What is the reason we bend out arms when we run, but hold them straight when we walk?
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We use our arms to produce torque (twisting force) to our bodies that counteract that produced by our feet. When we run, we need to move our arms faster in order to do that. With straight arms, we can choose to have them flapping around wildly (uncomfrotable), hold them stiff (strenuous), or lift them up (feels better).
When we walk, they won’t flap around since we’re moving them much more slowly, so using energy to hold them up is unnecessary.
When we walk our arms swing like pendulums in a motion opposite to the swing of the legs. This keeps the angular momentum even without the body having to twist from side to side.
When we run, the arm motions are also helping us to lift off the ground between steps, so they need to punch up while the corresponding foot is on the ground and then come down again to help with lift.
When I was doing long distance running in high school and college back in the 1990s we were taught to keep our arms relaxed and to swing them with the wrists at about waist level. This was all about conserving energy and it made it easier to take longer strides. When we got near the finish we could swing our arms at chest level which helped us move faster. I’m talking bout 10+ mile runs. It could also be complete bullshit but that is what we were taught back then
Wel have ya tried doing that? Not exactly effective ey
This reminds me of the T1000 in Terminator 2. Everyone he ran he was so fast and he bends his arms in a really interesting way.
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.
Also a slightly more physical reason: The length of a pendulum is what controls its frequency. The weight doesn’t matter, only its length. That means that when your arms are long, they swing slower, thereby fitting a lower frequency of steps. When you run (or go tippy tappy with your feet) you’ll naturally raise your arms to match the higher frequency of your steps.
Why do you need to match your arms to your steps? Because moving takes your whole body and we’ve spent thousands of years perfecting it.
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