Muscle Confusion is a Joe Weider principal. I'm sure he didn't invent it he just gave it a name and popularize it like he did so many other principals. It's a simple principal. Never do the same workout twice in a row. Change the weight, change the reps, change the equipment, etc. Keep your muscles confused as to what they will experience. I have used it for years. It's almost a must for me since I workout in a small gym. Many times the equipment or the weights I want are being used so I just modify my workout accordingly.