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My training is improving. Why have my periods stopped?

26 Oct 2026

By ProFertility

A woman in a blue jacket walking outdoors beside a lake with a water bottle

A period that stops after you increase training deserves attention, even if you feel strong and your performance is improving. Under-fuelling can disrupt reproductive function, but exercise is not the only explanation. Pregnancy, medicines, contraception and other hormonal conditions need consideration too.

You do not have to be trying for a baby for this to matter. Our guide to missing periods, exercise and low energy availability explains assessment, support and recovery in more detail.

Performance is one result, not a complete health check

A faster run, heavier lift or easier session can feel like reliable evidence that your routine suits you. Those achievements are real. The problem is asking them to answer a different question: whether your reproductive system is functioning as expected.

A training log and a menstrual record describe different parts of your life. If one improves while the other changes markedly, the answer is to put them together. It is not necessary to choose between respecting your sporting goals and taking the cycle change seriously.

That is the ProFertility view of proactive reproductive health: pay attention while there is something useful to investigate, rather than waiting until a future pregnancy plan makes the same symptom feel urgent.

A balanced-looking diet may still leave a fuelling gap

Energy availability describes the energy left for the body's other functions after exercise. The IOC's 2023 consensus on Relative Energy Deficiency in Sport, or REDs, describes how problematic low availability can affect reproductive function and other systems. It is not a diagnosis made from a photograph, a food label or one missed period.

Consider an illustrative situation: a person adds long training sessions while meals remain much as before. The food may be varied and nutritious, yet the demands have changed. The useful discussion concerns the whole routine—fuel, activity, recovery and health—rather than whether individual foods count as good or bad.

Body weight alone does not settle that discussion. Equally, an online energy calculator cannot establish why your periods have stopped. The IOC methodology paper highlights the difficulty of measuring intake and expenditure accurately in ordinary life and advises against using an energy-availability calculation to diagnose REDs.

What a nutrition trial adds—and what it does not promise

The REFUEL randomised trial, published in 2021, studied 76 exercising women with infrequent or absent periods. Over 12 months, the group assigned to increase energy intake was more likely to experience menstrual bleeding than the comparison group. The participants were young women recruited from two universities; the study was not a trial of pregnancy outcomes.

This supports taking fuelling seriously. It does not supply a personal calorie prescription, prove that every missed period is caused by eating too little or promise a recovery date. The authors also noted substantial dropout and that their recovery measure did not establish the quality of menstrual recovery.

A practical plan should therefore explain what is being addressed and how progress will be assessed. Copying another person's food target or race-training change skips the assessment that makes the plan relevant to you.

The first task is to establish the cause

The NHS lists several possible causes of missed periods, including pregnancy, stress, weight changes, exercise, contraception, breastfeeding and PCOS, now also called PMOS. ASRM's 2024 amenorrhea guidance describes a structured assessment rather than diagnosing from the exercise history alone.

Write down when your last natural period occurred, what changed in training or eating, medicines and contraception, and other symptoms. Bring existing reports if you have them. A clinician can decide which examination or tests are useful. You do not need to buy an entire fertility panel before seeking help.

The NHS advises a GP appointment after three missed periods in a row, and also for a missed period accompanied by other symptoms or newly irregular cycles. You can discuss a worrying change sooner; that advice is not a rule that you must wait before asking for care.

Reproductive health matters before a family-building decision

Sometimes a period is treated as relevant only to contraception or conception. That leaves an uncomfortable gap for someone who is not trying, is unsure about parenthood or is focused on sport, work or study. Their health still deserves a useful explanation.

For someone planning pregnancy, absent ovulation may affect the route forward. For someone not planning pregnancy, understanding and addressing the cause remains a valid goal. The assessment should begin with the person in front of the clinician, not an assumption about whether they want children.

Our female fertility reference connects the cycle with the wider reproductive picture. Lifestyle and fertility explains how health actions can fit alongside assessment without making conception a test of effort.

Leave with an action, an owner and a review

A useful next step might be investigation, nutrition support, an agreed training modification or care for a different hormonal condition. It should say who will interpret the findings and when the plan will be reviewed. If the first explanation does not fit the evidence, the plan should be reconsidered.

You should not have to diagnose yourself to be heard. Nor should a reassuring fitness result be used to dismiss a reproductive change. Bring the two stories into one conversation.

Read next: Missing Periods, Exercise and Low Energy Availability covers what to record, how assessment works and what meaningful follow-through can include.