It started out with Arthur Jones type training where all one needed to do was one set of 8-10 reps to failure per muscle group once or twice a week but it evolved to many different routines and forms. Mentzer routines are pretty high intensity . Probably half the stuff people do on here is high intensity if they are pushing it hard. Now the current workout involves slow negatives and medium speed concentrics , 30 10 30 . Sometimes its 3 30 second negatives per exercise . X Force is very high intensity, about as high as it gets for machines. It used to be if you were doing high volume and high reps it wasn’t considered hit but I say if you still are pushing it hard near or at failure it’s high intensity no matter how many reps or sets it is .
Scott