What is the reason we bend out arms when we run, but hold them straight when we walk?
In: 28
Normally your arms move forward when the opposite side leg moves forward.
When running your legs move faster. So we move our arms faster.
To do this we shorten the length of the arm.
For self-test. Flap your hand at the wrist. You can move it quite fast. Now flap your arm at the elbow. Not as fast. Now flap the whole arm, keeping it as straight as possible, at the shoulder. Slower of the three. Now fold your hand towards your shoulder and flap your arm using the shoulder. It will go faster than straight arm flapping.
To get the same speeds across all three joints you would need to use more energy at the higher arm joints keeping the arm straight. We shorten the arm by bending at the elbow so the arm can swing faster to stay in coordination with the faster leg motion.
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