cortisol levels do skyrocket and stay elevated for hours after training at a high level of intensity after about the 2hr mark +/-. for the most part there is only you can do to stimulate the muscles during a single training session, one of many cases when more simply isn't better. rest periods between sets should range anywhere from 30secs for endurance training, 60secs for hypertrophy, and 5-6min for those training for maximum strength. the long rest period at 5-6min allows ATP stores to be replenished to maximum levels