Appropriately Sized for School Age Children. The BOSU® Balance Trainer is a versatile piece of equipment that is ideal for static and dynamic balance training. It can also be used to integrate balance challenges into cardiovascular, muscular strength and endurance, core and flexibility training. The BOSU® can be used with the platform side either up or down to challenge balance using different body positions; hence the name BOSU® (BOth Sides Up). The Bosu® Sport 50 cm Balance trainer is a smaller version of the original 65 cm Bosu Trainer above. Features the same highly functional rim and base style as the original. The sleek, compact design allows for easy transportation and storage. The smaller size is recommended for use by lower elementary age children all the way through Jr. High School. Blue. Includes 1 BOSU® Sport 50 cm Balance Trainer.