Motor unit action potential (MUAP) measurements

Duration is measured as the time from the initial deflection of the MUAP from baseline to its final return to baseline. It is the parameter that best reflects the number of muscle fibers in the motor unit. Amplitude reflects only muscle fibers very close to the needle and is measured peak to peak. Phases (shaded areas) can be determined by counting the number of baseline crossings and adding 1. MUAPs are generally triphasic. Serrations (also called turns) are changes in direction of the potential that do not cross the baseline. The major spike is the largest positive-to-negative deflection, usually occurring after the first positive peak. Satellite, or linked, potentials occur after the main potential and usually represent early reinnervation of muscle fibers.