Musculature around the Sacroiliac Joint. Permission Joseph E. Muscolino. Manual Therapy for the Low Back and Pelvis - A Clinical Orthopedic Approach (2013).

Five Muscles of Sacroiliac Stabilization – Part 1 – Piriformis

Even when the original reason for the sacroiliac stabilization is valid, often the human body overdoes it and tightens the musculature excessively and/or keeps it tight long after it needs to be, so the musculature becomes stuck in a chronic pattern of hypertonicity.

Posterolateral view of the lumbar spine

Bones of the Lumbar Spine and Pelvis

The low back is defined by the lumbar spine, composed of 5 vertebrae, named L1-L5. The pelvis is defined by the bones of the pelvic girdle.