What is the function of the flexible keel in a prosthetic foot?

• A. It stores electrical energy for later use
• B. It provides non-linear spring action similar to the push-off phase of walking or running
• C. It acts as a rigid support with constant stiffness
• D. It dampens the knee during flexion

Answer: (B)

The flexible keel works as a compliant energy-storage and return element that mimics the push-off of the natural foot. As you step down, the keel flexes and stores energy like a spring. Then, as you move into propulsion, that stored energy is released, helping push you forward. This action is non-linear, meaning the resistance increases with more bend, providing a smooth initial response and stronger push-off as load grows. It’s not about storing electrical energy, it isn’t a rigid, constant-stiffness support, and it doesn’t damp the knee—those roles belong to other components of the prosthetic system.