Determinants of motor unit action potential duration

Objective: Motor unit action potential (MUAP) recordings are modeled by means of a single muscle fiber simulation program, to define two key subcomponents comprising the complete physiologic MUAP duration. A number of defining properties of these subcomponents are further developed. Methods: A single muscle fiber simulation program is utilized with various muscle fiber lengths and conduction velocities to generate near-field and far-field waveforms. Results: Two key subcomponents to the total physiologic single muscle fiber and hence MUAP duration are identified. One, defined as the near-field component, is directly dependent upon muscle fiber hemi-length. The other, defined as the far-field component, is independent of fiber length, but matches the internal action potential in duration. Both the near-field and far-field components are inversely dependent upon intracellular action potential conduction velocity. Additionally, temporal dispersion among the individual fibers contributing to a MUAP must be included in the overall MUAP duration calculation. Conclusions: It is hoped that this approach to MUAP duration may allow a more complete appreciation of the components contributing to the MUAP, than permitted by the empirically derived values for MUAP duration presently under clinical use.