Apparently the "advantage" they're considering is not the prostheses themselves, but that without calf muscles he might be less prone to building up lactic acid. He says it's not so, since his thigh muscles have to take up the extra load. Anyways ... that's what they were testing him for after the race. This was the first time he competed (was allowed to compete?) against so-called "functionally healthy" athletes, as a means of testing that hypothesis. Not bad, making second in his heat first try.