Postural threat influences the conscious perception of body position during voluntary leaning

Height-related changes in postural control can alter feedback used to control balance, which may lead to a mismatch in perceived and actual sway changes during quiet stance. However, there is still a need to examine how these changes affect the ability to detect limits of stability (and movements related to base of support limits).

The aim of this study was to examine how changes in height-related threat influence conscious perceptions of body position during voluntary balance tasks.

Twenty young healthy adults, fitted with kinematic markers on the right side of the body, stood on a forceplate mounted to a hydraulic lift placed at two heights (0.8 m and 3.2 m). At height (completed first), participants leaned as far forward as possible, at the ankle joint, while trying to remain as an inverted pendulum. Then, at each height, participants stood with eyes open, and voluntarily leaned to one of ten targets (10%-100% maximum lean) displayed visually as angular displacement of body segments on a screen. Once on target, participants reported a perceived position relative to their maximum lean. Balance confidence, fear and anxiety, and physiological arousal (hand electrodermal activity, EDA) were recorded and statistically tested using paired sample t-tests. Actual and perceived body positions were tested using repeated measures ANOVAs (height x target).

Height significantly increased EDA, fear and anxiety, and decreased balance confidence. Participants voluntarily leaned to all target positions equally across heights. However, at any given target position, the perceived lean changed with height. When participants are asked to lean to a target in at height, their amount of perceived lean was larger by 4.9%, on average (range: 1.8%-9.7%).

This modulation in perceived limits of stability may increase the risk of falls in those who have an increased fear of falling.