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Altered Muscle Activation Patterns during a Forward-Side Jump Following Functional Fatiguing Exercises: 2449 Board #196 May 29, 11

Muscle activation is a major contributor to the dynamic stability of the ankle joint. Neuromuscular fatigue may increase the risk of ankle injuries by inhibiting control of muscles, resulting in reduced joint stability. PURPOSE: To examine how functional fatiguing exercises affect muscle activation patterns of ankle musculature during a forward-side jump. METHODS: 25 healthy subjects (23.7±yrs, 175.0±8.7cm, 70.3±12.8kg) participated in this study. EMG electrodes were placed over tibialis anterior (TA), peroneus longus (PL) and gastrocnemius (GA). Subjects performed 5 forward-side jumps on a force plate before and after fatiguing exercises. Subjects ran on the treadmill for 5 min at between 5 and 6 mph. Next, subjects performed 20-sec lateral and 20 vertical jumps. Subjects performed one max vertical jump after each fatigue cycle. They repeated three exercises until RPE reached 17 and the vertical jump height fell below 80% of max vertical jump height. Functional linear models (α=0.05) were used to evaluate differences between preand post-fatigue for TA, PL, and GA activation 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. After the fatigue protocol, TA EMG amplitude decreased during 25-35% of stance, PL EMG amplitude decreased during 20-50% of stance and GA EMG amplitude decreased between 25-65% of the stance phase. CONCLUSIONS: The EMG amplitude of ankle muscles decreased during the deceleration phase of a forward-side jump. This lack of EMG activation may lead to a more inversion and plantarflexed position, increasing the risk of ankle injury. Further data are needed to determine if these muscle deficits result in increased injury.