This is truly a double-duty exercise. It serves two purposes. It builds explosiveness on the concentric (pulling) portion of a chin-up because each rep is re-set at the bottom of the movement.
It also takes you from single-chinner to multiple-chinner. This could be the result of increased grip strength and scapular retraction, which becomes a necessity since there's no need to swing, hump, or kip your way up.
related posts
Tip: Stretch This Muscle and Feel Awesome
Sit a lot at work? Then your glutes and core are going to get weak. Here's an exercise to fix that.
The Absolute Best and Worst Therapy Methods
Four of these rehab methods are great... and two are wasting your money. Here's what works and what doesn't. Bonus: Videos of the best techniques!
Strongman Training for Athletes
Although this article is aimed at athletes, if you're looking to get into shredded, athletic shape, try some of the exercises Coach DeFranco describes. You can practically feel the fat melting off your body!
Shifting Tension
Is it possible to put more stress on certain parts of a muscle?