Estimation of the compound intracellular action potential from surface-recorded muscle signals

The rising edge of a surface-recorded muscle potential contains information about the initiation of electrical activity at the muscle-fiber endplates. Differentiating the rising edge reveals a signal which in theory is proportional to a weighted sum of the intracellular action potentials (IAPs) of all the active fibers. The authors call this signal the compound IAP (CIAP). They show that the duration of the IAP can be estimated from the duration of the CIAP of a motor-unit action potential (MUAP), and that the dispersion in motor-nerve conduction velocities (MNCVs) can be estimated from the difference in durations of the CIAPs from distally and proximally evoked compound muscle action potentials (CMAPs).