When I achieved my first sternum chinup (2005-03-04), I could do:
- about 15 "perfect" deadhang pullups (chin over bar)
- 30 kipping chinups (with very bad form at end)
- 5 weighted pullups with 15kg sand in rucksack
(These are the "feats" I recorded at about that time. I don't know about rowing, I don't do this. Bodyweight was about 69kg.)
Given my rapid progress since then, I think sternum pullups and chinups are more about "skill" (or doing it right) then about pure strength.
You have to "arch" your back (pull shoulder blades together) strongly at the top to get your chest to the bar, and you need to do this at the right moment to make the chest hit the bar.
What really helped me achieve the first sternum pullup (sternum chinups are comparatively easy for me, as stated in my question) was to focus on the "arching" movement, performing it "dry" with a broomstick. After I practised that a few times, voila, I hit the bar.
I am now doing about 10 sternum chinups several times a day to GTG and get used to the ROM and arching. The sternum pullups will hopefully come along. After reading through the material cited above, I currently am inclined to focus more on increasing the numbers on my "good" sternum chinups than to waste time and motivation by focusing on correcting my "bad" sternum pullups. I hope I am being smart here, and not "wimping out".
Any thoughts on this?