A muscle pull is a condition where the muscles of the back are injured due to a traumatic pulling of the fibers. This tearing of the fibers is known as a muscle strain.

A sudden or abrupt movement that causes the muscles to stretch the muscles past their point of elasticity usually causes these injuries. While some back strains are the result of a high velocity impact  (an example is a car accident that causes whiplash), other types of pulls are caused by repetitive strain. For example, a person who maintains improper posture at a computer on a regular basis, or a tennis player who uses improper form may have their muscles tighten to the extent that something as simple as reaching for a salt shaker can cause them to pull a muscle. To add to the pain of a pulled muscle, the surrounding muscles react to the tear by stiffening to protect the injured muscle from further harm

On average it takes about six weeks to recover from a muscle pull with some relief being felt after about three weeks.  Scar tissue will continue to form past six weeks in some cases and as long as a year in severe back strains.