Fig. 1.

CMAP waveforms that varied depending on the position of the active recording electrode. (A) CMAPs obtained in a 24-year-old man. (B) CMAPs obtained in a 48-year-old man. The upper CMAPs (TM) were obtained by placing the active recording electrode on the belly of the upper TM, and the lower CMAPs (TM + 2 cm) were obtained by placing the active recording electrode 2 cm behind the belly of the upper TM. The three vertical lines indicate the onset latency, the latency of the first major deflection, and the latency of the return to baseline, respectively. “Amplitude” represents peak-to-peak amplitude (mV). “Duration” represents negative duration (ms). “The black arrow” in the upper CMAPs (TM) indicates a slight deflection originating from the supraspinatus muscle.