Electromyography (EMG), Surface

Activation of the muscle fibers that belong to a motor unit occurs via a nerve-muscle synapse, the neuromuscular junction, which involves a specialized area in the muscle membrane named the end-plate. When an action potential reaches this area traveling along a terminal branch of the axon of the motor neuron, acetylcholine is released at the neuromuscular junction and receptors in the end-plate are activated, thus leading to the generation of an action potential that propagates along the muscle fiber. A single motor neuron action potential leads to synchronous activation of hundreds of muscle fibers. Recruitment of multiple motor units results in asynchronus muscle fiber action potentials. The propagation of depolarized zones along the muscle fibers, which corresponds to the muscle fiber action potentials, generates an electrical field that can be captured via electrodes positioned in the area surrounding the active muscle fibers. The detected electrical activity is named the electromyographic (EMG) signal. Keywords: muscle fiber action potential; motor unit; SEMG signal; muscle activation interval; muscle fiber conduction velocity; muscle fatigue