Training With Your Cycle: What the Research Actually Says

For most of the last century, cycling training science was built almost entirely on male physiology. The way the menstrual cycle interacts with training was largely ignored. That has begun to change. Recent years have produced the first large meta-analyses and the first systematic reviews focused specifically on female athletes, and the picture they paint is more complicated than the popular story suggests.

The Four Phases

Briefly:

• Menstrual phase (days 1 to 5): Both oestrogen and progesterone at their lowest. Bleeding occurs. Iron is lost.
• Follicular phase (days 6 to 13): Oestrogen rises, peaking before ovulation. Progesterone stays low.
• Ovulatory phase (around day 14): Short window where oestrogen peaks and luteinising hormone surges.
• Luteal phase (days 15 to 28): Progesterone rises, particularly in the second half. Resting body temperature rises by around 0.5 degrees C. Ventilation rate increases.

A 28-day cycle is the textbook number. Cycles between 21 and 45 days are within normal range, and individual cycle length varies month to month for almost everyone.

Phase Characteristics vs Phase-Specific Training Rules

Two different kinds of claim get made about the cycle and training, and they often get muddled.

Phase characteristics are the well-documented physiological changes: core temperature rises in the luteal phase, ventilation increases, iron status varies. These are real and reproducible.

Phase-specific training prescriptions are claims like "do your hardest sessions in the follicular phase" or "ease off in the luteal phase." These are popular but the evidence base is much weaker than the confidence with which they are usually stated.

Knowing what your hormones are doing is useful. Following a calendar template that tells you when to go hard or rest is not what the controlled research consistently supports.

What the Evidence Actually Shows

The 2020 systematic review and meta-analysis by Kelly McNulty and colleagues in Sports Medicine pulled together 78 studies covering 1,193 participants. The overall effect of cycle phase on performance was trivial. A small reduction was observed in the early follicular phase compared to the late follicular phase specifically, with the response highly variable between studies.

The 2025 historical perspective by Anthony Hackney and colleagues reviewed 40 years of menstrual cycle research and reached a similar landing point: the group-level effect of cycle phase is small or trivial.

It is worth noting a 2025 methodological critique by Elliott-Sale and colleagues in Sports Medicine arguing that much existing cycle-phase research uses unverified phase assignment, which inflates noise and probably underestimates true individual effects. The honest read: group means underplay the picture, while individual variation is the real signal worth tracking.

Some athletes feel measurably worse in their luteal phase. Others feel no difference. Some report their best sessions during their period. This variation is real, but it is not predictable from cycle phase alone.

What Is Robustly Established

• Core temperature rises in the luteal phase by roughly 0.5 degrees C, with implications for heat management on long rides.
• Ventilation rate is higher in the luteal phase. Progesterone is a respiratory stimulant, which can make breathing feel harder at the same power output.
• Iron status varies across the cycle. A 2022 study by Alfaro-Magallanes and colleagues found ferritin and transferrin saturation lower in the early follicular phase. The hepcidin response to exercise was also lower at this time, which the authors suggest may indicate more favourable iron absorption, though absorption was not measured directly.
• Cycling durability may differ between sexes for submaximal parameters. A 2026 cycling-specific study by Elisa Pastorio and colleagues (n=16 males, 16 females, trained but not elite) found that after 90 minutes of heavy-intensity cycling, power at gas exchange threshold and respiratory compensation point held up better in female cyclists than male cyclists. Peak VO2 and neuromuscular fatigue declined similarly in both sexes. Single study, modest sample, but cycling-specific.

HRV, Resting Heart Rate, and the Luteal Phase

This catches people out: HRV tends to drop in the luteal phase, and resting heart rate tends to rise. Both are normal effects of progesterone, not signs of overtraining. Magnitude varies between athletes and even between cycles for the same athlete, and the change is sometimes too small to detect against day-to-day noise. Both numbers usually return to baseline within a few days of menstruation starting.

The practical point: comparing a luteal-phase HRV reading to a follicular-phase baseline will make today look worse than it is. Track your cycle alongside your HRV data and build the right baseline for each phase.

How the VeloCoach AI Coach Uses Cycle Phase

This matters because the popular framing is "cycle-aware training = downgrade workouts by phase." That is not what the VeloCoach coach does.

The coach reads your phase as context, alongside your HRV, sleep, training load, and RPE. It does not pre-emptively change your workouts because the calendar says it is day 18. What it does do, reactively:

• If you report that effort feels disproportionately hard relative to your power numbers in luteal, the coach validates that explicitly rather than telling you to push harder.
• If back-to-back hard days are scheduled and you are reporting accumulated fatigue, the coach may suggest spacing them differently.
• It extends warm-up guidance where the physiology supports it.

What it does not do: assume you will be slower or stronger in any phase, downgrade single intervals because of cycle day, or tell you what you should be feeling. The data leads. The calendar provides context for interpreting the data.

Hormonal Contraception

A significant portion of the cycling audience uses hormonal contraception: combined oral pills, the patch, the ring, hormonal IUDs. The four-phase framework above does not apply unchanged to these users because the natural cycle is suppressed.

This does not mean cycle tracking is irrelevant. The cycle-aware part of VeloCoach still works on hormonal contraception, it just tracks symptoms and training response rather than estimating phases. Pill cycles produce a withdrawal bleed week which is not a true menstrual period and the relevant performance research is much thinner here. Hormonal IUDs (Mirena, Kyleena) can suppress ovulation in some users and not others, producing variable patterns. Copper IUDs preserve the natural cycle but can increase menstrual blood loss, raising iron-status concerns.

In each case, the principle is the same: track your own data, identify your patterns, and let those patterns inform decisions. Pregnancy, postpartum, and perimenopause involve different physiology again and are out of scope here.

The Bottom Line

The evidence does not support strong universal claims about phase-prescribed training. It supports paying attention. Track your cycle alongside your training data, notice your own patterns over three or four cycles, and use it as one more piece of context.

Related Reading

• Fuelling the Four Phases: Nutrition and the Menstrual Cycle
• For Training Partners and Coaches: Cycle-Aware Training
• HRV for Cyclists: What It Tells You and What It Doesn't
• Sleep and Cycling Performance
• Overtraining: Signs, Causes and Recovery
• Periodisation for Amateur Cyclists