Synergists: Brachioradialis, Biceps Brachii (especially the long head)
Holding a dumbbell in each hand, sit on the preacher bench.
With your elbows flexed, place the backs of your upper arms flat on the arm rest.
Supinate your wrists (i.e. rotate them so that your palms face you).
Keeping your wrists supinated, inhale as you lower the dumbbells until your elbows are almost fully extended.
Exhale as you curl the dumbbells back up toward your shoulders.
At the top of the movement, hold for a count of two and squeeze your biceps brachii.
Repeat for the prescribed number of repetitions.
Comments and tips
Keep your back straight and your body still; only your forearms should move.
Keep your elbows in line with your shoulders.
Adjust the seat to ensure that your upper arms lie flat on the padded surface, from your armpits to your elbows.
With the dumbbell preacher curl and all other preacher curl exercises, the long (outer) head of your biceps brachii is activated more than is the short (inner) head because, at the top of the repetition, the short head enters into active insufficiency (that is, it develops slack).