What follows is an assistance exercise for chin-ups.
It involves overloading the body by doing a top hold and a negative.
Attached is a 60 kg kettlebell (132 lbs.).
The weak point in pullups and chin-ups tends to be the top range of motion in many. This is because the arms and lats have a bit less leverage here.
That’s why you’ll see people not able to get their chin over the bar (and chicken necking to try to do so). This occurs in repping them out, or especially with weighted pullups.
And the above exercise is just one option for strengthening this weak link.