Lower Leg Emg Alterations In Subjects With Ankle Instability During A Forward-side Jump Task

Abstract

Lateral ankle sprains are the most common lower extremity injury in sports and often lead to ankle instability (AI). The muscles that cross the ankle joint provide dynamic stability during functional movements with high loads. Altered neuromuscular patterns may play a role in perpetuating AI. PURPOSE: To examine neuromuscular patterns in subjects with AI during a forward-side jump task compared to healthy controls. METHODS: 80 AI (22.5±2.3 yrs, 175.2±9.5cm, 72.5±14.4 kg) and 60 control (22.1±2.7 yrs, 173.2±9.7cm, 68.1±12.8kg) subjects were categorized according to FAAM (ADL: 82.7±9.2% and Sport: 62.4±13.0%) and MAII (3.5±1.3). EMG electrodes were placed on the tibialis anterior (TA), peroneus longus (PL), and medial gastrocnemius (MG). Subjects were instructed to perform 5 forward-side jumps, landing with their involved leg on a force plate, then immediately transitioning into a lateral jump off to the side of the force plate. Functional linear models (α=0.05) were used to evaluate differences in EMG amplitudes of the TA, PL, and MG between AI and healthy groups during the forward-side jump. This analysis compared variables as polynomial functions rather than discrete values. Pairwise comparison functions as well as 95% confidence interval (CI) bands were plotted to determine significant differences. RESULTS: Figure 1. Compared to the control group, the AI group displayed decreased PL EMG amplitude during 20-45% of the stance and reduced TA EMG amplitude between 10-25% and 50-60% of the stance phase. AI subjects increased MG EMG amplitude throughout the entire stance phase. CONCLUSIONS: AI may result in a motor strategy that poorly positions the foot during movement, and lessens the effects of dynamic stability during movement. Further studies are needed to match these data with foot positions, and link these alterations to injury risk.