BACKGROUND: Limited knee flexion and increased muscle co-contraction during jump landing are believed to diminish outcomes after anterior cruciate ligament (ACL) reconstruction. The efficacy of jump training to improve patients' mechanical and neuromuscular deficits is understudied. HYPOTHESIS: Jump training will improve functional, mechanical, and neuromuscular outcomes and higher repetition training augmented by body weight support will result in better retention of gains. STUDY DESIGN: Randomized controlled trial; level of evidence, 1. METHODS: Thirty athletes (18 months after surgery) were screened, and 19 with mechanical deficits and limited clinical outcomes were enrolled in the trial. Testing included the International Knee Documentation Committee (IKDC) questionnaire, leg landing mechanics via motion analysis, knee joint effusion using a stroke test, and a surface electromyography-generated co-contraction index during a single-legged landing. Participants were randomly assigned to 1 of 2 groups: jump training with normal body weight (JTBW) and high-repetition jump training with body weight support (JTBWS). Knee effusion grading throughout training was used to assess joint tolerance. Changes in outcomes over time were analyzed with mixed-effects modeling. Immediate outcomes were compared with retention testing at 8 weeks after training by use of 2-way analyses of variance with effects of time and group. RESULTS: Significant effects of time were found during the training phase for all outcome measures, but no effects of group or sex were found. IKDC score (pooled; mean +/- SD) increased from 76 +/- 12 to 87 +/- 8 (p < 0.001). Knee flexion during single-legged landing increased from 57 degrees +/- 11 degrees to 73 degrees +/- 9 degrees (p < 0.001). Average co-contraction index decreased from 37 +/- 15 to 19 +/- 6 (p < 0.001). All measures were retained over the retention period in both groups. The relative risk of knee effusion of the JTBW group versus the JTBWS group was 4.2 (95% CI 2.25 to 7.71; p < 0.001). CONCLUSION: Jump training mitigated some risk factors for second injury and osteoarthritis in patients after ACL reconstruction. Training made lasting improvements in physical function measures as well as mechanical and neuromuscular coordination deficits. Higher repetitions used with body weight support did not improve retention but substantially reduced risk for effusion. CLINICAL RELEVANCE: Jump training is an efficacious intervention for athletes with poor outcomes after ACL reconstruction, and training with body weight support lessens the risk for excessive joint stress during practice. REGISTRATION: NCT02148172 (ClinicalTrials.gov identifier).

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