Decades of Exercise Research Excluded Women Over an Assumption That Was Wrong

Decades of research in fields such as exercise physiology have routinely left women out of studies entirely or included far fewer women than men, according to an exercise physiologist writing about the problem. The practice is not confined to old studies. It has continued in research from the past 20 years, even as many assumed the scientific community had caught up on including women equally.

Researchers often excluded women because of uncertainty over whether fluctuations linked to the menstrual cycle or hormonal birth control might affect measurements such as muscle function. Rather than resolve that uncertainty, many studies simply included fewer women or none at all. The pattern echoes an earlier era when women were discouraged from competing in the Olympics or in sports generally, over fears that physical exertion might harm their bodies or reproductive health.

A key study that helped change this thinking found that menstrual cycles typically do not significantly affect blood vessel function. It also found no meaningful differences in muscle function or performance between women using hormonal birth control and those who are not. Those findings helped researchers move past a 1995 study that had found the opposite and had long been cited as a reason to exclude women, because the variables seemed too complex to resolve.

In 2018, graduate students Ninette Shenouda and Stacey Priest questioned that reasoning. They tested whether measures of blood vessel and heart health during exercise were affected by the timing of the menstrual cycle or the oral contraceptive cycle, and found no significant day-to-day differences. Similar results have since emerged in other areas of exercise physiology, including how the menstrual cycle phase affects the response to resistance exercise training.

The gap in knowledge extends beyond exercise physiology. Researchers studying heart attacks have similarly found that symptoms and outcomes can vary between women and men, information now being used to improve care for both. Researchers are now working to compare women across the full lifespan and to fill similar blanks in other fields of science that have historically underrepresented women.