Why Do We Bend Our Arms When We Run?

Pedro_P

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▼ When you're walking or running, your legs are doing most of the work, but your arms are involved, too. And how they move depends on your gait.
As we walk, our arms usually hang naturally at our sides and are mostly straight. But when we run, our arms typically swing while bent at the elbow.
Why is that? Researchers recently investigated how arm position affects energy efficiency, and they found that walking with bent arms was actually less energy efficient than walking with straight arms.
A bent arm has a shorter arc than a straight arm; bent arms therefore require less energy to swing back and forth and should be more efficient for both running and walking, the researchers initially hypothesized.
But if bent arms are more energy efficient, why don't walkers naturally bend their arms? (▪ ▪ ▪)

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