MD-2011 Octagon Plastic Dumbbell Style:1,2,3,4,5kgs Material:sand inside,plastic outsideDumbbell exercises form an intergral part of most strength training programs.They can be used to develop the various different elements of strength.Such as maximal stength,hypertrophy or muscle mass,explosive power and strength endurance.To know more details about dumbbell,pls feel free to contact with us.