Looking Closely at the Muscles along the Spine

The muscles along each side of the spine are called paraspinal muscles. The paraspinals have a major role in protecting the spine. Some studies have suggested that too much weakness and fatigue in the paraspinals can increase the risk for a first episode of low back pain (LBP). But just what happens to the muscles to cause this problem? And when does a muscle go from being normal and healthy to being dysfunctional?

Some think it’s possible that LBP occurs when the balance of fibers within the muscle is off. The muscle works a certain way depending on what kind of muscle fibers are present. There are two muscle fiber types: type I and type II. Type I fibers develop less tension and more slowly than type II. The more type I fibers are present, the easier it is for the muscle to resist fatigue. Type II fibers work hard and fast, but they aren’t designed for stamina.

Scientists at the Musculoskeletal Research Group in England put this theory to the test. They compared 35 men who had chronic LBP with 32 healthy men without LBP. Each man was tested with a series of muscle fatigue tests over two days. After the tests, a small piece of the paraspinal muscle was taken for a biopsy exam.

No differences were seen in muscle fiber types between the two groups. The healthy group had stronger muscle contractions and greater endurance (ability to hold the contraction over time). The authors conclude that even though patients with chronic LBP have less paraspinal muscle strength, it’s probably not because of fiber type.