affect your energy levels: Some people have more energy in the early weeks of the cycle when their estrogen is high, then feel sluggish as it begins to fall.
“But there's so many other hormones going on at the same time that sweeping statements don't really help,” Ackerman says.
Furthermore, menstrual cycles are highly individual—how long each phase lasts, how high your hormone levels rise, how low they drop, and how you feel during each phase varies from person to person. And for people with menstrual disorders like endometriosis—which so often goes undiagnosed—it can be thrown off entirely.
You also might not ovulate in every cycle—which experts say is not necessarily cause to panic. This can happen to anyone for any number of reasons—such as stress, excessive exercise, obesity, and more.
And none of these hormonal fluctuations apply to those taking hormonal birth control.
“We can’t apply any of this if somebody is on a birth control pill,” Ackerman says. Oral contraceptives may mimic your menstrual cycle, but they create a very different synthetic hormonal environment. And some IUDs stop your cycle entirely.
The evidence is thin
Although this scientific field is gaining momentum, so far there just haven’t been many rigorous investigations into whether it’s worth syncing your workout with your cycle.
The best evidence linking the menstrual cycle to athletic ability is a phenomenon that occurs during the luteal phase—the final phase in the cycle. As progesterone rises after ovulation, so does a person’s basal body temperature, or the temperature of the body when it’s completely at rest. That heat could make your workout feel a little more challenging.
“So, if somebody is planning to go for a long run, and it's already a hot day, it might feel hotter, and that might affect their performance,” Ackerman says.
There’s also evidence that ligaments and tendons tend to be looser and more vulnerable to injury just before ovulation when estrogen peaks. Janse de Jonge says this serves an evolutionary purpose to help the body gear up for the changes it’ll undergo during pregnancy and childbirth. But the lesson here is just to be careful—not avoid exercise.
Less convincing are the claims that there are ideal times to perform certain types of exercise. For example, some studies suggest the rise in estrogen during the follicular phase is linked to strength gains—making it an ideal time for muscle training. But experts say the evidence is weak: It is only based on a handful of studies, and there are just as many that show no such link.
In fact, Gifford’s recently published study showed that female participants could work out at the same intensity for the same length of time during each phase of their cycle.
Ultimately, we need more studies with better data on women in sports.
What can you do in the meantime?
The good news is that you can already track your cycle to learn how hormonal changes affect your energy.
Start with the first day of bleeding. Don’t just track how many days you bleed but track how you feel: Were you tired? Did you have cramps? Did you have a headache?
You can also track your ovulation. Drugstores sell ovulation test kits that measure the levels of a certain hormone in your urine. “If there is a surge of that hormone in urine, then you'll be ovulating within the next 24 hours,” Janse de Jonge says.
After a couple months of tracking, you can start to identify patterns—such as fluctuations in energy—and assess what your body needs. But Jessica Linde James, who led the study with Gifford, says that means adjusting how much sleep you’re getting or how much water you’re drinking at certain points of your cycle—not switching up from HIIT workouts to yoga.
Ultimately, she says, it’s just about listening to your body: “If your body’s telling you, don’t go do squats in the gym today, then don’t do it.”
But just don’t let your knowledge of your menstrual cycle hold you back.
“We know that women have won Olympic medals during their period,” Ackerman says. “They've won Olympic medals on the pill, and they won Olympic medals during ovulation, the early follicular phase, the early luteal phase—so it's not a barrier.”