The Skinny on Speed

As trail runners, we are always trying to get our edge and stay ahead of the pack. How do I shave 10 minutes off of my North Face 100km PB? 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 to blame for making the top runner so fast? The world’s really fast distance runners tend to look so small and weedy, as if they would blow over in T1 conditions, 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 the best, hands-down. This nation has produced the highest quantity of world class runners. Two tribes are specifically to blame for their notably exceptional runners – the Kisii and the Kalenjin. I am almost certain that you have heard of the Kalenjin. If not, you have probably been living underneath a boulder. The Kalenjin 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 2:02:57 on 29th September 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 run under 2:10 in the Chicago Marathon. There were 32 Kalenjin who did it in October 2011.”

Vincent Sarich, who was an American Professor Emeritus in anthropology at the University of California in 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 1 elite athlete per 20 million males, Kenya has 80 elite athletes per every 1 million males. There are about 3 million Kalenjin, therefore Kenya will have about 240 elite male athletes at any one time 1.

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 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. We also eat our fair share of carbohydrates, so this is not a significant finding2.

Altitude 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 of a similar altitude, such as Peru, Nepal, and Lesotho, have not produced a rival number of great runners. Other Kenyan tribes have not even produced an equal amount of great runners as the Kalenjin.

Talent could be a possible explanation. These tribes used to partake in cattle raiding1. This raiding 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 killed off the slower runners and the faster runners procreated. Their talent was distilled. Bale and Sang3 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 have predominantly thin ankles and calves.

There were interesting findings from a study that looked at the Anthropometric, gait and strength characteristics of Kenyan distance runners4. These runners all had a low BMI (20.1 ± 1.8 kg.m²), a low body fat percentage (5.1 ± 1.6%) and small calf circumference (34.5 ± 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 study5 was conducted comparing 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. This means that if the very best black and white runners have the same VO2 Max values, then the black runners would outperform the white runners in endurance events because of their greater capacity to run for longer at a higher % 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 aways from this is that, if we know our own VO2 Max score, we can train smarter to slowly increase our VO2 Max % when racing, therefore increase our performance.

Muscle function and recruitment capacity – This study5 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 study6 found that black African distance runners have more Type II muscle fibers, and their Type II fibers were more similar to their Type I, 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 muscle more efficient as they are able to utelize more oxygen as energy.

Slow rate of heat accumulation – Everyone of us has run a trail race where your head feels like it is on fire and there is nothing you can do to overcome this heat accumulation except from slowing down, thus limiting your performance. This is not great for a 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 well described characteristics of 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 is 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 the rate of a rising body temperature. Foam rolling and dynamic stretching can help to improve muscle elasticity.

In concluding, we can improve what VO2 Max % 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.


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.

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