A decade ago, Danish scientists collected samples of Achilles tendons from 28 cadavers of various ages and measured the amount of radioactive carbon-14 in them. Above-ground nuclear tests in the 1950s and 1960s temporarily raised levels of carbon-14 in the atmosphere, meaning the amount found in any living tissue reveals when that tissue was actively growing or repairing itself. The results showed that the tendon core formed in the first 17 years of life, after which it became essentially inert.
This image of a seemingly lifeless tendon, an elastic band that connects the calf muscles to the heel bone, is troubling for two reasons. One is that many runners develop chronic Achilles tendon injuries and would like to believe that it is possible for the tendons to repair themselves. And there are, in fact, some researchers who now believe that a appropriate combination Rehabilitation exercises and targeted nutrition can trigger tendon healing.
The second reason is that the properties of your Achilles tendon seem to be associated with performance, and more specifically with how efficiently you run. For several decades, it has been speculated that one of the secrets to the international dominance of Kenyan brokers is their Exceptionally long and elastic Achilles tendons. Comparisons of trained and novice runners also reveal differences in tendon thickness, stiffness, and structure. A longer, stiffer tendon can store more energy as it stretches with each stride and then release that energy as you go. What is not clear is to what extent these differences are born of or the result of training.
That’s what he does a new study in Frontiers in physiology, from a research team in Germany led by Freddy Sichting of the Chemnitz University of Technology, particularly interesting. Sichting and his colleagues recruited 40 pairs of identical twins and asked them to complete a questionnaire about their physical activity and sports habits, classifying each person as active or inactive based on a threshold of one hour of training per week. The researchers then measured the stiffness of their Achilles tendons using a handheld device which basically rings your tendon like a bell and measures its vibrations.
On the surface, the results may seem a bit underwhelming. If you compare sets of twins that are active with pairs that are inactive, there doesn’t seem to be any difference in tendon stiffness. This is what it looks like:
But the picture changes if you only look at pairs where one twin is active and the other is inactive. In this case, active gastrocnemius tendons are 28 percent stiffer:
Since identical pairs start with identical genes, this is compelling evidence that long-term training changes Achilles tendon structure, and fits with previous studies that have found thicker, stiffer tendons in trained runners. These were not elite athletes, so superhuman levels of training were not required to change tendons. That said, the active subjects had been playing their main sport for an average of 15 years, so they had plenty of time to adjust.
The reason differences only appear when identical twins are compared is that the variance Among twin pairs is much larger than the variance within twin couples Training matters, but genes definitely matter too. That is also highlighted by another recent study, from an international team led by Nir Eynon of the University of Victoria, which added to the evidence that certain genetic variants make you more susceptible to tendon injuries. For example, versions of a gene called COL5A1 are thought to alter the structure of the collagen fibrils that make up tendons and ligaments.
There is another insight from Sichting’s study. They divided reported exercise activities into those that involved an aerial phase with both feet off the ground (such as running, basketball, or tennis) and those that did not (such as cycling, swimming, and walking). Twins who participated in sports with an aerial phase had much tighter Achilles tendons than those who participated in non-aerial sports, suggesting that jumping and landing are key triggers of adaptation:
I’d love to end this with three simple exercises to increase efficiency and protect your Achilles tendon from injury. (Imagine the clicks!) The truth is, there is still a lot of confusion and disagreement about exactly how tendons respond to different types of training, what role they play in running efficiency, and why they get injured. But the crucial point is that those Danish corpses were not telling us the whole story. Perhaps they were simply not active enough as adults to stimulate tissue renewal. To be sure, tendons take time to adapt, but they’re not inert rubber bands, and the more we learn about how to train them, the less likely they are to become your Achilles’ heel.
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