Effect Of Neuromuscular Fatigue On Emg Patterns In Subjects With Ankle Instability

Abstract

Hip abductors and ankle evertors provide dynamic postural stability and muscle fatigue decreases their function, which could lead to lateral ankle sprains. Ankle instability (AI) patients exhibited different neuromuscular control strategies during functional activities compared to healthy subjects. PURPOSE: Examine the effect of fatigue and AI on muscle activity patterns during a forward-side jump. METHODS: 25 AI (23.3±1.9yrs, 176.5±10.5cm, 70.9±11.4kg) and 25 control subjects (23.7±2.5yrs, 175.0±10.8cm, 70.3±12.8kg) performed 5 forward-side jumps before and after fatiguing exercises while EMG signals were collected from the peroneus longus (PL) and gluteus medius (GM). Subjects ran on the treadmill for 5 min at between 5 and 6 mph. Next, subjects performed 20-sec lateral, and 20-vertical jumps. A max vertical jump was measured after each fatigue cycle. Subjects repeated three exercises until RPE reached 17 and the vertical jump fell below 80% of max jump height. Functional linear models (α=0.05) were used to evaluate differences between two conditions (pre- vs post-fatigue) in each group (AI vs control) for PL and GM activation. This analysis compared variables as polynomial functions rather than discrete values. Functions of each condition as well as 95% confidence interval (CI) bands were plotted to determine significant differences. RESULTS: Figure 1. Group by fatigue interactions were found at initial contact in PL and between 30-35% of stance in GM. Fatigue decreased EMG amplitude of PL between 15-50% in the control group and during 0-70% of stance in AI group. Decreased GM activation was found during 30-40% of stance in AI group, but not in control group. CONCLUSIONS: AI group showed greater pre- to post-fatigue reduction in PL and GM EMG amplitude than the control group. Greater deficits of PL and GM activity may infer a greater risk for injury.