You're correct, although ATP is generally replenished to around 70% after a minute, and is muscle dependent, so you can work on another muscle group while one r

You're correct, although ATP is generally replenished to around 70% after a minute, and is muscle dependent, so you can work on another muscle group while one rests. I generally do a set of 10 or less, wait 1 minute, do another set and then do some yoga for the remainder of 3 minutes. I then switch to another muscle group and do the same. When I switch back to the original muscle group an additional 3 minutes have past or 5 minutes since the last set for that group. This allows for some oxidative stress, which stimulates mTor and thus mitochondrial growth, but also allows me to do more sets in a work out in less amount of time. I'm generally done in 30-45 minutes, but work out daily at home. While ATP takes a good amount of time to replenish, lactic acid take twice as long to clear out. So you really need to be resting 8-10 minutes between HIIT work outs, or just go home from the soreness. This doesn't seem as ideal if you don't want to spend all day in the gym.