Should you train around your menstrual cycle?
No. Across 78 studies, performance changed by a trivial amount, if at all, across the cycle, and a separate review found no phase effect on strength. Track your own symptoms if you like and adjust only when your own pattern is clear; low energy and low iron are bigger, better-documented problems.
What to do
- Don't rebuild your plan around cycle phases. The research shows no meaningful phase effect across groups of women.
- If you want to, log your cycle and symptoms. Our suggestion: only move key sessions after two or three cycles of your own data show a clear pattern.
- Don't change your training because of your type of contraception. Effects of the pill on performance are trivial.
- Missing three or more periods in a row, or a bone stress injury, is a reason to see a doctor. These can be signs of low energy availability.
- If you are often tired, train a lot or eat little or no meat, ask a doctor about an iron test. Don't start iron supplements on your own.
The idea
“Cycle-syncing” means changing training by phase of the menstrual cycle: harder in some weeks, easier in others. It has been popularized in books and podcasts, including by Stacy Sims, and widely on social media. It is an appealing idea. It also deserves a fair test.
What the research shows
Performance across the cycle. A large network meta-analysis pooled 78 studies (McNulty and colleagues, 2020). It found at most a trivial dip in the early follicular phase, the days around the start of a period. The effect size (ES) was −0.06. An effect size is a standard way of describing how big a difference is; anything this close to zero is considered trivial. The authors recommended a personal approach rather than general phase rules.
Strength. An umbrella review, a review of reviews, found no effect of cycle phase on strength or on how strength improves with training (Colenso-Semple and colleagues, 2023).
Elite athletes. An audit of studies in elite athletes judged the quality of the evidence “insufficient to confirm or refute” any phase effect (Sherwin and colleagues, 2025). In other words, the research is too weak to settle the question either way. That cuts both ways: it doesn’t prove phases never matter, but it gives no basis for a fixed phase plan.
Contraceptives. Oral contraceptives have trivial effects on performance (Elliott-Sale and colleagues, 2020). There is no reason to change training based on contraception type.
How the popular claims stack up
The verdicts below are about claims, not about any author.
- “Women are under-studied, and sex differences matter.” Supported. Women made up only about 15% of participants in the pooled training-intensity studies, and the elite-athlete audit above found the evidence base thin.
- “Plan training by cycle phase.” Not supported as a rule for everyone (McNulty; Colenso-Semple).
- “Women should never train fasted”, “a 30-minute protein window”, and phase-based hydration or carbohydrate rules, as popularized on social media and podcasts. A 2026 review of nutrition claims aimed at active women found these lack robust support (Matkin-Hussey and colleagues, 2026). We could not confirm that this review names any particular author. General fuelling advice applies instead.
A symptom-led approach
Group averages can hide individual patterns. Some women do feel worse on certain days. A reasonable approach, and our suggestion:
- Log your cycle and symptoms, if you find that useful. It is optional.
- Don’t change your plan automatically by phase.
- After two or three cycles, look for a repeating pattern. If hard sessions consistently go badly on the same days, move them. Use your own data, not a template.
The bigger issues: energy and iron
Two problems have stronger evidence than phase effects, and they are easy to miss.
Low energy availability (REDs)
REDs stands for relative energy deficiency in sport. It happens when you eat too little for the training you do. Warning signs include missed periods and bone stress injuries. The International Olympic Committee’s 2023 consensus warns against relying on a single calorie cut-off to diagnose it (Mountjoy and colleagues, 2023). Instead, its screening tool (CAT2) looks for signs, such as missed periods and a history of bone stress injuries. In a follow-up study, athletes flagged at higher risk by this tool were far more likely to get a bone stress injury (orange versus green rating: odds ratio 7.71) (Heikura and colleagues, 2024).
This is not only an elite problem. Between 19% and 47% of recreational female runners screened at risk of low energy availability (Karlsson and colleagues, 2023; Dervish and colleagues, 2023).
Signs worth taking seriously include changes to your period, bone stress injuries, weight loss you didn’t intend, persistent fatigue, restrictive eating and stomach problems. Three or more missed periods in a row, a bone stress injury at the top of the thigh bone, the sacrum or the pelvis, or two bone stress injuries within two years, are reasons to see a doctor. This is general information, not a diagnosis.
Iron
Up to 60% of female athletes are iron deficient, which costs an estimated 3–4% of endurance performance (Pengelly and colleagues, 2025). If you are female, vegetarian or vegan, train a lot or feel unusually tired, ask a doctor or clinician about a blood test for ferritin and haemoglobin. Don’t take iron supplements without testing and medical advice.
What we don’t know
- Most studies are small, and the elite-athlete evidence is weak overall.
- Group results can’t rule out individual effects. A few women may have real, repeatable patterns.
- Marathon outcomes have not been studied by cycle phase.
- Women remain under-represented in nearly all training research, so many general rules are built mostly on men.
Sources
- McNulty et al. (2020). Menstrual cycle phase and exercise performance: network meta-analysis of 78 studies.
- Colenso-Semple et al. (2023). Umbrella review of cycle phase and strength.
- Sherwin et al. (2025). Audit of menstrual-cycle research in elite athletes.
- Elliott-Sale et al. (2020). Oral contraceptives and exercise performance.
- Matkin-Hussey et al. (2026). Nutrition claims aimed at active women on social media.
- Mountjoy et al. (2023). IOC consensus on relative energy deficiency in sport.
- Heikura et al. (2024). REDs screening tool and bone stress injuries.
- Karlsson et al. (2023). Low energy availability risk in recreational female runners.
- Dervish et al. (2023). Low energy availability risk in recreational female runners.
- Pengelly et al. (2025). Iron deficiency in female athletes.
Last reviewed 13 November 2026.