Children use different anticipatory control strategies than adults to circumvent an obstacle in the travel path.

Carrying out the daily activities of work and play requires the ability to integrate available sensory information in order to navigate complex, potentially cluttered, environments. The expression of locomotor adjustment behaviour is still maturing during mid- to late-childhood (Grasso et al. in Neurosci Biobehav Rev 22(4): 533-539, 1998a; McFadyen et al. in Gait Posture 13:7-16, 2001), which raises the question, do children coordinate their body segments differently than adults when circumventing an obstacle in their travel path? Healthy young children (n=5; age 10.3+/-1.5 years) and adults (n=6; age 26.3+/-2.9 years) were asked to walk at their natural pace during unobstructed walking, as well as during the avoidance to the right or left of a cylindrical obstacle located in the travel path 3 m from the initial starting position. Fourteen infrared markers were fixed to participants and tracked using the Optotrak motion analysis system (60 Hz; Northern Digital Inc, Canada). Data analyses included center of mass (COM) clearance from the obstacle, gait speed, angular movement of the head and trunk (yaw, pitch and roll) and medial-lateral (M-L) COM displacement. Onset of change in these variables from unobstructed walking was also calculated as the time from OBS crossing. Although there were no differences in when adults or children altered their M-L COM trajectory, adults reoriented their head and trunk segments at the same time as their COM while children reoriented their head and trunk prior to changing COM direction. A comparison of foot placement data for this task indicated that while adults changed their gait patterns well in advance of obstacle crossing, children initiated M-L adjustments to gait patterns just prior to OBS crossing. Vallis and McFadyen (Exp Brain Res 152 (3):409-414, 2003) indicated that during circumvention of an obstacle, adults coordinate body segments for a single transient change in COM trajectory while maintaining the underlying travel direction. The present data suggest, however, that children partition obstacle avoidance into two tasks, initially steering with proactive movement of the head and trunk segments and finally making adjustments to their gait trajectory, via stride and step width changes, to ensure adequate obstacle clearance just prior to obstacle crossing. This study demonstrates different anticipatory control strategies used by children as compared to adults to circumvent obstacles in the travel path. The different head and trunk anticipatory segmental coordination suggests that children gather visual information differently when circumventing an obstacle in their travel path and are more dependent on visual input to guide their circumvention strategy.