I gave a try the other day at why we have knee pads but not elbow pads. But I think I might have been looking at it wrong. The main selective pressure is probably mainly the lever "spring" effect that acts through the heel bone and elbow bone, see drawing below. This took me a few days to realize. Also that elbow joints to two bones, radius + ulna, but, it could have evolved as a single ulnar joint surface, and radius jointing onto it, like in the knee with tibia + fibula, and then support "elbow cap", so I think it might be the "spring" effect primarily? Locomotion efficiency. I ❤ the spring effect / arrow in bowstring in the heelbone and how humans are specialized for persistence running some 2.5 million years ago, this is why I noticed that elbow bone must have been selected over "elbow cap" for same reason.
