Abstract
It is unclear whether there are clinically significant differences in amplitude, duration, and numbers of turns and phases if an electromyographic (EMG) study is performed near to, or far from, the endβplate zone. The effects of temporal dispersion of arriving muscleβfiber action potentials on quantitative motor unit action potential (MUAP) metrics were assessed in simulated and biologic muscles. Two muscle simulation models were studied with electrode recording positions near the motor endβplate zone and 50β75 mm away. When the electrode was moved away from the endβplate zone, averages of 20 MUAPs significantly decreased in amplitude and area, and increased in numbers of turns and phases, but there was no significant change in duration. In biologic muscles (both normal and pathologic), similar changes in average metrics were observed, but to lesser degrees; few were statistically significant. Zones of innervation in biologic muscles are broadly distributed and, during routine electrode studies, distances between random electrode placements and endβplate zones are therefore relatively short, leading to clinically insignificant changes in quantitative MUAP metrics with distance from the endβplate zone. Thus, electrode position within a muscle is unlikely to affect clinical MUAP interpretation. Muscle Nerve, 2007