Time-dependent EMG power spectrum parameters of biceps brachii during cyclic dynamic contraction

Abstract

Mean frequency and median frequency (MNF and MDF) features are global used parameters of EMG power spectrum to determine muscle fatigue. A major problem of these parameters is a non-linear relationship between muscle load and feature value, especially in large muscle and in cyclic dynamic contraction. To analyze the EMG signal in both of muscle fatigue and muscle load, we have been proposed time dependence of the MNF and MDF (TD-MNF and TD-MDF) of a time-sequential data. Moreover, the surface EMG signals that were used in this study were acquired from the biceps brachii muscle during round-trip dynamic contraction. After that TD-MNF and TD-MDF were calculated and compared with the standard MNF and MDF features which were calculated based on the whole data. Three statistical parameters including mean, median, and variance were used to apply with the selected efficient range of TD-MNF and TD-MDF in order to easily observe and use in an application. The result shows that mean parameter of selected TD-MNF have a better linear relationship with muscle load compared to the others and have a significant difference (p<0.005) between feature values for different loading conditions. In addition, it was found that there was a certain pattern of TD-MNF and TD-MDF for each data and each subject that has not been found in traditional MNF and MDF features. The optimal method of TD-MNF and TD-MDF was success when overlapping consecutive window was performed with 512-sample window size and 64-sample window increment. In conclusion, mean of the selected TD-MNF band can be used as both muscle load and muscle fatigue indexes. © 2011 Springer-Verlag.