Multi-axial motion is needed to walk comfortably and confidently on uneven ground, when your foot must adapt to whatever it encounters. A foot made with carbon fiber for energy storage literally gives you a spring in your step.
The carbon fiber acts as a spring, compressing as you apply weight and propelling you forward as your foot rolls, returning energy to your step as the spring releases.
A good prosthetic foot should also be strong, as it will be taking on huge force and torque as you walk and run.
Feet must also be small enough to fit within a foot shell, a cosmetic covering for the prosthetic foot, and thus fit within a shoe.
For people who cannot walk, the function is largely cosmetic.
For those who are most active, a prosthetic foot must mimic a normal foot during the act of walking.
Some prostheses have one spring in the heel and a second spring in the forefoot: just what you need for walking at various speeds, running, climbing hills or descending stairs with a secure, confident stride.
With carbon fiber, the longer the spring, the more energy it can store and the more responsive the foot will be.
For above-knee amputees, keep in mind that the higher the limb loss, the less control you will have of the prosthesis and the more you will need stability in your prosthetic foot.
Manufacturers categorize prosthetic feet by the user’s activity level.