I had trouble with the outer biceps for a while to. While Hammer curls are great, I also suggest doing your barbell curls/preacher curls with a closer grip. Switch it up by doing preacher curls one arm at a time as well.
Also, if you do incline dumbbell curls, have your arms facing away from each other. By that I mean, do curls with your inner arms sticking out in front of you. Sort of like if you were doing curls with cable crossovers, except don't lift your shoulders up. Your elbows should still be at your sides.
Lastly, if you do concentration curls, rest your elbow much closer to your inner thigh and only let the end of the dumbbell touch your chest instead of your shoulders when you reach the top of the movement.
Specific muscle training is tricky because you really need to concentrate on the muscles being worked (serratus anterior are a good example of this). I've also noticed recently (although this is a no-brainer) that bodyfat percentage plays a big part too. |