Fat Gripz ProFat Gripz work by instantly convert barbells, dumbbells, chin up bars and exercise machines handles into THICK BARS. Thick Bars (and Fat Gripz) work for many reasons including: Increased muscle activation thicker handles stimulate much more muscle activation in the hands, forearms and biceps. This increased muscle activation leads to greater muscle and strength gains especially in the arms. "Unlocking" muscle gains thick bars make your hands, fingers