The one arm dumbbell preacher curl is a good exercise for isolating the biceps and making them work independently. Adjust the height of the seat on the preacher bench so that when you sit on it, the back of your upper arms sitcomfortably flat on the padding.

Grab a dumbbell with your left hand and sit on the preacher bench.

The back of your left arm should be rest flat on the padding with your arm fully extended.

Place your right forearm on the padding for support.

Execute the exercise by slowly raising the dumbbell up and squeezing the bicep at the top of the movement.

Slowly lower the dumbbell until your arm is fully extended.

Repeat for desired reps, and then repeat thesame for the right arm.

Exercise Tips:

As a general rule, always hit the weakest arm first. In most cases this is the left arm.

Keep the rep timing slow, and control the weight on the way down.

Focus on only moving your forearm.