Deformation of foot cross-section shapes during walking.

To clarify the magnitude of shape change during walking, the shapes of four cross-sections (Forefoot, Instep, Navicular, and Heel) of the right foot during standing and walking were measured using a four-dimensional measurement system we developed (14 Hz) with an accuracy of +/-0.5 mm. Images of the sole were measured using a high-speed video camera (120 Hz). Cross-section shapes and derived dimensions were compared between the standing condition, first peak (P1), and midstance valley of two peaks (MSV) of vGRF during walking. Heel and Navicular cross-sections were more laterally inclined during walking than during standing by 6 degrees on average. Compared to at standing, breadth of the cross-section in contact with the ground was wider at the heel and instep at timing P1, and was wider at the forefoot and narrower at heel at timing MSV. Medial length was longer and dorsal arch was higher during walking than during standing. Plantar arch height did not differ between the three conditions. The maximum difference in plantar arch height between standing and P1 was 1.3 mm, much smaller than the inter-individual variation of 7 mm.