The adjustable incline bench introduces variation to the standard dumbbell biceps curl and changes the angle of attack on the biceps. Take the incline bench from a full 90-degree angle and drop it one or two notches down.
When you sit back down, the key here is to again keep your shoulders back and against the bench to isolate the biceps. As you fatigue, you may feel the body’s tendency to lean forward and utilize the chest and front delts, but this isn’t an exercise for those muscles, folks. Retract your shoulder blades and pin those elbows to your sides as you perform this exercise to work the intended muscle.
Additionally, most people may do a hammer curl, but standard biceps curl and get a better contraction from this angle on the bench.