The effect of vision elimination during quiet stance tasks with different feet positions

Highlights

• Centre-of-pressure parameters were affected by vision removal and stance type.

• Strongest effect of vision elimination was observed for narrower feet positions.

• Significant stance × vision interaction effect was observed for most parameters.

• The interaction was different in medial–lateral and anterior–posterior direction.

Abstract

Literature confirms the effects of vision and stance on body sway and indicates possible interactions between the two. However, no attempts have been made to systematically compare the effect of vision on the different types of stance which are frequently used in clinical and research practice. The biomechanical changes that occur after changing shape and size of the support surface suggest possible sensory re-weighting might take place. The purpose of this study was to assess the effect of vision on body sway in relation to different stance configurations and width. Thirty-eight volunteers performed four quiet stance configurations (parallel, semi-tandem, tandem and single leg), repeating them with open and closed eyes. Traditional parameters, recurrence quantification analysis and sample entropy were analyzed from the CoP trajectory signal. Traditional and recurrence quantification analysis parameters were affected by vision removal and stance type. Exceptions were frequency of oscillation, entropy and trapping time. The most prominent effect of vision elimination on traditional parameters was observed for narrower stances. A significant interaction effect between vision removal and stance type was present for most of the parameters observed (p < 0.05). The interaction effect between medio-lateral and antero-posterior traditional parameters differed in linearity between stances. The results confirm the effect of vision removal on the body sway. However, for the medio-lateral traditional parameters, the effects did not increase linearly with the change in width and stance type. This suggests that removal of vision could be more effectively compensated by other sensory systems in semi-tandem stance, tandem and single legged stance.

Introduction

Static balance tests (i.e. quiet stance tasks) are often used as part of functional assessment in elderly, athletes and other clinical populations [1], [2], [3]. Cross-sectional studies have shown that body sway parameters differ between young and elderly adults [4], as well as between healthy and health-deficient individuals [5]. Furthermore, these tests have shown predictive power for falls in the elderly [6], detection of pre- and post-injury changes [7] as well as adaptations to long-term exercise [8].

Quality of balance control has been shown to be dependent on sensory input. Proper sensory input enables accurate anticipation of body sway and preparation of corrective anticipatory postural adjustments [9]. Various sensory fields (i.e. plantar, joint and muscle proprioceptors as well as vestibular and ocular organs) give specific information on the position and movement of the body in space. Vision has been shown to effectively compensate for the loss of other sensory fields [10], [11]. In general, it has been suggested that removal of vision on its own increases body sway by more than one third in healthy young adults [12], [13]. Moreover, narrower stances (comparing parallel and single leg stance) have been shown to be affected greater by vision removal than wider stances [14], [15]. Interestingly, this effect was more pronounced in younger than in elderly subjects [15]. Most noticeable changes were observed in the centre of pressure (CoP) area [16] and path [17], although no changes were reported in the median frequency [17], [18].

Reports on how the effect of vision is dependent on stance type (i.e. different shape and width of feet placement) are limited. This question is relevant from a clinical as well as from a research perspective. Changing configuration and width of stance affects biomechanical characteristics of the human body, possibly affecting the sensory input from muscles and joints [18], [19] and consequently body sway. Clinicians use different types of stance configurations to modify sensitivity of a balance test according to age, injury or disease, regardless of possible differences in sensory re-weighting. Moreover, the research literature is usually limited to a small number of parameters, some of which have low reliability. The aim of this study was to assess the effect of vision on body sway by comparing stances of different configuration and width. We hypothesized that the effect of vision removal on body sway would increase linearly from wider towards narrower stance types, as suggested in the literature. Only parameters which proved as the most reliable in our previous research were used (data submitted for publication).