Menstrual cycle phase does not influence muscle protein synthesis or whole-body myofibrillar proteolysis in response to resistance exercise

It has been hypothesised that skeletal muscle protein turnover is affected by menstrual cycle phase with a more anabolic environment during the follicular vs. the luteal phase. We assessed the influence of menstrual cycle phase on muscle protein synthesis and myofibrillar protein breakdown in response to 6 days of controlled resistance exercise in young females during peak oestrogen and peak progesterone, using stable isotopes, unbiased metabolomics and muscle biopsies. We used comprehensive menstrual cycle phase-detection methods, including cycle tracking, blood samples and urinary test kits, to classify menstrual phases. Participants (n = 12) completed two 6 day study phases in a randomised order: late follicular phase and mid-luteal phase. Participants performed unilateral resistance exercise in each menstrual cycle phase, exercising the contralateral leg in each phase in a counterbalanced manner. Follicular phase myofibrillar protein synthesis (MPS) rates were 1.33 +/- 0.27% h(-1) in the control leg and 1.52 +/- 0.27% h(-1) in the exercise leg. Luteal phase MPS was 1.28 +/- 0.27% h(-1) in the control leg and 1.46 +/- 0.25% h(-1) in the exercise leg. We observed a significant effect of exercise (P < 0.001) but no effect of cycle phase or interaction. There was no significant effect of menstrual cycle phase on whole-body myofibrillar protein breakdown (P = 0.24). Using unbiased metabolomics, we observed no notable phase-specific changes in circulating blood metabolites associated with any particular menstrual cycle phase. Fluctuations in endogenous ovarian hormones influenced neither MPS, nor MPB in response to resistance exercise. Skeletal muscle is not more anabolically responsive to resistance exercise in a particular menstrual cycle phase.