Muscle strains are a very common cause of back pain, particularly in the low back. Muscle strains happen in this area when the fibers of the muscles are stretched and torn. Lumber (lower back) sprains are a different condition in that they affect the ligaments. A sprain occurs when these ligaments are torn from their attachments to the bones of the spine.
Both of these conditions can cause lower back pain, and on a basic level the treatment for each of these is similar. Symptoms might also include muscle spasms and pain that is associated with activity (often leading to a loss of mobility).
The first step in finding treatment for low back pain is to complete a full diagnosis to determine if the pain is caused by a lumbar strain or sprain, or another back pain condition.