Physical activity data correlate with fluctuations in estradiol

Approximately 1.8 billion people experience hormonal changes caused by the menstrual cycle, which impacts work, school, and health factors like physical activity. Prior research shows high-level insights, such as reduced activity during symptomatic days, but the day-to-day relationship between the menstrual cycle and physical activity remains unclear. We performed a 28-day study monitoring physical activity in 26 healthy, naturally menstruating women using an inertial measurement unit on the shank. A validated model estimated energy expended per step. Physical activity was significantly higher during the early-follicular phase than the late follicular phase due to more steps. Energy expenditure was compared with open-source daily estradiol and progesterone data collected from different study cohorts of healthy, eumenorrheic women. Peak estradiol and physical activity showed a correlation ( r 2 = 0.64) when activity was shifted by 2 days, suggesting a delayed relationship. Precisely measuring movement with wearable sensors could help uncover menstrual cycle effects on activity and improve health management and workplace policies.