Roll-over shapes of human locomotor systems: Effects of walking speed

Objective. To examine the hypothesis that roll-over shapes of non-disabled lower limb systems do not change appreciably with walking speed. Design. Repeated measures (n=24). Background. Roll-over shapes of three lower limb systems are presented. They are: roll-over shapes of the (1) foot, (2) ankle-foot, and (3) knee-ankle-foot systems. Roll-over shapes show the effective rocker (or cam) shapes that the lower limb systems conform to during the period in the stance phase of walking between heel contact and opposite heel contact. Methods. Roll-over shapes were measured by transforming center of pressure data from a laboratory-based coordinate system into each of three body-based coordinate systems. Knee-ankle-foot roll-over shapes were further characterized using a circular arc model. Results. From a statistical standpoint, the radii of the best-fit circular arcs did not change significantly with walking speed, while the forward shifts of the circular models did change significantly. However, the change in forward shift was not considered to be clinically significant. Conclusions. The biologic systems involved in developing the roll-over shapes adapt to changing conditions of walking speed, including increased loading amplitudes as speed is increased, to maintain similar effective roll-over geometries.Relevance Roll-over shapes provide insight into the workings of various lower limb systems by taking a new look at existing gait data. This insight could provide broad utility, helping to develop a better understanding of able-bodied and disabled human walking, and leading to the design of improved rehabilitation devices, surgeries, and therapies.