Visually-guided saccades attenuate postural sway under non-fatigued, fatigued, and stretched states

Muscular fatigue, which reduces force output and position sense, often leads to increased sway and potential balance impairments. In contrast, visually-guided saccadic eye movements (saccades) can attenuate sway more than fixating gaze on an external target. The goals of this study were to determine whether the use of saccades could reduce the increased postural sway in a fatigued state and to better understand the contributions to fatigue-induced increased sway. We compared the effects of gazing at a fixation point (FP) and performing saccades (SAC) on various spatial and temporal measures of the center of pressure (CoP) while participants stood as still as possible on a force plate. Participants used either a narrow or wide base of support and performed three trials for each eye movement condition (SAC, FP) in three states (non-fatigued-NF, stretched-S, and fatigued-F). Calf raises to exhaustion induced ankle fatigue. Extreme plantar- and dorsi-flexion induced stretch. SAC significantly decreased sway and increased time-series complexity (sample entropy) compared to FP. F increased sway and decreased time-series complexity compared to NF and S states, which were similar. Reduced force production, which accompanies muscle fatigue and stretching, did not account for increased sway associated with acute bouts of ankle muscle fatigue. Increased position sense often associated with muscle stretching likely compensated for any reduced force output for S, while the decreased position sense associated with F probably explained the increased sway in this state. Performing saccadic eye movements during quiet stance can help reduce sway under various states.