POWER SPECTRAL ANALYSIS OF SURFACE MYOELECTRIC SIGNALS DURING DYNAMIC CONTRACTIONS
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The stochastic nature of surface myoelectric signals (MES) requires the use of power spectral analysis for effective characterisation. Spectral changes during different types of muscular activity are monitored using spectral parameters like mean power frequency, ratios of powers in several arbitrarily chosen spectral bands and median frequency. The median frequency has been shown to be a reliable indicator of such changes during static contractions. Few such studies, however, are available in the literature for dynamic contractions. In this work, non-fatiguing, isotonic, constant velocity contractions of the right biceps brachii m. were studied. The median frequency and the spectral power were chosen as test indicators of any changes that may occur due either to the loading of the muscle, the angular velocity of contraction or the changes in joint angle (and hence the muscle length). A significant increase in median frequency was found with the loading of the muscle and also for a decrease in joint angle. On the other hand, no variation was observed due to velocity changes. The spectral power confirmed the expected dependence with loading, angular velocity of contraction and joint angle.