I beleive (although do not know for sure statistically) that the US has never before had as many fast runners over 5k and 10K as they do now, relative to the rest of the world. I am trying to distill down the possible causes. Can anyone offer their thoughts, in order of most infuence of apparent success.
So far in order of most influential causes, I believe the following.
1) A new belief that certain times are obtainable; for example 13:00 now seems non-African humanly possible. 13:20 is totally possible for college athletes.
2) Altitude tents
3) faster tracks
4) African immigrants (Lagat, Keflezghi etc..)