Jaw Muscle Electromyographic Response to Whole-Body Postural Perturbation

While whole-body postural control requires integration of the sensorimotor system, the involvement of jaw muscle activity in this control remains unclear.

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.

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.

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).

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.