The decline dumbbell curl changes the angle of attack and therefore the way in which your bicep muscles are challenged. You will need to lie chest down on a bench set at a 45° angle to begin this exercise. Holding a dumbbell in each hand, fully extend the arms (letting them hang down) and then simply bending the elbows bring the dumbbells up as close to your shoulders as you can. Hold at the top for a few seconds then slowly return to the starting position and repeat. Extend the number of repetitions the more comfortable the exercise becomes.