A new method of estimating the distribution of muscle fiber conduction velocities

A computer-assisted method of estimating the distribution of muscle fiber conduction velocities is described. An electrode array composed of 2 stimulating and 4 recording electrodes is used to record surface muscle action potentials (MAPs) in response to direct muscle stimulation. The velocity distribution and the single muscle fiber action potential (SFAP) are calculated from the recorded MAPs by an iterative method of estimation. The estimation is based on the assumption that the spatial orientation of each muscle fiber viewed from the recording electrodes is the same along the muscle fibers and a MAP is recorded as a linear summation of all SFAPs. The accuracy of this estimation is demonstrated using simulated MAPs. The method is also tested on MAPs containing simulated amplifier noise, stimulus artifact, and errors in distance between electrodes. Finally we applied this method to MAP recordings of the biceps brachii in 23 healthy subjects. The velocity distribution was successfully estimated in 20 cases. The average of the estimated distributions was smaller than that described by previous workers. The reasons for the difference are discussed.