It is the dominant and most superficial muscle of the gluteal region. It is an extremely thick powerful muscle, innervated by the inferior gluteal nerve (L5 S1,2).
gluteus maximus has an extensive origin from the ilium behind the posterior gluteal line, the back of the sacrum and coccyx and the sacrotuberous ligament.
It has a minor insertion (via its deepest fibres) onto the gluteal tuberosity of the femur. Its main insertion is into the iliotibial tract (a thick band of deep fascia) which runs from the iliac crest to the lateral condyle of the tibia.
gluteus maximus is a powerful extensor of the hip joint. It is especially
useful in movements such as getting up out of a chair or climbing stairs,
when the muscle must raise the weight of the trunk - "forced extension".