If you look closer at the Cadillac you will find the wooden bar that is attached half way up at the vertical poles: the push through bar! It has a square shape and you can attach springs from the top or bottom of the Cadillac. On this picture you can see the spring attached from the top, which means that there is resistance when you press down. The lower you press the more resistance is created. In this exercise you are kneeling with one arm on the push through bar and one arm reaching up by your head. Then as you press down and exhale you stretch to the side opening up your side ribs and lengthening your waist and strengthening the oposite side that contracts. Joseph Pilates always had in mind the importance of stretching using resistance at the same time to correct posture and create balance in our muscles. And it feels so great!