Not everyone may feel this way, but new research argues that humans evolved to become natural runners.
From our spring-loaded ligaments to our muscular behinds to our ability to sweat, the human body took the ideal shape of a long-distance runner starting some 2 million years ago, the researchers say. The long, lean build helped us scavenge widely scattered kills and could also have been an advantage when hunting down prey over long distances.
"We're lousy sprinters, but we're really great long-distance runners," said Daniel Lieberman, an anthropologist at Harvard University. "Anyone who jogs regularly can tell you that it feels good."
How can two legs be better than four when it comes to striding for long distances? Consider the fact that some 334,000 people ran marathons in the United States last year, and then try getting an antelope to run 26 miles, or a chimp, for that matter.
"You'd never beat a chimp in a 100-meter dash, but you could never get them to run a marathon," he said. "And they wouldn't like trying."
Evolutionary biologists have generally credited humans' ability to run as an offshoot of our ability to walk on two feet.
"How can anyone even conceive of an animal evolving a walking strategy that was entirely decoupled from a running strategy?" asks C. Owen Lovejoy of Kent State University in Kent, Ohio.
But in a study appearing in this week's issue of "Nature," Harvard's Lieberman and Dennis Bramble of the University of Utah argue that endurance running may have been so critical in early humans' survival that it played a role in shaping many aspects of our bodies.
The pair studied both modern human anatomy and the fossil record of early human ancestors to look for characteristics that would have specifically enhanced people's ability to run for long distances. They say most, if not all of these key features seem to have emerged 2 million years ago with the first appearances of the genus Homo -- the same group as modern living humans.
The peroneus brevis tendon, for example, made famous by Red Sox pitcher Curt Schilling's injury during the 2004 World Series, is one of several elongated tendons in the human body that the authors argue provides critical spring as a person runs. In apes and chimpanzees, the same tendons are much shorter, says Lieberman, and don't offer the same kind of spring-loading action.
Then there is the gluteus maximus -- the unusually large muscle humans carry at their rear. Why such bulk in back? Lieberman says it's for running and, again, this feature is less pronounced in our evolutionary ancestors.
"When we walk, we barely use the gluteus maximus," he said. "As soon as you start running, it plays a vital role to keep you from falling -- it stabilizes your trunk."
Other features the authors list that help us run include the arches in our feet, which offer spring in our step, and broad surface areas of our joints, which help distribute the shock of impact from running -- at least enough for ancient man, who didn't run on pavement and who never lived much longer than 40 years.