BACKGROUND: Obstacle avoidance and object prehension occur regularly in real-world environments (walking up/down steps and opening a door). However, it is not known how walking and prehension change when there is an increase in the level of difficulty of the walking task. RESEARCH QUESTION: We investigated the changes in walking and reach-tograsp when performing these two motor skills concomitantly in the presence of an obstacle on the ground positioned in different locations in relation to the object-to-be-grasped.
METHODS: Fifteen young adults walked and grasped a dowel placed on a support with the obstacle positioned at the step before (N-1), during (N) and after (N + 1) the prehension task.
RESULTS: The prehension task did not affect leading limb obstacle negotiation. Toe clearance and maximum toe elevation were lesser at obstacle position N + 1 than at obstacle position N-1 when combining grasping and obstacle-crossing task for the trailing limb. Step width increased in the presence of the obstacle-crossing task independent of obstacle location. The correlation between foot position before the obstacle and toe clearance revealed that the addition of the prehension task disrupted the relationship between these variables for the trailing limb. Foot placement and limb elevation were unaffected by the prehension task. The reaching component was unaffected by the increased level of difficulty of the walking task. The grasping component was affected by the increased level of difficulty of the walking task, as the time to peak grip aperture occurred earlier in the presence of the obstacle at position N, and may indicate a cautious strategy to grasp the dowel successfully. SIGNIFICANCE: Our results showed that prospective control is affected after the prehension since the attention to grasping may have impaired the acquisition of visual information for planning the trailing limb elevation.