Heavy Duty works in a VERY small group
I said I wouldn't enter this debate, but recent posts changed my mind.
Heavy Duty, SuperSlow, and all the others are simply variations on Arthur Jones' training ideas. Jones had no science background, nor did Mike Mentzer, or Ken Hutchins of SuperSlow Fame. They were all openly distainful of science and ideas other than their own, even thought they hadn't bothered to research any of them. Here's the real story on these guys.
Jones used to hunt and film wild animals in Africa. He'd be gone for 6 months or more with no training, then come back and resume training. When he'd hit a plateau, he'd reduce his workload and resume progress. This would go on for a few months, and then he'd be back in Africa. This was the genesis of "high intensity."
When he got the idea for his machines, he did so in an attempt to solve the physics of strength curves generated by free weights - like the way the squat, barbell curl, or chest press get "easier" at the lock-out position. To do this he used cams, but you'd need a cam specifically designed to each individual's limb lengths to really make this work. His "training" ideas came about when, having difficulty convincing gym owners of the "suoeriority" of his machines, he sold them on the idea that they could get better turn-over and more members if the gym weren't so full all the time. This could be accomplished by having people do circuit-type, one-set-per-bodypart workouts. It had some merits for conditioning, but none for bodybuilding. In an effort to get people to use his stuff, he wrote a series of articles in Ironman Magazine in the late 60's full of all kinds of speculation, and unsubstantiated claims. Bodybuilders, ever seeking the "Holy Grail" of training, tried this stuff - it didn't work. Not one of them who worked with Jones continued to train this way.
Ken Hutchins of SuperSlow, was a tech that ran an osteoporosis project for Nautilus to see if resistance training would help that condition (it does). They dreamed up SuperSlow since they had a frail population of old people they couldn't risk hurting (a good idea). It has been a dismal failure for bodybuilders who've tried it. Timmy Paterson was another of Jones' "go-fers" who now runs T-mag.
Mike used an very early version of Jones' training that had him doing as many as 6 sets for chest, and more for back, all after several warm-up sets. He published a small set of training booklets in the 70's outlining this. Ell Darden's off the record comment to me was that the Mentzer brothers could have trainind any way they wanted since they were built like rhinos. Mike knew little about physiology, biochem, and anatomy. The Weider mags claimed he was "Pre-med," but if so it was only because he attended college briefly. He refered to things like "throwing that switch to stimulating muscle growth" by training to failure. The fact was, he had no idea why or if any of this worked. How does exhausting the short-term anaerobic energy source in one set stimulate muscle growth? Also, go look at my earlier post about the "famous" Colorado Experiment with Casey Viator.
Muscle growth has been research for well over 100 years, and most of these finding contradict what the HIT people have to say. Are there some flawed studies? Sure - in every discipline.
Finally, in a select group of people, HIT will work on a limited basis. These generally are people who are GROSSLY overtrained that reduce their volume by 80% or more - this was most of Mike's and Jones' bodybuilding clients. Also, in people with very high ratios of white fast-twitch fibres (probably less than 2% of trainess - i.e. greater than 2 standard deviations off the norm), low numbers of sets with heavy weight will work better than volume routines.
Dan Duchaine talked about the flaw of assumming knowledge or intellegence simply because of greatness. Mike was a great bodybuilder, but his ideas, as well as those of the other HIT proponents lack an understanding of physiologic reality. They are ususally defended by those with very limited training experience, or those too young to remember this 35+ year line of nonsense that keeps being re-worked and promoted by one after the other who claims the have "THE" answer.