Jaw Muscle Electromyographic Response to Whole‐Body Postural Perturbation

BACKGROUND: While whole-body postural control requires integration of the sensorimotor system, the involvement of jaw muscle activity in this control remains unclear. OBJECTIVE: This study aimed to clarify the relationship between jaw muscle activity and whole-body postural stability by measuring jaw-opening and closing muscle activities, as well as whole-body postural sway during postural perturbations with two different levels of predictability. METHODS: Twelve healthy adults (7 males, 5 females; median age 21.0 years) underwent vertical perturbations by holding a bar at shoulder height. In the cued condition (C-cond), the participants were given a 3-s countdown before the bar was loaded with 3% of their body weight, whereas in the uncued condition (U-cond), the load was applied without prior cueing. Jaw-closing (masseter) and jaw-opening (anterior suprahyoid) muscle activities were measured using surface electromyography (EMG). Bar dynamics and center-of-foot-pressure (COP) were assessed with motion capture and a force plate. Bar-drop distances, EMG activity, and the proportion of trials with muscle activity exceeding baseline were compared between conditions using the Wilcoxon signed-rank test, Friedman, Mann-Whitney U and chi-square tests, as appropriate, with Bonferroni corrections. RESULTS: Vertical bar displacement was greater in the U-cond compared with the C-cond (-46.0 mm vs. -27.4 mm, the Wilcoxon signed-rank test, p < 0.05). Left anterior suprahyoid activity exceeded baseline in 91.7% of uncued trials versus 58.3% in cued trials (the chi-square test with the Bonferroni correction applied, adjusted p < 0.05). COP displacement increased when masseter and anterior suprahyoid muscle activity exceeded baseline in the U-cond (the Mann-Whitney U test with Bonferroni correction, adjusted p < 0.05). CONCLUSION: Increased activation of jaw-opening muscles during uncued perturbations compared with cued perturbations suggests that anterior suprahyoid muscles are recruited for postural control, supporting their involvement in maintaining stability.