A Comparative Study of Simultaneous Vibromyography and Electromyography with Active Human Quadriceps

Vibromyographic (VMG) signals, which are low-frequency vibration signals generated during muscle contraction, were studied in comparison with electromyographic (EMG) signals recorded simultaneously during isometric contraction of the human quadriceps muscles. The comparison was accomplished by evaluating the averaged root mean squared (rms) value, mean frequency (MF), and peak frequency (PF) of the VMG and EMG signals for four muscle contraction levels at joint angles of 30°, 60°, and 90°. The four contraction levels, namely 20, 40, 60, and 80% of maximum voluntary contraction (MVC), were estimated and controlled by the torque readings of a Cybex II dynamometer. It was found that the VMG and EMG under the same conditions on the same muscle group are in general equally sensitive to the levels of muscle contraction. Results show that the rms value of the VMG signal increases linearly, in a manner similar to the EMG rms/%MVC relationship, with increasing muscle contraction levels. Furthermore, the study indicates that the averaged MF (6-24 Hz) and PF (9-19 Hz) of the VMG signals are much lower than the MF (75-109 Hz) and PF (40-80 Hz) of the EMG signals. The slopes of MF/%MVC curves for the VMG and EMG are approximately the same for 60° and 90° joint angles (~3.1 Hz per 20% MVC for VMG and ∼ 2.6 Hz per 20% MVC for EMG). This slope similarity means that the rms/%MVC and MF/%MVC relationships of the VMG signal, like those of the EMG, may reflect muscle activation patterns, while the difference in frequency content between the VMG and the EMG reflects the morphological differences between the mechanical and electrical responses to muscle activation. It was also noted that the VMG signal, like the EMG signal, exhibits a feature of joint angle dependence. Results of all these studies show that the VMG, as a direct mechanical index of muscular contraction, has potential as a noninvasive tool for studying the mechanical behavior of active skeletal muscles. © 1992 IEEE