Can you name all four phases of the menstrual cycle? Unless you use a period-tracking app or just finished high-school health class, you probably can’t. That’s because for most women without hormonal conditions, the three phases in between periods—follicular, ovulatory, and luteal—don’t feel all that different.

But a whole new wave of fitness programs wants women to plan their workout (and in some cases, their diets), around those four phases. The concept is known as cycle syncing, and programs include overviews of the relative levels of different menstrual hormones throughout the cycle and exercises tailored to the generalized ups and downs in pain, energy, and other physiological states that can occur.

While the approach is no doubt helpful for some, the reality is these programs are based on both oversimplified versions of the wildly unique menstrual cycles people experience and out-of-context assumptions about new and sometimes unproven findings in sports medicine. And though cycle-syncing programs encourage people to become more familiar with the ways in which their own menstruating bodies work, experts fear women will unwittingly accept the sexist idea that they are governed by their hormones.

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