A large inflatable ball for gym work, also known as physioball or Swiss ball.
Writings – Articles
‘Have a ball!’ by Cathy Pollock on using a gym ball in Alexander Technique lessons, with five different activities.[1]
‘The Alexander Technique and the exercise ball’ by Posie Robins Roth contains activities for using a gym ball in an Alexander Technique class.[2]
Books
Roy Palmer, in his book, Zone Mind, Zone Body, uses an exercise ball for the purpose of staying balanced while sitting on the ball.[3]
Master the Art of Working Out by Malcolm Balk, Andrew Shields contains a section on working with an exercise ball.[4]