2016 Volume 43 Issue 6 Pages 445-452
Purpose: In recent studies, the potential utility of prosthesis/orthosis with a functional sole shape and gait evaluation through the sole shape has been suggested by the coordinate transformation of center of pressure (COP) trajectories from laboratory-based coordinate systems into body-based coordinate systems. However details of the functional plantar shape during normal walking are yet to be completely elucidated. The present study aimed to clarify intra- and inter-subject variation, differences due to conventions of the local coordinate system and applied methods of curve-fitting, and the speed dependency of sole shapes.
Method: Subjects walked along an 8-m walkway at five different speeds. Center of foot pressure and three-dimensional kinematics were measured. The measured data were transformed into two types of body-based coordinate systems, and two types of curve-fitting were then performed.
Results and conclusions: Intra- and inter-subject COP trajectory variation was extremely small. At extreme speeds, particularly at the fastest, the trajectory variationincreased in a few subjects. Coordinate transformation type was not found to affect trajectory consistency, whereas cubic curve approximation was slightly better than circular approximation. The relationship between major events during the walking cycle and COP trajectory was found to be speed dependent. Thus, the circular shape of COP trajectory obtained using the leg coordinate system indicates the potential utility of this shape for gait evaluation and orthosis/prosthesis with a fixed ankle joint, expect for use during fast walking.
