Phonomyography

Phonomyography (PMG), encompassing various terminologies like acoustic myography, sound myography, vibromyography, and surface mechanomyogram, is an avant-garde technique devised to gauge the intensity of muscle contractions. This is achieved by documenting the low-frequency acoustics produced during muscular dynamics.

While PMG doesn't attain the precision of its predecessor, mechanomyography, its ease of deployment is undeniable. A variety of sensors, ranging from condenser microphone elements to piezoelectric sensors and accelerometers, is employed for signal measurement when affixed to the skin. For aquatic environments, hydrophones prove effective in assessing immersed muscles.

Notably, while the muscle-derived sounds can be faintly discerned when the ear is in proximity to the contracting muscle, the bulk of its energy remains within the infrasound range, especially below 20 Hz, rendering it largely inaudible.

Technological Comparison

Comparative studies with electromyography (EMG) indicate that EMG signals usually undergo a bandpass filtering spanning from 10 Hz to 500 Hz. Conversely, PMG signals in specific experiments are confined to a range between 5 Hz to 100 Hz. Eminent researcher Orizio emphasizes the pivotal nature of a sensor's low-frequency response, which, according to his studies, should extend down to a minimal 1 Hz. For a visual representation of PMG waves, one can refer to the creative commons-licensed document: [1]

Historical Backdrop

The inception of muscle sounds in documented history can be traced back to the illustrious Jesuit scientist, Francesco Maria Grimaldi. His pioneering work, unveiled posthumously in 1665, set the foundation for subsequent revelations by the eminent English physician, William Hyde Wollaston, and the renowned German scientist, Paul Erman. Erman's research endeavors led him to collaborate with the genius, René Laennec. The concept of mechanical amplification was introduced to the scientific community by Hermann von Helmholtz. A comprehensive overview of the two centuries chronicling the discovery, recognition, and occasional overlooking of this phenomenon was meticulously compiled by Stokes and Blythe[8] in their 2001 publication.

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