An exercise ball is a ball constructed of soft elastic, typically in 5 diameters of 10-centimeter increments, from 35 centimeters (14 inches) to 85 centimeters (34 inches), and filled with air. The air pressure is changed by removing a valve stem and either filling with air or letting the ball deflate. It is most often used in physical therapy, athletic training and exercise. It can also be used for weight training.
The ball is also known by various other names, for instance: balance ball, birth ball, body ball, fitness ball, gym ball, gymnastic ball, physio ball, pilates ball, Pezzi ball, stability ball, Swedish ball, Swiss ball, therapy ball, or yoga ball.