Electrical Studies / Surface Electromyography
submitted by Dr. Gary Farr - Contact the author here. Last Updated April, 22, 2002	Save Money! Check out our special offers here.

What Is EMG?

The letters EMG represent Electro Myo Graphy, which refers to the measurement of electrical activity of muscles. In a similar way, ECG refers to Electro Cardio Graphy which is the measurement of electrical activity of the heart muscle. Just as cardiologists use ECG or EKG to accurately evaluate the heart, and neurologists use EEG to accurately evaluate the brain, Chiropractors, neurologists, researchers and clinicians use surface EMG to more accurately evaluate muscles. EMG measures the capacity of muscles to function.

How Does Surface EMG Work?

The small electric current, or signal, which comes from active muscles is detected by sensors placed on the skin directly above the muscles. The strength and pattern of the signal is seen on a computer screen and the data is collected in a software program that is able to run various analyses of the data to create useful reports regarding muscle function.

What Is The Difference Between Needle EMG and Surface EMG?

In needle EMG evaluations a needle electrode is penetrated into the skin and directly into the muscle. Needle EMG provides information about a single muscle fiber or the velocity of nerve conduction rather than information on the overall condition of a muscle. Surface EMG technology allows information regarding the overall muscle function and condition to be collected from the surface of the skin. This process is not painful to the patient.

Why is Surface EMG Used?

A sEMG system uses an electronic feedback technique to cancel out very low frequency changes (dc to fractions of a Hz) in the acquired physiological signal. Signals in this very low frequency range can arise as a result of the motion artifact phenomena. The Noraxon signal is remarkably free of noise due to skin or cable movement and offers a very stable baseline. In Noraxon's patented system information carried by the overall signal is effectively split into an "EMG only" component and a low frequency "motion artifact" component. The motion artifact component is literally subtracted from the overall signal allowing only the EMG signal to be presented.

Graph of electrical activity of muscles	A computer and software are used to interpret the signals from the muscles

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