Countermovement Jump Kinetic Impairments in Elite Athletes Before and After ACL Injury: Force-Time Waveform Versus Discrete Kinetic Analysis

Pre‐injury and post‐injury countermovement jump (CMJ) force‐time data were obtained for elite athletes 6 months after anterior cruciate ligament surgery (ACLR). Jump kinetics were analysed using a traditional phase‐specific approach, and force‐time data of the CMJ waveform were analysed using statistical parametric mapping (SPM). Elite athletes (n = 10; female n = 6, age = 22.0 ± 3.5 years, mass = 75.9 ± 11.5 kg) performed CMJ testing before (T0) and after ACLR (T1; 24 ± 3 weeks post‐surgery). Differences in discrete and continuous metrics were analysed for (1) within‐limb differences between T1 and T0 and (2) between‐limb differences at T1 and T0. Lower involved limb propulsive impulse (T1: 6.4 ± 1.6 N∙s/kg; T0: 7.7 ± 1.4 N∙s/kg, p = 0.002) and peak force (T1: 6.4 ± 1.6 N/kg; T0: 7.7 ± 1.4 N/kg, p = 0.002) were found after ACLR compared to baseline. After ACLR (T1), lower involved limb propulsive impulse was found compared to the uninvolved limb (involved: 1.26 ± 0.54 N∙s/kg; uninvolved: 1.58 ± 0.56 N∙s/kg, p = 0.007). SPM analysis revealed specific within‐limb force loss, notably reduced involved limb propulsion force at T1 compared to pre‐injury at T0 (p < 0.001) between 92% and 99% of the CMJ (end of propulsion) and between 36% and 37% of the CMJ (i.e., late unweighting to braking phase transition). SPM analysis revealed within‐limb CMJ force loss that was not seen with the discrete analysis, highlighting the complementary value of SPM waveform analysis alongside discrete analysis to identify neuromuscular impairments in stretch‐shortening‐cycle function in elite athletes after ACLR.