Reading 2

Unit 1- Reading 2

Page 9

Were humans born to run?

Compared to cheetahs, whose bursts of speed reach 70 miles per hour, or migrating wildebeests that roam over 2,000 miles a year, we humans must seem lead-footed homebodies.

As big as we are, we cannot seem to catch a cat or a mouse or even a chicken unless we can corner it or trick it.

But has our natural envy of a few fleet- footed species or our clumsiness in catching nimble escape artists caused us to underestimate ourselves? University of Utah biologist Dennis Bramble and Harvard University paleoanthropologist1 Daniel Lieberman think so.

In fact, they maintain that decades of research indicates that humans are very good runners indeed—perhaps the best in the world—when the distance gets long and the weather gets hot.

HOT TO TROT

To understand how they can make this claim, let’s consider what humans can do. The very best long-distance runners can run five-minute miles for several hours.

These efforts are amazing achievements, but even the casual jogger can often keep up an eight to ten minute a mile pace for several miles. Only a few animals of similar weight—large dogs, hyenas, wolves, and wildebeests—are capable of maintaining such speeds, and actually prefer to trot a bit slower. Even a thousand-pound horse will not cover long distances any faster than a good recreational jogger.

And in hot weather, humans may hold a decided advantage. One of the most incredible feats of human endurance is the annual Badwater-to-Mt. Whitney run in the United States. The race begins in Death Valley, California, at an elevation 285 feet below sea level, in July, the hottest month of the summer.

The runners run 135 miles, crossing several mountain ranges with a cumulative elevation gain of 13,000 feet, and finish at an elevation of 8,360 feet at the Whitney Portal trailhead, about halfway up the 14,440-foot mountain. Each year approximately 75 men and women enter the race with 60-80% finishing within 60 hours and with the winning time usually well under 30 hours. Despite temperatures reaching

130°F, there have been no fatalities so far. These men and women can probably outrun any animal on the planet.

What makes it possible for these people to undergo such an ordeal? It turns out that humans are beautifully designed to run long distances in hot weather. Long-distance running requires the ability to keep from overheating, and we humans have several advantages in this regard.

First, we release heat by sweating through millions of sweat glands rather than through panting. And because we have no fur, our sweat evaporates quickly. Our upright posture also helps immensely by exposing less area to direct sunlight and more surface area to the cooling effect of the wind we create as we run. We excel at keeping cool, while most other animals simply cannot shed heat fast enough to run long distances.

But cooling is not enough to explain our speed over long distances. A second advantage is our long stride. When Professor Bramble filmed his student David Carrier running alongside a horse moving at an easy gallop, he noticed that Carrier took fewer strides than the horse, indicating that Carrier’s strides covered more distance than the horse’s. Bramble was surprised by this and began considering what elements of human biomechanics make this possible.

Working with Daniel Lieberman at Harvard, he realized that humans, like horses and rabbits, can run without their heads bobbing up and down due to a piece of anatomy, the nuchal ligament, which links the head to the spine. This tendon-like band is not involved in walking, suggesting that it is an important anatomical feature for a species that at one time needed to run.

not walk, to find its dinner.

A SPRING IN OUR STEP

In fact, walking, it turns out, is a distinctively different motion than running. When walking, the heel hits the ground first, the leg straightens, and the body lurches forward a bit.

As the weight transfers to the ball of the foot, the arch stiffens and then pushes the body forward, with the other foot moving forward to keep the stride going. With running, the legs become large springs. You land more heavily on the arch of the foot and bend your knee, which causes the body’s center of gravity to lower.

The force from this hard landing is captured by the tendons of the foot and leg, particularly the calf muscles, and you spring forward as the tendons recoil. According to Bramble, these huge, springy tendons are not necessary for walking.

Huge, springy tendons explain where the energy comes from, but how do humans maintain their balance and keep from falling over?

All other two-legged animals that run fast, such as kangaroos and roadrunners, have large tails that serve as a counterweight to keep the animal balanced. Humans are obviously tailless, so how do they do it? Motion studies of runners on treadmills offer clues. Instead of a tail. we have a very large muscle, the glutew maximus, that connects our hips to our lower back.

This muscle does not do much when we walk, but it works very hard when we run. Its role. it seems, is to act like a brake on our torso to keep it from lurching too far forward when our foot hits the ground. Other anatomical features that facilitate running are our long necks and our shoulders.

We are able to twist our shoulders without moving our head, allowing us to pump our arms as another steadying mechanism that helps counterbalance our head and keep it upright.

There is no doubt, then, that humans are able to run, but why? Today most people are sedentary and run solely for pleasure or sport. Could it be that in our prehistoric past long- distance running was necessary for survival?

Sprinting fast allows an animal to drag down prey or escape a predator, but why would an ability to sustain a long run through hot weather be necessary? To hunt, perhaps? But didn’t prehistoric humans hunt by sneaking up on animals and spearing or clubbing them? That certainly seems more efficient than chasing an animal for miles until it drops from heat exhaustion.

Or is our ability to run a byproduct6 of some other ability? It seems running muscles also help us stand up quickly and climb things, and certainly our springiness helps us fight more effectively.

Any conclusions we draw at this point are preliminary. But knowing that we can run long distances may point us in the right direction for further study. It gives us clues as to how prehistoric humans lived.

Perhaps adult hunters needed to travel long distances to track a herd and return before dark. Humans do not see well at night and by running could extend their hunting range without constantly breaking camp and uprooting a family or village. Perhaps they needed to move quickly in order to reach prey killed by other animals and join in on the feast.

Getting quickly to distant food sources before animal rivals could reach them is one clear advantage of our running ability.

The debate undoubtedly will continue, with those who dislike sweaty activity naturally skeptical of any prehistory that forced us to move out of the shade. But those eighty or so people who attempt the Badwater-to-Mt.

Whitney run and the hundreds of thousands who run 26.2-mile marathons each year make it difficult to deny the obvious—some humans, if not all, are definitely born to run.