From pressure to force: a device-independent, predictive model of plantar loading for personalized orthoses

Plantar loading is conventionally characterized by peak pressure, yet peak pressure is a local force-to-area ratio set partly by the measuring device and by the foot-support interface, which limits its use as a portable input for foot-loading assessment and orthosis design. We tested whether the applied regional force is a more stable descriptor.

We used two large, open-access datasets acquired on different platforms (CAD WALK, RSscan; and StepUP-P150, Stepscan). Force was calibrated on both systems through a Newton impulse identity, and every footstep was registered onto a common, length-normalized anatomical frame.

The body-weight-normalized applied force was more reproducible between footsteps than the peak pressure, was preserved when the interface changed from barefoot to shod (a non-significant 0.7% change against a 32.5% collapse in peak pressure over the same trials), and was captured by a closed-form power law of body mass and walking speed that reproduced the measured force with a coefficient of determination of 0.96 (0.955 under leave-one-subject-out cross-validation), whereas the same model form explained only 0.33 of the peak pressure. On the common frame, the two platforms agreed on a single per-cell load map (cross-system correlation 0.95).

We release a device-independent loading specification, comprising barefoot regional force targets (0.86 body weight at the rearfoot and 1.10 at the forefoot), the universal load map, and the fitted model, that reconstructs the plantar force field of an individual from the body mass, walking speed, and foot length as a direct input for the design of personalized foot orthoses.