EMG – ElektroMyoGrafi

Electromyography (EMG) is a technique for evaluating and recording the activation signal of muscles.
An electromyography machine detects the electrical potential generated by muscle cells when these
cells are mechanically active, and also when the cells are at rest. The electrical source is the muscle
membrane potential of about -90mV. Measured EMG potentials range between less than 50 µV and up
to 20 to 30 mV, depending on the muscle under observation. Typical repetition rate of muscle unit firing
is about 7–20 Hz, depending on the size of the muscle (eye muscles versus seat (gluteal) muscles),
previous axonal damage and other factors.
The first documented experiments dealing with EMG started with Francesco Redi’s works in 1666. Redi
discovered a highly specialized muscle of the electric ray fish (Electric Eel) generated electricity. By
1773, Walsh had been able to demonstrate that the Eel fish’s muscle tissue could generate a spark of
electricity. In 1792, a publication entitled “De Viribus Electricitatis in Motu Musculari Commentarius”
appeared, written by Luigi Galvani, in which the author demonstrated that electricity could initiate muscle
contractions. Six decades later, in 1849, Dubios-Raymond discovered that it was also possible to record
electrical activity during a voluntary muscle contraction. The first actual recording of this activity was
made by Marey in 1890, who also introduced the term electromyography. In 1922, Gasser and Erlanger
used an oscilloscope to show the electrical signals from muscles. Because of the stochastic nature of
the myoelectric signal, only rough information could be obtained from its observation. The capability of
detecting electromyographic signals improved steadily from the 1930s through the 1950s and
researchers began to use improved electrodes more widely for the study of muscles. Clinical use of
surface EMG (sEMG) for the treatment of more specific disorders began in the 1960s. Hardyck and his
researchers were the first (1966) practitioners to use sEMG. In the early 1980s, Cram and Steger
introduced a clinical method for scanning a variety of muscles using an EMG sensing device.
It is not until the middle of the 1980s that integration techniques in electrodes had sufficiently advanced
to allow batch production of the required small and lightweight instrumentation and amplifiers. At present
a number of suitable amplifiers are commercially available. During the past 15 years, research has
resulted in a better understanding of the properties of surface EMG recording. In recent years, surface
electromyography is increasingly used for recording from superficial muscles in clinical protocols, where
intramuscular electrodes are used for deep muscle only.
There are many applications for the use of EMG. EMG is used clinically for the diagnosis of neurological
and neuromuscular problems. It is used diagnostically by gait laboratories and by clinicians trained in the
use of biofeedback or ergonomic assessment. EMG is also used in many types of research laboratories,
including those involved in biomechanics, motor control, neuromuscular physiology, movement
disorders, postural control, and physical therapy