[Paleopsych] NYT: Exercise: Walk, Don't Run, the Knees Say

[Premise Checker]

Exercise: Walk, Don't Run, the Knees Say
NYT August 31, 2004
By MARY DUENWALD

[General interest article. Everything I've read says that running uses 
only slight more energy than walking the same distance. So I'm not 
accepting this article for the nonce.]


Running may get you places faster than walking does, but it
is a less efficient form of locomotion because of the
demands it places on the knees, researchers have found.

For humans, running a given distance requires 50 to 80
percent more energy than walking the same distance does.
Horses and other four-legged animals, in contrast, use
roughly the same amount of energy to run a mile as to walk
it.

To figure out why humans are different in this way,
researchers at Harvard's Concord Field Station in Bedford,
Mass., filmed four healthy young men as they walked and ran
at steady speeds. As the men progressed from walking to
running, they steadily increased the amount of strength
used to work their hips until it almost doubled. The amount
of force at their ankles stayed fairly constant. But their
knees used five times as much force when they ran.

The research is reported in The Journal of Applied
Physiology.

The extra force is needed because, during running, the
knees must stay flexed to enable the leg to act as a
spring. And bending the knees means working the large
quadricep muscles of the thighs.

"In running, the leg must compress and extend like a pogo
stick," said Dr. Thomas J. Roberts, an assistant professor
of biology at Brown University and an author of the study.
"In walking you conserve energy because you move like an
inverted pendulum. You sort of pole-vault over your legs."

http://www.nytimes.com/2004/08/31/health/31exer.html