Abstract: A method of exercise or manipulative therapy is disclosed. The method includes obtaining a first mass of putty, introducing an additive to the first mass of putty, and physically manipulating the first mass with the additive in order to create a combined mass. The combined mass exhibits a noticeable change in stiffness relative to the first mass, yet retains substantially the same weight and color of the first mass. Additionally disclosed is a kit for providing manipulative therapy of varying difficulty to a user. The kit includes a first mass of putty and an additive, which is initially separate from the first mass. If the additive is combined with the first mass, a combined mass is created. The combined mass exhibits a noticeable change in stiffness relative to the first mass, yet retains substantially the same weight and color of the first mass.