The spine's wide range of motion—it can bend forward, backward, and sideways as well as rotate or twist—would not be possible without the surrounding layers of 140 overlapping muscles that provide strength and support to the back.
In order for the spine to move, some muscles need to contract and others must relax.
Closest to the spine is a network of three types of short muscles that, in addition to the ligaments, hold the vertebrae together. These are:
- the intertransverse muscles, which allow you to bend to one side or the other
- the interspinal muscles, which permit you to bend backwards and forwards
- the rotator muscles, which allow the spine to rotate from side to side.
Outside this inner layer of muscles are the erector spinae—two larger muscles that run the length of the spine on either side. The erector spinae assist in movement, support the spine (preventing it from falling forward), and absorb much of the stress of everyday activity.
When both erector spinae contract, the spine bends backwards; contracting just one side results in bending sideways.
The primary function of the outermost layers of back muscles is to move other parts of the body (for example, the trapezius and latissimus dorsi help move the shoulders and arms). These muscles also assist with the movement and support of the spine.
The abdominal muscles, besides allowing voluntary movement in the abdominal region, help to stabilize the lumbar region of the back. Thus, exercises that strengthen the abdominal muscles are also important in preventing future back pain.
Originally published in The Johns Hopkins White Papers: Back Pain and Osteoporosis (2011)
Lee H. Riley III, M.D.; Chief, Orthopaedic Spine Division, Johns Hopkins Medicine
Suzanne M. Jan de Beur, M.D.; Chief, Division of Endocrinology, Johns Hopkins Bayview Medical Center