Originally Posted by George Mounce
Whats the goal? Stabilizing the mid-line while doing a chin-up is all about ankle weights, but doesn't add much to the total weight of the pull-up (at least I don't think people could add even close as much as the other methods). The other two don't accomplish much more then add weight to a chin-up, and require the normal amount of mid-line stabilization.
Well, the challenge that you typically get from an unweighted L-chin-up comes from the fact that your center of mass is offset. It forces you to put your body behind the bar, pulling up with your arms at an angle, in a very small way, similar to the front lever pull-ups. So, adding more mass to the ankles increases this offset. While it becomes much more difficult, when weight is added, not much of that difficulty comes from a lack of ab strength.
This is what makes me wonder which method is preferable.
If you imagine the system of the bar, body, and additional weight, as the weight approaches infinity (wouldn't we all love to do a chin-up with infinity extra pounds?), the position of the center of mass varies greatly between ankle weights (at the ankles), a weight vest (in the torso, like a regular pull-up), and weight belt (slightly behind and below the torso). These are all drastically different exercises.
Fortunately, I have 2x10lb adjustable ankle weights. If I decide to use them, I'm certain that they will keep me plenty occupied for a while.