The principle of evaluating flat feet and high arches using a foot-sole pressure distribution system is based on mechanical measurement and spatiotemporal signal analysis.
It consists of a pressure sensor array (insole-type or pressure mat), a data acquisition device, and analysis software. The sensors can be resistive, capacitive, or piezoelectric, which convert contact pressure into electrical signals. After analog-to-digital conversion, time synchronization, and filtering, two-dimensional or three-dimensional pressure maps and time series are obtained.
Key parameters in static assessment include contact area, contact ratio in the arch region (commonly expressed as the “arch index or midfoot load ratio” representing the proportion of the midfoot), peak pressure, and pressure integral (pressure–time integral).
In flat feet, the collapse of the arch leads to an increased midfoot contact area, significantly higher midfoot pressure, and an increased arch index. At the same time, the overall contact area of the foot expands, and the load distribution between the rearfoot and forefoot tends to become more even, or the rearfoot load relatively decreases.
In contrast, high arches exhibit a reduced midfoot contact area, decreased arch index, low midfoot pressure, while the forefoot and heel show more peak pressures and concentrated pressure points. The pressure–time integral in certain local regions increases, indicating localized stress concentration.
The foot-sole pressure distribution system records pressure distribution along the footprint over time, producing the center of pressure (COP) trajectory, COP migration speed, load rate, and the proportion of load time in each foot region during different gait phases (heel strike, stance, toe-off).
In flat feet, the COP trajectory often shows pronation or medial deviation, a straighter COP path, and early midfoot load participation.
In high arches, the COP path may be narrow, with rapid pressure spikes appearing at the lateral forefoot and heel.
By comparing with body-weight normalized data, abnormal load patterns can be evaluated more objectively. Furthermore, by integrating pressure data with three-dimensional foot shape reconstruction, modern assessments can distinguish structural flat feet (bony) from functional flat feet (tendon or muscle-related), and guide the selection of orthotic thickness, support position, and material.
Analysis must also consider calibration, sensor resolution, sampling frequency, and walking speed. Therefore, repeated measurements, gait standardization, and statistical processing are usually employed to improve reliability.
The foot-sole pressure distribution system uses high-density sensor arrays and spatiotemporal signal analysis to quantify midfoot contact ratio, local peak pressure, pressure–time integral, and COP trajectory, distinguishing COP path characteristics between flat feet and high arches. It provides objective data for clinical diagnosis, orthotic design, and rehabilitation assessment, but must be combined with imaging and clinical physical examination to determine the cause and guide individualized intervention.
