The Menstrual Cycle & Performance: What the Science Actually Says

Why this matters

For decades, sports science was built almost entirely on male athletes. Women were often left out of studies because the menstrual cycle was treated as an inconvenient "variable" to control for. The result: a lot of confident-sounding advice about training "with your cycle" that runs far ahead of the actual evidence.

This article is the honest version. We'll explain what the cycle is, what each phase tends to do, and — just as importantly — what we don't yet know.

The cycle in one minute

A menstrual cycle is the roughly monthly rise and fall of two key hormones — estrogen and progesterone — orchestrated to prepare the body for a potential pregnancy. A "textbook" cycle is 28 days, but anywhere from 21 to 35 days is considered normal, and length naturally varies from cycle to cycle.

Day 1 is the first day of your period. From there, the cycle is usually split into four phases.

The four phases

1. Menstrual (≈ day 1–5)

Both hormones are at their lowest. This is your period. Many athletes worry this is their "weak" phase — but the research is reassuring: menstruation itself does not reliably reduce performance. The bigger practical issue is iron loss through bleeding, especially with heavy flow, which over time can drain ferritin and sap endurance.

2. Follicular (≈ day 6 to ovulation)

Estrogen rises. Many women feel strong, recover well, and tolerate hard sessions in this window. It's frequently a good time to slot key quality or strength work — if your readiness agrees.

3. Ovulatory (≈ 2 days around ovulation)

Estrogen peaks and there's a small testosterone bump. This is when a lot of athletes feel their best — a reasonable window for tests, PRs, or races. One caveat: peak estrogen is associated with greater ligament laxity, so keep technique tight on heavy lifts.

4. Luteal (post-ovulation → next period)

Progesterone rises (and estrogen has a second, smaller bump). In the late luteal phase — the premenstrual window — many athletes notice the same power feels harder, body temperature runs higher, heat tolerance drops, and sleep can suffer. This is where symptom-driven adjustments make the most sense.

So how big is the effect, really?

Here's the part most "cycle training" content skips. The largest review on this question — a 2020 meta-analysis by McNulty and colleagues covering dozens of studies — concluded that the effect of cycle phase on exercise performance is, on average, trivial-to-small.

That combination — small average, huge spread — is exactly why rigid, one-size-fits-all "phase plans" oversell. The cycle is a real signal, but for most athletes it's a gentle nudge, not a switch that turns performance on and off.

The thing that matters more than phase: energy availability

If there's one female-specific topic that outweighs phase timing, it's Low Energy Availability (LEA) — chronically eating too little for your training load. Sustained LEA is the engine behind RED-S (Relative Energy Deficiency in Sport), and one of its earliest warning signs is a cycle that becomes irregular or disappears entirely.

What to do with all this

1. Track first, adjust second. For 2–3 cycles, just log your period, energy, sleep, and how sessions feel. Patterns — if you have them — will emerge.
2. Trust symptoms over the calendar. If a hard session lands in your "good" phase but you feel flat, it's still a flat day. The reverse is also true.
3. Mind iron if your flow is heavy and fatigue lingers.
4. Fuel for the work. Don't let cycle-tracking become another reason to under-eat.