The  Reformer  is a sliding, bed-like platform anchored at one end of its frame with various resistance springs. The platform moves along a track by either pulling on ropes or pushing away from a stationary bar. The challenge of doing exercises on the Reformer comes from the resistance springs (sometimes lighter springs making the exercises much harder, other times heavier spring loads making it more challenging) while maintaining core and hip stability and in more advanced exercises the challenge is maintaining balance on a moving surface.

You begin by lying face up on a sliding carriage. After precise positioning by your trainer, you begin to move the carriage in and out with your feet pressing into a foot bar. But you're not doing the equivalent of "leg presses" in a weight room. Your trainer is telling you to maintain a neutral spine and pelvis, and to feel the movement originate from your deep, core muscles. You are reminded not to “fire” your quads, hip flexors, and knees, for these, after all, are the most over-worked areas of your body! Your trainer tells you how to work from the back of your legs (hamstrings) and to use the hip in a way that absorbs some of the stress from the knee. Then just when you think you've begun to get the hang of it, your trainer removes the stability of the foot bar! Now, your feet are in the loops at the end of leather straps, and you must maintain the same actions, only recruiting stability and control from deep within your core. Adding challenging movements such as stradles, and circles, and scissor movements.  All of a sudden you are losing the medial stability of your heels pressed together. Your workout gets increasingly challenging, and at this point, you are still "warming up."

Beautiful AMY CARLIN demonstrates another Pilates machine  called the Cadillac.  This machine consists of a padded platform with a cage-like frame above it. From this frame various bars or straps are attached by springs.