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Electromyography (Valerie Hunt)

Introduction
Electromyography (EMG) is a technique for evaluating and recording the activation signal of muscles. EMG is performed using an instrument called an electromyograph, to produce a record called an electromyogram. An electromyograph detects the electrical potential generated by muscle when these cells are mechanically active, and also when the cells are at rest. The signals can be analyzed in order to detect medical abnormalities or analyze the biomechanics of human or animal movement.


Electrical characteristics


The electrical source is the muscle membrane potential of about -90mV[1]. Measured EMG potentials range between less than 50 ?V 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. Damage to motor units can be expected at ranges between 450 and 780 mV.