This is a statue of Hercules battling the two-headed dog of the underworld, cerberus. It is yet another demonstration of Hercules using his super human strength to defeat a mythical monster. One monster, versus one super human, no tools involved.
The obturator internus may help to change the shape of the pelvis, pulling the sitting bones away from sacrum and adding tension to the sacrotuberous ligament. This then gives fibers of the gluteus maximus a firm foundation from which to act.