The key principle behind the reformer is resistance.
The springs allow for changes in resistance, and by pushing or pulling with arms or legs you can then initiate movement of the carriage along the frame to get a full-body, strength-building workout.

The mind, when housed within a healthful body, possesses a glorious sense of power.– Joseph Pilates

Reformer pilates gives a full-body workout, which in turn improves power, strength, flexibility and efficiency Here are some of the many beautiful benefits:
Tones muscles: A full-body workout that can help develop a strong core and tone a variety of major muscle groups.
Builds strength: Springs increase the exercise resistance and intensity to build strength.
Increases flexibility: Along with improving muscle strength you also improve flexibility and joint mobility. Because most of the exercises incorporate dynamic stretching.
Improves posture: Support a strong core, promote flexibility and realign the body and spine, which can result in tremendous improvements in postural alignment.
Prevents injury: By focusing on posture, form and fixing muscle imbalances, the Pilates reformer can create greater balance and efficiency to help prevent injury in the future. Most importantly you create a mind-body-spiritual connection through movement and breath!