Research challenges menstrual cycle-based workout “philosophy”

Research by McMaster University in Canada has challenged the common belief that timing resistance training to specific phases of the menstrual cycle boosts a woman’s body’s ability to build muscle and strength.

A study by kinesiologists at MacMaster – a public research university in Hamilton, Ontario, Canada – showed that exercising at various points in the cycle had no impact, positive or negative, on the synthesis of new muscle proteins, a process essential to building and maintaining muscle.

The results, published in the print edition of the Journal of Physiology, seem to debunk the popularly touted practice of cycle syncing, or tailoring workouts to align with the way hormones change throughout a woman’s menstrual cycle.

“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. “We saw no differences, regardless of cycle timing.”

Cycle syncing has been made popular by internet influencers to coordinate workouts, certain diets and lifestyle behaviours with the menstrual cycle. There are also fitness apps for tracking cycles, and social media channels are rife with advice and recommendations.

Proponents routinely cite a handful of scientific studies on animals as evidence that fluctuations in ovarian hormones can affect how human muscles respond to exercise – a view that the McMaster study now challenges.

“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,” says Stuart Phillips, the Canada Research Chair in Skeletal Muscle Health at McMaster who supervised the study.

“It is important to tailor your training to how you feel.”