Graduation date: 1998

Although research evidence clearly indicates support surface properties are a major factor contributing to fall risk among the elderly, investigations examining the influence of variations in surface conditions on the postural control of older adults during task performance have been limited. Thus, the primary purpose of the present studies was to determine whether the coordination and control of body kinematics exhibited by older adults during upright leaning (i.e., leaning forward through the region of stability) and gait would be different across variations in support surface properties. Secondary objectives of these studies included, examining if coordination and control measures of body kinematics differed as a function of the participants' level of postural stability and/or repeated exposure to the support surface properties. Three support surface conditions were selected for inclusion based on resistance properties to applied forces (i.e., normal and shear): rigid, high friction; compliant; and rigid, low friction. For both tasks performed, body kinematics for trials 1-3 (T1) and 10-12 (T2) from 12 completed trials on each support surface were analyzed using three-dimensional (3-D) video analyses. Results of separate univariate repeated measures analyses of variance yielded significant surface condition main effects for lower extremity coordination patterns and postural control strategies in the gait and leaning task, respectively. Additionally, a significant surface condition main effect and an interaction effect of surface condition by trial block were identified for the measure of head stability in the gait and leaning tasks, respectively. Differences in head stability and the control of lower extremity joint motions as a function of level of postural stability (i.e., group differences) were observed only during the walking task. Present findings indicate that during goal-directed behavior, the coordinated movements of the body and its segments emerge from constraints imposed by the interaction of the support surface, the task and the individual. The observed adaptations in the coordination and control of posture in response to support surface constraints evidenced in the present studies provide support for the theory of perception and the control of bodily orientation (Riccio & Stoffregen, 1988). / Graduation date: 1998