Changes in Strength, Jump Kinetics, and Inter-Limb Asymmetry Across the Second Half of the Season in Semi-Professional Female Soccer Players

Evidence on changes in strength and jump performance during the second half of the season in female soccer players remains limited. We assessed 18 senior semi-professional players (Tier 3, highly trained/national level) at the beginning, middle and end of this period for isokinetic knee extensor and flexor strength (60 and 180°/s), squat (SJ), countermovement (CMJ), single-leg CMJ (SL CMJ) and drop jumps (DJ) on force plates, and body composition. Data were analyzed with linear mixed models, with false discovery rate adjustment across time effects. Knee extensor peak torque at 60°/s decreased by 4.6% (95% CI −7.2 to −1.9%; adjusted p = 0.022), whereas knee flexor strength did not change. SL CMJ height increased by 13.1% (adjusted p = 0.038), most likely reflecting task familiarization, whereas no bilateral jump variable changed after adjustment. The better-performing limb differed between tests in 65–89% of players for SL CMJ variables. Body mass did not change, whereas body fat percentage decreased from 18.5% to 16.6%. In conclusion, squat and countermovement jump height alone did not detect the decline in quadriceps strength; isokinetic strength testing may therefore complement in-season jump testing, with inter-limb asymmetry assessed repeatedly rather than from a single timepoint.