Human beings have an assortment of keen advantages over other mammals when it comes to running. The following key ancestral insights have been are excerpted from Dr. Kelly Starrett’s book, Ready to Run: Unlocking Your Potential to Run Naturally. Next time you’re at a cocktail party or at a work lunch where you hear a healthy 20-something say, “I couldn’t run a 5k in a million years,” e-mail them a copy of these five reasons they’re wrong:

You have springs. When you walk, your feet, legs, and body use a pendulum-like motion. But shift into a run, and all the miraculous machinery that you were born with vaults into action—your hips, knees, ankles, and feet work in concert with your muscles and connective tissues to use gravity and elastic energy to bounce you along with breathtaking efficiency. “In fact, a running human’s legs store and release energy so efficiently that running is only about 30 to 50 percent more costly than walking in the endurance-speed range,” says Daniel Lieberman in his book The Story of the Human Body. “What’s more, these springs are so effective that they can make the cost of endurance running (but not sprinting) independent of speed: it costs the same number of calories to run five miles at a pace of either 7 or 10 minutes per mile.”

You have stable, springy arches. Your feet are serious machines designed not only for running, but also for fast running—as well as the quick, agile changes of direction that we associate with a star halfback in football. The mechanism that is the human arch, with its energy- returning spring action, helps reduce the energy cost of running by up to 17 percent, according to researchers. [R. F. Ker, M. B. Bennett, S. R. Bibby, R. C. Kester, and R. M. Alexander, “The Spring in the Arch of the Human Foot,” Nature 325 (1987): 147-49.]

You have super-elastic Achilles tendons. Just a third of an inch long in a chimp, the human Achilles tendon is 6 inches long. When you run, you show off the true power of your wondrous heel cords: They can store and release 35 percent of the mechanical energy produced when you run—something that doesn’t happen when you walk. The Achilles is all about helping you run.

You have a powerful butt. That’s right; your large glute muscles are not there just to fill out a pair of designer jeans. You can walk around with your glutes essentially asleep. Break into a sprint, however, and your butt becomes essential to your overall stability—it keeps you from doing a face plant with every step. The glutes are the largest muscles in your body, and if you put them to full advantage (a life of sitting in chairs can impede on the magnificent flow of power that your posterior chain was engineered
to channel), you will be using muscles that are relatively

You have ear canals like spacecraft guidance computers. Yes, even your ear canals are specialized for good running. Running involves a lot more banging around than walking does—just observe the figure-eight movement of a runner’s ponytail in action to get a sense of how much is going on as you bound down the road. Like a computer with gyroscopes, the ear canals transmit signals to your musculoskeletal system to correct for the constant flow of tiny imbalances incurred in a bipedal organism on the move.

If you have any doubts that, thanks to millions of years of evolution, you were born to run—whether you’re running on the field, on the court, in your combat boots, or in a marathon—read The Story of the Human Body. There’s a reason you have short toes, a narrow waist in contrast to wide shoulders (power generated through optimal rotation), a powerful butt, gyroscopes in your skull, and skin that radiates away excess body heat thanks to millions of sweat glands: You were designed to run like the wind.

Kelly Starrett, DPT, is a NYT Bestselling author and founder of