Reproducible effects of subjectively assessed muscle fatigue on an inhibitory jaw reflex in humans

ObjectiveTo evaluate the effects of exercise-induced, subjectively assessed muscle fatigue on an inhibitory jaw reflex, evoked by electrical stimulation of the upper lip. In addition, the reproducibility of these effects was assessed.DesignEight subjects participated in two experimental sessions that were two weeks apart. During each session, a baseline recording, a post-conditioning recording, and two recovery recordings were obtained. The post-conditioning recording was obtained immediately after provocation of jaw muscle fatigue by intense chewing. The endpoint of provocation was reached 30 s after a subject had crossed the value ‘6’ on a 10 cm long visual analogue scale.ResultsSubjectively assessed jaw muscle fatigue caused a decrease of about 50% in the size of the late inhibition in the post-conditioning recording (ANOVA: p = 0.001; Bonferroni contrasts: p < 0.05). Full recovery to baseline values was already achieved at the first recovery recording. No significant differences were found between both sessions (ANOVA, p = 0.677).ConclusionExercise-induced, subjectively assessed jaw muscle fatigue causes a reproducible, transient suppression in the size of the late inhibitory jaw reflex wave.