Nosratollah Hedayatpour,  Zahra Izanloo

N. Hedayatpour,  Z. Izanloo – Electromyographic responses of the quadriceps muscles to fast and slow perturbations after fatiguing exercise. FP 2017; 17(1); 24-27

Abstract

Introduction. An appropriate postural response of the quadriceps muscle to an unexpected perturbation reduces the risk of knee injuries. The aim of this study was to investigate the effect of fatigue on postural response of the quadriceps to fast and slow perturbations.
Material and method. Fatigue induced to the quadriceps muscle using a KinCom Isokinetic Dynamometer (Chattanooga, TN). Bipolar surface electromyographic (EMG) signals were simultaneously recorded from quadriceps components (vastus medialis, rectus femoris, and vastus lateralis) during pre- and post-fatigue postural perturbation performed at two different velocities of 120 ms and 250 mes.
Results. Maximal voluntary knee extension force and time to task failure were significantly reduced after fatiguing knee exercise (P < 0.05). The ARV of EMG during fast-perturbation was significantly higher than slow-perturbation (P < 0.05). Moreover, The ARV of EMG was significantly reduced during post fatigue perturbation, with a largest reduction identified for fast-perturbation compared with slow perturbation (P < 0.05).
Conclusion. Reduction in quadriceps muscle activity during post fatigue fast-perturbation was significantly larger than post fatigue slow- perturbation, most likely due to preferential recruitment of fast twitch muscle fiber which is more susceptible to fatigue. This may partly explain that why knee injuries is common after fast ballistic movement.

Key words:
Electromyography, Perturbation, Fatigue, Quadriceps, Velocity

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