An electromyograph (abbreviated to EMG) is a device used to measure and detect muscle conditions. It uses needle electrodes to discover informaiton about the muscles.
What is EMG?
EMG is most commonly used to detect muscle conditions such as Muscular Dystrophy, diseases of the neuromuscular junction (between the nerve and muscle) and nerve or nerve root injuries.
In a very simplistic overview, information is sent along nerves as an electrical impulse. When the impulse reaches a muscle, this triggers an action potential which passes through the muscle, causing the fibres to contract. The muscle membrane potential is measured, as is the rate of motor unit firing. An EMG may be performed alongside a nerve conduction study to get a full picture of the muscle/nerve injury.
What happens when you go for an EMG?
The machine used for EMG is an electromyograph. The process involves inserting needle electrodes into the muscle and so for this reason the test can be a little uncomfortable, although is not usually painful. The muscle may also feel tender or bruised the next day.
The number of needles depends on the size of the muscle being tested. Once the needles are inserted the patient is asked to make some small movements to fire the nerve and contact the muscle(s) in question. The information picked up by the needles is transmitted to an amplifier which is connected to a device that produces a readout. This can then be printed or displayed on a computer screen.
The size and shape of the waves produced provide the information required about the ability of the muscle and nerves involved.
There are very few risks involved with EMG so it is very safe to perform. The only risks are from minor internal bleeding due to insertion of the needles, as well as an extremely low risk of infection (all needles are new, sterile and sealed before the test and are discarded after use).