Two Curls in One
The Zottman Curl is a time-tested biceps builder. (George Zottman was a 19th century strongman known for his incredible arm strength [he could clean and press a 175-pound dumbbell while sitting in a chair]. The curl variation that bears his name can raise the caliber of your guns, as it combines a conventional cur movement with a reverse curl for one all-encompassing biceps and forearm blast.
How To Do It:
Hold a dumbbell in each hand and, keeping your elbows at your sides, curl the weights up as normal. At the top, rotate your palms 180 degrees to face downward, and then slowly lower the weights back to the starting position.
Because you are limited by how much weight you can reverse curl (which will always be less than what you can lift with your palms facing up), you will need to use a fairly light weight, but the overall muscle activation you will get will make up for it. The Zottman curl creates incredible tension in your biceps, brachialis (the muscle between your biceps and triceps), and brachioradialis (your main forearm muscle), leading to faster muscle growth.