A new study adds to growing evidence that, for runners, the Achilles tendon is the source of our powers.stevecoleimages/iStockPhoto / Getty Images
The Achilles tendon, which connects the calf muscles to the heel bone, is named for the legendary Greek warrior whose weak spot was his heel.
But a new study adds to growing evidence that, for runners, this tendon is instead the source of our powers. It was the evolution of a long and stretchy Achilles tendon, the findings suggest, that transformed our ancestors into fleet endurance runners who could lope across the savannah in pursuit of prey. And modern runners too, it turns out, may want to pay more attention to their ankles.
A research team led by Karl Bates of the University of Liverpool in Britain analyzed the running prowess of one of the most famous ancestral human skeletons ever found. “Lucy” was discovered in Ethiopia in 1974 and is thought to represent a transitional species that lived about 3.2 million years ago.
Bates and his colleagues used the fossilized bones to create a digital model of Lucy’s musculature, then used machine learning to simulate how fast she would be able to run and how much energy it would take depending on various assumptions. The results are published in the journal Current Biology.
The most important assumption turned out to be the form of her Achilles tendon and calf muscles. Apes have short, stubby Achilles tendons and calf muscles; humans have long, springy tendons that stretch with each running stride, storing and releasing energy like an elastic band.
When the scientists modeled Lucy’s running with a chimpanzee-like calf and Achilles, she could only hit a maximum speed of about 8 kilometres per hour. But when they gave her a human-like ankle, her maximum speed doubled and the amount of energy she required to run was cut in half.
For anthropologists and evolutionary biologists, the results fit nicely with the “born to run” theory that our bodies have been shaped by the demands of running. In addition to springy Achilles tendons, other adaptations such as powerful buttocks, shorter toes, and less body hair are useful for running but have no particular benefit for walking.
Modern runners may also like the idea that their hobby taps into an ancestral imperative – but there’s a more practical angle, too. Just like Lucy, you run faster and more efficiently when your calf muscles are strong, and your Achilles tendons are springy.
To generate force for running, you use your ankles, knees, and hip joints. But as you fatigue, it’s your ankles that tend to weaken first, forcing your knees and hips to take on more load and reducing your efficiency.
This tendency gets worse as you age. Last year, Max Paquette, a Canadian-born researcher at the University of Memphis, published data showing that young runners generate more force with their ankles, while older runners rely more on their hips because their ankles have weakened. This is one of the reasons older runners slow down.
The antidote is to strengthen your calf muscles, which you can do with conventional resistance exercises such as calf raises or with plyometric exercises, which involve explosive movements such as jumping and hopping. Plyometric exercises have an additional benefit, which is that they increase tendon elasticity, enabling your Achilles to store and release more energy with each stride.
A simple daily plyometric plan for runners that was tested in a recent study is hopping. Start by hopping for 10 seconds then resting for 50 seconds and repeat for a total of five times. Over the course of a month or two, reduce the rest and increase the number of repetitions until you’re doing 15 sets of 10 seconds of hopping with 10 seconds of rest. The total time remains just five minutes, and researchers in Germany found that this program improved running efficiency by 2 to 4 per cent after six weeks.
With this approach, you’ll be leveraging an advantage that Lucy and her fellow early human ancestors lacked – and more importantly, weak ankles won’t become your Achilles’ heel.
Alex Hutchinson is the author of The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.
