As you descend into a squat, the adductor magnus prevents your knees from caving inward (valgus collapse). It keeps the femur in a neutral alignment relative to the pelvis.

The sumo stance is the king of AM training. By taking a wide stance with your toes turned out, the adductor magnus is placed under a massive stretch at the bottom of the lift. Driving the floor apart and extending the hips recruits the AM like no other exercise.