Variations in Isometric Strength and Rate of Force Development Across the Menstrual and Hormonal Contraceptive Cycle...

To examine variation in maximal voluntary isometric contraction (MVIC), rate of force development (RFD), and hamstrings-to-quadriceps (H/Q) ratio across estimated menstrual cycle phases and intervals in hormonal contraceptive (HC) users among elite female football players. Forty-two players (non-HC: n = 21; HC: n = 21) completed twice-weekly quadriceps and hamstring strength tests during a 40-day pre-season period. Non-HC tests were categorized into estimated early follicular, late follicular, and mid-luteal phases using app/calendar tracking; corresponding intervals were applied for HC users. Self-reported fitness, sleep quality, performance, and menstrual-related symptoms were collected. Mixed ANOVAs examined MVIC, RFD, and H/Q ratio. In non-HC players, quadriceps MVIC was higher in the estimated late follicular phase than in the estimated early follicular (p < .001, d = 0.69) and mid-luteal phases (p = .004, d = 0.53). Quadriceps RFD was lower in the estimated early follicular phase than in the estimated late follicular (p = .026, d = 0.43) and mid-luteal phases (p = .001, d = 0.61). No clear phase-related variation was observed in hamstring strength or H/Q ratio. In HC users, MVIC, RFD, and H/Q ratio showed no meaningful variation across corresponding intervals. The estimated early follicular phase coincided with lower perceived performance, daily fitness, and sleep quality, and greater menstrual-related symptom prevalence. Quadriceps isometric strength and rapid force production varied across estimated menstrual cycle phases, whereas neuromuscular strength measures appeared more stable among HC users. Field-based monitoring may help contextualize short-term fluctuations in neuromuscular performance and perceived readiness.