Ive always read, from Mentzer's articles or proponents of his training philosophy about how HIT is the only scientifically sound way to train. Unfortunately I haven't read any real scientific studies to back that up. The much vaunted Colorado experiment inst what you would call scientifically sound. There was no control subjects or strict methodology used. A lot of the training philosophy seemed to depend on generalizations about human physiology such as each person is relatively the same and that stimulation applied will be relatively the same, recuperation times are relatively the same and if a person is not benefiting from training the automatic response is to decrease stimulation. It doesn't seem to take into account genetic variations in the human population such as recuperative variances and hormonal makeup. This is my initial opinion of HIT, though it might change as I look at it further.