Fascia · Lumbar spine

Thoracolumbar fascia

Fascia thoracolumbalis

A large diamond of dense connective tissue across the lower back. It matters because of what plugs into it: latissimus dorsi from the arm above, gluteus maximus from the leg below, and transversus abdominis and internal oblique from around the front. That makes it the crossroads where load travels between the upper body, the trunk and the legs — force from a pulling arm reaches the opposite leg through this sheet. It also wraps the erector spinae and multifidus in a stiff compartment, so when those muscles contract the fascia tightens and adds stability to the lumbar spine.