On the selection of concentric needle electromyogram motor unit action potentials: Is the rise time criterion too restrictive?

Concentric needle electromyogram motor unit action potentials (MUAPs) were recorded from the biceps brachii muscle of normal subjects and in patients with neuromuscular diseases. Although the MUAPs had a crisp sound and appeared sharp, their rise time (RT), measured from the maximum negative peak to the preceding maximum positive peak before it, was often >500 μs. All MUAPs with a RT ≤500 μs were recorded from within the motor unit (MU) territory. MUAP recordings from outside the MU territory had a long RT but also low amplitude (