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A groundbreaking study from kinesiologists at McMaster University has debunked the widely circulated belief that women can optimize muscle growth by timing resistance training to specific phases of their menstrual cycles. The research, published in the Journal of Physiology, found no significant impact—positive or negative—on the body’s ability to synthesize new muscle proteins based on cycle timing.
The findings contradict the popular internet trend of “cycle syncing,” which encourages women to adjust their workouts according to hormonal fluctuations throughout the menstrual cycle. According to Lauren Colenso-Semple, the lead author and a former graduate student at McMaster, “Our findings conflict with the popular notion that there is some kind of hormonal advantage to performing different exercises in each phase. We saw no differences, regardless of cycle timing.”
Research Methodology and Key Findings
For the study, researchers monitored the menstrual cycles of healthy young women for three months to ensure regularity. They noted that only about 12% of women have a consistent 28-day cycle with ovulation occurring on day 14—contrary to the common assumption of a “textbook” cycle.
Participants ingested a tracer molecule to measure muscle protein levels and performed heavy resistance exercises during two key phases of their cycles: the follicular phase, when estrogen levels peak, and the luteal phase, characterized by high progesterone levels. Researchers observed no difference in muscle protein synthesis between the two phases.
Challenging Cycle Syncing Trends
Cycle syncing has gained traction through fitness influencers, mobile apps, and social media advice, with proponents citing limited studies—mainly on animals—as evidence that hormonal fluctuations impact muscle response to exercise. However, this new study challenges those claims.
“Our 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. There is no physiological difference in response to the exercise,” explains Stuart Phillips, the Canada Research Chair in Skeletal Muscle Health at McMaster. “It is important to tailor your training to how you feel.”
The Need for Further Research
While this study provides clarity, scientists emphasize the need for further research, particularly in women’s health. Future studies should explore how training interacts with the menstrual cycle over long periods and examine the effects of oral and non-oral contraceptives on exercise responses.
Conclusion
This research marks an important step in debunking misinformation surrounding menstrual cycle-based training. Women can confidently pursue strength training without concern for cycle timing, focusing instead on their personal energy levels and well-being.
Disclaimer: The findings of this study apply to the parameters set by the researchers and may not account for individual physiological variations. Women should consult healthcare professionals or fitness experts for personalized training advice.
