Excuse the crappy picture, I took these images on my own pull-up bar in my bedroom, and this was literally the best possible angle I could have gotten to show my hands.
Anyway, the one-armed pullup is a nigh-mythical exercise that even I can barely do.
The humble pullup is by far one of the best exercises one can do to develop the upper body-for not only does it develop the size and strength of the latissimus dorsi (the big pulling muscles of the back), it also utilizes the entirety of the upper body as assistance and/or stabilizers: the forearms, hands, biceps, triceps, shoulders, and the abdomen all get a bit of a workout, as do the small muscles that make up the “rotator cuff”.
Indeed, one might humorously say that the pullup, and all of its variations, are the oldest of all exercises due to the fact that it predates genus Homo-while I cannot say which species it was exactly, at some point our hirsute ancestors found it more advantageous to grasp around arboreal supports rather than claw into them, and claws were gradually superseded by flat nails. This necessitated climbing via pulling the body upwards and over the branch or tree limb-movements that are functionally identical to the modern day anterior-grip (palms-out) pull-up and the muscle-up.
I emphasize “all of its variations” because, like most exercises that are worth doing, there are numerous ways to do the same basic exercise, all of which emphasize one muscle or area or another. Just as there are numerous variations of bench press, squat, deadlift, and push-up, so too are there numerous types of pull-ups.
To clarify, this article will only deal with the traditional pull-up series-smooth, stable pulls that lift the chin over the bar, from wall pulls to the one-handed pull-up. This article will not deal with muscle-ups (which are essentially a pull-up crossed with a dip), towel hangs (which are a hellacious method of forearm training, but do not utilize any pulling motion at all), or the supine pull-up, also called the Australian pull-up…
Anyway, read it here