Oral contraceptive pill phase does not influence muscle protein synthesis or myofibrillar proteolysis at rest or in response to resistance exercise

There is speculation that the use of oral contraceptive pill (OCP) affects skeletal muscle biology and protein turnover in response to resistance exercise; however, research in this area is scarce. We aimed to assess, using stable isotope tracers and skeletal muscle biopsies, how second-generation OCP phase affected muscle protein synthesis and whole body proteolysis. Participants (n = 12) completed two 6-day study phases in a randomized order: an active pill phase (active; week 2 of a monthly active OCP cycle) and an inactive pill phase (inactive; final week of a monthly OCP cycle). They performed unilateral resistance exercise in each study phase, exercising the contralateral leg in the opposite phase in a randomized, counterbalanced order. The active phase myofibrillar protein synthesis (MPS) rates were 1.44 ± 0.14%·day^-1 in the control leg and 1.64 ± 0.15%·day^-1 in the exercise leg (P < 0.001). The inactive phase MPS rates were 1.49 ± 0.12%·day^-1 in the control leg and 1.71 ± 0.16%·day^-1 in the exercise leg (P < 0.001), with no interaction between phases (P = 0.63). There was no significant effect of OCP phase on whole body myofibrillar proteolytic rate (active phase k = 0.018 ± 0.01; inactive phase k = 0.018 ± 0.006; P = 0.55). Skeletal muscle remains equally as responsive, in terms of stimulation of MPS, during active and inactive OCP phases; hence, our data do not support a proanabolic or catabolic, based on myofibrillar proteolysis, effect of OCP phase on skeletal muscle in females.NEW & NOTEWORTHY We discovered that women taking a second-generation oral contraceptive pill (OCP) showed no difference in integrated daily muscle protein synthesis or whole body myofibrillar proteolysis in the active or placebo pill phases of the pill cycle. Our data show that OCP phase neither influences skeletal muscle protein turnover in females and nor supports a marked procatabolic or anabolic effect.