Trunk sway jerkiness: A sensitive indicator of fear-related postural stiffening during virtual height exposure

Introduction: Wearable inertial sensors are effective, portable and low-cost tools for measuring postural stability. They capture the acceleration of body segments to objectively assess postural control via body sway. However, their application has not yet been adequately explored for assessing balance at height, where postural control is challenged. Height exposure can also evoke fear and anxiety, which may modify postural sway. In this study, we investigated whether inertial sensor-derived measures of trunk sway frequency and jerkiness can sensitively capture postural adjustments associated with height-related fear.Methods: Forty-two young adults (mean age 26.8 ± 5.6 years; 13 men, 29 women) were exposed to virtual heights (0 m, 20 m, and 40 m) in an immersive virtual-reality setting, while postural sway was recorded using accelerometers placed on the lower trunk at the level of the fifth lumbar vertebra (L5) and on the upper trunk at the level of the sternum (ST). Participants were divided into two groups: low fear and high fear. To characterize postural sway to each height level and each sensor location, two variables were calculated: 1) mean frequency (MF) and 2) integrated squared jerk (JERK).Results: With increasing height, MF significantly increased at both trunk levels in the high fear group but decreased in the low fear group, especially at ST. JERK significantly differed between the groups with a gradual increase with ascending height at both trunk levels in the high fear group. In contrast, the low fear group showed a slightly descending trend of L5 sway jerkiness, while at ST the trend was rather flat.Conclusions: Virtual height induced faster and jerkier trunk sway in participants with a high fear of heights, suggesting greater postural stiffening compared with those reporting low fear. Sway frequency and in particular sway jerkiness clearly reflect fear-related postural responses to height exposure in young adults. High JERK in the high fear group indicates jerky movements, whereas lower and stable JERK in the low fear group reflects smoother and more controlled motion. Virtual height exposure revealed strong associations with fear of height and identified JERK as the most sensitive and discriminative measure to distinguish low vs. high fear individuals.Acknowledgements: This work was supported by the Slovak grant agency VEGA No. 2/0098/25.Disclosure: This abstract is based on a previously published study (Bzdúšková et al., 2026).