Technical aspects of mechnomyography recording with piezoelectric contact sensor

Abstract

The piezoelectric contact sensor has been widely utilised in mechanomyography (MMG). The authors aim to clarify the mechanical variables (i.e. acceleration, velocity or displacement) reflected by the MMG signal detected with a piezoelectric contact sensor (PEC), and compare the results with those obtained simultaneously by an accelerometer (ACC). To measure the acceleration-frequency response, a mechanical sinusoidal excitation of 5 to 300 Hz at a constant magnitude of 0.01 G was applied to the two transducers. The acceleration-frequency response of the ACC transducer was confirmed to be almost flat. The PEC without any restriction of the transducer housing (including the combined seismic mass) demonstrated a similar response to the ACC transducer. The PEC transducer output with restricted housing decreased with increasing sinusoidal frequency and an attenuation slope of -40 dB/decade and phase angle of -180 degrees. The voluntary MMG signal during isometric knee extension was recorded simultaneously with the two transducers. The amplitude spectral density distribution of the MMG from the PEC transducer was narrow and the mean frequency was approximately one-half that obtained from the ACC transducer. The amplitude spectral density distribution with the PEC transducer resembled that of the double integral over time of the ACC transducer signal. The phase angle of the PEC transducer signal was different from that of the ACC transducer signal by approximately -180 degrees. These results suggest that the PEC transducer acts as a displacement meter of muscle vibration. In addition, differences in the MMG frequency components relating to the transducer type must be taken into consideration when investigating the mechanical activity of muscle.

Mechanical behaviour of condenser microphone in mechanomyography

“…displacement) was also similar to the force waveform (BARRY, 1992). During voluntary contractions, the amplitude spectral density function of the MMG from the piezoelectric contact sensor resembled that of the double integral of the ACC transducer signal (WATAKABE et al, 1998). in the present study, the frequency response of the voluntary MMG from the MIC transducer was similar to that from the double integral of the ACC transducer.…”

“…Various transducers have been used to record the MMG, including accelerometers (LAMMERT et al, 1976;BARRY, 1992;ORIZIO et al, 1996;AKATAKI et al, 1999), piezoelectric contact sensors (BOLTON Correspondence should be addressed to Dr K. Mita; e-marl: mitak@inst-hsc.pref.aichi 1989;BARRY, 1991;ORIZIO et al, 1994), condenser microphones (BOLTON et at., 1989;MATON et at., 1990;STOKES and DALTON, 1991) and laser distance sensors (ORIZIO et al, 1999). it is evident that the MMG signal detected with an accelerometer and laser distance sensor reflects the acceleration and displacement of the skin vibration, respectively, it is suggested that a piezoelectric contact sensor is indicative of displacement of the muscle vibration and that its mechanical behaviour is explained by a seismic system with a heavy mass element (WATAKABE et al, 1998).…”

Application of Acceleration Sensors in Physiological Experiments

“…Fatigue is ordinarily analysed from the changes in RMS (EMG RMS ) and median frequency (EMG MF ) of EMG signal, but according to additional references [5,6,11] a special method called mechanomyography (MMG) can be employed. MMG monitors amyostasia, which are small vibrations of loaded muscles.…”

sEMG Techniques to Detect and Predict Localised Muscle Fatigue

“…Usually, the aim of combining sensors with sEMG or other sensors is validation, labelling or improving the signal to noise ratio. To date, no consensus has been reached upon the ideal sensor technology to use for MMG recordings (Courteville et al, 1998;Gregori et al, 2003;Watakabe et al, 1998). The literature suggests that accelerometers are more appropriate than condenser microphones due to the effects of background noise.…”