The Skinny on Speed

AsianTrail illo-Speed (1)As trail runners, we are always trying to get our edge and stay ahead of the pack. How do I shave 10min off of my North Face 100km personal best? What do I have to do to beat Stone Tsang or John Ellis in just one 50km race? Have you ever wondered what physiological traits are the reason for which the top runners are so fast? The world’s really fast distance runners tend to look so small and weedy, as if the weakest typhoon could effortlessly blow them away, yet they seem to run at a pace rivalling that of a leopard. You’re a runner. You have put in similar training hours leading up to a big event, yet despite your tough and gruelling training schedule, you do not even match their pace on a bad day. What factors are to blame for shaming us mere mortals?

Let’s take a look at the Kenyans. When it comes to running, they are hands-down the best. This nation has produced the highest quantity of world-class runners. Two tribes are specifically notable for their exceptional runners — the Kisii and the Kalenjin. I am almost certain that you have heard of the Kalenjins. If not, you’ve probably been living underneath a boulder. The Kalenjins have won more than 50% of all Kenyan Olympic and Commonwealth Games medals. The new world record marathon holder Dennis Kimetto, from the Kalenjin tribe, set the record at 2h 2min 57s on Sept. 29, 2014. The three placing after him in that same race were also Kenyan.

David Epstein, senior editor at Sports Illustrated and the author of “The Sports Gene,” states that, “There are 17 American men in history who have ran under 2h 10min in the Chicago Marathon. There were 32 Kalenjins who did it in October 2011.”

Vincent Sarich, who was an anthropology professor at the University of California, Berkeley, calculated that Kenyans outperform the rest of the world in cross-country running by a factor of about 1700. This means that while the rest of the world has one elite athlete per 20 million males, Kenya has 80 elite athletes per every one million males. There are about 3 million Kalenjins, therefore Kenya will have about 240 elite male athletes at any one time.

So what are the biological factors that make these runners so fast? Scientists and sports gurus have researched all sorts of explanations over the years but have not come to a single conclusion. Is it diet? Altitude? Genetics? Training schedule?

Diet: This is not a big factor. The Kenyans eat lots of ugali, which is maize flower mixed with water and salt. It is a good source of carbohydrates. But we also eat our fair share of carbohydrates, so this is not a significant finding.

Altitude: This can also be ruled out as a factor. Kenya is based at a moderate altitude of 2300m. This altitude has moderate year-round temperatures, favouring year-round training and red blood cell production. In saying this, countries with a similar altitude, such as Peru, Nepal, and Lesotho, have not produced a rival number of outstanding runners — even other Kenyan tribes have not managed to bring forth as many great runners as the Kalenjins.

Talent: Perhaps a possible explanation. These tribes used to partake in cattle raiding. This practice would ensure that the best runners would obtain the most cattle and they would survive the longest by escaping the spears of the recently dispossessed cattle owners. This resulted in the best runners securing the most wives as they could provide them with the most cattle. Therefore, any genes determining running ability would be passed down through the generations as this cattle raiding practice killed off the slower runners while the faster runners procreated. Their talent was distilled. Researchers John Bale and Joe Sang state that because of this, “the Kalenjin men became not explosively muscular, but lean and tireless.”

Some scientists have also concluded that it is the shape of the Kalenjin tribe’s bodies. The Kalenjin tribe has predominantly thin ankles and calves.

There were interesting findings from a study that looked at the anthropometric, gait, and strength characteristics of Kenyan distance runners. These runners all had a low body mass index (20.1 kg.m² ± 1.8 kg.m²), a low body fat percentage (5.1% ± 1.6%) and a small calf circumference (34.5cm ± 2.3cm). This study concluded that the slim limbs of Kenyan distance runners may positively contribute to performance as there is a low moment of inertia, therefore requiring less muscular effort in leg swing. The study also found that the Kenyans had a short ground contact time. This may be related to an efficient gait and running economy as there is less time for the braking force (i.e. contact time) to decelerate the body’s forward motion.

Epstein backs this up in his book, stating that “thin ankles and calves are particularly important in running because your leg is like a pendulum. The more weight you have farther away from your centre of gravity, the more difficult it is to swing.”

