While a back strain may not sound like a serious injury, it can cause severe amounts of pain. Back strains are among the most common causes of back pain, and are responsible for countless emergency room visits each year. A back strain can occur at any age, but it is most common in people over the age of forty. A back strain is an injury to the tendons and/or muscles of the back, and can be caused from simple stretching injuries to partial or complete tears in the soft tissue. Microscopic tears of varying degrees can occur when the tissues are torn or stretched too far. These tears cause inflammation in the surrounding area, which often results in painful muscle spasms and limited range of motion. A back strain that has been present for days or weeks is referred to as acute, while chronic pain persists for longer than 3 months.