Read this article. Kenyan dominance in distance running. Comp Biochem Physiol A Mol Integr Physiol. 2003 Sep;136(1):161-70. Review.
According to Larsen, critical physiological factors for performance in running are maximal oxygen consumption, fractional VO2 max, and running economy. When comparing Kenyan and Caucasian elite runners, results revealed that Kenyan runners are to be able to run at a higher percentage of their VO2 max. A lower energy cost of running has been demonstrated in Kenyan elite runners. But in untrained adolescent Kenyan boys compared to their Caucasian counterparts, there was no difference. I think it’s probably a combination of both, genetics and their training. This is a very good article if you want the full text article email me and I’ll send it to you.
“Results on adolescent Kenyan and Caucasian boys show that these boys VO2max are running at a similar percentage of during competition. Kenyan elite runners, however, appear to be able to VO2max run at a high % of which must then have been achieved by training. A lower energy cost of running has been VO2max demonstrated in Kenyan elite runners and in untrained adolescent Kenyan boys compared to their Caucasian counterparts.”
“A difference exists in BMI and body shape, and the Kenyans long, slender legs could be advantageous when running as the energy cost when running is a function of leg mass.”
“Most of the Kenyans who are such good performers come from a group of eight small tribes
called Kalenjin, which number only approximately three and a half million people. Among the Kalenjin tribes, the Nandis have performed the best and they constitute only approximately 2% of the
Kenyan population. “
“the average proportion of European achievements in the six all time top 20 lists in the distances
from 800 m to marathon including steeplechase was 48.3% while the percentage of African results
was 26.6% of which the Kenyans produced 13.3%. Moreover, the majority of world record holders
were Europeans, and European gold medal winners at the Olympic Games and world championships
were not a rarity. Today, the proportion of European achievements is reduced to 11.7%, whereas
the percentage of Africans in the top has increased to 85.0%, of which 55.8% are Kenyans (IAAF,
All Time Outdoor Lists, June 2003, Fig. 1). The markedly reduced occurrence of Europeans in the
list is not due to them running slower now than earlier. It is simply related to the fact that runners
from East-Africa in particular now run so much faster (IAAF, 2002; Matthews, 1987). Even more
profound is the Kenyan dominance at the world cross-country championships, where Kenyan senior
men have won the team title on the long distance every year for the past 18 years. The performances of Kenyan men in middle- and long distance events at the Olympic Games and world championships on track underscore the Kenyan superiority.”
“In addition to having the proper genes to VO2max shape their bodies and thereby contributing to a good running economy, the Kenyan elite runners have trained effectively and used their potential to be in the upper range both in regard to and to a high utilization of this capacity VO2max during endurance running.”