A performance physiologist breaks down how hormones influence training.
Editor’s note: The research Sims references in this interview is based on cisgender women. We at Equinox understand that this conversation may not apply to all women but hope that everyone, regardless of how they identify, will be able to learn something new.
When Stacy Sims, MSc., Ph.D., was just an undergrad athlete on the Purdue women’s crew team, she realized that, no matter how hard they trained, the men’s team always seemed to progress and perform at their peak. Her team’s response to training, on the flip side, was “more hit or miss,” she says.
Sims, then an exercise physiology and metabolism major, started diving into the research, looking for an answer. Was there something the women’s team could do differently to enhance their performance? But she soon found herself stuck. Much of the research had been done on white, young, college-aged men, the reason being something along the lines of, “We don't know enough about men” or, “Women have a menstrual cycle, and it can interfere with the results,” she recalls. “Those didn't really sit well with me.”
Now a performance physiologist focused on female athletes, Sims is on a mission to change the way women are studied and give athletes the tools they need to train in a way that works with — not against — their physiology.
Here, she shares her take on how women’s hormones affect their ability to perform and what it means for exercise programming. Prefer to listen in? Check out the audio of the 2022 EQX+ chat with Sims.
How Hormones Affect Training and Performance
In general, many female athletes’ hormones change in sync with their menstrual cycle. A textbook menstrual cycle starts (read: day one) on the first day of a period and ends the day before the start of the next period. A “normal” cycle can last 24 to 38 days from start to finish, lengthening during the follicular phase, but a 28-day cycle is used as the “average” depiction.
The first portion of the cycle — the follicular phase — extends from day 1 until ovulation, roughly around day 14, says Sims. On day one, estrogen levels are at their lowest, and your body begins to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which then stimulates the growth of several egg-containing ovarian follicles. By day seven, estrogen levels have risen significantly, which stifles the secretion of FSH. When estrogen levels are high enough, your body suddenly releases a large amount of LH, triggering ovulation roughly a day later, according to UCSF Health. Throughout this phase, progesterone is also at its lowest and stays that way until after ovulation.
“At this point…women are ‘more like men,’ where we have a lower core temperature,” Sims explains. “We can access carbohydrates really well from our liver [and] muscle stores for intensity. We have signaling for reparation. We have better cognitive and reaction abilities. Our sleep patterns are different. And all of this has to do with the fact that the body is very robust to stress — even our immune system has changed to be more innate to capture virus and bacteria.”
After ovulation, the luteal phase begins, with the goal of creating a supportive environment for a potentially fertilized egg. For the first five or so days, progesterone levels continue to rise before gradually dropping back down if pregnancy doesn’t occur. Simultaneously, estrogen levels drop quickly, bounce back up during the mid-luteal phase, and finally trend back down toward the end of the menstrual cycle.
These hormonal changes aren’t always a good thing for the rest of your well-being: At this time, the immune system may be suppressed, due to the high levels of progesterone, research suggests. Your sleep may take a hit, too: Some studies have shown that the steeper rise in progesterone during the mid-luteal phase was linked with more time spent awake after initially falling asleep (known as wakefulness after sleep onset). Around day 28, hormone levels drop and the next cycle begins.
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So what do all these fluctuations mean for your workouts in the Club?
“When we're looking at hormones, it's all about creating a robust environment to support reproduction,” says Sims. “But if we take it out of that reproductive aspect and put it into a general life and training aspect, we can use these hormones to our advantage.”
Consider this: During the follicular phase, when your body is generally more resilient to stress, you might be able to push yourself even harder in the Club with high-intensity workouts — and still recover well enough for beneficial training adaptations, says Sims. Some studies suggest anaerobic capacity and muscle strength may be greatest during this stage.
When hormones rise after ovulation, you might see better results by easing up on intensity and increasing volume (think: steady-state cardio, higher reps with lower load). In the couple of days leading up to the next period, when progesterone and estrogen are getting ready to drop, the body is under the most stress, says Sims. At this point, a deloading period may be particularly valuable, says Sims; focus on technique work, yoga, and recovery modalities to work with your hormones and adapt to the hardcore training from the previous weeks.
