Kiara Barrett, Zachary A. Sievert, Hunter J. Bennett. Old Dominion University, Norfolk, VA.

BACKGROUND: Anterior cruciate ligament injury is one of the most common knee injuries, making up around 20% of all sports-related injuries. The implementation of neuromuscular training (NMT) has been shown to reduce biomechanical risk factors and increase neuromuscular control. Previous studies investigating NMT have focused on the effects of this training on dynamics, rather than coordination of the muscles contributing to a specific task. The purpose of this study was to quantify the effect of a 6-week neuromuscular training intervention on muscle synergies during a drop landing. METHODS: Eight participants (men=3, women=5) were recruited for this study. For each visit, EMG surface electrodes were placed on the right rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL), biceps femoris (BF), semitendinosus (ST), and medial gastrocnemius (GA). Participants were familiarized with the procedures, then completed five drop landings from a height relative to their maximal jump height. This procedure was repeated after the completion of six weeks of the intervention. The linear-progression training intervention consisted of one day of plyometric and two days of resistance training per week. All electromyography (EMG) signals were normalized to the maximum activation across all landing trials. Concatenated nonnegative matrix factorization was performed to determine muscle synergies and weightings. Preliminary analyses found two muscle synergies could explain 96% of the variance. Muscle weightings for each synergy were compared pre and post intervention. In addition, integrated EMG during landing of the BFLH, ST, and GA (%MVIC*sec) was compared using paired samples t-tests (p<0.05). RESULTS: In general, all muscles evenly contributed to each muscle synergy (range: 13%-20% each). Relative contributions to muscle synergies were not different between pre/post. ST (11.7±2.6%s vs. 11.3±2.3%s), BFLH (11.8±2.9%s vs. 11.5±2.6%s), and GA (11.8±2.7%s vs. 11.4±2.4%s) integrated EMG were not significantly different between pre and post (p=0.17, p=0.81, p=0.70, respectively). CONCLUSION: The NMT did not have a significant effect on integrated EMG levels in the BFLH, ST or GA. Our findings suggest changes in neuromuscular activation and synergy would not be the mechanism behind a reduction in ACL injury risk following similar training interventions.

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