Holding a dumbbell in one hand, kneel by the side of a flat bench.
Turn your palm downward (pronate your wrist) and place your forearm flat on the bench, with your wrist and the dumbbell extending off the edge.
Exhale as you raise the dumbbell by extending your wrist.
Hold for a count of two.
Inhale as you slowly lower the dumbbell to the starting position by flexing your wrist.
Repeat for the prescribed number of repetitions.
Repeat the exercise with your opposite arm.
Comments and tips
You can of course do both arms at the same time.
You can use the dumbbell one-arm reverse wrist curl to build mass in your forearms. However, as with all wrist-curling exercises, do not go very heavy. Your wrists are not designed to curl very heavy weights.