PURPOSE: To examine the effect of preloading eccentric exercise on pain sensitivity in healthy volunteers.

METHODS: In 20 healthy volunteers, pain-related sensations (6 items: pain, unpleasantness, fatigue, stiffness, tension, and soreness during maximum biting), and pain intensities induced by repeated electrical stimuli on the masseter and the hand palm were evaluated using a visual analog scale (VAS) of 0-100 mm. Eccentric exercise (6 min-test) or gum chewing (6 min-control) was used as preloading exercise to evaluate the effect on pain sensitivities before and after low-level clenching (15 min) performed 2 days after the preloading exercise.

RESULTS: Eccentric exercise induced only low levels of pain-related sensations 2 days later. However, the time course of temporal summation induced by four repeated electrical stimuli on the masseter was influenced by the type of preloading exercise, i.e., temporal summation increased after the low-level clenching (P = 0.016) when preloading was done by the eccentric exercise, while no significant change was observed when preloading was done by the gum chewing.

CONCLUSIONS: Eccentric exercise may facilitate pain sensitivity induced by subsequent low-level clenching via the central nervous system. In addition, it was demonstrated that pain sensitivity after the low-level clenching could be influenced by the type of preloading exercise. These experimental results may suggest that eccentric exercise could act as one of the triggering factors in the mechanism by which tooth clenching leads to a chronic pain condition in susceptible individuals.