Trail Notes | Hormones & Female Physiology

information, not destiny

Your Cycle Is Data,

Not a Training Calendar.

Your menstrual cycle may influence how you feel when you train. It does not decide what you are capable of doing.

For years, sport largely ignored the menstrual cycle. The correction has sometimes travelled too far in the other direction, with rigid schedules telling women exactly when they should lift, run hard, recover or avoid intensity.

Current research does not support one universal cycle-synced training plan. Average performance differences between menstrual-cycle phases appear small, and individual responses vary considerably.

What can be useful is tracking your own symptoms and training response over time. If a repeatable pattern appears, you can prepare for it without allowing a predicted phase to overrule how you actually feel.

Trail Note  ·  01

What changes across the cycle

The menstrual cycle is usually described through two main hormonal phases. The follicular phase begins on the first day of bleeding and continues until ovulation. The luteal phase follows ovulation and continues until the next period.

Menstruation occurs at the beginning of the follicular phase. Ovulation is an event between the follicular and luteal phases, not a week that reliably lands on day 14.

Cycle length and ovulation timing vary between people and can vary within the same person. Calendar estimates alone cannot confirm ovulation, which is one reason phase-based research and app predictions need to be interpreted carefully.

Trail Note  ·  02

What the performance research actually says

A major systematic review found that exercise performance may be slightly lower during the early follicular phase on average. The effect was trivial, the evidence quality was generally low and results varied substantially between studies.

That means the research does not justify telling every woman to place hard sessions in the follicular phase, expect peak performance at ovulation or avoid intensity in the luteal phase.

Some athletes experience clear and repeatable changes. Others notice little difference. The most evidence-aligned approach is to keep sound training principles in place, then individualise when your own data shows a meaningful pattern.

Trail Note  ·  03

Symptoms matter more than assumptions

Menstrual-cycle symptoms can affect training even when the average hormonal effect on performance is small. Cramps, heavy bleeding, migraine, digestive changes, breast tenderness, disturbed sleep, mood changes and premenstrual symptoms may all change what feels manageable.

The useful question is not “Which phase am I in?” on its own. It is “What am I experiencing, and does it meaningfully affect today’s training?”

Trail Note  ·  04

Heat, hydration and the luteal phase

Resting body temperature generally rises after ovulation during the luteal phase. It is biologically plausible that this may influence comfort or thermoregulation in hot conditions, but studies examining exercise in the heat have produced inconsistent results.

You do not need a different hydration formula simply because you are in the luteal phase. Use the same principles that apply throughout training: arrive hydrated, carry enough fluid for the conditions, include electrolytes when appropriate and respond to your known sweat rate and symptoms.

If your own tracking shows that heat feels consistently harder during a particular part of your cycle, prepare with cooler routes, earlier start times, realistic pacing and more deliberate cooling.

Trail Note  ·  05

Fuel the training, not a theoretical phase

Appetite and food preferences may change across the cycle. Some women feel hungrier before their period. That experience is valid, but current evidence is not strong enough to prescribe a universal phase-specific carbohydrate or protein plan for every female athlete.

Start with the fundamentals: enough total energy, carbohydrate matched to training demand, protein distributed across the day and adequate recovery nutrition. Do not suppress persistent hunger because you believe your intake should remain identical every day.

Trail Note  ·  06

What about injury risk around ovulation?

Some studies have found changes in knee ligament laxity across the cycle. That does not establish that an individual athlete is more likely to be injured on a specific predicted cycle day.

Systematic reviews describe the evidence connecting cycle phase with ACL injury as limited or inconsistent. There is currently no sound basis for telling trail runners to avoid hard or technical training around ovulation.

Use good injury-prevention practices throughout the month: progressive strength, appropriate technical preparation, sensible fatigue management and a warm-up suited to the session.

Trail Note  ·  07

Track patterns without creating rules

Tracking becomes useful when it connects cycle information with symptoms and training response. One difficult session is not a pattern. Look across at least three cycles before making larger planning decisions.

When a repeatable pattern appears, start with small changes. Move one key session, add recovery, plan additional symptom support or alert your coach. Keep testing whether the change actually helps.

Trail Note  ·  08

When race day lands on a difficult day

You cannot schedule every race around your cycle, and you do not need to. Prepare around symptoms you have actually experienced rather than assuming the phase will determine your performance.

Test your period products, clothing, bathroom plan, cramp-management strategy, fuelling and any clinician-approved medication before race day. Carry what you need and know where aid stations or toilets are located.

Then respond to the day in front of you. Many women perform well while menstruating and throughout the luteal phase. Awareness should improve preparation, not lower your ambition before the start.

Trail Note  ·  09

Not every athlete has a trackable natural cycle

Hormonal contraception can change or suppress natural hormonal fluctuations, and a withdrawal bleed is not the same as a natural menstrual period. Perimenopause, pregnancy, postpartum recovery, PCOS and other health conditions can also make cycle patterns less predictable.

You can still track symptoms, energy, sleep and training response. The goal is not to force every woman into the same four-phase model. It is to understand the physiology and circumstances of the athlete in front of us.

Your cycle can be useful information. Your individual experience is the part that makes that information actionable.

information, not destiny

Keep going with us

General education only, not medical advice. Seek qualified support for severe pain, very heavy bleeding, irregular or absent periods, suspected iron deficiency or symptoms that interfere with daily life.