PURPOSE: Injuries from falls are a serious health issue. Approaches to preventing falls should consider increasing relevant visual information of an obstacle. Obstacle parameters, such as position and height, may be specified by the visible structure of an obstacle. The present study examined the relationship between visible structure of an obstacle and locomotor behaviour. This relationship may be modified as a function of experience with navigating obstacles. Since workers at construction sites must navigate through cluttered environments with varied obstacles, these workers may have superior skills at avoiding obstacles. Therefore, the effect of work experience was also examined. METHODS: Nine construction workers and 10 age- and gender-matched control subjects participated. Subjects stepped over obstacles in an 8 m walkway. Three different obstacles were examined, arranged according to a hierarchy ranging from most to least visible structure: a solid obstacle, a three-edge outline obstacle and a top-edge obstacle. The obstacles were 10, 20 or 30 cm high. In addition, visual information was decreased with goggles which obstructed the lower visual field, removing information of the obstacle and foot-relative-to-obstacle in the two steps before the obstacle. All conditions were presented randomly. RESULTS: Higher risk of contact and higher lead and trail toe clearance variability were observed for the top-edge obstacle. Higher risk of contact was observed when the lower visual field was obstructed and for the 30 cm obstacle. Work experience did not influence risk of contact. Construction workers had lower trail toe clearances and lower trail toe clearance variability for the 10 cm obstacle, but were not different from controls for the 30 cm obstacle. CONCLUSIONS: Decreased visible structure of an obstacle resulted in increased gait variability and increased risk of contact. The changes are consistent with decreased accuracy of the sensory-to-motor transformation used to control the lead and trail limb during obstacle crossing when only the top-edge was visible. There is some evidence that construction workers were better able to transform the visual information to motor actions, as reflected by decreased gait variability, but these findings were not supported by decreased risk of obstacle contact.
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