Electromyogram (EMG) measures the response of muscles and nerves
to electrical activity. It's used to help find conditions that might be causing muscle
weakness, including muscular
dystrophy and nerve disorders.
How Is an EMG Done?
Muscles are stimulated by signals from nerve cells called motor neurons.
This stimulation causes electrical activity in the muscle, which in turn causes the
muscle to contract, or tighten. The muscle contraction itself produces electrical
For the purpose of EMG, a needle electrode is inserted into the muscle (the insertion
of the needle might feel similar to an injection). The signal from the muscle is then
transmitted from the needle electrode through a wire (or more recently, wirelessly)
to a receiver/amplifier, which is connected to a device that displays a readout. The
results are either printed on a paper strip or, more commonly, on a computer screen.
What Can an EMG Diagnose?
EMGs help diagnose three kinds of diseases that interfere with normal muscle contraction:
diseases of the muscle itself (most commonly, muscular dystrophy
diseases of the neuromuscular junction, which is the connection
between a nerve fiber and the muscle it supplies
diseases "upstream" in nerves and nerve roots (which can be due
to either nerve damage or ongoing nerve injury)
When Are the Results Ready?
Results are available immediately but a trained medical specialist, usually neurologist,
is needed to analyze and interpret them.