For those of us with two functioning legs, it’s easy to overlook the crucial role ankles play in walking. Every time we take a step, our Achilles tendons extend and contract and help power us forward. When amputees put on a standard carbon ankle prosthesis, they lose at least 50 percent of that propulsion. As a result, they typically can’t walk as fast or as far, and are more tired at the end of the day.