MAYBE africans train harder
MAYBE Not having the NCAA collegiate system helps them
BUT
I have had the opportunity to train with a lot of great runners, American record holders, olympians, do workouts with them as I'm sure a lot of people on this board have. They were almost all across the board training so hard that they were on the edge of injury the whole time. Flirting with that edge. How can they train harder than that?
Its how much they weigh period. Look at their legs. Look at the legs of a high school kid who you think "can compete with the Kenyans some day." See a difference. I remember the top ten 5k lists the year Bob Kennedy ran his pr and he was the heaviest one. He was pound for pound the best distance runner in the world but he wasnt the best distance runner in the world. The guy who weighed 119 pounds was. Less weight=faster running plus less injuries.
Running has a lot of factors but there are two principal ones. If one group of people is absolutely dominating than they must be dominating in one of these two realms because they trump everything.
1: How much oxygen you can deliver to the muscles
-Plenty of americans with 80+ Vo2 max
2: How much you weigh and where that weight is.
-Kenyans are light weight and more importantly light weight in the legs,
Everyone knows the difference running in racing flats makes. Imagine taking five pounds off of your legs. Now you're a kenyan.
There's all this bs and conjecture on this thread and then marathon mind posted the answer. They have lighter calves, studies have shown this. Everyone ignored him.