July 1, 2006 Computer models of human locomotion are helping engineers understand why walk and run instead of hopping and skipping. The models are revealing that walking and running are the most energy-saving ways a person can move. The models could help improve rehabilitation therapies and the design of prosthetic and orthotic devices.
ORLANDO, Fla.--To get from one place to another, we walk or run without thinking much about why. But these two engineers did wonder why humans move the way we do.
They look funny doing their research, but Manoj Srinivasan and Andy Ruina aren't comedians. They're mechanical and aerospace engineers studying human locomotion, or how people get around.
"You can imagine a person being able to go from point A to point B in all kinds of crazy ways. But people mostly choose to walk," Srinivasan, of Princeton University, tells DBIS. "The question is why?"
Srinivasan and his advisor, Ruina, designed a computer model to reveal the most energy-saving ways a person can move. Out of the thousands of possibilities, the computer chose walking and running, confirming a theory that's been around for hundreds of years.
Srinivasan says, "Walking is the least energy consuming at slow speeds, and running is the least energy consuming at fast speeds."
In a nutshell, we walk and run instead of skip because it takes less effort.
Andy Ruina, of Cornell University in Ithaca, N.Y., says, "So walking's the gait that people use where there's at least one foot on the ground, where your body moves approximately in a sequence of circular arcs."
The researchers were surprised, however, when the computer also chose a third gait.
"And as far as we can tell, this thing looks -- would look something like a tired run. Something like ... like that," Ruina says.
By studying the way we move, not only will researchers uncover more mysteries of the human body, but they hope to develop better prosthetic and orthotics devices.
Ruina and Srinivasan compared the three natural movements with what they call "many other strange and unpracticed gaits." Their computer model simulated human traits
BACKGROUND: People's legs are capable of a broad range of gait patterns, but we mostly use just two: walking and running. Cornell researchers have developed a computer model that could compare walking and running with an infinite variety of other gaits. It turns out that walking is the most energy-efficient gait for slow speeds and running is the most energy efficient gait for fast speeds. The new simulation also uncovered a "new", seldom-used gait for intermediate speeds that looks like "tired" running with slow motion landings.
THE STUDY: The Cornell researchers compared the mechanics of walking and running with many other gaits (such as skipping), using a set of computer models that simulated physical measurements such as leg length, force, body velocity and trajectory, forward speed, and work. The aim was to discover the most efficient means for a person to get from one place to another with the least amount of muscle work. When people walk, they swing their body over a relatively straight leg with each step; when they run, they bounce up off a bent leg between aerial phases. Both these use less energy than more unusual gaits.
ABOUT BIOMECHANICS: Biomechanics is the study of the anatomical principles of movement, such as how birds and insects fly; how fish swim; and the most efficient ways a human can move. When we walk, with every step, the foot strikes the ground on the outside edge of the heel, the shinbone twists inward, and the foot rolls inward to bear the weight, absorbing the shock of impact. Then the shinbone twists outward and the foot begins to lift at the heel, providing a springboard for the toes to push the body's weight forward off the ground. The foot then swings forward to repeat the cycle. Running has similar mechanics, but can be seen as a series of alternating hops from left to right leg.