It uses iron sand ball counterweight internally keeps it in the center to ensure the stability of the center of gravity of the energy pack, hard paper tube shaped in the middle to make sure long-term use of energy pack is not easy to deformation, the external cover a layer of EPE pearl cotton, both sides filled with high thickness EPE pearl cotton is fall-resistant to ensure effective protection of the body, the ground and the core of the product in doing a variety of training movements.