... 1, raw materials: the main material is cast iron, and some outsourcing is a layer of rubber. ... the iron bar, both ends of the solid ball, because practicing without sound, named dumbbell. Light-weight dumbbells ... = 0.4536 kilograms) and so on. The weight of heavy dumbbells 10,15,20,25,30 kg ... can traine a single muscle; such as increased weight, you need the coordination of multiple muscles, but ...