When you are training a client 2-3 times a week, how do you find the right balance between a structured and predictable program vs. a new challenging workout every time. I want my clients to make measurable progress, but I also want to keep my clients guessing and teaching them new things. Clients want to see progress, but that often involves a lot of repetition with certain exercises, but if you are always doing the same thing, your are not really doing a good job of challenging your clients. Any tips?