I recently wrote my initial views on an article entitled “Muscle–tendon interaction and EMG profiles of world class endurance runners during hopping” (1). The authors hoped to investigate the potential reasons as to why East African, in particular Kenyan, elite runners are so dominant in their field. In that piece, I finished off presenting that the control group were recreationally active Caucasian students. This isn’t great when we are actually trying to decide which side of the nature vs nurture debate the reasons for the East African dominance lies on.
Achilles’ heel may not be so weak
One of the main findings from the study that I didn’t previously discuss is that the Achilles tendon of the Kenyans was longer than that of the control group. Importantly, the controls WERE matched for height. As such, we’d expect their limbs, and subsequently tendons and muscles, to be of similar lengths. As would be assumed, for the same height, the limb length and muscle-tendon unit length were not different between the two groups. If anything, the Kenyans’ were slightly shorter in these variables, although not significantly. Despite this, the Kenyans’ Achilles tendon was significantly longer (a mean of 67.6 mm longer).
If you are wondering why we would be interested in the length of the Achilles tendon, I urge you to read my previous article. Briefly, a longer tendon might be more efficient; more of the movement at the joint could be caused by the tendon lengthening and then recoiling. If more work is performed by the tendon (which is passive), the muscle needs to work less; because the muscle shortens using energy manufactured by the body (the tendon doesn’t need this), if less shortening is done by the muscle then the movement is potentially more economical. If this is applied to running, a more economical running style allows us to run faster whilst manufacturing the same energy as someone less economical.
So Kenyan elite runners have a longer tendon (both in absolute length and relative to leg length) than non-elite Caucasian recreationally active students. This still doesn’t help on the nature vs nurture debate; is it due to their genetics, or their training?
The Alabama study
Previously, a group undertook a similar analysis (2) to the Elite Kenyan paper. However, a few well controlled aspects make that paper better. First, they removed the variable of training history; all subjects were sedentary. Second, they removed the variable of lifestyle (well as much as you can without making people live identical lives); all subjects lived, and had lived, in the same area of Alabama. Consequently, all subjects were middle-aged, sedentary women who lived in Alabama. The only main difference (there will always be minor differences) was that half were of an African-American ethnicity, and half of a Caucasian ethnicity. Within the Alabama study, similar measures of the muscle and tendon were taken. Additionally, the subjects’ walking economy was measured. This indicates how much energy the body needs to “manufacture” itself whilst walking at a given speed. The difference in tendon and muscle lengths reported in the Elite Kenyan study were the same as in the Alabama study; the Caucasian subjects had longer tendons (both absolute and relative to leg length). Based on these two studies, the longer tendon is NOT due to training history, but instead due to ethnicity.
So what…it doesn’t mean the Elite Kenyans are better because of this. And that is true, we can’t comprehensively deduce that.
However, the African-American women were also more economical when walking at the same speed. Not exactly running, but these were sedentary middle-aged individuals!!! This difference between the two groups was still present after both age and VO2max were accounted for. However, after adjusting walking economy for tendon length, the difference between the two groups was removed. With the main differences between the two groups of women being in the sizes of their muscle (shorter in African-American) and tendon (longer in African-American), and the body of research suggesting longer tendons are more efficient (due to their increased compliance), we can conclude that the longer tendon might (nothing is definite in research) be a key player in what makes the elite Kenyan runners better.
Importantly, this is only a conclusion based on the current evidence; effectively a working hypothesis. We need more data. But that’s fine, because I’m confident that Sano and their colleagues have more data they are planning on releasing.
(1) Sano, K., Ishikawa, M., Nobue, A., Danno, Y., Akiyama, M., Oda, T., . . . Komi, P. V. (2012). Muscle-tendon interaction and EMG profiles of world class endurance runners during hopping. European Journal of Applied Physiology.
(2) McCarthy, J. P., Hunter, G. R., Larson-Meyer, D. E., Bamman, M. M., Landers, K. A., & Newcomer, B. R. (2006). Ethnic differences in triceps surae muscle-tendon complex and walking economy. Journal of Strength and Conditioning Research / National Strength & Conditioning Association, 20(3), 511-8.
- Middle-distance running, Kenyans, and anti-climaxes (uksportsci.wordpress.com)
- Carry That Weight: Every Step Depends On Your Achilles Tendon (eastpennfoot.wordpress.com)