The technical and physiological characteristics of the vibromyographic signal

Eaton, Sharyn (1999) The technical and physiological characteristics of the vibromyographic signal. University of Southampton, School of Engineering Sciences, Doctoral Thesis, 280pp.

Record type: Thesis (Doctoral)

Abstract

Skeletal muscle contractions emit a low frequency sound (<100Hz) that can be detected by vibromyography (VMG) or mechanomyography (MMG). The aim of this study was to determine the future application of the VMG signal as a clinical tool in reflecting the physiological state or function of muscle during rehabilifation and diagnosis. In order to achieve this aim, the following was investigated. A) The technical characteristics: Three different transducers (the capacitance and piezoelectric accelerometers and the contact sensor) and the transducer/ amplifier system. B) The repeatability of the VMG signal at different force levels. C) Physiological characteristics of the VMG signal comparing 'normal' and 'abnormal' muscle function. Past studies on VMG have revealed that these three areas have received little attention.
The VMG signal was taken from the biceps brachii muscle at different contraction levels 10%, 50% and 80% maximum voluntary contraction (MVC) for within day (n=3) and between day (n=17) recordings. The signal from asymptomatic (n=29) and symptomatic (n=23) low back pain subjects was then compared. Recordings were taken from the erector spinae muscle at an incremental increase in voluntary contraction (10%-100%MVC). These recordings were repeated on the next day.
Results from this study have revealed the following: A) Technical characteristics : the lower cut-off frequency is important and insufficient attention in past studies has been given to the transducer-amplifier system. Additionally, the capacitance accelerometer was the favoured transducer due to its greater sensitivity to low frequencies, simplicity of use and ease of stabilising and coupling techniques to the skin. B) Repeatability of the VMG signal: For successive recordings, compared with precision (%C.O.V and L.O.A) and reliability (I.C.C), correlation (r value) of the VMG signal appears a much stronger and a more consistent statistic in the time and frequency domains. C) Physiological Characteristics: Although having a high individual variation, the erector spinae demonstrated a strong curvilinear relationship with increasing submaximal voluntary contraction (%MVC) reflecting the recruitment and rate coding strategies for this muscle. The VMG RMS for symptomatic low back pain subjects was considerably less than asymptomatic subjects suggesting a deficiency in muscle function. In contrast, the PSD was less favourable in distinguishing between the two subject groups. Reasons for these findings are discussed.
In future, the clinical application of the VMG RMS values may quantitatively assess paraspinal muscle force reflecting physiological changes in recruitment and rate coding strategies in 'normal' and 'abnormal' muscle function during rehabilitative care.

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