I jumped on the heavy duty bandwagon for years. After studying all the bodybuilding programs out there. Mike was one of the few to really explain WHY he developed the routine the way he did. I had some results with training heavy duty, but nothing special. I think doing one really intensive set is not so bad, it was the extremely infrequent workouts he recommended that was way off. Mentzer started out with arthur jones, doing threexweek, later dropped it to 2xweek. Then he wrote 'Heavy Duty' and advocated training a bodypart once/week, at first I thought he was onto something....but after training this way for quite awhile I realized that 7 days between bodyparts seemed too much, and I didn't I even need anywhere near that much time to recover. Then he wrote 'Heavy Duty 2: mind and body", at first I thought it was awesome, working out only about 6 sets for the whole body, working out a bodypart every two weeks, doing extremely intensive sets, like rest/pause, static holds going into negatives, etc. He seemed to be some eccentric bodybuilding genius. I honestly thought he was right. Other guys would laugh at me as I came to the gym and did my one set for each bodypart, and left in about 15 minutes. The truth is the training frequency was way off I think, as I hardly grew at all!!! I think if I did heavy duty type training, but worked out 2 or 3 times /week instead of 1xweek or less, I would have seen better results.
Now I work out three times/week whole body, doing clustering and Max-stim, and my results are SO EXTREMELY SUPERIOR TO HEAVY DUTY, that there is no way I would rank it second to HST. I think any program that doesn't have too much volume, or to little frequency, is FAR BETTER than heavy duty. Basically, low-volume, high frequency workouts like HST are the optimum for natural weight-lifters. Mentzer's workouts were EXTREMELY low volume, and EXTREMELY low frequency, and I think the extremely low frequency is the main problem.
He had some great ideas for sure, great guy, but he was lost in his own philosophical garbage there for quite awhile. He though fatiguing the muscle to twitching, slobbering failure was the ultimate key to hypertrophy, and that it was the ultimate sin to do more than one set per exercise, or god forbid train a bodypart more than once/week. The worst part of it was, he claimed to have the ONE TRUE SCIENTIFIC THEORY OF BODYBUILDING, meanwhile he said that all the scientific exercise research that exists is crap , and HE USED ABSOLUTELY NO SCIENCE AT ALL TO BACK UP HIS ClaiMS, HE ONLY USED WHAT HE TERMED 'REASON'. And HIS reasoning of course, however twisted or false it may have been was supposed to be absolutely true, all 'cause he read some book by Ayn Rand and thought he was enlightened or something.
I followed the guy pretty deeply, and honestly I think he lost his mind towards the end of his life.