Stretch‐shortening cycle force–time and power–time waveform analysis indicates limitations of the contralateral limb benchmark in athletes with ACL injury

Purpose Unilateral countermovement jump (CMJ single ) testing is commonly used after anterior cruciate ligament reconstruction (ACLR) to assess stretch‐shortening cycle (SSC) function and return‐to‐sport readiness. However, the impact of ACLR on contralateral limb SSC function is poorly understood, which may impact the utility of the contralateral limb benchmark. Therefore, statistical parametric mapping (SPM) was employed to: (1) evaluate interlimb CMJ single force–time and power–time deficits in athletes with ACLR; and (2) compare both limbs of athletes with ACLR to an enhanced CMJ single benchmark from healthy control athletes. Methods Canadian university athletes who returned to sport post‐ACLR ( n = 20) and healthy control athletes ( n = 187) performed maximal CMJ single testing on a force plate. The Sport Fitness Index (SFI) assessed perceived limb function, and healthy controls were divided into upper (GOOD SFI ) and lower (POOR SFI ) tertiles. Top‐ranked jumpers with GOOD SFI were sex‐ and sport‐matched to ACLR athletes to obtain an enhanced CMJ single benchmark (Control + benchmark). Interlimb and between‐group CMJ single curves were compared using SPM. Results No interlimb differences were found in healthy athletes in the GOOD SFI group. Healthy athletes in the POOR SFI group demonstrated interlimb force and power deficits over 12% ( p < 0.001) and 4% ( p = 0.006) of the CMJ single propulsion phase, respectively. Compared to the contralateral limb, the affected limb of the ACLR group showed reduced force and power over 8% ( p < 0.001) of the CMJ single propulsion phase. Conversely, the affected limb generated less force over 14% ( p < 0.001) and less power over 22% ( p < 0.001) of propulsion compared to the Control + benchmark. Conclusion The Control + benchmark revealed larger SSC impairments in the affected limb compared to the contralateral limb benchmark during CMJ single testing in athletes who had returned to sport post‐ACLR. Further, healthy athletes with poor perceived limb function demonstrated interlimb SSC impairments similar to the ACLR group, highlighting value in combining biomechanical testing with psychosocial measures in university athletes. Level of Evidence Level III, case–control study.