Cycle Syncing Your Strength Sessions: What the Evidence Actually Supports

Search social media for "cycle syncing" and you'll find detailed plans: heavy lifting and high intensity in the follicular phase, lower intensity, yoga and walking in the luteal phase, rest during your period. Apps offer phase-based workouts, and some coaches build whole programmes around them. The appeal is clear. After decades in which women were largely left out of sports science, as TriForward's "Mostly Men, Mostly Cyclists" describes, cycle syncing feels like training designed for women at last.

This article looks at the evidence for one part of that idea: strength training. Does strength change across the cycle? Do women gain more from lifting in one phase than another? And what should a female triathlete do with the answer? TriForward's "Reading the Research as a Female Triathlete" covers the wider question of how to judge research on women.

The menstrual cycle in brief

A typical menstrual cycle has two main halves, separated by ovulation:

• The follicular phase starts on the first day of your period. Oestrogen is low at first, then rises towards ovulation. Progesterone stays low.
• The luteal phase follows ovulation. Both oestrogen and progesterone are higher, then fall before the next period.

Cycle length varies between women and from month to month. The theory behind cycle syncing is that rising oestrogen in the follicular phase supports strength and muscle building, while higher progesterone in the luteal phase works against it. These hormones do act on muscle, so the idea is plausible. The question is whether it makes a practical difference.

Does strength change across the cycle?

The most direct answer comes from a 2020 meta-analysis by Richard Blagrove, Georgie Bruinvels and Charles Pedlar in the Journal of Science and Medicine in Sport. They included 21 studies of women with regular cycles and compared strength in three phases: early follicular, ovulatory and mid-luteal. A later review reports that these studies included 232 participants. They looked at maximal voluntary contraction, isokinetic peak torque and explosive strength.

• No comparison between phases was statistically significant (all p ≥ 0.26).
• All effect sizes were small, with Hedges g of 0.35 or less, and confidence intervals that included both positive and negative effects.
• There was no heterogeneity (I² = 0%), meaning the studies were consistent with each other.

The authors concluded that strength is minimally altered by hormone fluctuations across the cycle, but cautioned that methodological shortcomings mean this should be interpreted carefully.

Performance more broadly

A 2020 meta-analysis by Kelly McNulty and colleagues in Sports Medicine looked at exercise performance more broadly, including strength, endurance and sprint outcomes. It included 78 studies.

• Performance might be trivially reduced in the early follicular phase, the days around the start of a period, compared with all other phases (effect size −0.06).
• The largest difference was between the early and late follicular phases (effect size −0.14), still classed as trivial.
• The quality of evidence was rated low, and the results varied considerably between studies.

The authors concluded that general guidelines on adjusting exercise to cycle phase can't be made from this evidence, and recommended a personalised approach.

Inference: if strength doesn't change meaningfully across the cycle, the case for scheduling heavy lifting in one phase has to rest on a different argument, that the training response, rather than strength on the day, differs by phase.

The phase-based training trials

A small number of trials have tested this directly. The best known is a 2014 study by Eunsook Sung and colleagues in SpringerPlus. It involved 20 women with regular cycles who weren't using oral contraception, aged around 26.

• Each woman trained both legs on a leg press over three menstrual cycles.
• One leg did 8 sessions in the follicular phase and 2 in the luteal phase. The other did the reverse.
• The follicular-based leg gained more strength and muscle diameter than the luteal-based leg.
• Muscle fibre changes were seen only in the follicular-based leg, but the difference between legs wasn't significant.

A 2022 review by Jacob Kissow and colleagues in Sports Medicine drew on studies like this to conclude that follicular phase-based resistance training is possibly superior to luteal phase-based training for strength and muscle mass, and called for more research.

These studies are the basis for most cycle-syncing advice on strength. But they have important limits.

The umbrella review

In 2023, Lauren Colenso-Semple and colleagues, including Kirsty Elliott-Sale and Stuart Phillips, published an umbrella review in Frontiers in Sports and Active Living. Rather than reviewing individual studies, they assessed the quality of existing reviews on menstrual cycle phase and strength. They found five, including Blagrove's and McNulty's meta-analyses, rated from low to moderate quality.

Their conclusions:

• There was scant, low-quality and inconsistent evidence of meaningful phase differences in strength, performance or muscle growth.
• It was premature to conclude that short-term hormone fluctuations affect acute strength or longer-term training adaptations.
• The key training studies had methodological problems. In the Sung trial, ovulation wasn't confirmed. In another phase-based study, a change in lean mass of 0.2 kg in one group was, in the authors' view, within the measurement error of the scanner.

