How do passive lower-leg prostheses function during the gait cycle?

• A. They dissipate energy during mid-stance
• B. They store energy as springs in the forefoot but not during GRFs
• C. They provide active motor assistance through hydraulics
• D. They act as springs that store ground reaction forces (GRFs) and release force at the end of the gait pattern

Answer: (D)

The main idea is that a passive lower-leg prosthesis works like a spring. As the body weight loads the limb during early to mid-stance, the elastic components of the prosthesis (such as a carbon-fiber foot/ankle assembly) deform and store energy from the ground reaction forces. Then, as the gait progresses into late stance, that stored energy is released to help propel the body forward, providing push-off without any active actuator. So it’s not about dissipating energy or about active motors; it’s about storing energy from the GRFs during stance and returning that energy later in the gait cycle.