A key ingredient to become strong in an exercise (depending on the level of advancement) is build strength in various positions to get the full benefit of it such as various Push-Ups or in this case Pull-Ups. Some don't have the strength to even get an inch and just get stuck there. Now this isn't on the aspects of "Isolating" the muscles by doing a lot of movements for one specific exercise but by utilizing the power of Isometrics. We can build some incredible pulling strength using Isometric Exercises.
Do we have to get the chin over the bar in order to make the pull-up count? Yes and no depending on who you talk to. Some will say very much so and they're right, yet also, depending on a person's body type and the way their arms are, it's a matter of perspective. I have struggled myself getting the chin over the bar and have stopped right at the chin mark. I'm better at Chin-ups than regular Pull-ups which I know I can improve on using Isometrics as a progression tool to get stronger at them. I just never made it a priority until I decided to do so once the weather warms up.
The layers of positioning for Isometric Pull-ups can vary but the main areas are the dead hang, middle and at chin or over chin level. Steve Justa's Isometric Style was to do 8 layers or so of building strength for certain exercises like Squats, Push-ups, Arm Wrestling and other things. It worked for him as he was by far one of the most underrated Strongmen in history doing partials with weights most can't even fathom and had such arm and leg power through Isometrics that if you were to arm wrestle him or try to shove him, even a few inches would be a miracle since he was so damn solid even at his heaviest. This kind of protocol may not work for others because it can be time consuming with the amount of various Pull-Ups to work on.
Pulling movements help with the balancing of the musculature in order to be efficient in performing better. You can get away with Pushing stuff for so long before you start to have caved in chest. Push-Ups can do wonders but they won't give you that full "Wingspan" of a back. Isometrics for the back utilizing all sorts of directions can aid in building that Pull-Up Strength. It is possible for big guys to do Pull-ups, it's just harder in most cases and not always because they may be fat and all that, some muscleheads have awesome pulling strength but many can barely get over the middle part. Some guys can be over 300 lbs and get their chin over the bar which in itself is impressive and doesn't need to do a ton of reps to prove it.
You can do Aussie Pull-Up Isometrics, Angled Body Rows using Rings or Straps, working neutral grip, hands facing away, hands facing you, mixed grips, all can be done using Isometrics. When you strengthen those layers and practice moving, it builds strength in those weak points. Yielding & Overcoming Isometrics work well but personally I believe Overcoming can give you the best advantage. With Overcoming, you can stand on a stool or have a bar that can be adjusted to various heights without having to hang from it. I have a door hanging Pull-Up bar that I can just stand under and Pull from all sorts of grips and stand on a stool for the middle and upper portions.
The Yielding Isometrics can be trickier but doable because you're literally hanging and pulling up to a certain position, you can stop at certain points but you may not last long in that position. The best start is from the deadhang which is a great exercise on its own. You can make it an Overcoming by pulling up to a certain position and contract all the muscles in that position. I learned that from Ed Baran's Primate Power Course. Another idea is what's called a Hybrid Isometric where you get the best of both world's at the same time. A hybrid is when you fight gravity but also keeping position in a immoveable fashion. If you took a strap between the two poles of a pull-up apparatus and pull yourself up until the strap stops your feet and you can't go any further, that's a hell of a way to build strength right there. If you want to learn more about this, check out the book Overcoming Isometrics by Red Delta Project, there's an entire chapter showing and describing Hybrid Isometrics.
Although there's variety here, you're also getting an understanding of basic fundamentals on Isometric Training and how they can improve your movements using bits and pieces of strengthening the weak points. I'll be using this myself in my training and get better at doing pull-ups. If there's anyone who can teach you the true aspects of Pull-up Training it's Mike The Machine Bruce, a former Marine and Submission Wrestling Champion who's got not only the world's strongest neck but has a back that looks like it was carved from granite with a ripped to shreds physique. The other is Matt Schifferle of Red Delta Project who's incredible knowledge with DIY equipment and Strength Building Training personifies the modern day Physical Culturist that can help you fill in gaps in your arsenal and shoot them into the stratosphere using simplistic and low-skilled strength and conditioning exercises.
Get stronger in whatever it is you want to do and make the most of what's possible and suitable to your needs and goals. Pull your weight and keep being amazingly awesome.
BTW if you click on the link where it says Rings, you can get a cool 10% Discount when you punch in the code POWERANDMIGHT at checkout. My gift to you.