If you were to rotate your right leg to the left, then your femur would go through REAL internal rotation and would also be internally rotated RELATIVE to the Pelvis. However, if you were to keep your right leg planted and rotate your Pelvis to the left, your femur would have gone through no REAL motion but would still be internally rotated RELATIVE to the pelvis. Watch below as Dr. David Tiberio expresses this concept in greater detail.