EMG

Electromyography (EMG) is a diagnostic technique for evaluating and recording the electrical activity produced by skeletal muscles. It assesses the health of muscles and the nerves that control them (motor neurons). EMG data are obtained with electrodes placed on the skin over a muscle (surface EMG) or inserted into the muscle with a needle (intramuscular EMG).

Surface EMG captures summed electrical activity from many motor units and is commonly used to study timing of muscle activation, coordination, and biomechanical function. Intramuscular EMG records action potentials from individual motor units and is more selective but invasive, often used when precise motor-unit information is required for diagnosis or research.

During a typical intramuscular recording, a fine needle electrode records motor unit action potentials in response to voluntary contraction or electrical stimulation. Surface recordings allow examination of recruitment and interference patterns. EMG is often interpreted alongside nerve conduction studies (NCS) to evaluate the integrity of the peripheral nervous system.

Applications include the diagnosis of neuromuscular disorders such as radiculopathy, peripheral nerve injury, myopathy, and motor neuron disease; assessment of muscle function in rehabilitation and sports science; and intraoperative neuromonitoring. EMG also underpins research into motor control and assistive technology for prosthetics.

Limitations include susceptibility to noise and cross-talk, discomfort with needle electrodes, and the fact that EMG provides information about electrical activity rather than direct measures of muscle strength or fatigue. Safety considerations are generally favorable, with rare infections or bleeding.