Evaluation of Hjorth parameters in forearm surface EMG analysis during an occupational repetitive task

The Hjorth parameters are normalized slope descriptors (NSDs) usually used in sleep EEG processing for data reducing and/or automatic sleep stage scoring. In the present study NSDs of forearm surface EMG recorded from 9 subjects performing occupational repetitive movements are compared to conventional FFT spectral analysis. The correlation coefficients between the NSD labelled mobility and the FFT mean frequency range from 0.81 to 0.93. Results show that these time domain properties can also describe the spectral content of surface EMG during repetitive movements. Moreover, the NSD method offers a low cost calculation time since it is based on the sole concept of variance.