The mechanomyogram is the mechanical signal observable from the surface of a muscle

Muscle

Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

 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 vibration

Vibration

Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...

s are due to oscillation

Oscillation

Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...

s of the muscle fibres at the resonance frequency

Resonance

In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...

 of the muscle. The mechanomyogram is also known as the phonomyogram

Phonomyography

Phonomyography is a technique to measure the force of muscle contraction by recording the low frequency sounds created during muscular activity.Although less precise than the more traditional mechanomyography, it is considerably easier to set up...

, acoustic myogram, sound myogram or vibromyogram.

Signal Characteristics

The MMG is a low frequency vibration that may be observed when a muscle is contracted using suitable measuring techniques.

Measurement Techniques

It can be measured using an accelerometer

Accelerometer

An accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...

 or a microphone

Microphone

A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

 placed on the skin over the belly of the muscle. When measured using a microphone is may be termed the acoustic myogram.

Uses

The MMG may provide a useful alternative to the electromyogram (EMG) for monitoring muscle activity. It has a higher signal-to-noise ratio

Signal-to-noise ratio

Signal-to-noise ratio is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power. A ratio higher than 1:1 indicates more signal than noise...

 than the surface EMG and thus can be used to monitor muscle activity from deeper muscles without using invasive

Invasiveness of surgical procedures

There are three main categories which describe the invasiveness of surgical procedures. These are: non-invasive procedures, minimally invasive procedures, and invasive procedures ....

 measurement techniques.
It is currently the subject of research activity into prosthetic control and assistive technologies for the disabled.

History

Muscle sounds were first described in print by the Jesuit scientist Francesco Maria Grimaldi

Francesco Maria Grimaldi

Francesco Maria Grimaldi was an Italian Jesuit priest, mathematician and physicist who taught at the Jesuit college in Bologna....

 in a posthumous publication of 1665, which influenced the work of the English physician William Hyde Wollaston

William Hyde Wollaston

William Hyde Wollaston FRS was an English chemist and physicist who is famous for discovering two chemical elements and for developing a way to process platinum ore.-Biography:...

 and the German physicist Paul Erman

Paul Erman

Paul Erman was a German physicist from Berlin, Brandenburg. He was the son of the historian Jean Pierre Erman , author of Histoire des refugis....

. The latter enlisted the aid of René Laennec

René Laennec

René-Théophile-Hyacinthe Laennec was a French physician. He invented the stethoscope in 1816, while working at the Hôpital Necker and pioneered its use in diagnosing various chest conditions....

. Mechanical amplification was first employed by Hermann von Helmholtz

Hermann von Helmholtz

Hermann Ludwig Ferdinand von Helmholtz was a German physician and physicist who made significant contributions to several widely varied areas of modern science...

. The past two centuries of repeated rediscovery and neglect of the phenomenon were summarised by Stokes and Blythe in 2001.