The purpose of the rotations expander is unversal. It can be used as a pocket fitness tool or as a warm up tool. It works on the principal of the interplay between centrifugal force and mass inertia. The faster the disc is accelerated and slowed down again, the bigger the applied force is. This way the 150 kg heavy aluminium disc can produce forces of 10 kg or more on the handgrip. It has ash wood handles for an optimum hold.