I think it has everything to do with environment and the ability to adapt to survive, I assume those distance runner training in a brutal environments and race in ideal cool settings, so of course they run faster with the same effort. Boxers do this all the time, the training in higher elevations and to enhance their stamina on fight night. If a white person was born in the hood and raised there, chances are he/she would have the same strengths and weakness as everyone else in the environment. Put a black kid in a different environment and the results will reflect the environment the child was raised in. Remember the movie ” Trading Places”?