BACKGROUND: Ankle sprains comprise 30% of all soccer injuries and can lead to long term issues like chronic ankle instability (CAI). Current research examining the impact of muscle activity of the tibialis anterior (TA) and the medial gastrocnemius (MG) on the risk of developing CAI is limited. The purpose of this research was to determine the impact that muscle activity of the lower extremity muscles has on stability and injury risk in soccer players. METHODS: Twenty-Three Division 1 National Collegiate Athletic Association (NCAA) women’s soccer players performed a validated dynamic balance task, the Y-Balance Test (YBT), while muscle activity of the primary ankle stabilizers in the sagittal plane (TA and MG) were measured using surface electromyography (EMG). For the task, participants balanced on one leg, then reached as far as possible with their other leg on a sliding block, and then returned to the starting position. The participants performed the task in three directions: anterior (ANT), posteromedial (PM), and posterolateral (PL). EMG readings from the TA and MG for each reach distance were recorded and normalized to the participant’s maximum isometric voluntary contraction (MVIC) for that muscle. A series of paired samples T-tests were conducted to analyze potential differences in mean muscle activity for the TA and MG for each of the three reach directions. RESULTS: The left TA had a significantly lesser amount of mean muscle activity in both the anterior (ANT) (t = 2.929, p = 0.008) and posteromedial (PM) (t = 2.356, p = 0.028) reach directions. In the ANT direction, the participants had a mean muscle activity of 23.19 ± 10.10% for their left TA and 32.60 ± 15.40% of their MVIC for their right TA. In the PM direction, they had had a mean muscle activity of 25.82 ± 12.77% for their left TA and 32.96 ± 15.28% for their right TA. In both directions, players displayed significantly better muscle activity for the left leg than the right. No significant differences were found for the other analyses. CONCLUSIONS: Female soccer players in this study displayed significantly better muscle activity in the TA for their left leg, (the non-dominant leg for all but one participant) in the ANT and PM directions. This may be attributed to the players using their left leg to plant and stabilize their body while they kick the ball with their right leg.

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