Supplementary Material for: Aging Delays Completion of Head Rotation Cycles in Continuous Gaze Stabilization Exercises Despite Putative Healthy Vestibular Function

Introduction: aging is associated with loss of balance, with falls being the leading cause of death
among elderly in the United States. Gaze stabilization exercises (GSE) improve balance control in vestibular populations and could be useful to prevent falls in healthy individuals. However, the extent to which aging affects head kinematics in GSE is unknown.
Methods: forty-eight young (n=25, 24 ± 6 years, 60% female) and older (n=23, 66 ± 5 years, 56% female) adults completed six 30-second GSE. Participants were asked to maintain gaze fixation on a stationary target while continuously performing head movements in pitch (e.g., vertical) and yaw (e.g., horizontal) directions. The visual target was placed on the wall 1m or 2m away, or hand-held at arm’s length. Head kinematics were recorded with an inertial measurement unit placed on the back of the participants’ head.
Results: older adults took significantly more time (e.g., delay) to complete cycles of head rotation compared to young participants across all GSE. Such delay was further increased during pitch head rotation while fixating gaze of the 1m target. The range of velocity (ROV) of head rotation, however, was equivalent between groups in all GSE.
Conclusion: aging leads to the maintenance of head cycle ROV at the expense of delayed cycles of head rotation, suggesting an age-dependent prioritization strategy (e.g., adapt duration first vs range second) during continuous head movements. The distance of the visual target and head movement direction influenced elderly performance and should be considered when prescribing GSE to older populations.