Reproducibility of the electromyogram.

Electromyographic recordings of masseter muscles were taken during mastication without the introduction of an experimental variable. The amplitude, duration, and sequence of the onset of muscle bursts were used to evaluated the recordings. Amplitude showed the most variation during the same session, at different sessions, and between three different areas of the masseter muscle. Onset showed the least variation during the same session and at different sessions; duration showed the least variation between areas.