Molecular markers of skeletal muscle hypertrophy following 10 wk of resistance training in oral contraceptive users and nonusers

The objective was to determine whether skeletal muscle molecular markers and SC number were influenced differently in users and nonusers of oral contraceptives (OCs) following 10 wk of resistance training. Thirty-eight young healthy untrained users (n = 20) and nonusers of OC (n = 18) completed a 10-wk supervised progressive resistance training program. Before and after the intervention, a muscle tissue sample was obtained from the vastus lateralis muscle for analysis of muscle fiber cross-sectional area (fCSA) and satellite cell (SC) and myonuclei number using immunohistochemistry, gene expression using PCR, protein expression, and myosin heavy chain composition. Following the training period, quadriceps fCSA (P < 0.05), SCs/type I fiber (P = 0.05), and MURF-1 mRNA (P < 0.01) were significantly increased with no difference between the groups. However, SCs/total fiber and SCs/type II fiber increased in OC users only, and SCs/type II fCSA tended (P = 0.055) to be greater in the OC users. Furthermore, in OC users there were a fiber type shift from myosin heavy chain (MHC) IIx to MHC IIa (P < 0.01), and expression of muscle regulatory factor 4 (MRF4) mRNA (P < 0.001) was significantly greater than in non-OC users. Use of second-generation OCs in young untrained women increased skeletal muscle MRF4 expression and SC number following 10 wk of resistance training compared with nonusers.NEW & NOTEWORTHY The effect of oral contraceptive use on the skeletal muscle regulatory pathways in response to resistance training has not been investigated previously. Here we present novel data, demonstrating that use of second-generation oral contraceptives in young untrained women increased skeletal muscle regulatory factor 4 expression and satellite cell number following 10 wk of resistance training compared with nonusers.