(6) EVALUATION OF HORMONAL CONTRACEPTION EFFECTS ON STRENGTH AND POWER ACROSS THE MENSTRUAL CYCLE

49.5% of female athletes report using hormonal contraceptives, with oral contraceptives (OC) and intrauterine devices (IUD) most commonly used. The biphasic response of endogenous hormones in eumenorrheic (EUM) females is altered with the delivery of exogenous hormones, which may have undesirable consequences on muscle strength and power performance. PURPOSE: To evaluate the effects of OC and IUD use, compared to a EUM cycle, on maximal strength and power between menstrual cycle (MC) phases. METHODS: Sixty healthy, active women (mean±standard deviation (SD); Age: 26.5±7.0 yrs, BMI: 22.5±3.7 kg/m²; total lean mass (LM): 43.4±5.0 kg) who were monophasic OC users (n=21), had a hormonal-IUD (H-IUD; n=20), or had regular naturally occurring menstrual cycles or were using a non-hormonal IUD (EUM; n=19) were recruited. Women using hormonal contraceptives were required to utilize the same form for ≥6 months; EUM women had consistent menstruation for ≥3 months. Participants were required to exercise ≥3x/week with <7 hrs of vigorous activity and <4 days of resistance training. One repetition max (1RM) was measured from leg press and bench press, peak force (PF) from knee extension and upright row isometric dynamometry, and power from counter movement jump (CMJ) and reactive strength index (RSI; cm/s). Participants were randomly assigned to begin in the follicular phase/placebo pill (FP) or in the luteal phase/active pill (LP) and were tested once in each phase. Estimates of total LM, leg LM, and arm LM were measured via dual energy x-ray absorptiometry. Separate univariate ANCOVAs were used to assess the change from FP to LP between groups, with LM as a covariate.

Results: Leg press 1RM was significantly different across the MC between groups (p=0.027), with higher leg press 1RM in the LP for the OC group (mean difference[MD: ∆LP-FP]±standard error [SE]: ∆7.3±4.5 kg; p=0.045) compared to the H-IUD group (∆-8.8±4.6 kg; p=0.045). All groups demonstrated similar bench press 1RM (OC: Δ-0.9±0.6 kg; H-IUD: Δ-0.2±0.6 kg; EUM: Δ0.4±0.7 kg), knee extension PF (OC: Δ9.7±11.8 N; H-IUD: Δ0.7±11.9 N; EUM: Δ-1.9±12.3 N), upright row PF (OC: Δ-5.8±5.9 N; H-IUD: Δ3.0±6.1 N; EUM: Δ9.3±6.2 N), and CMJ (OC: Δ0.4±1.5 cm; H-IUD: Δ-0.7±1.5 cm; EUM: Δ-2.5±1.5 cm) between phases. For RSI, the OC group (Δ-3.7±4.0 cm/s) and the H-IUD (Δ-2.5±4.1 cm/s) demonstrated greater RSI in the FP. The EUM group demonstrated greater leg press 1RM (∆ 6.1 ± 4.7 kg)in the LP, while RSI (Δ-7.0±4.1 cm/s) was greater in the FP.

Conclusions: Collectively, strength and power were similar across the MC for OC and H-IUD users. Lower body strength was greater in the LP for OC users (5% increase) suggesting measures lower body maximal strength may be influenced by hormonal contraception type. H-IUD and EUM saw greater strength in the FP, although not significant. PRACTICAL APPLICATIONS: As hormonal contraception may impact strength and power across the MC, strength and conditioning staff should be aware of the type of contraceptive methods used by their athletes. OC and H-IUD altered strength by an average of 4.8%, which may correspond to ~15-20 lb difference between MC phases. These small changes may affect acute performance but may be less relevant for overall training and testing.

Acknowledgements: ACKNOWLEDGEMENTS: This study was supported by a grant from the National Strength and Conditioning Association Foundation.