LAUSR

OBJECTIVE to determine whether skeletal muscle molecular markers and SC number were influenced differently in users and non-users of oral contraceptives (OCs) following 10 weeks of resistance training Methods: Thirty-eight young healthy untrained users (n=20) and non-users of OC (n=18) completed a 10-week 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. RESULTS 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 MHC IIx to MHC IIa (p<0.01) and expression of MRF4 mRNA (p<0.001) was significantly greater than in non-OC users. CONCLUSION Use of 2nd generation OCs in young untrained women increased skeletal muscle MRF4 expression and SC number following 10 weeks of resistance training compared to non-users.