<Non-linear Change Of Foot Morphology And Foot Arch Integrity With External Load>

The human feet enable efficient impact absorptions and push-offs in weight-bearing exercises (i.e., walking or running) through foot deformation, particularly the medial longitudinal foot arch. Yet, no studies investigate the relationship between foot deformation and external load, leading to a limited understanding of the material properties of the inter-metatarsal tissues and the mobility of the metatarsals. PURPOSE: To explore how foot morphology and arch integrity change with external loads. METHODS: Twenty healthy females (18.8 ± 0.9 years old, 162.6 ± 4.1 cm and 47.9 ± 3.2 kg) voluntarily took 3D foot scans under five bodyweight (BW) conditions: 0.1BW (sitting posture), 0.5BW (bilateral foot standing), 1.0BW (single foot standing), 1.5BW (single foot standing with 0.5BW weight) and 2.0BW (single foot standing with 1.0BW weight). Foot morphology and foot arch (shape and stiffness) variables were measured and calculated from 20 feet for each condition. One-way ANOVA tests and linear regression analyses were conducted. RESULTS: Significant differences were detected in foot width (p = 0.013) and hallux height (p < 0.001) but without statistical differences among 0.5BW, 1.0BW, 1.5BW and 2.0BW. All the foot arch variables showed significant differences (p ≤ 0.002) but differences for variables except the arch stiffness index were not found among 1.0BW, 1.5BW and 2.0BW. Generally, it showed an exponential increase or decrease with an increase in external load. CONCLUSION: The foot and foot arch deformed nonlinearly with an increase in external load, and the deformation reached an apex at around an individual’s body weight. Table 1. - Values of foot morphology and arch variables under different bodyweight (BW) conditions. Variables Loading Weight 0.1BW 0.5BW 1.0BW 1.5BW 2.0BW Foot Morphology (mm) Foot length 226.5±7.9 229.9±7.8 230.0±7.1 230.5±7.4 231.1±7.3 Truncated foot length 163.1±5.7 165.6±5.6 165.7±5.1 166.0±5.3 166.5±5.2 Foot width* 88.8±3.4 90.8±3.8 91.8±3.8 92.3±3.8† 92.4±3.6† Hallux height* 25.6±2.4 22.8±2.0† 22.1±1.7† 21.9±1.8† 22.0±1.7† Medial ankle condyle height* 77.1±4.7 71.4±4.1† 70.7±4.2† 70.2±3.8† 69.4±4.2† Ball girth 217.8±7.8 219.8±8.2 220.7±7.8 220.9±7.9 220.7±7.4 Tarsal girth 214.5±6.3 215.8±5.5 215.5±5.4 215.6±5.2 215.7±5.1 Foot Arch Arch height (mm)* 12.8±2.5 8.8±2.4† 7.9±2.2† 7.5±2.5† 6.7±2.0†‡ Dorsum height (mm)* 63.5±3.0 59.7±3.2† 59.6±2.8† 57.7±3.0† 58.1±3.1† Navicular height (mm)* 40.1±4.0 35.1±3.3† 37.2±3.3 36.6±3.4† 36.6±3.1† Medial arch angle (°)* 140.0±5.5 138.8±4.3 143.8±4.1‡ 141.9±3.9 143.3±4.6‡ Arch height index* 0.393±0.025 0.363±0.025† 0.362±0.021† 0.357±0.022† 0.352±0.023† Arch stiffness index* 1.0 0.940±0.018† 0.938±0.019† 0.925±0.022† 0.915±0.022†‡^ Supported by the Innovation and Entrepreneurship Projects for Shenzhen University Students (X.L.) and the China Scholarship Council (S.M.). Supported by: Supported by the Innovation and Entrepreneurship Projects for Shenzhen University Students (X.L.) and the China Scholarship Council (S.M.).