During a typical High Intensity Training (HIT) workout, a single set per exercise is performed. This set is comprised of 6-10 reps for the upper body and either 8-15 or more commonly 12-20 reps for the lower body, done to failure. Dead Lifts usually have a rep range of 5-8 reps, and calves are sometimes trained with 1-2 sets of failure.
HIT style also emphasizes muscle exhaustion. You may not be able to lift a weight for another rep, but you will be able to hold it statically for a further period (second stage of failure) and finally lower a weight at a slow controlled speed (third stage of failure). Until all three (lifting, holding and lowering) parts of an exercise can no longer be completed in a controlled manner a muscle cannot be considered thoroughly exhausted/exercised.
High Intensity - 1 set. This is a typical HIT workout. Perform only a warm-up set and one workout set of every exercise.
Medium Intensity - 2 sets. This is not a typical HIT workout. If you are used to a high volume program, but want to switch to HIT training, you may want to do intermediate volume training until you are able to generate more intensity in the first workout set.
Lower Intensity - 3 sets. This is not a HIT workout. If you are used to a very high volume program (5 or more sets of many reps), but want to switch to HIT training, you may want to do intermediate volume training until you are able to generate more intensity in the first workout set.