Kneel down on one knee behind an incline bench and place your same-side arm on the bench. Grab a hold of the dumbbell "hammer" style and hold it up in a vertical position in front of your face. This is your starting position.
Lower the dumbbell down until it almost touches the bench and then raise it back up until your forearm is almost vertical. Then do the same with the other side. You should always keep tension in your biceps. Repeat entire movement for the desired or prescribed number of repetitions.
Perform this exercise in a smooth and fluid motion
Keep constant tension in your biceps throughout the entire movement
Don't extended your arm completely on the downward portion of the movement
SPECIAL NOTES & LEVEL of DIFFICULTY VARIATIONS
To increase the level of difficulty, slow down the movement or use a heavier dumbbell.
The key to this exercise is the incline. This slight change in the angle is what targets your lower head and gives you a fuller and more elongated look to your biceps. You may need to do a few practice reps with a light dumbbell just to get a feel for the mechanics of this exercise - we certainly recommend doing this if you are a beginner.
Another thing to point out is that you don't have to do this exercise on your knee; you can do it standing up as long as you find an adjustable bench that is higher and has a longer backrest pad. You can even do a modified version of this exercise on a high preacher bench or a free-standing preacher stand (well-equipped gyms will usually have this one).