What is the primary action of the gluteus maximus?

• A. Hip adduction
• B. Hip flexion
• C. Hip internal rotation
• D. Hip extension and external rotation

Answer: (D)

The primary action of the gluteus maximus is hip extension with external rotation. Its fibers run from the posterior pelvis to the femur and, when it contracts, they pull the thigh backward, extending the hip—especially when the hip is already flexed, such as standing up from a chair or climbing stairs. At the same time, the muscle’s orientation supports rotating the thigh outward, contributing to external rotation. That combination is why it’s the main function.

Hip adduction, flexion, and internal rotation are not the primary roles of this muscle. Adduction is mainly handled by the adductor group, flexion by hip flexors like the iliopsoas, and internal rotation by other rotators such as gluteus medius/minimus.