When monopolarly-recorded surface myoelectric signals from the vastus medialis muscle were analyzed by FFT (Fast Fourier Transform) to obtain an amplitude spectrum, we found a“dip”in amplitude of around 80 Hz. Using the frequency at the“dip” (Turning Frequency : TF) as a cut-off point, the raw myo-electric signals were divided into high frequency components (HFC) and low frequency components (LFC) .
1) TF appeared in the amplitude spectrum from all recording electrodes when the tension reached 60%MVC.
2) TFs shifted to higher frequencies with increased tension.
3) Using cross-correlation analysis, LFCs showed conductivity along muscle fibers. In contrast, a pair of HFCs from nearly fastened electrodes appeared in phase, but a pair of HFCs from distant electrodes showed no relation.
HFCs and LFCs, derived by using TFs from surface myoelectric signals, showed different characteristics in conductivity. This suggests that TF can be a useful analyzing method extracting new information from surface myoelectric signals. Further study is needed to pursue the relation between HFCs and LFCs, and physiological parameters.