Phonomyography (PMG) (also known as acoustic myography, sound myography, vibromyography, and surface mechanomyogram) is a technique to measure the force of muscle contraction by recording the low frequency sounds created during muscular activity. Although, until recently, less precise than the more traditional

mechanomyography The mechanomyogram (MMG) is the mechanical signal observable from the surface of a muscle when the muscle is contracted. At the onset of muscle contraction, gross changes in the muscle shape cause a large peak in the MMG. Subsequent vibrations are d ...

, it is considerably easier to set up. The signal is measured using

condenser microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

elements, piezoelectric sensors,

accelerometer An accelerometer is a tool that measures proper acceleration. Proper acceleration is the acceleration (the rate of change of velocity) of a body in its own instantaneous rest frame; this is different from coordinate acceleration, which is acc ...

s, or a combination of sensors attached to the skin.

Hydrophone A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates an electric potenti ...

s have also been used to measure muscles immersed in water. Improvements in microphones and contact transducers (piezoelectric devices), as well as recording systems, has meant that they have become available in a size and of a quality that enables them to be applied to a normal daily setting outside the clinic and the laboratory setting. These new possibilities provide a clinical tool for the assessment of patients with musculoskeletal complaints during daily activities, or assessment of athletes in terms of efficiency in use of muscles. The sound created by muscle movement can be heard with the ear pressed up to a contracting muscle, but most of the energy is low frequency, below 20 Hz, making it inaudible

infrasound Infrasound, sometimes referred to as low status sound, describes sound waves with a frequency below the lower limit of human audibility (generally 20 Hz). Hearing becomes gradually less sensitive as frequency decreases, so for humans to perce ...

. Electromyography signals are typically

bandpass filter A band-pass filter or bandpass filter (BPF) is a device that passes frequencies within a certain range and rejects ( attenuates) frequencies outside that range. Description In electronics and signal processing, a filter is usually a two-p ...

ed from 10 Hz to 500 Hz, by comparison. PMG signals are limited to 5 Hz to 100 Hz in some experiments. Orizio states that the low-frequency response of the sensor is the most important feature, and should go as low as 1 Hz. Images of PMG waves are available in this creative commons-licensed document, "''Mechanomyographic amplitude and frequency responses during dynamic muscle actions: a comprehensive review''".

History

Muscle sounds were first described in print by the Jesuit scientist Francesco Maria Grimaldi in a posthumous publication of 1665, which influenced the work of the English physician

William Hyde Wollaston William Hyde Wollaston (; 6 August 1766 – 22 December 1828) was an English chemist and physicist who is famous for discovering the chemical elements palladium and rhodium. He also developed a way to process platinum ore into malleable ingot ...

and the German scientist

Paul Erman Paul Erman (29 February 1764 – 11 October 1851) was a German physicist from Berlin, Brandenburg and a Huguenot of the fourth generation. He was the son of the historian Jean Pierre Erman (1735–1814), author of ''Histoire des réfugiés'' ...

. The latter enlisted the aid of

René Laennec René-Théophile-Hyacinthe Laennec (; 17 February 1781 – 13 August 1826) was a French physician and musician. His skill at carving his own wooden flutes led him to invent the stethoscope in 1816, while working at the Hôpital Necker ...

. Mechanical amplification was first employed by

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Associatio ...

. The past two centuries of repeated rediscovery and neglect of the phenomenon were summarised by Stokes and Blythe{{cite book , first1 = Maria , last1= Stokes , first2 = Max , last2 = Blythe , title = Muscle Sounds in physiology, sports science and clinical investigation , publisher = Medintel , location = Oxford , year = 2001 , isbn = 978-0-9540572-0-6 in 2001.

References

:8. Harrison, A.P., Danneskiold-Samsøe, B., Bartels, E.M. - Portable acoustic myography – a realistic noninvasive method for assessment of muscle activity and coordination in human subjects in most home and sports settings. Physiol Rep. Jul 2013; 1(2): e00029. Published online Jul 10, 2013. http://physreports.physiology.org/content/1/2/e00029 Medical tests Neurophysiology Neurotechnology Neurology procedures