From a distance, the balls for the ball run look like large exercise balls – the ones some people sit at their desks with to relieve their spinal discs – but up close they are something else entirely. Namely more spheres than balls, made of a solid plastic material, and quite heavy; Balancing them back onto their shelves at the end of the training session is not that easy for an individual. Sphere – like a unicycle or tightrope, this is primarily something that involves balance. You have to keep taking small steps to keep from falling.