Influence of second generation oral contraceptive use on adaptations to resistance training in young untrained women. J Strength Cond Res 36(7): 1801-1809, 2022-The study purpose was to determine effects of using second generation oral contraceptives (OC) on muscle adaptations to resistance training in young untrained women. Twenty users and 18 nonusers of OC completed a 10-week supervised progressive resistance training program. Before and after the intervention, muscle cross-sectional area (mCSA) of the quadriceps was measured using magnetic resonance imaging and muscle fiber CSA (fCSA) was determined by immunohistochemistry. In addition, body composition (DXA, fat mass/fat-free mass), maximal isometric muscle strength (dynamometry), 5 repetition maximum (5RM) leg press strength, counter movement jump (CMJ) height, and average power using a modified Wingate test were determined. Serum hormone analysis ensured OC compliance and 4-day food records documented dietary intake. After the training period, quadriceps mCSA (OC: 11.0 6 6.0% vs. non-OC: 9.2 6 5.0%, p 5 0.001), type II fCSA (OC: 19.9 6 7.9% vs. non-OC: 16.6 6 7.2%, p 5 0.05), muscle strength (knee extension, knee flexion and 5RM, p , 0.001), and functional power (CMJ, AP, p , 0.001) were significantly increased with no significant difference between the groups. However, a tendency toward a greater increase in fat-free mass (FFM) in the OC group was observed (OC: 3.7 6 3.8% vs. non-OC: 2.7 6 3.5%, p 5 0.08). Collectively, use of second generation OCs in young untrained women did not significantly improve adaptations to 10 weeks of resistance training compared with nonusers. The trend toward greater gains in FFM in the OC group warrant future studies.

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.