SWING ... When our hands are empty why do our arms swing when we walk? ... If you walk with a bag in your hands your arms do not swing.
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Universe Of Life
ANSWERS: 2
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As a counterweight, the arm-swing helps balance our upright body while walking, jogging, and running. Evolution. Spinal-cord paleocircuits, which govern the rhythmic, alternating movements of arm-swinging evolved (in tandem with those of the legs) for locomotion. The act of swinging the arms while walking--and of pumping them while running--is an evolutionary holdover from earlier days, when the arms (used as forelimbs) participated with the legs in quadrupedal locomotion.
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Arm-swinging improves biomechanical efficiency, says Michael McPartland, Ph.D., of Harvard's BioMotion Laboratory. Notice during a walk or run that your limbs are "out of phase," left leg forward and right arm backward, etc. This way, body torque from the leg and arm swings counter each other, stabilizing the torso and head. To prove this, try a brisk walk or slow jog with arms tightly crossed against your chest. Now both your hips and shoulders will rotate by an undesirable amount, wasting energy. Or try jogging and moving your arms "in phase," right arm and left arm forward together, etc. "This is very difficult and unnatural. And the faster you jog, the goofier it gets!" http://www.cincinnati.com/freetime/strange/030499_strange.html
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