Timing of Muscle Activation Is Altered During Single-Leg Landing Tasks After Anterior Cruciate Ligament Reconstruction at the Time of Return to Sport.

Objectives: It is well known that alterations in landing mechanics persist for years after anterior cruciate ligament reconstruction (ACL-R). Nevertheless, existing literature is controversial in reporting successful or unsuccessful recovery of prelanding muscle activation timing after ACL-R. The study aimed at comparing myoelectric and kinematic patterns during landing tasks between ACL-R and healthy subjects. Design: Cross-sectional study. Setting: Institutional research laboratory. Patients and Intervention: Fifteen male athletes after ACL-R using patellar tendon and 11 using hamstrings autograft at the time of return to sport were recruited. Fifteen healthy athletes served as control group. Participants performed 4 different single-leg landing tasks arriving onto a force plate. Main Outcome Measures: Electromyographic (EMG) activity of knee extensors and flexors, normalized vertical ground reaction force (vGRF), and knee angular displacement were recorded. Results: In all the tasks, preimpact EMG duration was longer in ACL-R (112±28 ms in the knee extensors; 200±34 ms in the knee flexors) compared with healthy participants (74±19 ms in the knee extensors; 153±29 ms in the knee flexors; P< 0.05). Initial contact (IC) and maximum postimpact knee angle were lower in ACL-R (9±7 degrees at IC; 39±12 degrees at maximum flexion) compared with healthy participants (17±9 degrees at IC; 52±15 degrees at maximum flexion; P< 0.05). Normalized vGRF was higher in ACL-R compared with healthy participants (3.4±0.5 and 2.7±0.6; P< 0.05). Conclusions: At the time of return to sport, ACL-R subjects showed altered motor control strategies of single-leg landings. These alterations may lead to uncoordinated movement, hence increasing the risk of reinjury.