Which muscle tilts the pelvis posteriorly?

• A. Semimembranosus
• B. Vastus Intermedius
• C. Gluteus Maximus Lower Fibers
• D. Adductor Magnus

Answer: (A)

Posterior tilt of the pelvis comes from hip extension. Muscles that cross the hip and extend the thigh pull the pelvis backward. The semimembranosus is one of the hamstrings crossing the hip and knee; when it contracts, it extends the hip, which rotates the pelvis into a posterior tilt. Because it acts directly on hip extension, it is the most straightforward mover for tilting the pelvis backward.

The vastus intermedius doesn’t cross the hip, only the knee, so it doesn’t affect pelvic tilt. Adductor magnus mainly adducts the thigh (with a hamstring part that can extend, but it’s not the primary driver of posterior tilt). Gluteus maximus lower fibers do extend the hip and can contribute to posterior tilt, but semimembranosus provides the clearest, direct action for tilting the pelvis backward.