If your bending over somewhat from the waist, the shoulder girdle influence is reduced quite a bit. A prime example would be the DB concentration curl. Or even cable curls for that matter (can also try overhead cable curls for reduction of shoulder influence). With concentration curls the elbow/tricep is dug into the supporting knee/inner thigh. Even leaning back, like when doing Incline curls, reduces the influences of the shoulders. Most any standing curling exercises will recruit the shoulder girdle for extra support when doing the actual curling arc. In any event, no one is going to completely isolate the biceps. Even the pec's, back and triceps (to a lesser degree) are brought into play when curling. If you were to numb those supporting muscle groups, no or little curling action would be possible. Any muscle area acts as a unit, never by it's self.
Probably the Scott/Gironda stand/bench and overhead cable curls (with a training Bud pressing/holding the elbow in a straight up position) would be the best attempt when the focus is on the biceps. And wanting to take the shoulder girdle out of the element. Also the flat bench curl, sitting on the end of a bench and resting the elbows against that edge while curling (use a towel or pad for the elbows). Another seldom seem one is to lay flat on a bench and curl a pair of DB's from that position. I've suggested elbows dug into the ab's while curling for quite a while now, but for best results a close grip seems to work the best. But help your self to what ever grip suits you the best. Can be very effective as can leaning against a wall with the elbows touching that wall. Also done with the back against a sturdy post. Takes the need for a Arm Blaster away (just my view..whatever; the AB is another hyped piece of equipment but if it works for you than so much the better).
If you wish to include the TUT (Time Under Tension) method with any curling than try the one and one half system. Or the 2/3's ROM rep scheme as mentioned in another thread. Twenty one's are also effected. In any event, dozens of ways to work the biceps for proper results. Good luck..
