Cycle Syncing vs. Science: Should You Train by Your Period?

By Dr. Mélanie DesChâtelets, ND · Naturopathic Doctor and Menopause Society Certified Practitioner · Burnaby and virtual care across BC

One of my members asked a great question: I talk about how important exercise is for PMOS (formerly PCOS), but I never say how to customize it to your menstrual cycle. Cycle syncing is everywhere right now, and I get the appeal. It sounds scientific, it sounds empowering, and women are genuinely craving research built for women’s bodies. But my honest worry is that it slows some people down. So let’s look at what the research actually says about training across your cycle, and how to move through your month without adding more rules to your life.

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What is cycle syncing, and does it work?

Cycle syncing is the idea that you should match your workouts to the phase of your menstrual cycle: a certain kind of training during your period, another around ovulation, and so on. The spirit behind it is something I agree with, and we’ll get to that. But the popular version leaps well past the evidence, and it can quietly turn movement into one more set of rules you’re afraid to break. So let’s separate the part that’s worth keeping from the part that’s stretching the science.

Where does cycle syncing get it right?

It’s right that the research has real gaps. Most exercise physiology was done on men, because their hormones don’t fluctuate the same way, which made for tidier, more standardized studies. Even many studies on women estimate cycle phase by the calendar rather than by hormone testing or the body’s own signs and clues, which weakens the conclusions. So yes, we need more and better research for women, by women, about women. As exercise physiologist Dr. Stacy Sims, PhD, puts it, “women are not small men.” We metabolize, recover, and respond to fuel and stress differently, and that deserves attention. No argument from me there.

Isn’t training by your cycle “personalized”?

Here’s the irony. In the name of personalization, cycle syncing breaks the cycle into tidy boxes and then tells everyone to do the same thing at the same time. That’s not personalization, that’s templating, and it makes big assumptions: that your cycle is the number one predictor of your performance, and that you feel the same every single month. Think about the variation in your own cycles, month to month. And what about life? The toddler who wakes you at 2 a.m., the deadline that ate your sleep, the iron that’s low again, the week grief flattened you. Are we really going to say “it’s ovulation day, time for this workout”? Your cycle is one input. I love you being more connected to it, but it’s one input. So is your sleep. So is your stress. So is your nutrition. So is your capacity. So is context.

What does the research actually say?

A large review of 51 studies in women with regular cycles (which may not extrapolate to PMOS, where cycles often aren’t regular) concluded that performance might be trivially reduced in the early follicular phase, roughly day one to five, basically your period. “Trivial” is the operative word. In the clinic we separate statistically significant from meaningful: it may be true that some women perform slightly worse on their period, but does it change your life? If you got eight bicep curls instead of your usual ten, do we actually care? A 2023 critical review out of McMaster University found an absence of high-quality evidence for designing resistance-training programs around cycle phase. A 2024 German strength study (regular cycles only, measuring leg-press reps to exhaustion) found the early follicular phase slightly less favourable for max strength, with substantial variation between studies. The honest takeaway across all of it: there’s a hint of slightly lower performance on your period in some women, and that’s it. None of these say “don’t care.” They say: ask her, the individual.

What outcomes actually matter?

Let me flip the tone. At a population level, we’re trying to get adults to 150 to 300 minutes of exercise a week. And the outcomes that research ties to hitting those targets aren’t “two extra reps.” They’re body composition, all-cause and cause-specific mortality, and disease progression in conditions like hypertension, type 2 diabetes, and cancer recurrence. People who hit those targets literally live longer. So I genuinely don’t care if once in a while I lift eight times instead of ten because I listened to my body. Even Dr. Stacy Sims, PhD, once a “train by your cycle” voice, has shifted to “train by your readiness,” because so many things feed readiness. That’s the more evidence-based move: not rules, not restrictions, just informed flexibility.

Should you avoid HIIT with PCOS?

One claim I see a lot: skip high-intensity interval training because it raises cortisol, and high cortisol can worsen insulin and therefore PMOS. Here’s what the research actually shows. Yes, intense exercise raises cortisol, that’s physiology. But it rises and then it comes back down. Our bodies are built to be adaptable. And when we look at HIIT studied specifically in PCOS, it improves insulin resistance, improves inflammation and metabolic markers, and increases menstrual frequency, the outcomes we actually care about. So I don’t worry about a temporary cortisol bump and then leap to assumptions about what it “should” do, when the measured outcomes are clearly positive. And to be clear, HIIT isn’t mandatory. Non-HIIT, moderate exercise is beneficial too, so don’t let any of this pull you away from the real goal: 150 to 300 minutes a week, in whatever form you’ll actually keep doing.

So what should you actually do?

Don’t let the conversation get more complicated until you’ve mastered level one. Level-one mastery is consistency: getting to 150 to 300 minutes of moderate-intensity exercise a week, plus about two weight sessions. Don’t make it harder than that. Your number one job is finding what drives you, what makes you want to show up, because in the long run attendance matters more than anything else. I like a Good/Better/Best approach: a version of your goal that’s easy on a hard week, an average goal for an average week, and a stretch goal for a strong one. Keep it personal by checking in with yourself, and remember it’ll rarely be a single input that decides everything.

▶ Want the full deep-dive through the actual studies? Watch the complete video here. I also made you a Good/Better/Best goal-setting framework so your plan can flex with real life. Grab it by joining Shift Society and heading to the classroom.

This article is educational, not medical advice or a diagnosis. If something here resonates, bring it to your healthcare team, who can look at it through the lens of your individual health.

Main references

1. McNulty KL, et al. The Effects of Menstrual Cycle Phase on Exercise Performance in Eumenorrheic Women: A Systematic Review and Meta-Analysis. Sports Med. 2020. PubMed
2. Colenso-Semple LM, et al. Current evidence shows no influence of women’s menstrual cycle phase on acute strength performance or adaptations to resistance exercise training. Front Sports Act Living. 2023. PubMed
3. Teede HJ, et al. Recommendations from the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. J Clin Endocrinol Metab. 2023. PubMed