title: Balance control and anti-gravity muscle activity during the experience of fear at heights.
abstract: Fear of heights occurs when a visual stimulus causes the apprehension of losing balance and falling. A moderate form of visual height intolerance (vHI) affects about one third of the general population and has relevant consequences for the quality of life. A quantitative evaluation of balance mechanisms in persons susceptible to vHI during height exposure is missing. VHI-related changes in postural control were assessed by center-of-pressure displacements and electromyographic recordings of selected leg, arm, and neck muscles in 16 subjects with vHI while standing at heights on an emergency balcony versus standing in the laboratory at ground level. Characteristics of open- and closed-loop postural control were analyzed. Body sway and muscle activity parameters were correlated with the subjective estimates of fear at heights. During height exposure, (1) open-loop control was disturbed by a higher diffusion activity (P < 0.001) and (2) the sensory feedback threshold for closed-loop control was lowered (P < 0.010). Altered postural control was predominantly associated with increased co-contraction of leg muscles. Body sway and leg and neck muscle co-contraction correlated with the severity of subjective anxiety (P < 0.050). Alterations in postural control diminished if there were nearby stationary contrasts in the visual surrounding or if subjects stood with eyes closed. The performance of a cognitive dual task also improved impaired balance. Visual heights have two behavioral effects in vHI subjects: A change occurs in (1) open- and closed-loop postural control strategy and (2) co-contraction of anti-gravity leg and neck muscles, both of which depend on the severity of evoked fear at heights.
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany.
authors.forename: Max
authors.initials: M
authors.lastname: Wuehr
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany ; Institute for Clinical Neurosciences, University of Munich, Munich, Germany.
authors.forename: Guenter
authors.initials: G
authors.lastname: Kugler
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany ; Department of Neurology, University of Munich, Munich, Germany.
authors.forename: Roman
authors.initials: R
authors.lastname: Schniepp
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany.
authors.forename: Maria
authors.initials: M
authors.lastname: Eckl
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany.
authors.forename: Cauchy
authors.initials: C
authors.lastname: Pradhan
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany ; Department of Neurology, University of Munich, Munich, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Jahn
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany ; Institute for Clinical Neurosciences, University of Munich, Munich, Germany.
authors.forename: Doreen
authors.initials: D
authors.lastname: Huppert
authors.affiliation: German Center for Vertigo and Balance Disorders (DSGZ), University of Munich, Munich, Germany ; Institute for Clinical Neurosciences, University of Munich, Munich, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Brandt
keywords: Balance control; fear of heights; muscle activity; muscle co‐contraction; visual height intolerance
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