Cycle syncing workouts: what two reviews found about training by menstrual phase

Cycle syncing is the idea that training should follow the phases of the menstrual cycle: that the same workout lands differently in one part of the cycle than in another, and that a plan can be built around that. It is a popular idea, and the question behind it is a fair one, because sex hormones do change across the cycle. Whether that shows up in how a person performs is a separate question. Two reviews have gathered the experimental studies on it.

This article is informational material, not medical advice. The app does not diagnose anything, and the article does not tell you what to do. Whether it is fine to exercise during your period, or what to do about pain or heavy bleeding, is a question for a doctor, and it is not answered here.

Cycle syncing workouts: the idea and the question

The research question is narrower than the trend. It does not ask whether the cycle matters to how you feel, which is something many people report. It asks whether measured performance, meaning endurance and strength, differs between phases when you compare studies that took measurements in two or more defined phases.

Both reviews below ask exactly that. One pools performance across all kinds of exercise outcomes. The other looks at resistance (strength) training, both acute performance and long-term adaptations. Both ask whether the phase of the cycle makes a difference.

What the largest meta-analysis found

McNulty and colleagues searched four databases for experimental studies that measured exercise performance in at least two defined phases of the cycle. They followed the PRISMA reporting guidelines and included 78 studies. The population is stated in the title: eumenorrheic women, meaning women with regular cycles. Results may not carry over to people whose cycles are irregular (McNulty et al., 2020).

The first analysis, on 51 of the studies, compared the early follicular phase with all other phases pooled together. For both endurance and strength outcomes the effect was described as trivial, with slightly lower performance in the early follicular phase: an effect size of −0.06, with a 95% credible interval from −0.16 to 0.04. The interval crosses zero, so a difference of exactly nothing is within the range the data allow.

The second analysis, a network meta-analysis of 73 studies, compared every phase with every other, using direct and indirect comparisons. The largest difference was between the early and the late follicular phase: −0.14, with an interval from −0.26 to −0.03. That is the biggest gap between any two phases in the whole review, and it is still small.

The authors also ranked the phases with a statistic called SUCRA, which expresses how likely a phase is to be poor, or among the poorest, for performance. The early follicular phase scored 30%. All the other phases scored between 53% and 55%. In other words, one phase stood slightly apart, and the remaining five were hard to tell from each other.

The reviewers rated the quality of the evidence as "low" (42%). Their conclusion was that performance might be trivially reduced in the early follicular phase compared with all others. Then they added the sentence that matters most for this topic: because of the trivial effect size, the large variation between studies and the number of poor-quality studies, general guidelines on exercise performance across the cycle cannot be formed.

What the umbrella review found about strength training

Colenso-Semple and colleagues went one level up. They did not read individual experiments; they read the published meta-analyses and systematic reviews on how cycle phase relates to performance and adaptation in resistance training (Colenso-Semple et al., 2023).

The first thing they report is disagreement. The published reviews gave highly variable findings on the supposed effects of female sex hormones on strength, performance and muscle growth (hypertrophy). The second is method. The authors note a pattern of poor and inconsistent practice in how studies verify which phase of the cycle a participant is in. If the phase is not confirmed reliably, a comparison between phases rests on shaky ground, whichever direction it points.

Their conclusion is an opinion, and the paper labels it as one: it is premature to conclude that short-term fluctuations in reproductive hormones appreciably influence acute exercise performance, or longer-term strength and muscle-growth adaptations to resistance training. They also open with a point about why this matters beyond sport. Women have been left out of exercise science research, often because of the assumption that cyclical hormone changes would affect resistance training results.

Where the two reviews agree and where they differ

They agree on the main point: the evidence does not support general rules of the form "in phase X, do Y". They also agree that study quality is a problem. McNulty's team count the number of poor-quality studies among their reasons, and Colenso-Semple's team point at weak phase verification.

They differ in emphasis. The meta-analysis finds a small, possible dip in the early follicular phase, with low-quality evidence behind it. The umbrella review is more reserved and says the case for any appreciable effect has not been made. These are not opposite findings: a trivial effect with a wide interval and a "premature to conclude" are two ways of describing the same thin evidence. The two papers also share an author, Kirsty Elliott-Sale, which is worth knowing when you count them as two independent opinions. Both author teams declare no conflicts of interest.

What this does not tell you

• Whether cycle syncing works or does not. By these two reviews, the effect of the phase is on average small and uncertain. The McNulty authors conclude that general recommendations cannot be formed and advise a personalised approach. That is not evidence that planning around the cycle is harmful, and it is not evidence that it helps.
• What happens in any one person. The meta-analysis authors cite large variation between studies, and their own recommendation is a personalised approach, based on how each person responds to exercise across the cycle. A pooled average of this size cannot say how any one person responds.
• How people feel. The reviews are about measured performance. They do not address fatigue, mood, pain or how a workout feels. Our earlier article on weather and the menstrual cycle covers what has and has not been measured about symptoms across the cycle.
• Anything about safety. Neither source says whether exercising at any particular point of the cycle is advisable or not. If you have a question about that, it is a question for a doctor.
• Irregular cycles. The meta-analysis covers women with regular cycles. Both reviews also depend on how well the phase was established in the underlying studies, and the umbrella review calls that weak.

What you can look at in your own data

The research leaves "personalised" as the authors' own recommendation. For someone who tracks, the practical version is looking at their own record.

In MeteoHealth you can log your cycle, and the app lines up the cycle phase against your energy, wellbeing, sleep and HRV. Separately, it reads workouts from Apple Health and compares their duration and intensity with your sleep and wellbeing. There is no single view that pairs cycle and workouts directly, so a question like "do I feel different after training in one phase?" is one you would have to read across two separate views. For what HRV is and why your own trend matters more than a single reading, see HRV explained.

Two limits apply. What the app knows about your cycle is what you entered. And a pattern in your own entries describes what happened to you in those weeks. It is not a mechanism, and it does not carry over to anyone else. It is also the one place where your own response is visible, which is the thing the meta-analysis authors say a recommendation should be based on.