Believe it or not, the biceps were meant for more than just flexing and doing endless sets of curls. The biceps are incredibly strong and functional pulling muscles and should be trained accordingly.
Unfortunately, most lifters believe the only way to get big arms is to perform every curl variation known to man. Not true. Ever seen the arms of elite male gymnasts? They're huge, and they do very little, if any, direct arm work. So how do they get big biceps? They do a TON of straight-arm work.
If you want to fully develop your biceps and take your strength to the next level, start with these three straight-arm biceps variations:
Using two red mini-bands and preferably two gymnastic rings, loop the bands around the rings and then around an anchor point, like a pull-up bar. Then crisscross the bands, protract your shoulders, and perform flyes with your arms perfectly straight. You'll feel a tremendous amount of tension, especially in the lower biceps near the insertion point.
This is one of my favorite straight-arm exercises. You can get an awesome pump and easily adjust the resistance simply by walking your body forward or back.
This one requires two light-to-medium weight dumbbells and an incline bench. Position yourself high on the bench and protract the shoulders. Lock out the elbows completely to keep all the tension on the biceps. Emphasize a range of motion that keeps maximal tension on the biceps throughout the entirety of the rep. Flye the dumbbells together at the top.
Here's a more advanced variation. Due to the unstable nature of the rings, first, make sure you have the requisite strength to hold a ring support hold for at least 20-30 seconds with proper technique before trying external rotations.
As you externally rotate the rings, you'll feel a tremendous amount of tension on your lower biceps and brachialis muscles. It's an amazingly simple and effective exercise to really strengthen your biceps.