HEAVY DUTY™ - a Scientific Perspective

Dave Smith, PhD
Manchester Metropolitan University, UK

James Fisher, MSc
Southampton Solent University, UK



Sometimes potential newcomers to Mike Mentzer’s HEAVY DUTY™ high-intensity training inquire asking for referrals to studies conducted that support Mike’s teachings. The following article is quite substantial in answering this type of question, and the writers are certainly credible and qualified based upon their experience and education. I would like to introduce the writers to you:

Dave Smith is Senior Lecturer in Sport Psychology at Manchester Metropolitan University, which is one of the largest exercise science facilities in Europe. Dave had worked previously as a personal trainer utilizing high-intensity training with considerable success. Dave knew Mike for some years and had even written articles for Mike in the past. They had a mutual respect for each other.

James Fisher is Senior Lecturer in Sports Conditioning and Fitness at Southampton Solent University and is also an Assistant Coach with the British Wheelchair Basketball team, where he is involved in the athletes’ conditioning. Again, he is a strong advocate of high-intensity training. It is my hope that James will write an article for Mikementzer.com in the future as he finishes his current study which might also further support Mike’s HEAVY DUTY™ teachings and philosophy.




Ten years after his death, Mike Mentzer’s HEAVY DUTY™ high-intensity training philosophy still generates a huge amount of debate amongst bodybuilders. In his books, Mike claimed that his HEAVY DUTY™ training was, in essence, a scientific approach to training. Indeed, ‘The Science of Bodybuilding’ in Chapter 3 of HEAVY DUTY© (also known as HEAVY DUTY 1), outlines his key training principles. However, although at face value his approach certainly appears logical, it is difficult for most trainees to evaluate whether the scientific research on resistance training substantiates this claim. This is simply because most people do not have easy access to the (sometimes obscure) body of work examining this topic. This article, therefore, aims to explore the scientific literature on resistance training to put Mike’s theories to the test. In it, we will examine some of the key tenets of HEAVY DUTY™ to determine whether it truly does represent a scientific approach to bodybuilding. Though the article is not meant as a comprehensive review of the resistance training literature, or of Mike Mentzer’s views on every single aspect of resistance training*, we will summarize the key findings relating to the main tenets of the HEAVY DUTY™ approach.

* For a comprehensive explanation and discussion of Mike’s key training principles, see High Intensity Training the Mike Mentzer Way© (Mentzer & Little, 2003) and The Wisdom of Mike Mentzer© (Little & Sharkey, 2005)

Intensity and the Importance of Training to Momentary Muscular Failure:
Mike often focused in his writing on his principle of ‘intensity’, which he defined as the percentage of momentary muscular effort being exerted (see, for example, High Intensity Training the Mike Mentzer Way©, chapter 5). This in itself is controversial, as the term ‘intensity’ is often used in the literature to refer to load. For example, and typically, Willardson and Burkett (2008) and Fry (2004) point out that it is a common term for percentage of 1 repetition maximum (%1RM). This definition is problematic. For instance according to this definition, if one individual performs an exercise with a weight of 80% of 1RM, and performs one easy repetition with that weight, this person is training more ‘intensely’ than another individual who performs a hard set to momentary muscular failure with 79% of their 1RM. Clearly this is nonsensical; Mike’s definition of intensity seems much more logical as it refers to how the word ‘intensity’ is usually used in the exercise setting, i.e. to refer to the severity of the exercise. He argued that trainees should exercise to the point of failure, as this will ensure individuals make a sufficient inroad into the body’s reserve capacity to stimulate muscular adaptations:

“Carrying a set to a point where you are forced to utilize 100 percent of your momentary ability is the single most important factor in increasing size and strength”
--- Mike Mentzer (High Intensity Training the Mike Mentzer Way©, p. 41).
A similar suggestion was made by Willardson (2008), who suggested that training to momentary muscular failure may provide greater stimulation to the higher threshold fast-twitch motor units which are capable of producing the greatest increases in strength and hypertrophy. Thus, training to momentary muscular failure is theoretically more beneficial simply because doing so would ensure recruitment of as many motor units and muscle fibres as possible. Unfortunately, few studies have directly addressed the concept of training to momentary muscular failure whilst accurately controlling for other variables such as load, volume and frequency. Those that have, however, have produced some interesting findings.

