Lower back (erector spinae)

The columns of muscle either side of the spine that hold you upright and extend the back. With the deep multifidus, they resist the pull of gravity and stabilise each spinal segment.

This muscle in 3D

Drag to rotate · scroll to zoom — see the shape, origin and insertion of the lower back (erector spinae). 3D model via Sketchfab (CC-BY).

Anatomy

Muscles: Erector spinae (iliocostalis, longissimus, spinalis), with deep multifidus

Origin: Sacrum, iliac crest and lumbar vertebrae.

Insertion: Up the ribs and vertebrae to the neck (running the length of the spine).

Actions:

• Spinal extension (straighten / arch the back)
• Resist flexion under load (keeping a neutral spine)
• Side-bending and rotation control
• Segmental stability (multifidus)

How the muscle works

They work mostly isometrically to keep the spine neutral while the hips and legs do the lifting. In a deadlift they don't 'lift the weight' so much as prevent the spine from rounding under it.

Fibre-type bias: Strongly postural (type I), endurance-built — active all day maintaining posture.

Functional role: Upright posture, safe lifting, and protecting the spine in every loaded movement.

Common problems

• Non-specific low-back pain
• Muscle spasm / strain from poor lifting mechanics
• Multifidus inhibition after back pain

Training & stretching

Hip hinges with neutral spine, back extensions, bird-dogs, carries, deadlifts.

Child's pose, knees-to-chest, cat-camel mobility.

Fix or train this

• Lower Back Pain
• Build Muscle (Plateau)