The resistance of the reformer means you'll get results from your workouts faster. The tension of the springs on the moving carriage adjust to different levels of difficulty. As you become stronger and more proficient with the reformer, you progress from reclined exercises to ones that put less of your body surface on the carriage, meaning you need to use more of your own strength and coordination to execute the moves. You may even notice greater definition in your arms, legs and abs after just a few months of consistent work on the reformer.