Volume conduction in electromyography: Experimental and theoretical review

This article reviews and correlates theoretical and experimental results on the recorded single motor unit action potential (MUAP) obtained from skeletal muscle in terms of volume conduction. A short mathematical derivation to develop the recorded action potential from single muscle and nerve fibers in terms of solid angle geometry is presented in the body of the paper and a complete derivation in the Appendix. The theory is then used to explain how biphasic, triphasic, and polyphasic single MUAPs are recorded. Both theoretical and experimental results show that the recorded action potential will decrease with the square of distance from the electrode to the active fiber. The shape, amplitude, and duration of the waveform is dependent on many factors which are explained in the text.