“Ancient humans exploited the fact that humans are good runners in the heat,” Dr. Bramble said. “We have such a great cooling system” — many sweat glands, little body hair.
There is other evidence that evolution favored endurance running. A study in The Journal of Experimental Biology last February showed that the short toes of the human foot allowed for more efficient running, compared with longer-toed animals. Increasing toe length as little as 20 percent doubles the mechanical work of the foot. Even the fact that the big toe is straight, rather than to the side, suggests that our feet evolved for running.
“The big toe is lined up with the rest, not divergent, the way you see with apes and our closest nonrunning relatives,” Dr. Bramble said. “It’s the main push-off in running: the last thing to leave the ground is that big toe.”
Springlike ligaments and tendons in the feet and legs are crucial for running. (Our close relatives the chimpanzee and the ape don’t have them.) A narrow waist and a midsection that can turn allow us to swing our arms and prevent us from zigzagging on the trail. Humans also have a far more developed sense of balance, an advantage that keeps the head stable as we run. And most humans can store about 20 miles’ worth of glycogen in their muscles.
And the gluteus maximus, the largest muscle in the human body, is primarily engaged only during running. “Your butt is a running muscle; you barely use it when you walk,” Dr. Lieberman said. “There are so many features in our bodies from our heads to our toes that make us good at running.”
-The Human Body Is Built for Distance
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