This is a more advanced exercise which is performed on the Reformer in this video. The purpose of this is to strengthen the abdominals, hamstrings, gluteus maximus, it increases the spinal flexibility, as well as hamstring flexibility and improves spinal alignment. This exercise should be taught by a certified instructor.
As always consult your doctor before embarking on an exercise program.
Something Extra: Breakfasts that Fight Fat Spring 2011 Running Shoe Guide
Have a great weekend.