Current distance relations for fiber stimulation with pointsources

The following results are based on computer simulations and on activating function analysis. In the near field, denervated muscle fibers as well as nerve fibers with a sealed ending are easier to stimulate in the central region than with electrodes close to the end. When electrode-fiber distance is increased, the electrode location for optimal stimulation efficacy shifts from a central position to a region beyond the fiber end for cathodic stimulation and to a position above the terminating part of the fiber for anodic currents. The phenomenon becomes more pronounced with increasing distance between the electrode and fiber axis, because in the far field, the current-distance relation changes from quadratic to cubic, whereas stimulation at the fiber end obeys a rather constant quadratic law.