Cancer82 - gearbox is right
First there are many styles of HIT, there isnt one style what fits all. With HIT you shouldnt be doing many sets, once you have warmed up you should be doing one or two workinbg sets and thats it, usually one working is enough but depends on the muscle group you may throw another in to make sure its at total failure and beyond

personally I would either incorporate dropsets in my working set or forced and negs. If you read some of my workouts you will see how I use them but an example would be - incline dumbell press, ive fully warmed up and on my working set which would be a weight what I would be able to do around 4,5 reps- what I mean by this is it would be impossible to do another rep no matter what I am at total positive muscle failure and not one further rep can be obtained, at this stage I would do two forced reps which my training partner would help me with, this would take me beyond failure and into the pain zone, at this stage I cant do another rep, ive done 2 forced and now I will do 2 negatives, I will slowly lower the weight and my partner will help me get it up to do another neg - after postitive strength as totally gone the only strength you have left is negative or static so by doing negs at this stage after forced you have recruited every single muscle fiber in your upper chest and you have overloaded the muscle completely, this will produce some serious size

BUT you have to make sure your going to failkure on at each section, dont leave anything in the tank and kid yourself, when your doing your reps you must go to failure wheather thats at 4 ,5,6 reps what eevr it is you go to total positive failure then do 2 forced reps and then 2 negative reps and the job is done....thats forced and negtaives....dropsets are another method to take you to total failure and beyond
Do you understand this?