Book Recommendation: Loaded Guns
So I just got back from training a client at Lake Merced in San Francisco, and lo and behold, we ran into a crap load of other trainers with their clientele. Never ran into other trainers there before, but for some reason today, it's like every trainer in the city decided to do outdoor training at Lake Merced AND occupy the pull-up bars.
It's good though, because people should learn how to do real pull-ups and not those exercise machines of denial and self-delusion that assist you in doing pull-ups.
If you can whip out 15 full range pull-ups (not chin-ups, which are underhanded) without jerking your body up, then you should consider harder pull-up variations. There are 12 variations you can use to make things more interesting. If you train in these variations, then you're heading into more elite athleticism, one that is closer to gymnastics. And we know how strong, explosive and built gymnasts are.
One variation that is extremely difficult is the pull-up with scapula retractions. There is no use in describing it to you, so it's really best to recommend the only video/book that features it: Larry Scott's Hidden Secrets video and Larry Scott's book Loaded Guns.
You may find Loaded Guns on Amazon, but I don't think "Hidden Secrets" is being sold anymore. That video showcases a mix of conventional and unconventional exercises, all which are meant for the hardcore bodybuilder. Although the look of the video is a little dated now, the exercises are pretty damn awesome. The pump you will get in certain exercises is phenomenal.