electromyography

Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. It is used to assess muscle function, diagnose neuromuscular disorders, and study motor control. Modern EMG includes needle (intramuscular) EMG and surface EMG, and is often integrated with nerve conduction studies to evaluate both muscles and the nerves that supply them.

Needle EMG uses fine-wire or needle electrodes inserted into a muscle to record motor unit potentials (MUAPs) and insertion activity, providing information about motor unit size, shape, recruitment, and firing patterns. Surface EMG uses electrodes placed on the skin over a muscle to measure the summed activity of many motor units. Recordings may be qualitative or quantitative, describing patterns such as interference activity during voluntary contraction, MUAP morphology, recruitment order, and firing rates. Safety considerations include minimal risk of infection or bleeding, with some discomfort at insertion; limitations include sampling bias, cross-talk from adjacent muscles, and difficulty assessing deep muscles.

Clinical indications include suspected neuropathies and radiculopathies, myopathies and neuromuscular junction disorders, peripheral nerve injuries, and muscle disorders. EMG data help localize pathology, assess severity and prognosis, guide rehabilitation, and monitor recovery. In research, EMG supports investigations of motor control, biomechanics, fatigue, and prosthetic or assistive device control. The interpretation requires specialized training, standardized protocols, and correlation with clinical findings and imaging.

History: The study of muscle electrical activity has roots in 19th‑century physiology, with pioneers such as Emil du Bois-Reymond. Modern clinical EMG and nerve conduction testing were developed in the mid‑20th century with advances in electrode technology, signal processing, and normative data.