Menstrual cycle found to affect women’s reaction time, but not as much as being active

Women performed best on cognitive tests during ovulation but physical activity level had a stronger influence on brain function, according to a new study from researchers at UCL.

The study, published in Sports Medicine–Open, explored how the different phases of the menstrual cycle and physical activity level affected performance on a range of cognitive tests designed to mimic mental processes used in team sports and everyday life, such as the accurate timing of movements, attention, and reaction time.

The team found that women had the fastest reaction times and made the fewest errors on the day of ovulation, when the ovaries release an egg ready to be fertilized (and when women’s fertility is at its peak).

But while cognitive performance fluctuated across the menstrual cycle, much greater differences were observed between those who were active and those who weren’t. Compared to active participants, inactive participants had reaction times on average around 70 milliseconds slower and made around three times as many impulsive errors, regardless of cycle phase.

The researchers say the findings are particularly relevant to women’s sport, where slightly quicker reaction times of around 20 milliseconds may make the difference between sustaining or avoiding an injury like concussion. Previous research on elite athletes has suggested injuries are more common at certain points during the menstrual cycle, and the authors say that these changes in cognition might partially explain this occurrence.

However, while a difference of 20 milliseconds is likely to be inconsequential in everyday life, the much larger difference between active and inactive groups is more significant, where 70 milliseconds could determine whether we regain balance after tripping over an obstacle or not.

Dr. Flaminia Ronca, lead author of the study from UCL Surgery and Interventional Science and the Institute of Sport, Exercise & Health, said, “This is the first time we’ve directly measured ovulation in this context and we found that cognitive performance was at its best during this phase, with participants reacting around 30 milliseconds faster compared to later in their cycle, during the mid-luteal phase before periods begin. At elite level, this could make the difference between sustaining a serious injury in a collision or not.

“But the really interesting finding for me is that the difference between those who were active and inactive was much greater at around 70 milliseconds, which is enough time for the brain to register a stimulus and initiate a voluntary reaction, and is therefore far more meaningful for everyday life.

“This shows the importance of incorporating some form of recreational physical activity into our lives. It doesn’t have to be that intense or competitive to make a difference—and crucially, it’s something that we can control.”

The research included 54 women aged 18–40 who were naturally menstruating (not using hormone-based contraception), who were categorized into four groups based on their athletic participation level: inactive (reported not taking part in any form of structured exercise), recreationally active (taking part in at least two hours of structured exercise a week), competing in any sport at club level, and elite (competing in any sport at national or international level).

The researchers tracked participants across the four key phases of the menstrual cycle. Participants completed a 10-part questionnaire to assess their mood and completed cognitive tests on the first day of menstruation, two days after the end of menstruation (late follicular phase), on the first day ovulation was detected, and between ovulation and menstruation (mid-luteal phase).

Confirming previous findings from UCL researchers, the new study showed that reaction times were slower during the mid-luteal phase, likely due to increased levels of the female sex hormone progesterone, which is known to slow the brain down. However, this did not lead to more errors, suggesting that slower processing speeds observed during this phase do not necessarily compromise accuracy.

More errors were seen in the late follicular phase (just after the period ends). The researchers say it is not known yet why this would be the case.

Participants again reported lower energy and more symptoms during menstruation, yet these subjective experiences did not correlate with actual performance. 55% of participants believed their symptoms during menstruation were impairing their performance, but the researchers found no evidence of this—in fact, reaction time was also faster than during the mid-luteal phase.

Evelyn Watson, an author of the study from UCL Surgery and Interventional Science and the Institute of Sport, Exercise & Health, said, “It’s great to see that while participants assumed that they were performing worse during menstruation, the findings don’t demonstrate any detriment to cognition. If anything, cognitive performance peaked during ovulation. This is a positive outcome that we hope can help develop a new narrative in female health and performance.”

Dr. Ronca concluded, “Working exercise into our day doesn’t need to be difficult. Some of our previous studies have shown that 15 minutes of moderate activity is enough to boost our mood and cognitive performance. That’s equivalent to taking a brisk walk around the block or cycling to the shops.”