Muscles of the back may produce spasm or extreme muscle stiffening after a traumatic injury or repetitive strain. The difference between a repetitive strain and a traumatic injury is that with a repetitive strain the muscles are being irritated over a long period of time until they reach a point that finally triggers the spasm.
The muscles then spasm to protect the area from further injury. For example, a person who has improper posture at a computer on a regular basis, or a golfer who plays frequently with bad form may have their muscles tighten over time, but the muscles may not start to spasm until something as simple as reaching for a glass of water occurs. This spasm can be extremely painful and lead to tearing of the muscles if undue stressors are placed on them. This tearing will than lead to guarding of the back musculature through extreme stiffening to protect the area from further harm.
With proper care for the area, the pain in the back musculature should lessen over three weeks, but it should be noted that the healing of the area continues and doesn’t even peak until at least six weeks following the initial injury. This is due to scar tissue formation which initially acts like the glue to bond the tissue back together. Scar tissue will continue to form past six weeks in some cases and as long as a year in severe back pulls