Psoas muscle - Definition

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The psoas major is the muscle that extends from each side of the lumbar vertebra at the base of the back to the inside of the thigh near the groin. It inserts via a tendon on a small tuberosity of the upper section of the femur, called the lesser trochanter, which is the tendon shared with the iliacus muscle, sometimes called the iliopsoas muscle. The psoas major has the same functions as the iliacus muscle in flexing and laterally rotating the thigh, but also controls the movements of the torso when seated. It is worth noting that there is a minor psoas muscle, which is not present in all individuals as around one in three do not have one.