Like she's carrying invisible suitcases. --Elaine (describing a woman who walked without swinging her arms; Seinfeld, April 14, 1999)
Body movement. To move the upper limbs back and forth rhythmically with the legs while walking.
Usage: As a counterweight, the arm-swing helps balance our upright body while walking, jogging, and running. In dances, such as the locomotion, swim, and twist, vigorous arm-swinging gyrations express inner feelings and moods in time to music's rock-'n-roll beat.
Observation. Restless, back-and-forth motions of the arms above a conference table, e.g., may reveal an unconscious wish to "walk away" from meetings or discussion groups.
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.
Infancy. At three months of age, we use our forearms and hands to raise our bodies off the floor in preparation for crawling. As babies, we find moving pleasurable for its own sake (Chase and Rubin 1979:153), and begin advancing one limb at a time--on all fours--between the 6th and 9th months of life. In a gait typical of quadrupeds, our arms reach alternately forward as the opposite hind limb crawls forward on the knee. (N.B.: Adults make surprisingly good quadrupeds, as well. In 1988, e.g., a man crawled 28.5 miles around a level track without stopping, to prove it could be done [McFarlan 1991:199]. From 1984-85, a man crawled 870 miles to please a Hindu goddess [McFarlan 1991:199].)
Neuro-notes. Paleocircuits for arm-swinging originated in the aquatic brain. Today, arm-swinging is still mediated by the basal ganglia. Like walking itself, our vestigial arm movements are unconscious and out of awareness. Motionless arms (and a shuffling gait), meanwhile, are symptomatic of shortages of the neurotransmitter, dopamine, in the basal ganglia (as in Parkinson's disease).
The human arm-swing is innate.