Energy is stored in the feet as they deflect under the loads of walking.
Some of this stored energy can be returned as the foot straightens near the toe-off position. However, in addition to having proper energy storage, there needs to be an appropriate roll-over shape created in order to have comfortable walking. With previous prosthetic feet, the level of flexibility is inseparable from the roll-over shape during walking. This invention makes it possible to separate the functions of roll-over shape and energy storage. Furthermore, creating an appropriate roll-over shape for smooth comfortable walking can be done with or without use of flexible materials.