Superior fatigue resistance: A study was conducted comparing a group of black runners consisting of Kenyans, Ethiopians, South Africans, and Moroccans to South African white runners. The participants had similar marathon times and similar VO2 max scores and were set to run a marathon on a treadmill. The study found that the black runners completed the marathon at a higher VO2 max (89%) than the white runners (81%). This showed that the black runners have a much greater resistance to fatigue. Meaning that if the very best black and white runners have the same VO2 max values, the black runners would still outperform the white runners in endurance events because of their greater capacity to run for longer at a higher percentage of the same VO2 max. This hypothesis has, unfortunately, not been evaluated as there are not enough elite white runners in the world to match the performances of the best Kenyans, Ethiopians, Moroccans, and South Africans. What we can take away from this is that, if we know our own VO2 max score, we can train smarter to slowly increase our VO2 max percentage when racing, and therefore increase our performance.

Muscle function and recruitment capacity: The study mentioned above also looked at muscle function and found that black distance runners could complete more contraction/relaxation cycles before they developed fatigue. This makes sense as they would be able to resist fatigue by utilising a higher level of skeletal muscle recruitment, prolonging the onset of ‘hitting a wall.’ Another study found that black African distance runners have more Type II (fast twitch) muscle fibers, and their Type II fibers are more similar to their Type I (slow twitch), particularly regarding their high capillary density and high mitochondrial enzyme content. This high capillary density would ensure that oxygen delivery to, and metabolite clearance from, the muscles is more efficient. Having a high mitochondrial enzyme content would also make the muscles more efficient as they are able to utilise more oxygen as energy.

Slow rate of heat accumulation: All of us have ran a trail race during which our head felt like it is on fire, and there is nothing you can do to overcome this heat accumulation except slow down, thus limiting your performance. This is not a great racing scenario. The ability to slow the rate of heat accumulation when running fast would be highly advantageous. Factors that slow the rate of heat accumulation when running fast are: small size and high running efficiency. These are both characteristics describing Kenyan distance runners. Size can be worked on as you can always become smaller to improve your running performance. Ask most top runners what their ‘fighting weight’ or best running performance weight is and it will always be on the lower end of their scale. Running efficiency can also be worked on by improving the elastic energy return systems of the muscles. The more that the muscle acts as a spring, the less energy it will consume and the more efficient it will be. This more elastic, efficient muscle will enhance performance by slowing down the rate of metabolite accumulation causing fatigue, and prolonging the rate of a rising body temperature. Foam rolling and dynamic stretching can help to improve muscle elasticity.

In conclusion, we can improve what VO2 max percentage we perform at, our overall body weight, therefore size, and our muscle elasticity. So, despite the fact that we will never be as fast as the Kenyans, we can tweak a few factors to make us skinnier, more efficient, and quicker, and hopefully catch Stone Tsang and John Ellis on the trails soon. That is the skinny on speed.


Jessica Phillips is an exercise physiologist and running consultant at Joint Dynamics. She loves trail running and escaping manic city life to explore the many mountains and single tracks that Hong Kong has to offer.



  1. Noakes, T.D., (2001). Lore of Running; Fourth Edition; pg.s 406-408; 433-437., Oxford University Press, South Africa.
  2. Christensen, D.L., van Hall, G., Hambraeus, L. (1998). Food intake of Kalenjin runners in Kenya: A field study. Journal of Sports Sciences 16, 500.
  3. Bale, J., Sang, J. (1996). Kenyan Running: Movement Culture, Geography and Global Change. Frank Cass, London.
  4. Kong, P.W., de Heer, H. (2008).Anthropometric, gait and strength characteristics of Kenyan distance runners. Journal of Sports Science and Medicine 7, 499-504.
  5. Bosch, A.N., Goslin, B.R., Noakes, T.D. (1990). Physiological changes during a simulated marathon in black and white athletes. European Journal of Applied Physiology 61, 68-72.
  6. Weston, A.R., Karamizrak, O., Smith, A., Noakes, T.D., Myburgh, K.H. (1999). African runners exhibit greater fatigue resistance, lower lactate accumulation, and higher oxidative enzyme activity. Journal of Applied Physiology 86, 915–23.

By Jessica Phillips

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