Still, even changing technology and the changing gene pool in sports don't account for all of the changes in performance. Athletes have a different mindset than they once did. Have you ever seen in a movie when someone gets an electrical shock and they're thrown across a room? There's no explosion there. What's happening when that happens is that the electrical impulse is causing all their muscle fibers to twitch at once, and they're throwing themselves across the room. They're essentially jumping. That's the power that's contained in the human body. But normally we can't access nearly all of it. Our brain acts as a limiter, preventing us from accessing all of our physical resources, because we might hurt ourselves, tearing tendons or ligaments. But the more we learn about how that limiter functions, the more we learn how we can push it back just a bit, in some cases by convincing the brain that the body won't be in mortal danger by pushing harder. Endurance and ultra-endurance sports serve as a great example. Ultra-endurance was once thought to be harmful to human health, but now we realize that we have all these traits that are perfect for ultra-endurance: no body fur and a glut of sweat glands that keep us cool while running; narrow waists and long legs compared to our frames; large surface area of joints for shock absorption. We have an arch in our foot that acts like a spring, short toes that are better for pushing off than for grasping tree limbs, and when we run, we can turn our torso and our shoulders like this while keeping our heads straight. Our primate cousins can't do that. They have to run like this. And we have big old butt muscles that keep us upright while running. Have you ever looked at an ape's butt? They have no buns because they don't run upright. And as athletes have realized that we're perfectly suited for ultra-endurance, they've taken on feats that would have been unthinkable before, athletes like Spanish endurance racer Kílian Jornet. Here's Kílian running up the Matterhorn. (Laughter) With a sweatshirt there tied around his waist. It's so steep he can't even run here. He's pulling up on a rope. This is a vertical ascent of more than 8,000 feet, and Kílian went up and down in under three hours. Amazing. And talented though he is, Kílian is not a physiological freak. Now that he has done this, other athletes will follow, just as other athletes followed after Sir Roger Bannister ran under four minutes in the mile.