Characteristics of muscular contraction caused by magnetic stimulation

Characteristics of muscular contraction induced by magnetic stimulation were studied using isolated gastrocnemius muscles of a frog. The figure-eight coil position was regarded as 0 degrees when the direction of induced current was parallel to the muscle fiber axis, and 90 degrees when the induced current was perpendicular to the muscle fiber axis. Muscular contraction readily occurred with lower outputs of magnetic stimulation at 0 degrees and 180 degrees, but it was weak at 90 degrees and 270 degrees. Magnetic stimulation did not directly induce muscular contraction but it acted on the synapses forming end plates to muscle cells, and muscular contraction occurred if the direction of the eddy current was parallel to the nerve which innervated the muscle cells.