Our Yuck-E-Medicine Balls are filled with smoothly rounded polymer balls, free-floating in a non-toxic sea of gel. This creates a perfectly weighted ball that form fits to the curves of the human body. As gravity begins to pull on the internal balls, their rolling causes the medicine ball to roll across and down the body in a tractor-like movement that both stimulates and massages the body. Additionally, the balls can form fit to the user's hand, turning them into comfortable handles for holding and lifting. Also makes a great tool for increasing proprioceptive input into the joints.