Lower Extremity Muscle Activation Changes Following a Standard 6-week Neuromuscular Training Program

Abstract

Sex-dimorphic neuromuscular control patterns evident during landings are proposed to increase female anterior cruciate ligament (ACL) injury risk compared to males. Training programs aimed at modifying these high-risk patterns have been demonstrated to be an effective intervention for reducing ACL injury rates. It is unclear, however, how such programs lead explicitly to fewer ACL injuries. We propose that females adopt control strategies following training that more effectively counter potentially hazardous impact-induced external loads. PURPOSE: To examine the effects of a 6-week neuromuscular training program (NTP) on lower extremity muscle activation during a single-leg land and cut task. METHODS: Twenty three (12 trained, 11 control) recreational female athletes had lower extremity muscle electromyography (EMG) data quantified during 10 single-leg land-and-cut trials before (Base), immediately (Post 0), and six weeks (Post 6) after a six-week NTP. Surface EMG electrodes were secured over the muscle bellies of the medial (MH) and lateral hamstrings (LH), vastus lateralis (VL), vastus medialis (VM), rectus femoris (RF), and medial (MG) and lateral gastrocnemius (LG) of the dominant limb. The average RMS amplitudes were calculated for each muscle during two jump landing phases; 100 ms prior to ground contact (Pre) and ground contact to 50% of stance (Re). Pre and Re co-contraction indices were also quantified for thigh muscle pairs (VL-LH and VM-MH). Subject based means of the dependent variables were submitted to two-way repeated measures (time) ANOVAs to test for the main and interaction effects of time and group. RESULTS: Subjects demonstrated significantly (p < 0.05) greater Pre and Re LH and MH muscle activation, Re LG muscle activation, and Pre and Re VL-LH and VM-MH co-contraction at both Post 0 and Post 6 time points. Increases in Pre VM (p = 0.014) and Re MG (p = 0.006) activation were only noted at the Post 6 follow-up. CONCLUSION: Lower extremity muscle activation increased during dynamic single-leg landings following a 6-week NTP. Specifically, females increased hamstring and gastrocnemius activation magnitudes, and relative activation of the hamstrings to quadriceps, which may reduce ACL injury risk. Importantly, these beneficial adaptations may even be retained six weeks following training.