I agree the bicep either contracts or it doesn't, which leads to overall growth. BTW I don't read the BB mags bc most are full of useless information, but a couple of class in exercise physiology does help. OK, maybe you can't isolate your lower bicep, but your bicep is made up of at least two different heads How many times have you heard of someone doing a particular exercise to increase the peak of their bicep, making their thigh sweep greater, making their lats wider, working their upper or lower chest, working the front of their calves or the rear, or working the long head of the bicep. If you can make your thigh sweep greater by doing squats or leg presses with your feet closer together then you can work the lower part of the bicep more than the overall muscle. Each muscle group is made up of different sections and you can work them in isolation, it will still require the entire muscle to contract but that particular area will receive most of the work. Just like working forearms, you can work different sections of the forearm and if think you can't I won't post another reply to try to disprove your theary, I'll just have better developed bis, tris and forearms.