What muscles or muscle groups are targeted by these different variations of pull-ups: 1.) standard (overhanded), 2.) chin-ups (underhanded), and 3.) the neutral or parallel close grip pull-out (thumb is nearest the body - can done in an equipment similar to the 'Iron Gym')? What are the differences in the muscles these pull-up variations target?
Illustrations of the neutral or parallel close grip pull-out:
I also would specifically like to know if the modified chin-up as illustrated above, target different muscles compared to a standard pull-up or a standard chin-up? Or does it target similar muscles to one of the two?
Context and reason for question: I would like to know which pull-up variation targets which muscles, so I could use that variation in my workouts and try to focus on a certain muscle. E.g. If my biceps need work (which I do), then I could choose an optimal pull-up variation to use.
I'm also interested in learning what muscles the neutral or parallel close grip pull-up targets (I don't get good results on either Wikipedia or Google), as it is a pull-up variation that can be done in the equipment I use (similar to the 'Iron Gym' equipment).