A device has been designed to simultaneously measure the vertical pressure and the anterior-posterior and medial-lateral distributed shearing forces under the plantar surface of the foot. The device uses strain gauge technology and consists of 16 individual transducers (each with a surface area measuring 2.5 × 2.5 cm) arranged in a 4 × 4 array. The sampling frequency is 37 Hz and data may be collected for 2 s. The device was calibrated under both static and dynamic conditions and revealed excellent linearity (±5%), minimal hysteresis (±7.5%), and very good agreement between applied and measured loads (±5%). Vector addition of the distributed loads gave resultant forces that were qualitatively very similar to those obtained from a standard force plate. Data are presented for measurements from the forefoot of 4 diabetic subjects during the initiation of gait, demonstrating that distributed shear and pressure on the sole of the foot can be measured simultaneously.
The authors are with the Department of Biomedical Engineering, The Lerner Research Institute, The Cleveland Clinic Foundation, 9500 Euclid Ave., Cleveland, OH 44195.