ASSESSMENT OF MUSCULAR FATIGUE USING VIBROMYOGRAPHY

The purpose of this study was to investigate the behavior of electromy ographical (EMG) and vibromyographical (VMG) signals in the time and f requency domains during a fatigue protocol. EMG and VMG records were o btained from the rectus femoris (RF) and vastus lateralis (VL) muscles of 11 adult male subjects during sustained, isometric knee extensor c ontractions performed at 70% of maximal voluntary contraction (MVC). T he average median frequencies of the power density spectra decreased d uring the fatigue protocol for the EMG (from 73 to 54 Hz for RF, and f rom 75 to 57 Hz for VL) and the VMG signals (from 40 to 19 Hz for RF, and from 25 to 12 Hz for VL). Raw EMG signals remained the same qualit atively throughout the fatigue protocol, whereas corresponding VMG rec ords appeared to become ''smoother.'' The results of this study indica te that the pronounced decrease in the high-frequency content of the V MG signal may be observed in the time domain as a ''smoothing'' of the signal, and thus, that the raw VMG records (which may be displayed re adily online) can be used to assess qualitatively the onset and progre ssion of muscular fatigue. (C) 1994 John Wiley and Sons, Inc.