The lower back muscles work together with tendons and ligaments to allow for smooth and controlled movements between the upper body, pelvis, and legs. Tendons and ligaments are connective tissue that attach muscle to bone and bones to other bones.
There are 3 main muscle groups in the lower back – the extensors, flexors, and oblique muscles. Let’s take a closer look.
The extensors lie at the back of the lumbar spine and form the bulk of the lower back muscles. This group mainly consists of the quadratus lumborum, erector spinae, and multifidi.
The quadratus lumborum is a flat quadrangular-shaped muscle that extends upward from the iliac crest and iliolumbar ligament to the transverse processes of the first four lumbar vertebrae and the lower part of the twelfth rib.
The erector spinae lie vertically on either side of the spine and are further divided into the longissimus thoracis and iliocostalis lumborum. They extend from the transverse processes of the first 4 lumbar vertebrae to the iliac crest. ,
The multifidi are a set of deep muscle bands that extend from the spinous process of a lumbar vertebra to the mamillary process of a vertebra 2 to 5 levels below.
The extensor muscles help bend the spine backward.
The flexors lie in the front of the lumbar spine. The main muscle in this group is the psoas major, a spindle-shaped muscle, which extends from the transverse processes of vertebrae T12 to L4 to the upper part of the thigh bone.
The flexor muscles help bend the trunk and hip forward and arch the lower back.
The oblique muscles lie on the side of the lumbar spine and include the internal oblique and external oblique.
The internal oblique is a broad and thin muscle that extends upward from the iliac crest to the lower three ribs.
The external oblique lies above the internal oblique and extends from the lower seven ribs to the iliac crest.
Together with the surrounding abdominal muscles, the obliques help bend the trunk forward.
A combined effort from all three muscle groups enables more complex movements, such as spinal rotation and side-bending.
Strain to a lumbar muscle, also called a pulled muscle, can cause mild to severe pain and stiffness in the lower back. Most lumbar muscle strains feel better within a few days, but sometimes, they can last much longer depending on the severity.
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