Study finds correlation between daily physical activity and estradiol fluctuations across menstrual cycle

Hormonal Harmony: How Estrogen May Drive Daily Activity Levels

Key Finding: A new study reveals a significant link between the natural ebb and flow of estradiol and daily physical activity in menstruating women, suggesting hormones may help dictate movement patterns.

The Study at a Glance

Published in npj Women's Health, the research analyzed data from 26 healthy, naturally menstruating women not using hormonal contraceptives. Daily physical activity was tracked using a shank-worn inertial measurement unit, with active energy expenditure calculated via a validated machine-learning model.

These activity records were then compared against external reference hormone data from previous studies of healthy eumenorrheic (regularly menstruating) women.

Key Findings

• A clear hormonal-activity link emerged: A significant correlation was found between daily activity and estradiol levels—but only when activity data was shifted by two days relative to estradiol. This suggests that changes in estradiol may precede and potentially drive changes in movement.

• Progesterone's role was minimal: The relationship with progesterone was weak and negative, aligning best with no time delay.

• The ovulation window matters most: At the group level, active energy expenditure consistently rose after estradiol increased and declined after estradiol dropped, with the most pronounced effects occurring across a 10-day window around ovulation.

• Phase-specific differences: Activity was higher in the early follicular phase than in the late follicular phase, a trend driven by increased step count rather than energy expended per step.

What This Means

The authors propose that naturally occurring hormonal fluctuations may influence physical activity, likely through estradiol's physiological and psychological effects (e.g., energy levels, mood, motivation).

They suggest that wearable activity monitors could one day complement menstrual-cycle and reproductive-health tracking. However, they caution that validation with simultaneous hormone and activity measurements in the same individuals is still needed.

Important Limitations

• Separate cohorts: The study used different groups for activity and hormone data, aligning cycles via the LH surge. Findings reflect group-level patterns, not individual-level tracking.

• Small, homogenous sample: Participants were exclusively young, healthy, naturally menstruating women.

• Uncontrolled variables: Factors like work schedules, illness, sleep, stress, and lifestyle were not accounted for.

• Short monitoring window: Activity was recorded for only 28 days, likely truncating the luteal or follicular phases for cycles longer than 30 days.

• No hormone verification: Without participant-specific hormone measurements, anovulatory cycles could not be detected.

Bottom Line

Daily physical activity measured by wearable devices correlates at the group level with estradiol fluctuations during the menstrual cycle. However, further research in larger, more diverse populations with simultaneous hormone and activity tracking is essential to confirm and extend these findings.