Hi Vroom,
Another exercise that I have been performing in order to work up to one-arm chin ups is to start from a one arm dead hang and then pull yourself up as high as you can. Then hold that position for 3 seconds (minimum). In time you will be able to pull yourself higher and higher until you are finally able to achieve the full range of motion.
I actually got the idea to do this method from advice that Coach Sommer gave on working on a straddle press to handstand. The method seemed applicable to a one arm, so I’ve been giving it a shot. So far my range of motion has indeed improved. I’m past the half way mark with my right arm and just about half way with my left.
I also perform negatives (trying to stop myself as high as possible during the descent) on the days I don’t perform the above exercise.
I would also go along with suggesting that you stay away from the lat pull down machine (or even the assisted pull up machine, which is honestly a closer approximation to the movement involved in a one arm). I tried working in that manner for a while, and while I did improve, it didn’t help me in my attempts to do a unassisted one arm.
What you need to do is to teach your muscles to exert greater amounts of force, not to teach them how to exert lesser amounts more times. Sure, the second method will build muscle, and may improve the amount of total weight you’re moving, but it won’t necessarily help you to be able to move your bodyweight more efficiently.
Good training,
Sentoguy