Analysis of calculated electrical activation of denervated muscle fibers in the human thigh.

Finite difference models of the human thigh are used to analyze the excitation process in the fibers of denervated skeletal muscles in conjunction with functional electrical stimulation (FES) via surface electrodes. The Matlab tool "FES-Analyze" was developed to simulate and analyze the super-threshold regions in a human thigh. Action potential is simulated with a muscle fiber model of the Hodgkin Huxley type and with a generalized form of the activating function. With FES-Analyze it is possible to compare the stimulation at the end of the muscle fiber and the stimulation at the central part of the muscle fiber, both in cross- and longitudinal-section, as well as to observe the effect of different impulse intensities and lengths during FES. Simulating with "Standard Values" of the pulse duration (20 ms) and the amplitude (80 V) one discovers that the main part of the activation takes place at the end of the muscle fiber. To obtain activation at the central part of the muscle fiber, higher amplitudes and longer pulse durations are needed.