The effect of oral contraceptives on the early response to resistance exercise training in women

Abstract

Resistance exercise is widely recognized for its health benefits and capacity to induce cellular adaptations in skeletal muscle. Beyond increases in strength and hypertrophy, resistance exercise training promotes changes in muscle fibre cross-sectional area, fibre type composition, and satellite cell content and activation. Estrogen, a primary sex hormone, plays a key role in differentiating male and female physiology and has been implicated in sex-specific differences in muscle physiology. Oral contraceptives (OCs) contain synthetic versions of estrogen and progesterone that mimic the hormones naturally cycling in females. Since estrogen has been investigated for its potential influence on muscle mass and function, these synthetic hormones found in OCs may influence skeletal muscle. We hypothesized that women using oral contraceptives would exhibit a more pronounced muscle adaptive response, including enhanced satellite cell content, compared to non-OC users following resistance exercise training. Twenty-eight women (n=14 taking the OC pill, n=14 naturally cycling individuals, average age 21.9 in OC users and 20.5 in non-OC users) were enrolled in a 4-week resistance exercise training program with weekly muscle biopsies to assess the temporal changes in muscle adaptation. Contrary to our hypothesis, the data revealed that OC and non-OC users did not exhibit differential responses in the early stages of resistance training. Interestingly, in both groups, the satellite cell pool expanded over the first 3 weeks of exercise training and then plateaued. These results provide valuable insights into the timeline and regulatory mechanisms underlying resistance exercise-induced adaptations in OC users and non-users. Moreover, this study establishes an important framework for future research exploring muscle physiology in populations of women taking the oral contraceptive pill.