-Perform a traditional dumbbell biceps curl, pausing at the top of the motion.

-Twist your hands until your palms are facing away from your shoulders (in reverse curl position).  Basically, twist your right wrist inwards to the left, and vice versa.

-In a slow, controlled movement, lower the Dbells with your palms facing the ground.  At the bottom of the motion, twist your wrists back into the traditional curl grip (palms facing up, towards shoulder).

-That is 1 rep

The diagram shows the most used muscles on this exercise