Gorilla Chin/Crunch

How to do it

Hang from a chin-up bar using an underhand grip (palms facing you) that is slightly wider than shoulder width.
Now bend your knees at a 90 degree angle so that the calves are parallel to the floor while the thighs remain perpendicular to it. This will be your starting position.
As you exhale, pull yourself up while crunching your knees up at the same time until your knees are at chest level. You will stop going up as soon as your nose is at the same level as the bar. Tip: When you get to this point you should also be finishing the crunch at the same time.
Slowly start to inhale as you return to the starting position.
Repeat for the recommended amount of repetitions.

What muscles does the Gorilla Chin/Crunch work?: Mainly the abs, with help from the biceps, lats.
What equipment do I need?: Nothing but your bodyweight.
Is it good for beginners?: It is rated intermediate level.
How do I track progress on it?: Log each set and beat the weight or reps from last time. Liftrung shows your last set beside the next one and estimates your one-rep max from your sets.

Exercise descriptions: free-exercise-db, public domain.