Measurement of 3D foot deformation durring waking using digital image correlation method

Abstract

Detailed understanding of the foot deformation during walking is important for ergonomic design of shoe and orthopaedic diagnosis. However, quantitative description of the foot deformation and skin strain during walking have not been fully investigated due to difficulty of measurement. In this study, we aimed to clarify the three-dimensional (3D) human foot deformation and the foot skin strain during bipedal walking by means of digital image correlation (DIC) method. The 3D-DIC method is an optical method to measure 3D deformation of an object by using the stereo-triangulation and the image correlation of speckle pattern on the object surface. Five adult male participants were asked to walk along a walkway at a self selected speed. The dorso-lateral and medial surfaces of the right foot during the stance phase of bipedal walking were filmed using four synchronized high speed cameras. The right foot surface was sprayed with aqueous black ink to draw the speckle pattern. We calculated time change in the 3D foot shape and the skin strain distribution during walking. The accuracy of the shape and deformation measurement was confirmed to be about 0.1 mm, sufficiently accurate for quantitative description of the foot deformation. Our results demonstrated that in the early and late stance phase, the foot surface around the cuboid were stretched in the mediolateral direction. In the late stance phase, the lateral surface of the rear foot was stretched in the dorsopalmar direction vice versa in the medial surface. Proposed methodology may serve as an effective tool to clarify how external surface of the human foot dynamically behaves during walking.