Start: A preacher bench shifts the angle so the first part of the curl is harder and the last part is easier. Some believe this helps the biceps grow longer, but we disagree. However, this exercise does help your biceps get bigger and stronger. Gravity works against your biceps in the first few inches of this movement, a very different effect from a standard curl. Here's how to do this exercise: Grab a barbell or EZ-curl bar with a shoulder-width, underhand grip, and position yourself on the preacher bench so the top of the pad almost touches your armpits. Start with your upper arms against the pads and your elbows slightly bent.
Finish: Keep your back straight as you curl the weight up until your forearms are just short of perpendicular to the floor. Return to the starting position.
Shift the emphasis to your brachialis and forearms with an overhand grip. Don't try this with a straight barbell; its too tough on your wrist.