Elsevier

The Foot

Volume 21, Issue 4, December 2011, Pages 193-197
The Foot

Review
Evolution of the Achilles tendon: The athlete's Achilles heel?

https://doi.org/10.1016/j.foot.2011.08.004Get rights and content

Abstract

The Achilles tendon is believed to have first developed two million years ago enabling humans to run twice as fast. However if the Achilles tendon is so important in terms of evolution, then why is this tendon so prone to injury – especially for those more active like athletes. The Achilles tendon had an integral role in evolving apes from a herbivorous diet to early humans who started hunting for food over longer distances, resulting in bipedal locomotion. Evolutionary advantages of the Achilles tendon includes it being the strongest tendon in the body, having an energy-saving mechanism for fast locomotion, allows humans to jump and run, and additionally is a spring and shock absorber during gait. Considering these benefits it is therefore not surprising that studies have shown athletes have thicker Achilles tendons than subjects who are less active. However, contradictory to these findings that show the importance of the Achilles tendon for athletes, it is well known that obtaining an Achilles tendon injury for an athlete can be career-altering. A disadvantage of the Achilles tendon is that the aetiology of its pathology is complicated. Achilles tendon ruptures are believed to be caused by overloading the tensed tendon, like during sports. However studies have also shown athlete Achilles tendon ruptures to have degenerative changes in the tendon. Other flaws of the Achilles tendon are its non-uniform vascularity and incomplete repair system which may suggest the Achilles tendon is on the edge of evolution. Research has shown that there is a genetic influence on the predisposition a person has towards Achilles tendon injuries. So if this tendon is here to stay in our anatomy, and it probably is due to the slow rate of evolution in humans, research in genetic modification could be used to decrease athletes’ predisposition to Achilles tendinopathy.

Section snippets

How the tendon has evolved

The development of the Achilles tendon helped facilitate the evolution from apes with a herbivorous diet to early hominins which had an omnivorous diet [3]. The Achilles tendon is absent or short in apes, meaning that their calf muscles extend right down to their tarsal bones [7]. This gave early apes the ability to display arboreal locomotion which corresponded with their herbivorous diet [3]. However the previously abundant food supplies in their environment became sparser and seasonal and so

The tendon in athletes

Some studies have observed that the Achilles tendons in athletes are much thicker than compared to the tendons in subjects who are less active [10]. Emerson et al. found using ultrasonography, that the thickness of the Achilles tendons in gymnasts was significantly higher in five of the six measures carried out than the control group [10]. Ying et al. compared the thickness and cross-sectional area of the Achilles tendons belonging to subjects who frequently exercised (two hour exercise

Why is the tendon the way it is?

The plantaris muscle has a long delicate tendon which is stretched during walking and running exactly like a length of elastic [13]. An advantage of the Achilles tendon is that it is an important elastic energy store [13]. The plantaris tendon is able to return over ninety percent of the energy stored in this way during walking and running [13]. This is an important mechanism for camels and kangaroos in their locomotion [13]. During gait, kinetic energy lost at one stage of a stride is stored

Is it here to stay?

The debate about the future existence of the Achilles tendon has been conjured due to its vulnerability to injury. It does not seem comprehensible that a multifunctional tendon which is vital in bipedal locomotion should be so prone to damage, and even more prone in physically active and fitter humans. One study found that athletes who obtain an Achilles tendon injury can be for them career altering. It found that out of all the national American football players who sustained an Achilles

How will it continue to evolve?

If the Achilles tendon has more evolutionary flaws than advantages for fast bipedal locomotion, then maybe it has no more evolutionary potential to offer. As already discussed the Achilles tendon cannot keep getting longer in length, as this would be detrimental to bipedal locomotion. However maybe there is room for evolution to change the insertion site of the tendon or to bring another mechanism instead of the Achilles tendon in order to give efficient fast bipedal locomotion. Local tendons

Conclusion

In summary the Achilles tendon is here to stay in our anatomy. This is not only because of the evolutionary advantages its possesses such as facilitating fast bipedal locomotion, acting as a spring and shock absorber during gait, supplying an energy saving mechanism during movement and being the strongest tendon in the body. Another valid reason why this tendon will stay in our anatomy for many generations to come is because the rate of evolution in the human species is very slow [37].

Conflict of interest

None.

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