(5) ADOLESCENT ATHLETES WITH A HISTORY OF ANTERIOR CRUCIATE LIGAMENT RECONSTRUCTION EXHIBIT PERSISTENT DEFICITS IN JUMP PERFORMANCE AND REACTIVE STRENGTH

Purpose: The purpose of this study was to compare jump performance and reactive strength during a depth jump (DJ) for adolescent athletes with a history of anterior cruciate ligament (ACL) reconstruction vs. adolescent athletes without a history of ACL injury. Methods: This case-control study included 15 adolescent athletes (8 males, 7 females) with a history of ACL reconstruction (ACLR group) and 30 adolescent athletes (16 males, 14 females) without a history of ACL injury (control group). The average ages of the athletes in the ACLR and control groups were 16.1 ± 0.7 years and 16.3 ± 0.7 years, respectively. Athletes in the control group were matched to athletes in the ACLR group based on sex, age (within 2 years), and sport. Two athletes were included in the control group for each athlete in the ACLR group (2:1 match). The athletes in the ACLR group had undergone ACL reconstruction 6-8 months prior and planned to return to competitive sports. Data were collected as part of their standardized return-to-sport testing. All athletes performed three DJ trials where they dropped from a 30 cm high box, landed, and immediately performed a maximal vertical jump. A force platform was used to record ground reaction force (GRF) data during performance of the DJ trials. The following performance variables were generated based on the vertical GRF data: jump height (based on flight time), ground contact time, peak propulsive force (normalized by body weight), and the reactive strength index (RSI). The RSI was calculated by dividing jump height by ground contact time, with higher values reflecting greater reactive strength or “explosiveness”. Two-tailed, independent t-tests were conducted to compare the ACLR and control groups for each dependent variable (alpha level = 0.05). Cohen’s d effect size (ES) statistics were calculated to quantify the magnitude of the between-group differences and interpreted as follows: 0.2 = small effect, 0.5 = medium effect, 0.8 = large effect. Results: There were significant differences in jump height (p=0.04; ES = 0.67) and RSI values (p=0.04; ES = 0.68) between the groups, while ground contact time (p=0.15; ES = 0.47) and peak propulsive force (p=0.16; ES = 0.46) were not significantly different. The ACLR group exhibited lower jump heights (31.4 ± 10.1 cm vs. 38.3 ± 10.5 cm) and RSI values (0.74 ± 0.34 m/s vs. 1.02 ± 0.45 m/s), compared to the control group. Conclusions: Despite completing rehabilitation and preparing to return to sport, athletes with a history of ACL reconstruction exhibited persistent deficits in jump height and lower body reactive strength, compared to athletes without a history of ACL injury. Practical Applications: The deficits exhibited by the athletes who had undergone ACL reconstruction could limit their ability to perform at their pre-injury level and/or may have contributed to their initial ACL injury. Rehabilitation and strength and conditioning professionals should be aware that athletes who have undergone ACL reconstruction often continue to exhibit neuromuscular performance deficits, even as they transition back to sport. If possible, it may be beneficial for these athletes to begin working with a strength and conditioning coach or athletic trainer to facilitate continued neuromuscular recovery/gains, even after formal rehabilitation has ended. Our findings highlight the importance of emphasizing a “return to performance” after ACL reconstruction Acknowledgements: None.