A recent study reports that menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar protein breakdown in response to resistance exercise. Researchers found no significant anabolic advantage to performing resistance training in any particular phase of the menstrual cycle.
Published in The Journal of Physiology, the study involved 12 premenopausal women assessed during the late follicular (high estrogen) and mid-luteal (high progesterone) phases. Using a crossover design with counterbalanced conditions, participants performed unilateral resistance exercises over two randomized six-day phases while the contralateral leg served as a control. Muscle biopsies, stable isotope methodologies, and deuterium oxide tracing were used to measure protein turnover.
Resistance exercise significantly increased MPS (P < 0.001), but menstrual cycle phase had no effect on resting or exercise-stimulated MPS or MPB. Myofibrillar protein synthesis rates in the follicular phase were 1.33 ± 0.27% d⁻¹ in the control leg and 1.52 ± 0.27% d⁻¹ in the exercised leg. In the luteal phase, these rates were 1.28 ± 0.27% d⁻¹ in the control leg and 1.46 ± 0.25% d⁻¹ in the exercise leg.
"Skeletal muscle is not more anabolically responsive to resistance exercise in a particular menstrual cycle phase," said lead author Lauren M. Colenso-Semple from the Exercise Metabolism Research Group, Department of Kinesiology, McMaster University, Hamilton, ON, Canada. The study's corresponding author was Stuart M. Phillips.
The study employed rigorous methods to confirm menstrual cycle phases, including cycle tracking, urinary ovulation tests, and blood hormone analysis. Muscle biopsies were taken from the vastus lateralis, and deuterium oxide tracing was used to measure muscle protein turnover over five days.
Metabolomics analysis identified 1,376 unique biomolecules, but no notable phase-specific differences were observed in circulating blood metabolites.
Given the substantial inter-individual variability in cycle length and hormone levels observed in the study, the researchers emphasized the importance of direct hormone measurements rather than relying on assumed menstrual cycle timing.
The findings contradict speculation that the follicular phase might be more advantageous for muscle anabolism due to higher estrogen levels compared to the luteal phase with its higher progesterone levels.
These results have important implications for female athletes and exercise science research. The authors suggest that "premenopausal female participants should not be excluded from exercise science studies solely on concerns about their hormonal status as a potential confounding variable, at least in studies involving muscle protein anabolism and likely other outcomes."
The study adds to the growing body of literature questioning the impact of ovarian hormone fluctuations on exercise-induced muscle adaptation. The researchers suggest future longitudinal studies to examine muscle hypertrophy and strength development in response to resistance training across multiple menstrual cycles.
While the article states no competing interests, the corresponding author S.M. Phillips has received grant funding from various organizations including the Canadian Institutes for Health Research and holds patents licensed to Exerkine Inc., though he reports no financial gains.