Pilates is a physical fitness system that was developed in the early 20th century to strengthen, stretch and stabilise key muscles. Pilates instructors encourage their clients to use correct alignment, centring, concentration, control, precision, breathing and flowing movement to build strength, flexibility and lean muscle tone. Emphasis in Pilates is on lengthening the body and aligning the spine, rather than on bulking and shortening the muscles. Pilates either takes place on a mat, with a barre, or with the use of a reformer -- a machine which provides resistance to lift against. Practitioners believe that mental and physical health are essential to one another and use this method of total body conditioning to achieve this balance.