Your back contains more than 20 named muscles arranged in distinct layers, from the large, visible muscles near the surface to small stabilizers buried deep along the spine. These muscles are generally divided into three groups: superficial, intermediate, and deep. Here’s what each group is called and what it does.
Superficial Back Muscles
The superficial layer sits closest to the skin and contains the muscles most people picture when they think of “back muscles.” These are technically extrinsic muscles, meaning they primarily move the shoulders and arms rather than the spine itself.
Trapezius: The large, diamond-shaped muscle that spans from the base of your skull down to the middle of your back and out to each shoulder blade. It controls shrugging, pulling your shoulder blades together, and tilting your head back.
Latissimus dorsi: Often called the “lats,” these are the widest muscles in your body. They fan out from your lower and mid-back to your upper arm bone. The lats pull your arms down and back, powering movements like pull-ups, swimming strokes, and rowing.
Rhomboid major and rhomboid minor: Two stacked muscles between your spine and shoulder blade. They retract the shoulder blade, pulling it toward the midline of your back. The minor sits above the major and is smaller, but both do essentially the same job.
Levator scapulae: A strap-like muscle running from the top of the shoulder blade to the upper neck vertebrae. As the name suggests, it elevates (lifts) the shoulder blade and also helps tilt the neck to one side.
Intermediate Back Muscles
Tucked beneath the superficial layer, the intermediate muscles sit just above and below your ribcage. Their primary job is moving the ribs during breathing.
Serratus posterior superior: Located in the space between your shoulder blades, underneath the rhomboids. It lifts the upper ribs to help expand the chest when you inhale.
Serratus posterior inferior: Positioned at the bottom of the ribcage, beneath the lats. It pulls the lower ribs downward during forced exhalation, such as when you cough or blow out candles.
Deep Back Muscles: The Erector Spinae
The deep, or intrinsic, muscles are the true back muscles. They developed in the back during embryonic growth and exist specifically to move and stabilize the spine. The largest and most important group here is the erector spinae, a set of three parallel columns running along each side of the vertebral column from the pelvis to the skull.
Iliocostalis: The outermost column, closest to your sides. It has three regional divisions (lumborum, thoracis, and colli) that together span from the sacrum and pelvis up to the mid-neck. The iliocostalis extends the spine and bends it sideways.
Longissimus: The middle column and the thickest and longest of the three. It also divides into three parts (thoracis, colli, and capitis), reaching from the pelvis all the way to the base of the skull behind the ear. The longissimus extends and side-bends the spine, and the upper portion helps turn and tilt the head.
Spinalis: The innermost column, running closest to the spinous processes (the bumps you can feel along the center of your back). Like the others, it has three divisions (thoracis, colli, and capitis). The spinalis primarily extends the spine.
Together, the erector spinae keep you upright against gravity. When both sides contract at once, they straighten and extend the spine. When one side contracts alone, the trunk bends to that side.
Deep Back Muscles: The Transversospinalis Group
Beneath the erector spinae lies a group of shorter, diagonally-oriented muscles collectively called the transversospinalis group. These muscles run at angles between vertebrae and serve as the spine’s fine-tuning system, stabilizing individual vertebrae during movement.
Semispinalis: The most superficial of the three. Its upper portion attaches to the skull, so when both sides contract it pulls the head backward, extending the neck. When only one side fires, it rotates the head to the opposite side.
Multifidus: Perhaps the single most important stabilizer of the spine. These short, thick bundles span two to four vertebrae at a time and run the full length of the vertebral column. The multifidus keeps individual vertebrae steady during bending, lifting, and twisting. Weakness or poor activation of the multifidus is closely linked to lower back pain.
Rotatores: The deepest of the group, spanning just one or two vertebrae each. They are most developed in the thoracic (mid-back) region. Like the multifidus, they stabilize the spine and rotate the trunk to the opposite side.
The Smallest Deep Muscles
At the very deepest level, tiny muscles connect one vertebra to the next. The interspinales link the spinous processes of adjacent vertebrae and assist with small spinal extensions. The intertransversarii connect the side projections (transverse processes) of neighboring vertebrae and help with subtle lateral bending. These muscles are thought to play an important sensory role, acting as position sensors that tell your brain exactly where each segment of your spine is in space. That feedback helps coordinate the larger muscles around them.
Quadratus Lumborum
The quadratus lumborum, or QL, is a deep rectangular muscle on each side of the lower back, connecting the lowest rib to the top of the pelvis. Anatomy texts describe it as an extensor and lateral stabilizer of the lumbar spine, though research suggests it contributes less than 10% of the force during a side bend. Its real significance may be positional: it sits at a crossroads of forces from surrounding muscles, influencing how tension is distributed across the lower back. The QL also plays a role as an accessory breathing muscle and helps transfer load between your upper and lower body.
How the Layers Work Together
A key structure that ties all of these muscles together is the thoracolumbar fascia, a strong sheet of connective tissue in the lower and mid-back. This fascia has three layers that separate and envelop the deep muscles (the erector spinae, multifidus, and quadratus lumborum), and its collagen fibers blend directly into the outer coverings of multiple trunk muscles. The result is an interconnected network that transmits force between muscles, bones, and joints. When you lift a heavy box, for instance, force generated in one muscle can travel through these fascial connections to stiffen adjacent structures and protect the spine. The stiffness and density of these fascial links directly influence how stable a joint is, because they can change the effective leverage of the muscles crossing that joint.
In practical terms, the superficial muscles handle the big, powerful movements of your arms and shoulders. The intermediate muscles assist breathing. The deep muscles keep each vertebral segment stable and allow controlled spinal movement. All three layers coordinate through the fascial system to let the spine move as a cohesive whole while staying protected under load.