Which of the following exercises is not suitable for performance at the Springboard?

The Swan exercise is generally not performed on the Springboard because it requires a different setup than what the Springboard provides. In Pilates, the Swan typically emphasizes spinal extension and is best executed on a mat or a reformer where the body can leverage its full range of motion without the constraints of a spring system. The Springboard is designed for exercises that utilize the springs to aid in resistance training and spinal articulation in a controlled manner.

Leg Circles, Pull Up, and Tree are exercises that align more closely with the capabilities of the Springboard, allowing for effective use of its springs to help in executing movements that require stability and strength. The Springboard supports the resistance needed for these movements while still allowing for proper form and alignment. Thus, the Swan is the exercise that does not fit appropriately within this specific apparatus.