Static Arm Bicep Curls
A good variation on the dumbbell curl is the Static Curl. This is a great move to incorporate when you are trying to breakthrough a plateau or just to change up your routine. The static curl works exceptionally well because it forces your bicep to work at the toughest part of the curl–when your arm is parallel to the floor or 90 degrees with your body.
Begin with a dumbbell in each hand, in position to begin normal curls (elbows at your sides and forearms parallel to the floor). Leave one arm static (or in parallel position) and curl up with the other arm 4 times. Then leave that arm static and curl up with the other arm 4 times. Your static arm will be contracted, tense, and working hard the entire time your other arm is curling.
Do a total of 16 reps before resting (that would be 8 on each arm, 4 at a time). Rest for 1 minute and begin again. The goal is to complete 3 sets of this. Pick a weight that allows you to complete all 16 reps, you should be fatiguing around rep 8 so that the last 8 are really hard.
Oraclefitness.com posted this video on youtube that will show you exactly how this move is performed.