In the follicular phase, estrogen and follicle-stimulating hormone begin to rise, nudging the ovaries to nurture an egg for release and thickening the uterus for its arrival, Dr. Mahalingaiah said. According to proponents of cycle syncing, in this phase the body is primed to take on stress and can recover more quickly. Juliana Antero, a researcher at the French Institute of Sport, leads a program in the French sports ministry called Empow’her, which has been tailoring the training schedules of professional athletes to their cycles ahead of the 2024 Olympic Games. Ms. Antero said that, anecdotally, she has observed “a burst of energy” during this phase among athletes, which means they “are better at high-intensity training loads, they run faster, and they are more powerful.” As part of their personalized training regimen, the highest-intensity activities are scheduled during the follicular phase.
The egg’s release — ovulation — is followed by the luteal phase, characterized by high levels of the hormone progesterone, which is responsible for maintaining a stable environment in the uterus for a fertilized egg. The luteal phase can be associated with premenstrual syndrome symptoms, like bloating and low energy. In this window, the body may be better suited to lower-intensity activities with increased recovery time between workouts, said Stacy Sims, a sports and nutrition physiologist and former athlete who studies menstrual cycles and performance in professional athletes.
But cycles rarely follow supposedly typical patterns of peaks and troughs, said Dr. Clancy, who is also the author of “Period: The Real Story of Menstruation.” “If we look at the hormone cycles of hundreds of people, we don’t find anybody who looks like the textbook.” For example, some women skip ovulation for a few cycles or have multiple surges of estrogen. And it remains unclear whether cycle syncing makes sense for women using hormonal forms of birth control.
The bits of scientific and anecdotal evidence showing fluctuations in performance or energy throughout the menstrual cycle also don’t prove that syncing workouts to the cycle will optimize fitness. “From a medical standpoint, there is no good evidence,” said Dr. Asima Ahmad, a reproductive endocrinologist and the chief medical officer of a fertility benefits provider called Carrot Fertility. “It’s not something that I advocate for with my patients.”
Ms. Antero and Ms. Scott acknowledge the lack of research on the method, which they said is a symptom of a broader gap in research on women’s health. One of the main aims of the Empow’her program is to fill that void, Ms. Antero said. She plans to publish the results of the training program after the Olympics.
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