Figure 1.

Waveforms obtained using SFN electrode and CN electrode in the SFEMG program in ALS and healthy controls. Consecutive discharges of the same motor unit were recorded from the extensor digitorum communis muscle during voluntary contraction. (a) Recorded by SFN electrode in a normal subject, (b) recorded by CN electrode in a normal subject, (c) recorded by SFN electrode in an ALS patient, and (d) recorded by CN electrode in an ALS patient. The low-cut filter setting was 500 Hz for (a) and (c), 1 kHz for (b) and (d). Signals recorded with CN were visibly indistinguishable from single-fiber waveforms, although the former might actually comprise synchronized and near-simultaneous action potentials from more than one muscle fiber. SFN: Single-fiber needle; CN: Concentric needle; SFEMG: Single-fiber electromyography; ALS: Amyotrophic lateral sclerosis.