A small wearable-sensor study suggests that daily movement may rise and fall with shifts in estradiol levels, offering new clues about how menstrual-cycle physiology shapes real-world activity, according to a June 21 article.
The study, published in the journal npj Women’s Health, found that women's daily physical activity was correlated with fluctuations in the hormone estradiol across the menstrual cycle. The researchers monitored physical activity in a cohort of 26 healthy young women who were not using hormonal contraceptives by using a single shank-worn inertial measurement unit. Active energy expenditure was calculated using a validated machine-learning model and compared with external reference hormone data from previous studies.
The findings showed a significant correlation between daily activity and estradiol fluctuations when activity was shifted by two days relative to estradiol levels. This suggests that changes in estradiol may precede changes in movement. In contrast, the relationship between progesterone and activity was weak and negative. The strongest association between active energy expenditure and estradiol occurred during a 10-day window around ovulation.
Researchers noted that increased physical activity is associated with higher levels of estradiol based on prior animal and human studies. However, unlike some earlier research, this study observed an increase in activity during the early follicular phase due mainly to participants taking more steps rather than expending more energy per step. The authors said factors such as menstrual symptoms or other behaviors were not examined, so reasons for this increase remain unclear.
The authors propose that wearable monitors could provide useful data to complement other reproductive-health measures but caution that their findings are limited by sample size, lack of participant-specific hormone measurements, and potential confounding factors like work schedules or sleep quality. "Overall, the study suggests that daily physical activity measured by wearable devices correlates at the cohort level with fluctuations in estradiol during the menstrual cycle and may offer a convenient, non-invasive way to study how menstrual-cycle physiology relates to movement," they said.
