Extracellular potentials from skeletal muscle

Abstract

A mathematical model for the calculation of volume-conducted field potentials from active skeletal muscle fibers in an anisotropic extracellular medium is developed, based on the principles of electromagnetic field theory (details of this derivation are given in Appendix I). Two specific cases are considered for a finite volume conductor: (a) the single active muscle fiber located arbitrarily within the anisotropic volume conductor and (b) the single active motor unit consisting of a group of active muscle fibers activated by a single motor nerve. The motor unit may also have an arbitrary distribution of component fibers, and these fibers may be activated either synchronously or asynchronously with an arbitrary excitation pattern. The model is shown to be useful in the prediction of surface electromyographic (EMG) waveforms due to the activity of bioelectric sources lying within the anisotropic muscle medium that constitutes the volume conductor. Thus this field theoretic model represents a first approximation to the study of multifiber activity and its contribution to the surface EMG.