I want to really hit my abs and be able to do those "castro's" properly. (watch his workout, it's awesome.)
I'm also trying to get more comfortable on the bar, holding my own weight for extended periods, etc.
It's difficult because of my long arms but that in itself is an advantage. I just need to keep the right intensity.
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Also on the pull up bar, I'm trying to really isolate my serratus anterior. I'm not really comfortable lifting weights over my head, so I don't do dumbbell pullovers. (I don't even like doing skull crushers.)