Why do people wave their arms when walking?

A person making a step forward “falls” leaning on one of the legs, and since the support is not strictly under the center of gravity, the support creates an uncompensated moment of force relative to the center of mass, which creates a moment of momentum that twists the body. To avoid this twisting, we move our arms, creating an opposite moment of momentum, which compensates for the rotation. By pressing their hands to the body, a person spends 12% more energy to compensate for the torque. In addition, swinging the arms compensates for the up and down movement of the body when walking. Without hands, a person has to spend 63% more energy to smooth out this effect.