For example, Rodney et al. (1994) reported significantly greater gains (41.2% to 19.7%) in dynamic strength when training to muscular failure compared to sub-maximal sets of exercise. Similarly, Schott et al. (1995) reported significantly greater gains in isometric strength when training to failure compared to stopping the exercise short of failure (24.9kg to 14.3kg), and Drinkwater et al. (2005) reported significantly greater dynamic strength gains (9.5% to 5%), and also peak power for a bench press throw exercise when training to muscular failure compared to not training to failure (40.8W/10.6% to 25W/6.8%). Notably Folland et al. (2002) reported no significant difference in strength increase between a training time of around 7 minutes (to failure) and 25 minutes (not to failure), suggesting that the same strength gains could be achieved in approximately 30% of the time by training to momentary muscular failure. Overall, therefore, the evidence suggests that individuals should be encouraged to train to momentary muscular failure, as this appears to maximize muscle fibre recruitment and leads to greater improvements than sub-failure training.

Training Volume:
Mike argued that one set to failure per exercise was sufficient to trigger an adaptive response and that any more exercise would simply be wasted effort and possibly counterproductive in that it would increase the likelihood of overtraining:

“…one set to failure is all that is required to stimulate an increase in strength and size – with no number of lesser sets having the same effect”
– Mike Mentzer (Muscles In Minutes, p. 26).
The number of sets is one of the most controversial issues in resistance training, and one of the most well-researched. Reviews, such as those conducted by Carpinelli and Otto (1998) and Smith and Bruce-Low (2004), have concluded that one set per exercise produces optimal results. In the Carpinelli and Otto paper, they found that single sets produced optimal results in 33 studies out of the 35 they reviewed. In contrast, Peterson et al. (2004, 2005) also analyzed this issue and claimed that multiple sets were superior. However, their own data clearly did not support their conclusions as in fact there was no statistically significant difference between the effect sizes of the different training volumes (see Carpinelli’s excellent 2009 article for a discussion of this issue). Overall, therefore, the weight of evidence strongly supports the HEAVY DUTY™, one set to failure approach.

Training Frequency:
In contrast to many bodybuilding authorities, who suggest training up to six days per week (sometimes even twice per day), Mike argued in his revised HEAVY DUTY© (1993) book that bodybuilders should train no more than three times per week with each muscle group trained no more than once per week. Later, in HEAVY DUTY II: Mind and Body© (1996), Muscles In Minutes© (2000), and High Intensity Training the Mike Mentzer Way© (2003), he argued that even this routine would constitute overtraining for many people and advocated a training frequency of once every several days at the most, with those especially prone to overtraining advised to train every 5-7 days (and in some cases even less frequently) using primarily compound movements (a method he termed ‘consolidation training’). Some have argued that such training frequencies are not sufficient to induce optimal muscle gains. However, the scientific research appears to suggest otherwise. A plethora of research, reviewed by Carpinelli et al. (2004) and Smith and Bruce-Low (2004), suggests that there is little or no difference between training 1, 2 or 3 x/week for both trained and untrained persons. Though no research has been published to date examining the effectiveness of consolidation-type training (the second author of this paper is undertaking such a study at present), there are some interesting findings on the recovery period following intense resistance training which appear very supportive of the need for relatively infrequent training to ensure recovery. For example, Cleak and Eston (1992) considered maximal eccentric exercise of the biceps, reporting changes in relaxed joint angle and swelling between 24 and 96 hours. In fact, maximal isometric strength had not returned within the 96 hour period. Newham et al. (1987), also considering maximal eccentric biceps exercise, reported a 50% decrease in strength immediately after training, and only a recovery to 80% of that prior to training after 2 weeks!

Another recognized indicator of muscle damage is swelling as measured by magnetic resonance imaging. A study by Nosaka et al. (1996) with untrained persons reported enlargement of trained muscles from 1-day post training up to 23-days post training, further suggesting that adequate recovery from intense training sessions can take considerable time.

Other research has reported significantly elevated creatine kinase levels and rating of perceived muscle soreness at 96 hours post exercise, as well as significantly elevated resting metabolic rate 48 hours post exercise (Dolezal, et al., 2000). All this research seems to suggest that recovery from hard training takes days, and in some cases up to several weeks. Therefore, it is very important to allow adequate recovery time between workouts, and this might be several days or even longer depending on the individual. Indeed, Mike argued latterly that attempting to prescribe rigid guidelines for frequency of training was a mistake as individual needs varied so much in this regard, something borne out by the above studies, all of which found considerable inter-individual variability.

