The human anatomy does not have a specific muscle called the psoas muscle, the psoas muscle is the general name for a series of muscles in the lower back, including a number of muscles. The more commonly mentioned muscles in the front include: psoas major, psoas minor, and iliacus. The psoas major muscle starts at the 12 thoracic – 5 lumbar vertebrae and ends at the trochanter, which plays the role of hip flexion; the psoas minor muscle starts at the 12 thoracic – 1 lumbar vertebrae and ends at the iliac pubic ramus, which plays the role of hip flexion; the iliacus muscle starts at the iliac wing and ends at the trochanter, which plays the role of hip flexion. The more commonly mentioned posterior muscles are the thoracolumbar fascia, the erector spinae, and the deep transverse spinous process group, including the multifidus, piriformis, interspinous, and intertransverse spinous process muscles, which are commonly referred to clinically as lumbar muscle strain, generally referring to strain of the transverse spinous process muscle group. In addition, there are many muscles of different sizes in the low back that work together to accomplish various fine movements of the low back.