Image: Trails in Mallorca, Spain
Martin Llobera
Trails used by humans exhibit zigzags, or switchbacks, when they traverse steep hillsides, such as this one in Mallorca, Spain.
updated 2/22/2008 3:03:37 PM ET 2008-02-22T20:03:37

A straight line may be the shortest distance between two points, but on a steep slope, zigzagging is the fastest way to go, a new study confirms.

On flat terrain, a straight line is typically still the best way to get from point A to point B. But climbing up a steep hill is a whole different ballgame; the mechanics and energy costs of walking up a hill alter the way we negotiate the landscape.

"You would expect a similar process on any landscape, but when you have changes in elevation it makes things more complicated," said study author Marcos Llobera of the University of Washington. "There is a point, or critical slope, where it becomes metabolically too costly to go straight ahead, so people move at an angle, cutting into the slope. Eventually they need to go back toward the direction they were originally headed and this creates zigzags. The steeper the slope, the more important it is that you tackle it at the right angle."

Llobera and co-author T.J. Sluckin of the University of Southampton in the U.K. developed a simple mathematical model showing that a zigzagging course is in fact the most efficient way to go up or down a steep slope.

Most people don't need a model to tell them that though, they do it without even thinking.

"I think zigzagging is something people do intuitively," Llobera said. "People recognize that zigzagging, or switchbacks, help but they don’t realize why they came about."

The work is detailed in the Journal of Theoretical Biology.

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