Body movement . To move the upper limbs back and forth rhythmically with the legs while walking . As a counterweight , the arm-swing helps balance our upright body while walking, jogging, and running. At three months of age, we use our forearms and hands to raise our bodies off the floor in preparation for crawling . In a gait typical of quadrupeds, our arms reach alternately forward as the opposite hind limb crawls forward on the knee.
Adults make surprisingly good quadrupeds, as well.
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.