Re: "why Blacks are such fast runners?" -- off-topic on legs, etc
Yes -- seems to me I read that Neanderthals, stocky and with short legs (and, proportionally, shorter shins in particular), have advantages in hill-climbing and conserving heat in cold climates, compared with long-limbed people.
I have short, muscular legs. I run poorly, though whether that is entirely due to physiology or whether poor form can be blamed is up for grabs. I jogged for many years, but my thudding gait is now impossible; my lower back is done with it. I can climb a steep hillside just fine, though, even with a pack. Neanderthals is my peeps. (Not really, perhaps, but in spirit!)
Parenthetically, it's very imprecise to say "blacks" or "Africans" are better runners. Ever see a Mbenga or Mbuti person who is an internationally competitive runner? You won't. These black Africans tend to be less than 5 feet tall. Better be more specific, and say the Oromo and Kalenjin peoples of Africa are sometimes excellent runners. As mentioned, natives of Africa are more genetically diverse than the rest of Homo sapiens combined. (Reffie: BioNews)