Effect of Oral Contraceptive Use on Muscle Hypertrophy Following Strength Training.

Oral contraceptives (OC) are widely used by women, while their interactions with strength training are yet to be resolved. This study investigated the effects of OC use on muscle hypertrophy and strength adaptation to heavy strength training in young adult women. Fifteen habitual OC users and 17 non-OC users (NOC) with regular menstrual cycles completed ~12 weeks of strength training, which spanned three menstrual cycles for the NOC group. All participants were young, healthy, and strength-untrained. Isometric knee-extensor strength, muscle cross-sectional area of the vastus lateralis (ultrasound imaging), and body composition (DXA) were used to evaluate training adaptations. Blood samples for estradiol and progesterone analyses, dietary registrations, and questionnaires assessing appetite, vitality, motivation, recovery status, and sleep duration were collected during the intervention period. Both groups experienced gains in lean mass and muscle strength. However, the OC group demonstrated a significantly larger increase in arm lean mass (5.5% ± 3.9% [mean ± standard deviation] vs. 2.9% ± 2.8%, p < 0.05) and vastus lateralis cross-sectional area (10.0% ± 4.1% vs. 5.3% ± 4.4%, p < 0.05) compared to the NOC group. Despite these differences, there was no significant group difference in lower body strength gains. Both groups reported similar levels of appetite, dietary intake, vitality, motivation to exercise, and perceived recovery throughout the study, although the OC group slept an average of 42 min longer per day. Our findings suggest that OC use potentiates muscle growth during strength training, although further research is needed to elucidate the underlying mechanisms and long-term effects.