Suitable cutoff frequency of low-pass filter for estimating muscle by surface electromyogram

Integrated electromyogram (IEMG) is obtained from surface electromyogram (SEMG) by full wave rectification and smoothing. It is well known that IEMG in isometric contraction is increase monotonously with the muscle force increment. For smoothing, the low pass filter (LPF) is normally used. When the change of the muscle force is faster, there is the case that the simple relationship between the muscle force and IEMG is not approved. Therefore in this study, we examined the suitable cutoff frequency of LPF for obtaining to IEMG. We measured the muscle force and EMG from the first dosal interosseous (FDI) in the periodical movement. EMG is converted to IEMG with various cutoff frequencies by computer. After that we picked out the cutoff frequency that has good correlation. Our results showed that we must change the cutoff frequency for LPF depending on the change speed of muscle force.