Back to Kriterion
← Reference library

Does Your Cycle Phase Change How You Should Train?

Cycles2 min readMcNulty et al. (2020); Elliott-Sale et al. (2021); Mountjoy et al. (2023)

The phase articles describe what is common, not what will happen to you. The difference between two women dwarfs the difference between two phases.

Key points
  • Reviews find the effect of cycle phase on performance small and inconsistent.
  • Treating a phase as a rule would invent a precision the research does not have.
  • Comparing your own reps in reserve across phases, over about three cycles, shows whether you have a pattern.
  • Periods that stop or turn irregular while you train hard are not a phase effect. They are a reason to see a GP.

Why every phase description is hedged

Every phase description in the Cycles articles is deliberately hedged: often, commonly, many find, never you will. That is not caution for its own sake. Systematic reviews of exercise performance across the menstrual cycle find effects that are small and inconsistent, and the difference between two individual women dwarfs the difference between two phases, meaning knowing which phase someone is in predicts far less about a session than knowing who she is. Treating a phase as a rule (it's ovulation, add 5% to your squat) would invent a precision the research doesn't have, in an app whose whole credibility rests on not doing that elsewhere.

Checking your own pattern

What the evidence does support is checking whether your own pattern exists: comparing your logged reps in reserve, meaning how many more you could have managed, across your own phases, over enough cycles that one rough week does not read as a trend. That is what the Your Data card on the Cycle screen is doing, and why it asks for roughly three cycles before it says anything.

Until then

Until then, the phase text here is a reasonable starting hypothesis to train by, useful from day one, not a verdict on your body specifically, and it only ever gets sharper from your own logs, never less useful while you wait.

When training changes your cycle

One pattern is not a matter of phase at all. Training hard while eating too little for it can make periods irregular or stop them altogether. The International Olympic Committee calls the underlying problem low energy availability, part of Relative Energy Deficiency in Sport, and it affects bone health as well as the cycle. A missing period is not something to train around. It is worth a conversation with a GP.

See a GP if…
  • You've missed your period three times in a row
  • Your periods have become irregular, especially since you started training harder or eating less
  • Period pain or heavy bleeding regularly stops you training or doing ordinary things
How Kriterion uses this

Kriterion's phase guidance is free and always hedged, and the Your Data card on the Cycle screen checks your own logged effort across phases before it claims you have a pattern at all.

References

  1. McNulty KL, Elliott-Sale KJ, Dolan E, et al. 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.
  2. Elliott-Sale KJ, Minahan CL, de Jonge XAKJ, et al. Methodological considerations for studies in sport and exercise science with women as participants: a working guide for standards of practice for research on women. Sports Medicine, 2021;51(5):843-861.
  3. Mountjoy M, Ackerman KE, Bailey DM, et al. 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023;57(17):1073-1097.

Last reviewed 28 Sep 2026 · Next review due Sep 2029

Kriterion is the app this reasoning is built into

It measures your maintenance calories from what you actually ate against what the scale actually did, tells you how firmly the number is pinned down, and checks its own past predictions against your results. Free logging, UK food data, and no ads.