They highlighted several problems common across the research:

• Cycle phases were often estimated, for example by assuming a 28-day cycle, rather than confirmed with blood or urine tests.
• Samples were small and results varied.
• Some studies combined oral contraceptive users with naturally cycling women.

They recommended that, without high-quality evidence, training should be tailored to the individual rather than to cycle phase, and that women should record their cycle and symptoms as one factor among many, alongside sleep, nutrition, stress and injury.

Why the reviews disagree

The Kissow and Colenso-Semple reviews drew different conclusions from largely the same small group of studies. Inference: this is a common situation in early-stage research. A few promising trials point in one direction, and reviewers differ on how much weight to put on them given their limitations. The honest summary is that phase-based lifting might help, but the evidence is too weak to recommend it over a well-designed standard programme.

There is also a practical problem. Inference: phase-based plans assume you know which phase you're in. Many women don't have regular 28-day cycles, cycle length varies from month to month, and ovulation can't be identified reliably from a calendar alone. In the research, this was one of the main weaknesses. In real life, it would be bigger.

What about hormonal contraception?

Many women use hormonal contraception, which suppresses the natural hormone cycle. A 2020 meta-analysis by Kirsty Elliott-Sale and colleagues in Sports Medicine looked at exercise performance in oral contraceptive users. It included 42 studies with 590 participants.

• Oral contraceptive users might have slightly lower performance on average than naturally menstruating women, but the effect was likely trivial.
• Results varied considerably between studies, and most were rated moderate, low or very low quality.
• Performance was consistent across the pill cycle, with no meaningful difference between pill-taking and pill-free days.

The authors concluded that there was no basis for general guidance on oral contraceptive use for performance, and recommended an individual approach. Inference: cycle syncing plans built on natural hormone fluctuations don't apply to women whose cycle is suppressed by hormonal contraception.

What matters more: symptoms

While the effect of cycle phase on strength appears small, the effect of symptoms on training is clearly large. In 2021, Georgie Bruinvels and colleagues surveyed 6,812 exercising women, recruited through the Strava app, in the British Journal of Sports Medicine. None used combined hormonal contraception. Their mean age was 38.

• Mood changes or anxiety were reported by 90.6%.
• Tiredness or fatigue by 86.2%.
• Stomach cramps by 84.2%.
• Breast pain or tenderness by 83.1%.

Women with more frequent symptoms were more likely to miss or change training, miss competitions, miss work or study, and use pain medication. Inference: for most women, the practical question isn't which phase they're in, but how they feel on a given day. That is something a training plan can adapt to without needing to predict hormone levels.

Reading the studies as a triathlete

Even if phase-based lifting were proven to work, there are reasons to be cautious about applying it directly to triathlon. All of the following is inference from the studies above rather than a tested finding:

• The participants weren't endurance athletes. The Sung trial and most of the studies in the meta-analyses involved young women who weren't training for endurance sport. None tested women combining lifting with 8 to 15 hours of swimming, cycling and running a week.
• The effects were measured over a few months. A triathlete's strength training runs across a whole year, with a winter build and a lighter maintenance phase in the season. A small difference over three cycles may or may not add up over that time.
• Triathlon training doesn't pause. Even if lifting were moved to one phase, key bike and run sessions would still fall in every phase. A plan that crowds heavy lifting into the follicular phase also crowds more fatigue into those weeks.
• Racing can't be scheduled by cycle. Race dates are fixed, so whatever phase you're in on race day, you'll need to perform. Knowing that strength and performance change only trivially across the cycle is, if anything, reassuring.

The more useful lesson from this research for a female triathlete may be the one from the Bruinvels survey: symptoms are common, they affect training, and they deserve attention in their own right. TriForward's "Reading the Research as a Female Triathlete" covers how to weigh studies like these, and "Same Lifts, Different Plan?" covers what is known about how women respond to strength training generally.

