Recently an article came out that got me really excited. I had found out about it through Twitter (this really is a great tool, and I strongly suggest you get on it…and say hi @UKSportSci). As soon as I saw the tweet, I wanted to know more…immediately. It was an article that, based on the title, could be MASSIVE in my field. Reading it was, unfortunately, full of anti-climaxes though. I’m just hoping that they collected more data, and are doing the tactic of getting as many papers out as possible. The title of the paper is “Muscle–tendon interaction and EMG profiles of world class endurance runners during hopping” (1; the link below should provide a copy of the article to read in full).
East African dominance
As a background, East Africans, specifically Kenyans and Ethiopeans, dominate middle and long distance running. There are many hypotheses bouncing around in the scientific and the athletic communities, but ultimately it comes down to one debate; nature vs nurture. Are these athletes so dominant because of their genetics? Or are they dominant because of the lives they lead; either in general or within their training?
A number of researchers have tried answering these questions through a scientific approach. However, a large number of these have been based on the physiology of the athletes. The problem with this is we are finding out that it is not so much the physiology of the athlete that differentiates elite athletes from each other.
Biomechanics of running
Although the ability to produce energy is a core component of becoming an elite runner, it does not appear to be the discerning factor in separating the elite runners from each other. Instead, it is how much the athlete can get from a given amount of energy, which is proving key. Specifically, within the middle and long distance runners, differences in running economy are showing high correlates with performance. Running economy is a measure of how much energy the body manufactures relative to the speed the athlete runs at i.e. a lower energy manufacture for a given speed results in a greater running economy.
However, a better running economy does not necessarily mean an athlete requires less energy to run at a given speed. But it does mean the athlete doesn’t need to manufacture as much energy through the formation, and subsequent breakdown, of ATP (the energy source of muscles; Adenosine Triphosphate). The most economical athletes may be able to get “free” energy, without manufacturing it themselves. Traditionally, when a muscle contracts and shortens, the joint moves. This muscular contraction requires the breakdown of ATP. Although an immediate store of ATP is present in the muscle, this is only dominant for a few seconds. For anything else, especially middle and long distance running, ATP is needed to be manufactured, which requires an energy intensive process from the body.
Using elasticity to be efficient
We are finding out that in actions like hopping, walking, and running, it is not so much the muscle that produces the movement. Instead, it is the tendon. With the use of ultrasound imaging that allows us to see the muscle and tendon, we have found out that the tendon can be represented quite accurately by an elastic band; it turns out, it is not a rigid structure we once believed it to be. Instead, tendons get stretched when pulled, and subsequently recoil when the external force has been removed or reduced; much like an elastic band does when you let go. In running, when we land, the leg compresses i.e. ankle and knee bend. This action stretches the achilles tendon at the back of the ankle, and the patellar tendon at the front of the knee. The compression of the leg, and subsequent stretching of the tendons, is caused by us falling to the ground due to gravity. As such, the energy that is stored in the tendon following stretching, is relatively free i.e. it was not manufactured by our body. This stored energy can then be used to shorten the tendon and cause extension at the knee and push-off of the foot. It is suggested that those athletes who utilise more of this stretching and recoiling of the tendon to cause movement at the joint, are more economical in their running.
It was this hypothesis that Sano and colleagues (1) wanted to analyse in the current study; do Kenyan elite runners get a greater addition to performance from their tendons?
To do this, they tested the interaction of the muscle and tendon, and subsequent performance, during a maximal hopping task. Choosing hopping may seem a little counter-intuitive if we are wanting to understand running. However, by using hopping as the task, they were able to isolate the ankle joint. Hopping should also “be less sensitive than running to the possible influence of the thinner lower leg of Kenyans” (1); it is easier, and therefore more economical, to swing a thinner leg through the air.
Kenyans’ tendons are better
What they found was that relative to the stretching of the tendon during landing, the shortening of the tendon during push off was greater in the Kenyans. As I described above, stretching a tendon will store energy within it. This can then be used for recoiling. However, not all of the stored energy is re-used during recoiling. Some of it is lost either as heat or transferred to the surrounding tissues. The amount of energy that is lost is referred to as hysteresis. So the Kenyans were able to reuse more of the energy stored within their tendons i.e. they had a lower amount of hysteresis. Importantly, this doesn’t necessarily mean the Kenyans are more economical runners because of this; the level of free energy gained from recoiling of the tendon could be similar in Kenyans and their competitors. However, it does suggest that Kenyans need to put less energy into the tendon during lengthening for a given energy release during shortening.
During the hopping task, despite hopping to a greater height and producing a greater power, the Kenyans showed less length change of their muscle and tendon. This could mean one of two things (a) the rate of force development and peak force was greater within the Kenyans, or (b) the moment arm of the achilles tendon was smaller in the Kenyans. Unfortunately, the authors did not report joint angle changes which would have allowed us to deduce whether the second hypothesis was correct, and subsequently allow us to calculate how much influence the first hypothesis might have had. The moment arm is the distance between the tendon and the joint. As such, for a given shortening of the tendon, if the moment arm is smaller, the joint rotates more than if the moment arm was larger.
Fortunately, previous research has shown that there is a very good relationship between the achilles tendon moment arm and running economy, with a smaller moment arm being correlated with a greater running economy (2, 3; reference 2 is available free at the link below and is well worth a read). This is thought to be because for a given shortening of the muscle and/or tendon, the ankle rotates more, as compared to a larger moment arm. As such, although we are not able to confirm this directly, the findings of reduced tendon and muscle length change within the Kenyans is in-line with what has been shown before.
So what if they are better…
So, the elite Kenyan runners were able to produce a greater performance i.e. greater jump height and power, despite less change in length of the tendon and muscle. This is great because muscles are stronger at specific lengths, normally at their mid-range. As such, if the reduced change in muscle length means they are more likely to work in this position (i.e. less deviation from it), performance can either be greater (i.e. greater power production seen in hopping), or it becomes easier to produce a certain performance level because the muscle is working at a relatively lower level. Additionally, if the tendon is more economical (i.e. less hysteresis), when loading the tendon by the same amount as a less economical tendon, the Kenyans are able to get more energy in return. And remember, the energy that is stored in the tendon from it being stretched, is relatively free due to it coming from the landing of the athlete during running.
That’s all great. Some interesting findings. The big problem with this paper, and the strength of these findings, is that the elite Kenyan runners were compared to “relatively active” (1) Caucasian male students. So all the above differences are compared to a control group that were controlled for height, but not ethnicity or training status and lifestyle. As such, we are still left with the ultimate question…are East African endurance runners, in particular Kenyans and Ethiopieans, better and more consistent due to their genetics, or due to their training or lifestyle; is it Nature or Nurture???
That is why, for me, this paper was an anti-climax; it promised so much, but did not deliver.
(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) Scholz, M. N., Bobbert, M. F., Van Soest, A. J., Clark, J. R., & Van Heerden, J. (2008). Running biomechanics: Shorter heels, better economy. Journal of Experimental Biology, 211(20), 3266.
(3) Raichlen, D. A., Armstrong, H., & Lieberman, D. E. (2011). Calcaneus length determines running economy: Implications for endurance running performance in modern humans and neandertals. Journal of Human Evolution.
Sano K, Ishikawa M, Nobue A, Danno Y, Akiyama M, Oda T, Ito A, Hoffrén M, Nicol C, Locatelli E, & Komi PV (2012). Muscle-tendon interaction and EMG profiles of world class endurance runners during hopping. European journal of applied physiology PMID: 23229882