This was talked about a lot back in the '80's due to blacks taking over in most sports. So ABC and Peter Jennings set out to find the cause. What they found was that the black race, on average, has more muscle molecules/cells, don't know the exact break down, per square MM/inch, whatever that measurement was, than other races.
So they've got denser muscles on average than the 4 other races which allows their muscles to do better what muscles do. It's science. This is on average, but we see that it's unquestionable. You never hear anyone talk about this.