'Back pain' is pain felt in the human back that usually originates from the muscles, nerves, bones, joints or other structures in the vertebral column. Back pain may have a sudden onset or can be a chronic pain; it can be constant or intermittent, stay in one place or radiate to other areas. It may be a dull ache, or a sharp or piercing or burning sensation. The pain may radiate into the arms and hands as well as the human leg or human foot, and may include symptoms other than pain. These symptoms may include tingling, weakness or numbness. Back pain is one of humanity's most frequent complaints. In the United States of America, acute low back pain (also called lumbago) is the fifth most common reason for physician visits. About nine out of ten adults experience back pain at some point in their life, and five out of ten working adults have back pain every year. The spine is a complex interconnecting network of nerves, joints, muscles, tendons and ligaments, all of which are capable of producing pain. Large nerves that originate in the spine and go to the legs and arms can make pain radiate to the extremities.