By default his hands and feet are IK-parented to his BODY. If his left arm's IK is set on, and if his left hand is IK_parented to his BODY, and if the walk designer moves him by moving his hip and not by moving his BODY, rhen his BODY stays still as his hip enc move, and therefore his elft hand stays with his BODY. The BODY is an invisible body part which is the parent of his root segment . A human's root segment is his hip.