A couple of years ago, Runner’s World published a fascinating article on what it’ll take to produce a sub-2 hour marathon. The pace of new records being set in the marathon has accelerated (no pun intended) in recent years.
If you took thousands of newborn children and raised them in Sprint Factories, to do nothing but run fast, and then culled out all but the very best, you could produce runners who could achieve very high speeds. But there is a strong social resistance to the idea of spending all those human lives in order to create such a monster. Americans got all bent out of shape during the cold war, when the Russians started selecting school girls to be olympic class athletes, to gobble up all those undeserved gold medals by inhumanely impeding social development.
So thee is a deep divide between the speed that can potentially be attained physiologically by a human organism, and one that can attained by a normal member of the human social fabric within current ethical paradigms…
Has some articles and speculation on this
He suspects that a sub 9.5 in the 100 m is possible but not much more