The frontal electromyographic adaptation response. A potential source of confounding.

Undergraduates were recruited to provide a descriptive analysis of the frontal electromyographic (EMG) adaptation response. Following placement of sensors, subjects were instructed to lie quietly for 15 minutes. Averaging data across subjects, a statistically significant adaptation response was produced in the direction of relaxation that required about 11 minutes to stabilize. The adaptation course varied greatly among subjects as a function of the initial EMG value. A criterion of stability was recommended that would individualize the adaptation period.