Back balls look like two balls, a little smaller than tennis balls, joined together. They are used to mobilize or increase movement in the spinal joints of the upper back, which often become stiff. The gap between the balls is large enough for the bony back bones to sit in so that pressure is only placed on the joints and not on the bones. They can be used whilst sitting or standing but are best used when lying on them. The first uses can sometimes be uncomfortable, but after getting used to them they do not cause any discomfort and are great to get the upper back joints moving better. They help to improve posture and shoulder range of movement when used on a daily basis.