Menstrual Cycle Phase Doesn’t Impact Muscle Growth, Study Finds

For years, many exercise physiology studies have excluded women, based on the belief that fluctuations in reproductive hormones during the menstrual cycle could skew results. However, a new study published in the Journal of Physiology is challenging this assumption.

Challenging the Anabolic Window Theory

Some have proposed that the follicular phase of the menstrual cycle, when estrogen levels are high, might be more favorable for muscle growth (anabolism) compared to the luteal phase, when progesterone is the dominant hormone. The idea is that estrogen may play a role in muscle repair and growth. To test this, researchers at McMaster University in Canada conducted a study with 12 young women. The participants underwent resistance exercise training, and muscle protein synthesis (MPS) and myofibrillar protein breakdown (MPB) were measured during both the follicular and luteal phases of their menstrual cycles.

What Did They Find?

The results of the study indicated that resistance exercise did indeed stimulate MPS, which is essential for muscle growth. However, the researchers found no significant differences in MPS or MPB between the follicular and luteal phases. In other words, muscle growth in response to exercise was not influenced by the menstrual cycle phase.

Busting the Myth of Hormonal Influence

This research suggests that the belief that women need to plan their training around their menstrual cycle to maximize muscle growth may not be supported by scientific evidence. While hormonal fluctuations undoubtedly cause physiological changes in women, these changes don't seem to significantly affect muscle protein synthesis or breakdown.

Key Takeaway

The bottom line is that women can focus on their training without worrying about timing it around their menstrual cycle. This study provides evidence that the menstrual cycle phase does not appear to be a determining factor in muscle protein synthesis after resistance exercise.