(ORDO NEWS) — The Achilles tendon, the largest tendon in the human body, acts like a rubber band that connects the calf muscle to the calcaneus. While we know that it works like a spring that stores and releases energy as the legs move, it’s not entirely clear how it responds to exercise and training, if at all.
More precisely, are the characteristics of our Achilles tendons genetically determined at birth, or can the tendons actually adapt to prolonged physical exertion, protecting them from the stress and injury associated with overload? To find out, a new study took 40 pairs of identical twins and asked them about their exercise habits over the past few years.
The results of these interviews were then compared with the tissue characteristics of their Achilles tendon, measured using a hand-held oscillating instrument. In particular, the researchers looked at the mechanical stiffness of the tendon, a sign that it is capable of storing more energy.
“There is much debate about the adaptation of the Achilles tendon in response to exercise,” the researchers write in their recently published paper.
“Most published research is currently limited to elite athletes and selected physical activities. In addition, existing research on tendon adaptation does not control for genetic variation.”
The team found that there was more variability in Achilles tendons in both groups, but there was no big difference in tendon stiffness when comparing active versus inactive pairs of twins – evidence that genetics play a role in Achilles tendon characteristics.
However, in unequal pairs, where one twin was more active than the other, the active individual’s tendons were 28 percent stiffer on average. This suggests that there is some scope for training and safe adaptation of the Achilles tendon with regular, non-elite-level exercise.
The findings are consistent with previous studies done with elite runners, which have shown that they have thicker and stiffer Achilles tendons. There has also been previous evidence that tendon stretching induces a range of cellular and molecular responses.
“Our study provides the first evidence that individual Achilles tendon stiffness is determined in part by genetic variation,” the researchers wrote.
“In addition, the study also shows that recreational-level exercise can induce Achilles tendon adaptations when regularly stimulated over many years.”
The researchers reported another finding: Exercises that involve “air phases” such as basketball and running – where the feet are completely off the floor – have a greater impact on the Achilles tendon than exercises such as swimming or cycling.
“It seems likely that regular air phase exercise may increase the risk of Achilles tendon injury from overload. Therefore, people who engage in air phase exercise should slowly increase their training intensity level to give the Achilles tendon enough time to adapt to the high shock load.” load,” concludes the team.
As always, further research should provide scientists with more details about why this is happening. Larger samples of twins with more varied training schedules and more varied types of exercise would be helpful.
Going forward, the new research could help athletes adjust their training schedules, casual runners improve their technique, and doctors treat (or prevent) injuries to this important body part.
“[The new results] offer new insights into the effect of genetic variation on individual Achilles tendon stiffness, which should be more carefully considered in future studies,” the researchers wrote.
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