Postural Stability and Visual Verticality Perception of Neck Disturbance of the Middle-aged during Quiet Standing

[Purpose] This study investigated postural stability and visual vertical perception of healthy middleaged subjects before and after induction of dorsal neck muscle fatigue. [Subjects] Fourteen subjects (3 males, 11 females) were recruited from the community. [Methods] To induce neck extensor muscle fatigue, participants pushed their heads against a myometer. The average center of pressure (COP) displacement in the medial-lateral (ML) and anterior-posterior (AP) directions and average sway velocity were measured on a force platform, and the error in visual vertical perception was measured using the rod and frame test. [Results] The average COP displacement in the AP direction and average sway velocity were significantly different between before and after induction of neck muscle fatigue. No difference in the average COP displacement in the ML direction or errors in visual verticality perception was observed before and after neck muscle fatigue. [Conclusion] In the presence of visual input, dorsal neck muscle fatigue induced postural instability, but not visual vertical misperception. After isometric or repetitive neck extensor muscle contraction for a long period, taking a rest for a while before changing posture from sitting to standing is recommended for workers, to avoid an increase in postural sway in standing, which may lead to an accidental fall.