Group running = v competitive atmosphere (prob a bit like the Jamaican sprinting success, lots of role models to aspire to?)
Plus genetics - otherwise those with west african ancestry would tend to do better in the longer distance running - body type has a lot to do with it.
"Saltin's group has quantified this observation. Compared with Danes, the thinner calves of Kenyans have, on average, 400 grams less flesh in each lower leg. The farther a weight is from the center of gravity, the more energy it takes to move it. Fifty grams added to the ankle will increase oxygen consumption by 1%, Saltin's team calculates. For the Kenyans, that translates into an 8% energy savings to run a kilometer. "We have solved the main problem," declares Henrik Larsen of the Copenhagen center. "Kenyans are more efficient because it takes less energy to swing their limbs." Other scientists say the jury is still out on the Kenyan question. But "I think Saltin is probably the most correct that anyone is at the moment," says physiologist Kathryn Myburgh of the University of Stellenbosch in South Africa, who is exploring the role of Kenyans' training.
However, slim lower legs are not the whole story. Kenyan runners also have a higher concentration of an enzyme in skeletal muscle that spurs high lactate turnover and low lactate production. Saltin says that this results in an "extraordinarily high" capacity for fatty acid oxidation, which helps wring more energy out of the muscles' biochemical reactions. Because intense training alters the body's biochemistry, Saltin says that he can't say for sure whether the ezyme levels are due to genes or training. But he adds, "I think it's genetic." Research in South Africa jibes with the Copenhagen group's findings.
A team led by exercise physiologist Adele Weston of the University of Sydney, Australia, compared black South Africans, whose running strengths are similar to those of Kenyans, with white runners. The two groups had similar VO2 max values?that is, when putting out maximum effort, they used up the same amount of oxygen per kilogram of body weight per minute. But the black runners were more efficient in their oxygen consumption, lasting on a treadmill at maximum speed for twice as long as the whites. As with the Kenyans, the black South African runners accumulated less lactate and had higher levels of key muscle enzymes."
www.jonentine.com/reviews/AAAS_peeringUnderTheHood.htm