Menstrual cycle and running

Yes: running during your period is safe, and many runners find it eases cramps and lifts their mood. Adjust to how you feel rather than skipping sessions by default.

• Research finds at most a small, inconsistent effect of the cycle on performance; differences between runners are larger than between phases.
• Some feel heavier or warmer in the days before the period: ease the pace, or swap a hard session for an easy one if needed.
• Heavy periods raise the risk of low iron: lasting tiredness or breathlessness is worth a blood test.
• Periods that become irregular or stop for 3 months or more can signal under-fuelling: see a doctor.

Logging your cycle in Apple Health helps you spot your own patterns.