The dumbbell preacher curl is a good exercise for isolating the biceps and making them work independently. Grab a set of dumbbells and sit on the preacher bench.

The back of your upper arms should be flat on the padding. If they're not flat, adjust the seat down.

Keeping your eyes facing forward, slowly lower the dumbbell down until your arms are fully outstretched.

Pause, then curl the dumbbells back up to the starting position.

Repeat for desired reps.

Preacher Curl Tips:

Keep the movement slow and controlled.

Do not pause at the top of the movement, as this allows your biceps to rest.

Use a full range of motion by lowering the dumbbells until your arms are fully extended.