The FLEX ARMS uses clinically demonstrated EMS technology. Using EMS, you FLEX ARMS sends a signal to the nerves in the arms via the Gel Pads, which in turn causes the biceps and triceps muscles to contract and relax, rhythmically. The result over time are firmer, stronger and more toned upper arms. Requires the FLEX BELT CONTROLLER which is sold seperately. Accessory Pack includes FLEX ARMS garments, 4 medical-grade Gel Pads, Carry Pouch and Instruction Manual.