Spatiotemporal mapping of plantar shear forces during human walking using a flexible thin-film sensor

During walking, the foot is subjected to complex vertical and shear ground reaction forces, which play critical roles in gait mechanics and the development of foot pathologies. However, plantar shear stress has been less investigated due to measurement difficulties. This study aimed (1) to evaluate the accuracy of a newly developed thin-film shear force distribution sensor in measuring plantar pressure and shear stress during walking, and (2) to characterize the spatiotemporal features of plantar shear loading throughout the stance phase. Five healthy male adults participated in walking experiments using the thin-film sensor affixed to a force plate for reference. The sensor measures normal and shear forces with a resolution of 24 × 24 sensing points over a 312 × 312 mm area. Force outputs were sampled at 100 Hz and compared with the ground reaction forces obtained from the force plate. The integrated vertical and shear components from the thin-film sensor showed good agreement with the force plate data, confirming its accuracy and reliability. Spatiotemporal shear maps revealed dynamic changes in magnitude and direction across stance: posterior shear beneath the heel during early stance, medial rotation at mid-stance, and anterior propulsion beneath the forefoot during push-off. This sensing system enables continuous mapping of plantar shear and pressure distributions, providing a practical tool for gait analysis and the prevention of foot disorders such as diabetic ulcers and hallux valgus.