An ankle prosthesis comprises a foot prosthesis. A lower ankle is pivotably secured to the foot prosthesis at an ankle joint. An upper ankle is connected to the lower ankle in a manner that permits vertical movement of the upper ankle relative to the lower ankle. A coupling spring is biased in an extended condition. The coupling spring is connected at a first end to the upper ankle. A second end of the coupling spring is movable in a first condition which is engaged to the lower ankle and in a second condition engaged to the foot prosthesis. Energy is stored in compression of the coupling spring when the coupling spring is in the first condition and energy is released from the coupling spring when the coupling spring is in the second condition.
