Sensor Insoles: A Review

Plantar pressure measurement, or pedobarography, is an essential tool for analyzing human motion in healthy individuals and patients. Across the reviewed literature, sensor insoles are motivated as wearable, mobile solutions for assessing pressure distribution in applications including diabetic foot monitoring, rehabilitation guidance, assistive device control, and sports performance analysis. This review evaluates the current state of the art with particular attention to sensor technologies, sensor quantity and placement, participant cohorts, and reference standards. The focus lies on original works with innovative designs, preferably supported by ambulation experiments. The modalities covered include resistive, capacitive, inductive, piezoelectric, triboelectric, and optical sensing approaches. We identify a lack of proper sensor calibration, gait-based verification, and human study validation, and propose a gold standard based on testing machines and instrumented treadmills to ensure comparability across studies. The bidirectional interaction between insole insertion and foot-sole mechanics is examined, with tissue stiffness identified as a key source of uncertainty in sensor signals. Guidelines are provided for sensor dimensions and unobtrusive insole designs to foster natural gait. Finally, future directions include the development of multimodal sensors to compensate for the limitations of individual modalities and the emerging trend of multiaxial sensing for capturing shear components in pressure distributions.