Some electromyographic parameters of experimental tooth clenching in adult human subjects.

Eight adult human subjects exercised maximal voluntary tooth clenching until fatigue and pains were experienced, and could no longer be endured, in the right masseter muscle. The integrated electrical activity in the right masseter muscle was determined as a ratio of the different isometric exercises, and it showed a consistent decrease from onset of fatigue, via onset of pains, to the endurance of pains, possibly because of progressive muscle fatigue. The relative muscle activity might have determined the perception of the moment of onset of fatigue in the masseter muscle, and the perception of the moment of muscle exhaustion, but not the perception of the moment of onset of muscle pains.