THE BIPHASIC MORPHOLOGY OF VOLUNTARY AND SPONTANEOUS SINGLE MUSCLE-FIBER ACTION-POTENTIALS

The extracellular morphology of single muscle fiber action potentials (SMFAPs) is anticipated by volume conductor theory to be triphasic. Si ngle muscle fiber action potentials recorded during single muscle fibe r studies (500 Hz to 20 kHz) usually appear triphasic; however, when r ecorded with an open bandwidth (1 Hz to 20 kHz) they are found to be b iphasic. Fibrillation potentials recorded with a single fiber electrod e and open bandwidth have identical biphasic morphologies as volitiona l SMFAPs. Computer simulations suggest that the intracellular action p otential models currently used to derive simulated extracellularly rec orded SMFAPs must have the repolarization phase considerably prolonged to yield the clinically recorded potentials. This implies that either the models presently used require significant modification, or there is some distortion of the transmembrane source current induced in need le recording studies such that biphasic and not triphasic potentials a re detected. (C) 1994 John Wiley & Sons, Inc.