In the late 70s and early 80s, Mike Mentzer began to publish his ideas about his form of training know and Heavy Duty training. He came out with a series of specialization booklets concentrating on each body part. This is the collection of booklets that he would also sell during his famous seminars, and contains specialization courses for Legs, Chest and Back, Arms and Deltoids. Heavy Duty Delts ebook is 16 pages long.