Mike trained about 3 to 6 sets a body part not counting non taxing warmups. He trained a body part directly either once a week or twice when he trained for the 1980 Olympia using the ABA split then next week using the BAB split. To illustrate the rotation on Monday he trained Legs, chest and triceps. One Wednesday it was back, delts and bicep. His last training day for the week was back to legs, chest and triceps. The next week he rotated it to Monday starting with back, delts and biceps.
When he got out of the nut house and got into personal training is when he came up with the outrageous abbreviated workouts. Nice to train someone for 15-20 minutes and say see you in 10 days. It seems most personal trainers preach HIT because they can fit so many more people into their schedule. Think a trainer is going to stand by for a guy doing a 90 minute or a 120 minute workout? Mentzer could fit so many clients in with his bull shit workouts that he never did.
Mentzer started his HIT journey training three days a week training the whole body each workout winning the Mr. America contest. From there he went to a two way split with four workout days a week. From there he was influenced by Mr. Florida Frank Calta to adopting the rotation for recuperation three day a week workout I typed about above.