This story is from the category Artificial Intelligence
Date posted: 10/02/2009
Contrary to popular belief, decades-old research and legions of power walkers, arm swings are a reflexive response to leg movement.
We swing our arms simply because it would take extra mental and physical effort to keep them still, says Herman Pontzer, a biomechanics researcher at Washington University in St Louis.
Pontzer didn't set out to overturn the long-held belief that shoulder muscle contractions help drive the human gait.
Previous research seemed to have settled any doubts. For instance, a 1939 study by Herbert Elftman, an anatomist at Columbia University in New York, first argued this point. Three decades later, another team recorded electrical activity in deltoid muscles as people walked.
Looking merely to confirm these findings while teaching an undergraduate laboratory class, Pontzer asked his students to test a critical prediction of the model: as a person walks, their arms and legs should move in tandem.
Instead, the students discovered that a person's arms and legs move slightly out of sync. Our torsos act as a dampener, causing arm motions to lag slightly behind the legs, he hypothesised.
A scale model showed the same lag. "I went to [a store] and we spent half an hour in the toy section looking for a big box of Legos and spent the rest of the night building that thing," he says.
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