PurAthletics Air Balance Disc. The PurAthletics Balance Disc prevents back discomfort, relieves stress on the spine. Promotes "active sitting". Helps with spinal alignment, improving posture. Increases intensity when stretching or doing lunges. Use the Balance Disc while standing, kneeling or sitting. Improves balance & strengthens the core. Includes Hand Pump & Free downloadable Instructional Sheet, & DVD at zenathletics.com