In vivo magnetomyograms of skeletal muscle

Magnetomyography (MMG) is a new noninvasive technique inspired by the magnetoneurographic method of J.P. Wikswo (IEEE Trans. Biomed. Eng., Vol.BME-30, p.215-21, 1983). MMG is used to detect action currents in a muscle, which is immersed in a highly conducting fluid. The detection coil is of a toroidal shape, with the muscle passing through the center of the coil. For a long muscle which fits tightly in the toroid, it is to be expected that magnetic fields correspond almost completely to the intracellular longitudinal (axial) currents in active muscle fibers. An experimental setup with specific coils for rat and mouse skeletal muscles was developed. It is sensitive enough to detect currents from single motor units. The technique can be used to record stimulated twitch activity in live muscle as a function of force level, coil position along the muscle, temperature, etc. By simulating the response with a finite-element forward model, it is possible to calculate action currents under various experimental conditions