McMaster Study Debunks Myth: Menstrual Cycle Has No Impact on Muscle Growth

New research from McMaster University challenges the belief that aligning resistance training with menstrual cycle phases enhances muscle growth. The study, published in the Journal of Physiology, found no measurable effect of cycle timing on the body’s ability to synthesize muscle proteins, contradicting the popular trend of “cycle syncing” for exercise.

Lead author Lauren Colenso-Semple explains, “Our findings conflict with the idea that hormonal fluctuations provide an advantage to training at specific times. We saw no differences in muscle protein synthesis across cycle phases.”

Researchers monitored participants’ menstrual cycles over three months before conducting resistance training sessions during both the follicular and luteal phases. By tracking muscle protein synthesis, they confirmed that neither phase impacted muscle-building responses.

Cycle syncing, widely promoted on social media and fitness apps, often cites animal studies to support its claims. However, this research suggests that women can train effectively at any point in their cycle.

“There is no physiological difference in exercise response based on cycle timing,” says Stuart Phillips, senior author and Canada Research Chair in Skeletal Muscle Health. “Women should tailor their workouts to how they feel rather than following unproven cycle-based training plans.”

The researchers emphasize the need for further studies on women’s health, including the effects of contraceptives on training outcomes.
McMaster Study Debunks Myth of Menstrual Cycle Impact on Muscle Growth

A new study from McMaster University challenges the widely held belief that aligning strength training with menstrual cycle phases enhances muscle growth. Published in the Journal of Physiology, the research found no significant impact of cycle timing on the body’s ability to synthesize muscle proteins, disproving the popular fitness trend known as “cycle syncing.”

Breaking the Cycle Syncing Myth
Cycle syncing, a practice promoted by social media influencers and fitness apps, suggests that women should adjust their workouts based on hormonal fluctuations throughout their menstrual cycle. Proponents claim that resistance training during the follicular phase (when estrogen peaks) leads to greater strength gains, while the luteal phase (when progesterone is higher) requires a gentler approach. However, McMaster researchers found no scientific basis for these claims.

“Our findings conflict with the idea that certain phases of the menstrual cycle provide a hormonal advantage for strength training,” says lead author Lauren Colenso-Semple, a former graduate student in McMaster’s Department of Kinesiology. “We saw no measurable differences in muscle protein synthesis, regardless of cycle timing.”

How the Study Was Conducted
To test the effects of cycle timing on muscle growth, researchers monitored the menstrual cycles of young, healthy female participants for three months to confirm their regularity. Participants then performed heavy resistance exercises during two key phases of their cycles:

The Follicular Phase (when estrogen is at its highest)
The Luteal Phase (when progesterone peaks)
To track muscle protein synthesis, researchers used a tracer molecule—an advanced method for measuring the body’s ability to build new muscle proteins. The results revealed no significant difference in muscle-building responses between the two phases.

Scientific Evidence vs. Social Media Trends
Despite the lack of scientific support, cycle syncing has gained traction in the fitness industry, with apps, coaches, and influencers advocating for cycle-based training programs. Much of this advice is based on limited research, often derived from animal studies rather than human trials.

“There’s no evidence that timing workouts with menstrual cycle phases leads to better results,” says senior author Stuart Phillips, Canada Research Chair in Skeletal Muscle Health at McMaster. “Women should feel confident lifting weights and conditioning their muscles at any point in their cycle without concern for hormonal fluctuations.”

What This Means for Female Athletes and Fitness Enthusiasts
This research suggests that women can train effectively throughout their cycle, focusing on consistency and personal well-being rather than trying to align workouts with hormonal changes.

“It’s more important to listen to your body and adjust workouts based on how you feel rather than following unproven cycle-based training plans,” Phillips emphasizes.

The study also highlights the need for more research in women’s health, particularly regarding the effects of contraceptives and long-term training adaptations.

Final Takeaway
For those looking to optimize their fitness, the key takeaway is clear: menstrual cycle phases do not determine muscle-building potential. Instead of relying on cycle syncing, women should prioritize well-structured strength training programs, proper nutrition, and recovery to achieve their fitness goals.