Pain felt in the back usually originates from the muscles, nerves, bones, joints, or other structures in the spine. The pain can often be divided into neck pain, upper back pain, lower back pain, or tailbone pain. It 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, piercing, or burning sensation. The pain may radiate into the arm and hand, into the upper back, or into the lower back, (and might radiate into the leg or foot), and may include symptoms other than pain, such as weakness, numbness or tingling. Back pain is one of humanity's most frequent complaints. In the U.S., acute lower 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, and all are capable of producing pain. Large nerves that originate in the spine and go to the legs and arms can cause pain to radiate to the extremities.