The Dynamical Systems Theory (DST) views locomotion as an emergent coordinated behavior.  Coordinated movements of the lower extremity segments are necessary to facilitate safe walking.  Obstacles and low friction conditions are two types of perturbations that could potentially cause instability.  The purpose of this study was to investigate the effects of shoe traction and obstacle height on lower extremity coordination during walking to better understand the mechanisms employed to avoid slippage following obstacle clearance.

        Ten male subjects walked at a self-selected pace (±5%) during eight different conditions: four obstacle conditions (0%, 10%, 20%, & 40% of limb length) while wearing two different pairs of shoes (low and high traction).  Frictional forces were calculated from the ground reaction forces (GRF), which were recorded using a Kistler force plate (960 Hz) following obstacle clearance.  Videography was collected at 60 Hz from the sagittal view.  Kinematic data were analyzed during the stance period only.  A two-way repeated measures ANOVA was performed on the subject means for each parameter.

       The force ratio (Fy/Fz) trace portraits friction in-vivo.  The force ratio trace peaks did show significant differences between the low and high traction shoe conditions, as expected.  In addition, all peaks generally increased with increases in obstacle height.  The timing of the stance period was significantly altered due to both traction and obstacle height. The results from the coordination parameters indicate that as an obstacle was introduced within the walking cycle, a significant amount of change was seen in intralimb coordination.  The introduction of a low traction shoe had as a result a more in-phase relationship.  Furthermore, the increasing obstacle height resulted in a more in-phase relationship for both shoes.  Even though a change in behavior was not witnessed, an increase in variability (or decrease in stability) of the behavior was observed due to increases in obstacle height.  The higher the obstacle and the lower the shoe traction, the more unstable the system became.  These changes in phasing relationship and variability are indicators of alterations in coordinative behavior, which if pushed further may have lead to falling.