Foot pronation monitoring using wireless biaxial force sensing system

Measurements of multi-axial Ground Reaction Force (GRF) can provides quite useful information for monitoring abnormalities of gait during Activities in Daily Living (ADL). Measuring multi-axial GRF using ambulatory GRF sensing systems is difficult due to the height of sensor and the number of sensors used. Therefore, we developed a wireless GRF sensing system having the low height (12 mm) and the capability of sensing simultaneously lateral and vertical GRF using only four optical sensors. The proposed biaxial force sensor showed the low interference rate (less than 0.1 %) and excellent repeatability (0.6 %). We extracted the lateral and vertical GRFs via Bluetooth communication during normal and pronated/supinated walking and presented a three dimensional vector diagram employing center of pressure and GRFs to provide visualization of the ratio between the lateral and vertical GRFs according to the amount of foot pronation. In healthy subjects, the lateral forces were observed less than 10 % of their bodyweights, while large lateral forces were observed in over pronated/supinated walking up to 20 %.