As the Flow-bag designed to be filled with water and air. The inner ball is a standard gym ball diameter 45 cm equipped with a filling hole, not a water valve as the Flow-Bag. The flow-ball is an ideal solution particularly suitable for functional training. Flow-Ball can be used either as a destabilizing training tool and as an unstable base. The flowing of water makes the ball highly destabilizing and forces the user to an intense work of balance and control that involves the whole body. We advise filling the WaterBall with a few liters of water (3 lt. for beginners, 5 lt. for intermediates, 8 lt. for advanced) for the performance of multi-planar and multidirectional exercises. FlowBall has 6 handles for hands and feet: 4 padded hand grips and 2 foot grips adjustable with Velcro placed on the same side.