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

Colenso-Semple, Lauren M, McKendry, James ORCID: https://orcid.org/0000-0002-9951-0590, Lim, Changhyun ORCID: https://orcid.org/0000-0002-5437-8063, Atherton, Philip J, Wilkinson, Daniel J, Smith, K ORCID: https://orcid.org/0000-0001-8971-6635 and Phillips, Stuart M ORCID: https://orcid.org/0000-0002-1956-4098 (2025) Oral contraceptive pill phase does not influence muscle protein synthesis or myofibrillar proteolysis at rest or in response to resistance exercise. Journal of Applied Physiology. ISSN 1522-1601

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Abstract

There is speculation that oral contraceptive pill (OCP) use 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 two of a monthly active OCP cycle) and an inactive pill phase (Inactive; final week of a monthly OCP cycle). Participants 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 %•d-1 in the control leg and 1.64 ± 0.15 %•d-1 in the exercise leg (p < 0.001). The Inactive phase MPS rates were 1.49 ± 0.12 %•d-1 %/d in the control leg and 1.71 ± 0.16 %•d-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 does not support a pro-anabolic or catabolic, based on myofibrillar proteolysis, effect of OCP phase on skeletal muscle in females.