Synergists: Biceps Brachii (long or outer head), Brachioradialis
Sit on the preacher bench with a dumbbell in your hand.
Supinate your forearm (turn your palm upward), bend your elbow so that the dumbbell faces your shoulder, and rest your upper arm flat on the bench.
Inhale as you lower the dumbbell until your arm is almost fully extended.
Exhale as you curl the dumbbell to the starting position.
Repeat for the desired number of repetitions.
Repeat with your opposite arm.
Comments and tips
Keep the whole of your upper arm, from elbow to armpit, flat on the bench.
Adjust the seat for comfort and leverage.
If you don’t have access to a preacher bench, use the head of an inclined bench.
The dumbbell preacher curl targets your brachialis, not your biceps. When it comes to arm curls, if your elbow is by your side or behind you and you use a supinated (underhand) grip (e.g. incline dumbbell curl), you target your biceps, while your brachialis and brachioradialis act as synergists. If your elbow is in front of you and you use a supinated grip (e.g. dumbbell preacher curl and concentration curl), you target your brachialis, while your biceps and brachioradialis act as synergists. If your elbow is by your side, behind you, or in front of you and you use a hammer grip or a reverse grip (e.g. hammer curl and reverse curl), you target your brachioradialis, while your biceps and brachialis act as synergists.
Building your brachialis makes your upper arm look bigger because it lies between your triceps and biceps, which it pushes apart. Part of your brachialis also sits under your biceps, which it props up, giving you a bigger biceps peak.