Phonomyography (PMG) (also known as acoustic myography, sound myography, vibromyography, and surface mechanomyogram) is a technique to measure the force of

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

contraction by recording the low frequency sounds created during muscular activity. Although, until recently, less precise than the more traditional mechanomyography, it is considerably easier to set up. The signal is measured using condenser microphone elements, piezoelectric sensors,

accelerometer An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...

s, or a combination of sensors attached to the skin. Hydrophones 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 frequency sound or incorrectly subsonic (subsonic being a descriptor for "less than the speed of sound"), describes sound waves with a Audio frequency, frequency below the lower limit of human audibility ...

Electromyography Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyo ...

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. It is the inverse of a '' band-stop filter''. Description In electronics and s ...

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 Francesco Maria Grimaldi (2 April 1618 – 28 December 1663) was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna. He was born in Bologna to Paride Grimaldi and Anna Cattani. Work Between 164 ...

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 i ...

and the German scientist Paul Erman. The latter enlisted the aid of René Laennec. Mechanical amplification was first employed by

Hermann von Helmholtz Hermann Ludwig Ferdinand von Helmholtz (; ; 31 August 1821 – 8 September 1894; "von" since 1883) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The ...

. 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