Electromyography is the recording of electrical changes present in muscles at rest or evoked by voluntary movement. It is an obligatory investigation in neuromuscular disorders.
Activity is recorded by introducing a concentric bipolar needle electrode - for several motor units - or a single fibre electromyography electrode - for single units - into the target muscle, and taking measurements at rest and at increasing strengths of contraction.
In the normal muscle, there should be no electrical activity at rest. Voluntary contraction will generate a characteristic biphasic response, i.e. a positive phase followed by a negative one. Increasing the strength of contraction should add further motor unit contractions to the record.
Last reviewed 01/2018