If one week your run flies and the next it feels like you're carrying a backpack of rocks, you're not imagining it. In a survey of 6,812 women who exercise, 86% reported tiredness at some point in their cycle. Your fitness hasn't gone anywhere; it's how you feel that changes.
Should I train by cycle phase?
The "personal bests in the first half, yoga in the second" plan sounds logical, but research doesn't back it up. A large 2020 review found performance was slightly lower on average in the first days of a period, but the difference was tiny and results varied a lot between studies. So the authors gave no general rules and advised looking at each person individually.
For strength training, a 2023 paper pulled all the reviews together and came to the same conclusion: there's no good evidence yet that phase noticeably changes strength or muscle growth.
So why do some days feel so different?
Most often it's symptoms: among those same 6,812 women, 91% noticed mood changes or anxiety, 84% cramps and 83% sore breasts. The more symptoms someone had, the more often she skipped or changed a session. Then add things that have nothing to do with your cycle: short sleep, stress, too little food, built-up training load.
So how do I plan?
Keep your usual plan and decide in the morning based on how you feel. If you have plenty of energy, stick to the plan; if it's hard going, cut the pace, distance or weight.
For a couple of cycles, note in your diary how each session felt and how you slept. If there's a pattern, you'll see it and can schedule easier days ahead of time.
How do I run or do yoga on my period?
The same as any other day, if you feel comfortable. When you have cramps, easy running, walking and yoga help many people. A tampon or cup keeps leaks away on a run, and you can pair either with period pants for extra security. Dark shorts and spare underwear in your bag add peace of mind.
Common questions
Why do I have zero energy on my period?
One common reason for runners is heavy periods and low iron. Among London Marathon runners, 36% had heavy periods, and for nearly half of them their cycle got in the way of training.
Are inversions OK on my period?
Yes, if you're comfortable. The rule comes from some yoga schools, and no study has shown harm. If you'd rather not, choose poses lying down.
What if my cycle is irregular?
Go by how you feel and your diary: note how each session went and how you slept. After a couple of months you'll see whether some days come easier, even without predictable dates.
What if I'm on the combined pill?
The combined pill stops ovulation, so you don't have phases in the usual sense. The same guides apply: how you feel and your diary.
In short
- Decide each morning, by how you feel, what today's session looks like
- For a couple of cycles, log how each session felt
- For a run on your period, use a tampon or cup plus period pants
Source: Sports Medicine: Menstrual cycle and exercise performance
Educational content; it does not replace professional medical advice.