Lower back muscle or ligament (soft tissue) strain is one of the most common causes of acute and chronic lower back pain. Soft-tissue injury is classified as "acute" if it has been present for days to weeks. If the pain lasts longer than three months, it is referred to as "chronic."  This occurs as a result of a failure to heal due to persistent underlying causes.

Lifting a heavy object, twisting, or a sudden movement can cause muscles or ligaments to tear. Often soft tissue injuries occur during trivial movements such as bending forward or other routine activities due to underlying tendinopathy. Pain may be immediate or not felt until the following day.

With a lower back strain, the severity of the pain can be severe and disabling, depending on the extent of strain and the lower back muscle spasms that result from the injury.