Muscle · Lumbar spine

Psoas major

Musculus psoas major

The only muscle that connects the spine directly to the leg. Psoas major starts on every lumbar vertebra — bodies, discs and transverse processes, from T12 down to L5 — runs forward over the brim of the pelvis, and ends on a small knob on the inner thigh bone. That path makes it two things at once: the strongest hip flexor you have, and a muscle with a grip on each lumbar segment, which is why the founder's document gives it both hip flexion AND lumbar stabilization. It is also the muscle that shortens when you sit, and it sits at the top of Momentum's tight list: the low back pain flow begins by releasing the hip flexors, and hip pain is attributed to tight hip flexors with weak stabilizers. Deep, powerful, and surrounded by structures worth respecting — which is what makes it the most clinically loaded muscle in this region.