Muscle strain in the lower back or upper back/neck. Most episodes of acute lower back pain are caused by muscle strain, such as from lifting a heavy object, a sudden movement or a fall. The low back pain can be very severe and last for several hours, several days or even a few weeks. When back muscles are strained or torn, the area around the muscles can become inflamed. With inflammation, the muscles in the back can spasm and cause both severe lower back pain and difficulty moving. The large upper back muscles are also prone to irritation, either due to de-conditioning (lack of strength) or overuse injuries (such as repetitive motions). Upper back pain may also be due to a specific event, such as a muscle strain, sports injury, or auto accident. Massage can help work out the spasm/irritation and improve range of motion. Read more in Back muscles and low back pain and Causes of upper back pain.