Position yourself with your chest against a bench, your triceps resting on the bench, your arms shoulder width apart and bent, and your hands grasping a bar with an underhand grip. Slowly straighten your arms, lowering the bar, until your arms are fully extended. This is the starting position. In a controlled manner, curl the weight up and then lower it again to full extension. Resist the weight on the way down. Preacher curls can be done either sitting or standing. For variety, use dumbbells for this exercise. Avoid curling the weight up too high and pulling the elbows up too high on the pad.