Effect of obstacle depth and height on step-over behavior: Focus on age-related changes

Obstacle avoidance during locomotion is a crucial motor skill, especially in environments with uneven terrain. However, the combined effects of obstacle dimensions and aging on this ability remain unclear. This study aimed to investigate whether the action of stepping over an obstacle changes proportionally with obstacle size and how these movements evolve with age. We recruited fourteen young participants and fourteen older participants. Participants were instructed to step over an obstacle placed five meters away under nine different conditions with varying obstacle dimensions. The smallest obstacle had dimensions of 5 cm × 5 cm (height × depth), and both height and depth were increased by 5 cm increments to reach the largest obstacle size of 15 cm × 15 cm, resulting in three levels each of depth and height conditions. An analysis of variance on the leading-foot clearance revealed significant interactions between height and depth, demonstrating a height-dependent depth effect on clearance, independent of age. Furthermore, significant interactions between height and age were observed for the heel-obstacle distance, which refers to the landing position after stepping over the obstacle. This indicates that older adults consistently landed closer to the same position at each obstacle height, whereas the landing positions of young adults moved farther away as the obstacle height increased. Our findings suggest that although both young and older adults can immediately scale the dimensions of the obstacle and consistently adjust their leading-foot movement accordingly, the landing movements of older adults follow an inflexible strategy that could potentially be riskier.