As the name remarks it is a circle or two circles linked (it depends on the school and license) because every Pilate’s school has its own magic circle, it has sometime different parts to place your elbows, arms or hips.
It is an exercise that Joseph Hubertus Pilates invented for pregnant women who wanted to keep working out and specially performance Pilates’ exercises to keep in a good shape. Be able to work out standing up or lying down on the floor made easier the practice of Pilates exercises for pregnant women.
I must warn you, although you can read about it in the chapter about questions and answers, the Pilates Method is not adequate for pregnant women, just only for those who are experts and their teachers or trainers knows about the pregnancy!
