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Usually performed on rings, but can be performed on a bar. On rings, begin hanging with a false grip with arms fully extended—shoulders open and hands pronated. Perform a pull-up and at its peak, push the chest forward and swing the elbows backward to above the shoulders. Press out as you would in a ring dip, finishing with active shoulders, fully extended arms, and rings externally rotated about 45 degrees.
See Issue 18 of the Performance Menu for an article on developing a mature muscle-up.