Which exercise is NOT commonly associated with trunk stabilization on the Cadillac?

The hamstring curl is not commonly associated with trunk stabilization on the Cadillac because it primarily focuses on isolating the hamstring muscles in the back of the thigh. This exercise typically involves bending the knee and bringing the heel towards the glutes, emphasizing the lower body rather than the stabilization of the core or trunk.

In contrast, the other listed exercises serve to engage and stabilize the trunk. The chest expansion in a standing position emphasizes the upper body while ensuring that the core is engaged to maintain stability. The cat stretch involves flexion and extension of the spine, which necessitates trunk engagement to control movement. Arm circles while standing also call for core stabilization to maintain posture and prevent excessive movement in the lower back, ensuring the trunk remains stable. This focus on trunk engagement is essential in Pilates to promote strength and control in the body's center.