Psoas major muscle

The psoas major muscle is a muscle of the abdomen that connects the spinal column in the lower back to the femur (the bone of the upper leg). When contracted, it flexes and lateral|laterally rotates the hip. The psoas major is one of the primary movers in walking and running in people with good posture. It is one of the major components of what is known as the 'core' muscles.

Origin
The psoas major originates at many points in the low back: the transverse processes of the first through fifth lumbar vertebrae, the bodies of the twelfth thoracic vertebra and the first through fifth lumbar vertebrae and the intervertebral discs between them.

Insertion
The psoas major inserts on the femur, at the middle surface of the lesser trochanter.

Innervation
The psoas major is innervated by the anterior primary rami of L1 and L2.