Sport and the cycle

Should you train more lightly on your period? Should you plan races around your cycle phase? The internet is full of confident answers. Science is far more cautious – and that’s good news.

What the research says

In 2020, a team of researchers from the UK and Brazil pooled 78 studies on whether cycle phase affects exercise performance in women with regular cycles. The conclusion: in the early follicular phase – the first days of the cycle – performance might be reduced, but the effect is “trivial”, meaning very small.¹

The authors add two important caveats. The differences between studies are large, and the quality of the evidence was rated “low”. So, in their view, general guidelines on training by phase can’t be formed. Instead they recommend an approach tailored to each individual woman.¹

But the symptoms are real

A small effect on performance doesn’t mean you don’t feel your cycle. A study of 6,812 exercising women from several countries who weren’t using combined hormonal contraception shows how common symptoms are:²

• mood changes or anxiety – 90.6%;
• tiredness – 86.2%;
• stomach cramps – 84.2%;
• breast pain or tenderness – 83.1%.

The more and the more frequent the symptoms, the more likely women were to miss or change training, miss a competition, work or study, and take painkillers.² In fairness: some of the authors work for a company that makes a cycle-tracking app for athletes.²

Everyone is different

A 2024 review of 39 studies found huge differences in how athletes experience their cycle: between 2.8% and 100% of participants in different studies said their cycle harmed their performance. The main reason was symptoms.³

In other words: if your cycle gets in your way, it isn’t “all in your head”. And if it doesn’t, you’re not an exception either.

There is no one-size-fits-all training plan by phase. There’s your cycle – and it’s worth getting to know.

Moving through the pain

The NHS lists gentle exercise among the things you can try yourself for period pain – yoga, swimming, walking or cycling, for example. Heat (a warm bath, a hot water bottle) and massaging your tummy and back can help too.⁴ You don’t need to set a record. Sometimes a walk is enough.

When training stops your period

Too much training can do the opposite – stop your periods altogether. The NHS lists “doing too much exercise” among the causes of missed or late periods, alongside stress and sudden weight loss.⁵

The International Olympic Committee describes Relative Energy Deficiency in Sport (REDs) – a condition in which an athlete takes in too little energy for what they spend in training, with harmful effects on health and performance.⁶ A missing period isn’t a sign that you’re training “seriously enough”. It’s a sign that something is wrong.

What you can do

1. For a few months, note which day of your cycle it is and how you feel in training – strength, energy, mood, pain.
2. Once you see your own pattern, plan the hardest sessions for the days you usually feel best.
3. On painful days, choose lighter movement rather than complete rest, if that helps you.⁴
4. If you avoid training because your bleeding is very heavy, or you’re constantly tired and short of breath, talk to a doctor – these can be signs of heavy periods.⁷
5. If you’ve missed 3 periods in a row, see a doctor.⁵

Sources

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. Bruinvels G, Goldsmith E, Blagrove R et al. Prevalence and frequency of menstrual cycle symptoms are associated with availability to train and compete: a study of 6812 exercising women recruited using the Strava exercise app. British Journal of Sports Medicine, 2021;55(8):438–443.
3. Oester C, Norris D, Scott D et al. Inconsistencies in the perceived impact of the menstrual cycle on sport performance and in the prevalence of menstrual cycle symptoms: A scoping review of the literature. Journal of Science and Medicine in Sport, 2024;27(6):373–384.
4. NHS (UK National Health Service). Period pain.
5. NHS. Stopped or missed periods.
6. Mountjoy M et al. 2023 International Olympic Committee’s (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 2023.
7. NHS. Heavy periods.