In the age of (dis)information, fitness and wellness advice is everywhere on social media platforms like TikTok and Instagram—much of it misleading, entirely false or even dangerous. Now, new research has officially debunked one trend: cycle syncing, a concept pushed by fitness influencers that encourages women to time their workouts according to specific phases of their menstrual cycle to boost muscle growth.
At a time when more women are embracing strength training for its wide-ranging benefits, the concept might seem like the ultimate gym hack— but not so, according to a new study from McMaster University published this month in The Journal of Physiology.
The study involved 12 healthy young women with regular menstrual cycles, which were tracked using blood and urine tests to accurately determine their cycle phase. Participants also ingested a tracer molecule, a special substance that helps track and measure protein levels in the body. Each participant completed two exercise trials—one during the late follicular phase (when estrogen is high) and one during the mid-luteal phase (when progesterone is high). In each phase, they performed resistance training.
Ultimately, the research team found that the menstrual cycle phase had no effect on muscle protein production—muscles responded about the same in both phases.
“Our findings conflict with the popular notion that there is some kind of hormonal advantage to performing different exercises in each phase,” said Lauren Colenso-Semple, lead author of the study and a former graduate student in the Department of Kinesiology. “We saw no differences, regardless of cycle timing.”
As she noted on LinkedIn, the lack of difference should be considered welcome news for female fitness enthusiasts.
“Women can ditch the confusing and complex cycle syncing recommendations and ignore any fearmongering about oral contraceptives,” she wrote.
The study’s supervisor, Stuart Phillips, the Canada Research Chair in Skeletal Muscle Health at McMaster, noted that the work shows that women who want to lift weights and recondition their muscles should feel free to do so in any phase of their cycle.
“It is important to tailor your training to how you feel,” he added.
The researchers highlighted the need for more studies focused on women’s health, specifically research that examines how natural hormonal changes during the menstrual cycle—as well as external hormones like birth control— influence muscle growth and strength over time, using a more rigorous approach than in previous studies.
Some proponents of cycle syncing, however, praise the approach not just for fitness but for other areas of life as well, from skincare routines to social engagements and even scheduling certain activities for times when they feel most energized.
There’s no doubt about it—hormones are complex and woefully understudied. With such gaps in research and women left in the dark, several apps have hit the market to help women navigate their cycles and their transition into menopause, such as Clue and Flo. Smart ring maker Oura and human performance wearable company Whoop are also making strides in the women’s health space.
