The effect of hormonal contraception on skeletal muscle hypertrophy and strength over an 8-week training intervention in recreational female strength athletes

Abstract

Background: There is limited research on how hormonal contraceptives (HC) may influence skeleton muscle hypertrophy and strength adaptations from resistance exercise training (RET), with no studies to date investigating long-acting reversible contraceptives (LARCs). Current research on HC shows mixed results regarding their impact on hypertrophy and strength. Furthermore, most research has been conducted on individuals with little to no prior RET experience, highlighting the need for studies on trained populations. Purpose: This study aims to investigate the influence of HC usage on skeleton muscle hypertrophy and strength adaptations in female strength athletes with RET experience following an 8-week training intervention. Method: Forty-one recreationally active female strength athletes in Tromsø, Norway, were recruited to investigate the effect of HC on hypertrophy and strength adaptations following an 8-week RET intervention. Participant were divided into three groups based on their current HC usage: combined oral contraceptives (COC), long-acting reversible contraceptives (LARC), or non-hormonal contraceptives (NHC). Strength and body composition were measured at baseline, at 4 weeks, and at the end of the 8-week RET intervention. Body composition was measured with dual-energy x-ray absorptiometry (DEXA), while strength was measured using a 3-repetition maximum (3RM) in the Smith machine Larsen bench press and the seal row. Differences between the HC groups and the NHC group were investigated with an analysis of covariance (ANCOVA). Result: Of the 41 participants included in the study, 33 completed the training intervention, with 3 participants being post-hoc excluded due to HC type, leaving 30 participants for the final analysis. No significant difference was detected in body composition between the HC group and the NHC group. Significant strength increases were found in the LARC group (p <0.05) and COC group (p <0.01) for the 3RM seal row, when compared to the NHC group. All groups showed no significant increase in body composition from the intervention, however, all significantly increased in both strength tests from baseline to mid-test (week 1-4) and to post-test (week 1-8). Conclusion: This study is one of the first to investigate and compare the effect of RET on hypertrophy and strength adaptations in female athletes with prior RET experience who used COCs or LARCs. The main findings were that the LARCs group significantly increased strength in the 3RM seal row, suggesting that LARCs use may positively influence posterior back strength. Nevertheless, as this is the first study to investigate LARC usage and RET adaptations, additional comparative research is required.