SCIENCE: How do loads and time of day effect the foot and the medial longitudinal arch?

Abstract

Problem: The foot muscles are loaded due to the everyday locomotion. It is generally accepted that the foot shape changes over the day. Since the medial longitudinal arch is supported by the foot muscles, we can suppose that the supporting function can be reduced through fatigue. Time of day and load-induced changes of the foot shape can directly effect shoes and orthotics. However, there are only few studies that examine the change of the foot shape during the day. The present study researches the question if the foot shape changes depending on the load and the measuring time (time of day).

Method: In the univariate cross-section analysis the feet of 27 trained and healthy male runners were examined. The examination of the study participants was carried out in one day during two measuring times in the morning and in the evening. The foot morphology was determined with the help of a 3D-laserscanner during three load situations (sitting 10% BW, standing on both legs 50 % BW, standing on one leg 100% BW). Among others the Bony Arch Index (BAI) and the Dorsal Arch Index were determined. With the help of the BAI a classification of the longitudinal arch of the random test of the study participants was carried out.

Results: The load situation had a big significant impact on all measured values. The foot seems to get longer, wider and more lowered with increasing loading. Also significant changes could be determined between the two measuring times. The foot is more lowered in the evening than in the morning. With the help of the classification of the longitudinal arch two groups with flat (n = 11) and normal (n = 16) could be identified. A significant effect of the interaction of the load could be determined with the classification of the longitudinal arch. The markedness of the lowering is bigger within the group with a flat longitudinal arch.

Discussion: The biggest changes of the foot shape could be detected between the sitting (10 % BW) and the standing on both legs load position (50 % BW). For that reason the unloaded foot shape seems to be only slightly interrelated to the functionally loaded foot shape. Thus the molding of the foot in an unloaded position would have to be questioned for the design of the orthotic and the last. Since the presented foot changes already could be seen in trained people, these should be detected more remarkably in untrained or pathological feet in future studies.

Dominik Gräßle (BFTS GmbH, Cologne, Germany) Kai Heinrich (Institute of Biomechanics and Orthopaedics, German Sport University Cologne, Germany)

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