For the average person the total length between outstretched arms from tip to tip is about the same as that person’s height, give or take an inch or two. Phelps’ wingspan however is fully three inches longer than his height. It’s hard to say if this abnormality is the key to success in his signature stroke, the butterfly, but it certainly helped at Beijing in 2008 when Phelps dramatically won the 100m gold by outreaching Serbia’s Milorad Cavic by just a fingertip after an awkward final half-stroke.