MOTOR UNIT ACTION-POTENTIAL DURATION RECORDED BY MONOPOLAR AND CONCENTRIC NEEDLE ELECTRODES - PHYSIOLOGICAL IMPLICATIONS

Controversy exists regarding motor unit action potentials (MUAPs) reco rded with monopolar v concentric needle electrodes. All investigations to date have used different instrumentation parameters combined with different motor unit potential populations to assess comparative durat ions for MUAPs. In this investigation, the same MUAP was analyzed for both monopolar and concentric needle electrodes with identical instrum entation parameters. Monopolar needle electrodes were found to record MUAPs with slightly longer durations, a result that reached statistica l significance. Manual wideband high-resolution MUAP analysis demonstr ated durations approaching 30 ms for both electrodes, which is differe nt from the approximately 10 ms presently measured for both electrode types. A hypothesis was proposed whereby the total duration of current flow, which is directly proportional to muscle fiber length, is the p rimary determinant of MUAP duration. The physiologic implications of t his hypothesis are discussed.