Measurement of motor unit action potentials: procedural considerations.

Many factors influence the observed magnitude and shape of motor unit action potentials (MUAP). Several of these are related to procedures used during the electromyographic examination. An examiner must be aware of the procedural factors which may alter his observations. These include the following: strength of contraction; placement of the ground and reference electrodes; site, depth and pattern of electrode penetration; distance of active electrode penetration; distance of active electrode discharging unit; and separation of observation sites. The number of different MUAP observed and the number of observations of each MUAP become important when formulating a statistical report. The acceptable level of variation between serial samples of the same motor unit may determine the number of different units available for analysis. The selection of the point where the MUAP begins, ends and deflects maximally can influence the recorded observations.