Putting it into practice

The following suggestions are inference from the research above, not a tested programme:

1. Follow a standard, well-designed strength plan. The same principles of progression, loading and recovery apply throughout the cycle. TriForward's "Same Lifts, Different Plan?" covers how women respond to strength training.
2. Track your cycle and symptoms alongside training. Over a few months, you may see your own patterns.
3. Adjust for symptoms, not phase. If cramps, fatigue or poor sleep affect a session, reduce the load, swap the session or rest, as you would for any other reason.
4. Don't skip heavy lifting in the luteal phase on principle. The evidence doesn't support it, and it would remove roughly half of your training opportunities.
5. If a phase-based plan suits you, keep the total amount of heavy lifting across the month the same, so the plan changes when you lift rather than how much.
6. Get persistent or severe symptoms checked. They often have treatable causes.

A triathlon scenario

The following example is illustrative, not drawn from a study. A 34-year-old triathlete lifts twice a week through the winter. She's started following an app that tells her to lift heavy only in the follicular phase. Her cycle varies from 26 to 35 days, so the app's phase predictions are often wrong, and she's been skipping about half of her heavy sessions.

Based on the evidence, she might:

• Go back to lifting twice a week throughout the month, progressing as normal.
• Keep tracking her cycle and symptoms, noting which days she feels particularly flat or has pain.
• Plan a lighter session for the days she typically feels worst, if a pattern appears, rather than for a predicted phase.
• Talk to her GP if her periods become very irregular or stop, especially as her training increases in spring.

Common mistakes

• Treating a plausible mechanism as proof. Oestrogen and progesterone do affect muscle, but the measured effect on strength is small.
• Skipping training based on a calendar. Phase predictions are unreliable without testing, especially with irregular cycles.
• Applying cycle syncing to hormonal contraception, which suppresses the natural cycle.
• Ignoring symptoms because the plan says it's a heavy day.
• Accepting missing periods as normal for an athlete. They need medical assessment.

What we don't know

• Whether phase-based training produces meaningfully better results in larger, well-controlled trials with confirmed phases.
• How the cycle affects trained athletes rather than young non-athlete women.
• Whether endurance training alongside lifting changes any phase effect.
• How perimenopause, with its irregular hormone changes, affects strength training.
• Whether tracking symptoms and adjusting sessions improves long-term results, since this sensible approach hasn't itself been tested in a trial.
• How hormonal contraceptives other than the pill, such as hormonal coils, implants and injections, affect strength training, since the meta-analysis here covered oral contraceptives only.

References

• Blagrove RC, Bruinvels G, Pedlar CR. Variations in strength-related measures during the menstrual cycle in eumenorrheic women: a systematic review and meta-analysis. Journal of Science and Medicine in Sport, 2020;23(12):1220–1227. doi:10.1016/j.jsams.2020.04.022
• McNulty KL, Elliott-Sale KJ, Dolan E, Swinton PA, Ansdell P, Goodall S, Thomas K, Hicks KM. The effects of menstrual cycle phase on exercise performance in eumenorrheic women: a systematic review and meta-analysis. Sports Medicine, 2020;50(10):1813–1827. doi:10.1007/s40279-020-01319-3
• Sung E, Han A, Hinrichs T, Vorgerd M, Manchado C, Platen P. Effects of follicular versus luteal phase-based strength training in young women. SpringerPlus, 2014;3:668. doi:10.1186/2193-1801-3-668
• Kissow J, Jacobsen KJ, Gunnarsson TP, Jessen S, Hostrup M. Effects of follicular and luteal phase-based menstrual cycle resistance training on muscle strength and mass. Sports Medicine, 2022;52(12):2813–2819. doi:10.1007/s40279-022-01679-y
• Colenso-Semple LM, D'Souza AC, Elliott-Sale KJ, Phillips SM. Current evidence shows no influence of women's menstrual cycle phase on acute strength performance or adaptations to resistance exercise training. Frontiers in Sports and Active Living, 2023;5:1054542. doi:10.3389/fspor.2023.1054542
• Elliott-Sale KJ, McNulty KL, Ansdell P, Goodall S, Hicks KM, Thomas K, Swinton PA, Dolan E. The effects of oral contraceptives on exercise performance in women: a systematic review and meta-analysis. Sports Medicine, 2020;50:1785–1812. doi:10.1007/s40279-020-01317-5
• Bruinvels G, Goldsmith E, Blagrove R, Simpkin A, Lewis N, Morton K, et al. Prevalence and frequency of menstrual cycle symptoms are associated with availability to train and compete: a study of 6812 exercising women recruited using the Strava exercise app. British Journal of Sports Medicine, 2021;55(8):438. doi:10.1136/bjsports-2020-102792