A Caveat on ‘Cycle Syncing’ Your Workouts
Social media users have twisted this research to imply that you shouldn’t do heavy lifting during, say, the days before your period or easy endurance runs during the follicular phase. But that’s not the case. In fact, this advice from influencers, while well-intentioned, perpetuates the myth that women are “delicate” during certain times of the month.
It doesn’t mean you’re not able to hit PRs in athletic feats during certain phases, either. “I get frustrated because people have tried to merge performance and training together,” says Sims. “So performance can be [anything] from a mental task to actual physical performance, like a race. And we know that there is no negative day in the menstrual cycle for performance — the one thing in one day at one point in time.”
Hormones are just one part of the equation. Nutrition and mental health, for instance, can both influence how well you perform at a given task, says Sims. “There is no research to support menstrual cycle differences on performance,” she reiterates. “But when we look at how we can harness these hormones for training — again, there isn't a negative day — what we are doing is we are working with our body's stress resilience to maximize what we are doing.”
In other words, if your body is primed for high-stress situations at the start of your cycle, you might be able to garner noteworthy adaptations if you were to practice, say, sprint-interval training for four or five days in a row during that phase. But that doesn’t mean you can’t do that same program later in your cycle when you’re less resilient to stress, says Sims. You just might feel a bit more fatigued and have slightly less adaptation to that training, she says.
That’s why Sims advocates for people to shift away from the mindset that hormonal changes are a limitation. “It's more of an ergogenic aid that is ingrained in the female body, and understanding it allows you to dial in specific physicalities to get more adaptation without having to put in that much more work,” she says.
How to Maximize Adaptations According to Your Hormones
Again, there’s no “right” or “wrong” time of the month to do certain workouts. But if you want to maximize your adaptations, you might make slight tweaks to your fitness approach.
Say you love taking classes that combine lifting and cardio, like Ropes & Rowers or TRX Max Circuit. During the follicular phase, Sims recommends going “as hard as you can.” “As we get closer to ovulation, if you have a tendency to have soft tissue injuries, then maybe you want to not lift such heavy loads, because there is a slight risk of having more lax ligaments because of [the hormones],” says Sims. If you’re not prone to those injuries, continue to push your limits, especially in regards to strength; “your muscles will respond and regenerate really quickly due to the estrogen surge,” she explains. Around this time, your body is more attuned to recovery, she says. Of course, it’s still important to stretch and do proper cool-downs, but you may not need to prioritize recovery as heavily as you would at later phases, she adds.
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After ovulation, in the early-luteal phase (roughly days 15 to 22), you might switch to higher volume, lower-intensity work. If you’re craving a HIIT class at this time, get after it. Just make sure to prioritize carbohydrate consumption before you head into your workout, which can ensure you’re fueled enough to hit those higher intensities. Note, your heart rate may not get as high during the follicular phase, says Sims, so your training zones may look a little different.
In the late-luteal phase, “some women feel bulletproof right before their period starts, and some women don't — [it] depends on how fast those hormones have dropped, and that's why it's very individual,” says Sims. “So if you're someone who feels bulletproof, that means your hormones have dropped already, and you're good to go for high intensity. But if you're someone who feels flat and you have a little bit of bloating and some symptomology of PMS, again, take care of yourself. This is the time to work on technique.”
The Bottom Line
Your menstrual cycle and the hormonal fluctuations that come with it can impact how you feel and perform during a workout, due to changes in sleep, stress response, and nutrient metabolism.
But that doesn’t mean you should be designing your entire workout program around it. According to a 2023 systematic review, there just isn’t enough high-quality evidence to support the idea that short-term changes in hormones can considerably influence acute exercise performance or long-term adaptations.
Instead, view it as one factor to consider — just like nutrition, sleep quality, stress levels, and motivation — when configuring your training sessions. Be open to adapting that plan based on the symptoms you’re experiencing each day, not your hormones.