An arm blaster is a harness with a metal plate. The harness slides over your neck, allowing you to lock your arms into the grooved sections of each side of the arm blaster’s metal plate.
The arm blasters primary purpose is to ensure greater isolation on the biceps when performing different variations of bicep curls e.g. EZ curls and dumbbell curls. This isolation is achieved due to the grooved sections of the arm blaster holding your elbows in place. When performing a traditional bicep curl without an arm blaster when your form begins to deteriorate the natural thing to do is to begin to use momentum and swing backwards with your elbows to muscle the weight up. The arm blaster holds your elbows firmly in place, forcing your biceps to work harder to curl the weight up as they no longer have any assistance.