Analysis of foot shape deformation during walking and its application to designing insole

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The purpose of this study is to measure and quantitatively clarify the foot shape changes during walking in order to obtain grounds for designing the custom insole from individual foot shape. Insole can be used to improve the comfort by adjusting the differences between the shapes of the foot and last. For this purpose, a cat walk (BxLxH=100x800x100 [cm]) with a glass plate (35.5x40 [cm]) set in the middle was constructed. Four load cells were set under the glass plate, and the ground reaction force was measured (120 Hz). Video images of the sole were captured with a high frequency video camera (200 Hz) from below the glass plate. An in-house 4D shape measurement system consisting of 12 video cameras was set around the glass plate, and the shapes of four cross sections on the foot were measured (14 Hz). The right foot was measured for 45 subjects during walking and standing with weight distributed equally on both feet. Six measurements were measured from the sole video images, and the heights of the plantar arch and dorsal arch were measured from the instep cross-section data. Measurements at standing were compared with those at the first peak or the bottom of 2 peaks of the ground reaction force. It was found that compared to the measurement at standing, (1) the medial arch length increased but the lateral arch length does not during walking; (2) ground contact breadth at the ball and instep increased at the mid stance phase; (3) height of plantar arch does not decrease during the mid stance phase. The results suggest that the foot shape measured in the standing posture may be used as the basis for designing custom insole.