Developmental trends in skilled locomotor behavior over uneven terrain

Abstract

The primary focus of this thesis was to examine the development of obstacle avoidance strategies in children. In particular, the role played by vision in modulating the locomotor pattern over obstacles was investigated. A theoretical model was proposed and its components were addressed. In order to pursue this goal, three studies were planned and conducted.

The goal of the first study was to characterise the contribution of visual exteroceptive input to obstacle avoidance strategies. Exteroceptive information refers to identification of location and features of objects and surfaces in the environment. For a child, the perception of exteroceptive information and the appropriate motor pattern modulation of the intended action are processes that are developed through sensory-motor integration. Exteroceptive information was manipulated through a combination of two obstacle heights and two obstacle widths, all with high contrast between the obstacle and the ground. Subjects (n=25, 2 to 58 months of walking experience) were asked to step over an obstacle placed in their travel path. Video recording with a split screen two-camera system was done to qualitatively document each child's performance. Seven IREDs were placed on specific anatomical landmarks (right and left hip and toe, right knee, ankle and heel) and sampled using the OPTOTRAK motion analysis system (Northern Digital, Canada). From the displacement of the markers from leading toe off to trailing foot contact, four dependent measures were obtained: leading and trailing toe clearance, leading hip elevation and leading foot placement before the obstacle. Results from the qualitative measures did not reveal developmental trends, indicating that children were able to perform the task but they need to tune their limb trajectories to safely clear the obstacle. The kinematic measures confirmed the qualitative results indicating that obstacle height influenced the modulation of the limb displacements over the obstacle.

The second study examined the role of exproprioceptive information in modulating the locomotor pattern over obstacles. Exproprioceptive information refers to the identification of the body parts relative to one another and relative to the objects and events in the environment. Exproprioceptive information was manipulated through a combination of two obstacle heights with low contrast and by either restricting or not vision from both limbs. Subjects (n=20, from 8 to 62 months of walking experience) were asked to wear a neck collar and step over an obstacle placed in their travel path. Qualitative video analysis was performed as in the first study. Kinematic analysis was done on the displacement of five IREDs (right and left eye, shin and right and left toe) to obtain gait and head parameters. The results from the qualitative measures (failure rate) exhibit a developmental trend, indicating that a more challenging environment was necessary to exhibit this trend. Gait kinematic measures (leading and trailing toe clearance and foot placement before the obstacle) replicated the results of the first study. Head kinematic measure (pitch angle magnitude) revealed a developmental trend in spatio-temporal acquisition of exteroceptive and exproprioceptive information, especially when vision was restricted.

The third study focused on the contribution of the effector system's intersegmental dynamics during locomotion over obstacles through a kinematic analyses of the swing limb. Kinetic analysis offers a special opportunity to verify the exploitation of the passive and active forces acting on the limb during the swing phase. Successful trials from the first study were reanalysed through the inverse dynamics technique, which allows the isolation of the muscle moment from motion dependent moments and gravity. The muscle moments around the hip and the ankle joints were modulated as a function of obstacle height. This modulation revealed that the nervous system was actively controlling the swing limb flexion over the obstacle, even though it is not efficient.

The results of the three studies support the proposed theoretical model.