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.
Dumitru
D
D
Department of Rehabilitation Medicine, University of Texas Health Science Center at San Antonio, 78284-7798, USA. dumitru@uthscsa.edu
King
J C
JC
Zwarts
M J
MJ
D000200:Action Potentials / Q000502:physiology; D004558:Electric Stimulation; D004566:Electrodes; D006801:Humans; D007366:Intercostal Muscles / Q000294:innervation / Q000502:physiology; D008959:Models, Neurological; D009046:Motor Neurons / Q000502:physiology* / Q000648:ultrastructure; D018485:Muscle Fibers, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D009431:Neural Conduction / Q000502:physiology