I see your point about blacks, although I think that blacks from Africa are probably still stronger and more athletic than whites, given proper nutrition of course. I admit that I don’t have any hard data on this, but I think it can be inferred from evolution, in that Africa is a physically harsher region of the world than anything whites have had to deal with. Also, I’m pretty sure the reason the reason the Europeans began the African slave trade was that the Africans were generally strong.
I disagree that that can be inferred from evolution. “Black” refers primarily to people of subsaharan african descent. They populated mainly tropical areas which are ideal human habitats. Especially in prehistoric times(where most of evolution has taken place) when hunting and gathering was the primary means of existence. Living in the frozen rocks in Norway is a great deal harsher. Short growing seasons, ice,…
Could you explain why you believe that africans were chosen to be slaves because of their racial strength? I would supect they were chosen because they were tribal and uneducated and easier to enslave. If I wanted to kidnap some people I would choose them that have bows and arrows rather then muskets. Individuals were probably chosen-or more likely survived the boat ride across the pond, because of their strength, but I seriously doubt that the group was chosen because primarily because of their strength. The tall long-limbed africans you have in mind were actuially only found in 3 parts of africa and are not typical of the population. One of those areas was west africa, where a great many of the slaves came from-because it was closer to the westindies.
The primary genetic difference as I understand is limb length. Shorter limbs are easier to get blood to and therefore keep warm in colder climates. This causes a decisive difference in running speed for obvious reasons. And thus in any sport dependent on sprinting. Also cyclecell anemia which causes physical weakness while providing resistence to malaria.
Another factor you are not taking into account, which is huge, is cultural emphasis of particular sports. Why is it that Americans don’t ever win the world cup in cricket even though there are more americans then there are British, Irish, Pakistanni, or Australians? Cause we don’t play the game. I had an acquaintence who was black and did not play basketball. He jokingly described it as almost a passage of manhood. If you didn’t play basketball you just weren’t a man. I, being white, have never felt a similiar pressure in regard to sports. I have felt that consistent pressure with regard to learning and wealth production though.
“every man in the same country, if he be able-bodied, shall, upon holidays, make use, in his games, of bows and arrows… and so learn and practise archery.” Edward III. Low and behold, England became good at shooting arrows to the point that English longbowman were imported as mercenaries. Perhaps the English are genetically better at pulling their arm back to their ear?? 
Even diet could have a major impact. Consider the average height of Asians born here with milk as a staple in their diet compared to their ancestors. Blacks eat different food then whites, generally.
I try to be real careful with genetic determinism. It’s a complicated subject because the results(what people(x) are) all meet at a nexus of environment, culture, freewill and genetics and they are each impacted by the others. To make a statement like blacks are genetically better at sports is just not accurate. What you can say is that blacks from certain areas of africa tend to have longer limbs proportional to their torsos and that trait is primarily caused by genetics. A lot less interesting perhaps, but a lot more true.
Regarding the intelligence issue, their was a book that came out several years ago called ‘the bell curve’. In it, they determined that the average black IQ was 85 and the average white IQ was 102. So you might say that blacks are genetically less intelligent then whites or you might consider the other issues at play such as the accuracy of an IQ test as a measure of “intelligence” or cultural issue such as emphasis on education which has been shoen to cause an apparent increase in IQ scores.