Repetition Duration:
Mike advocated that repetitions should be performed slowly and deliberately with the weight always under full control to maximise muscle tension. In Muscles in Minutes©, he advocated a duration of about four seconds on the positive (lifting) and the same on the negative (lowering) portion of the repetition on most exercises, with a two second pause in the fully contracted position. Comprehensive reviews of this topic (Bruce-Low & Smith, 2007; Carpinelli et al., 2004) have supported Mike’s claim that a relatively slow cadence can produce optimal gains in strength and hypertrophy, but that ‘super slow’ (10:4 to 10:10 cadence) training does not offer additional advantages (Mike held that conducting “super slow” training beyond his recommended cadence could actually hold back the bodybuilder’s progress, because he would get tired quicker). For example, Johnston (2005) considered force production in a case study, reporting little difference in forces generated or experienced where movement was performed at repetition durations that maintained muscular tension (including 10:10, 5:5, and 2:4 (concentric: eccentric). Nevertheless, when attempting to move the load explosively, forces increased by as much as 45% initially, but then decreased by 85% for most of the repetition. This is likely due to the excess force provided to overcome the inertia being so great that momentum carries the weight through the rest of the range of motion. Johnston suggested that explosive lifts would likely recruit fewer muscle fibres due to momentum and that the diminished recruitment through most of the range of motion would be less effective for enhancing muscle function. This has previously been reported by Hay et al. (1983) with arm curl exercises. A study by Tran, Docherty and Behm (2006) considered decrement in force production and rate of force development, noting significantly larger decreases following sets of 10 repetitions at a 5:5 repetition duration compared to 10 repetitions at 2:2, and 5 repetitions at 10:4 repetition durations. This larger decrease in force production suggests fatigue in a larger proportion of muscle fibres, potentially stimulating greater growth and strength/power gains. Also, Bruce-Low and Smith (2007) specifically considered the risk of injury from ballistic exercises, reporting some disturbing statistics suggesting that explosive lifting can cause injuries to the wrist, shoulder, elbow and lumbar regions. Overall, therefore, Mike’s recommendation of a relatively slow speed of movement during resistance exercise seems both efficacious and prudent according to the research findings.

The Importance of Genetics:
Mike strongly emphasized in his writings that not everyone could develop to the same degree, and that although everyone can improve with proper training, few people have the genetic predisposition to enable them to develop a Mr. Olympia physique. Indeed, he devoted whole chapters in HEAVY DUTY© and in High Intensity Training the Mike Mentzer Way© to this issue. This issue is often evaded in the bodybuilding magazines and books, and yet there is now a large body of evidence that various genes do indeed play a huge role in response to training. For example, myostatin [an “anti-growth” genotype, inhibiting muscular development] appears to be important, and research suggests the genetic variation in the IL-15RA (receptor-a gene) is a significant moderator of muscle mass in response to resistance training. Other genotypes include ciliary neurotrophic factor (CNTF), where the G/G and G/A genotypes have shown significantly greater muscular strength compared with the A/A homzygotes. There is also alpha-actinin-3 (ACTN3), where the R577X genotype is generally associated with muscle function, contractile properties and strength/power athletes and could modulate responsiveness to training. Stewart and Rittweger (2006) provide a comprehensive review of molecular regulators and genetic influences, and suggest that these genetic effects likely account for 80-90% (!) of the variation in muscular strength and cross-sectional area.

A very simple demonstration of the importance of genetics is shown by Van Etten et al.’s (1994) study. This reported significant increases in fat-free mass for a mesomorphic (muscular) group after 12 weeks of resistance training, where an ectomorphic (thin) group recorded no significant improvement having followed an identical training routine. Therefore, it appears that those who are naturally lean and muscular to start with, can gain strength and size to a much greater degree than naturally ‘skinny’ individuals. So, as Mike often emphasised, genetics are a key factor in bodybuilding success. As Arthur Jones once said on this topic, you simply can’t make a silk purse out of a sow’s ear. However, as noted above, everyone can improve on their existing condition with proper training, and a great deal of exercise science research suggests that HEAVY DUTY™ is an effective way for individuals to maximize whatever potential they do have.

--- Dave Smith and James Fisher

© Copyright 2011 – Dave Smith and James Fisher –
THIS ARTICLE IS WRITTEN EXCLUSIVELY FOR MIKEMENTZER.COM AND WITHOUT THE WRITTEN PERMISSION OF JOANNE SHARKEY, CEO/PRESIDENT OF MENTZER-SHARKEY ENTERPRISES, INC., IT CANNOT BE DOWNLOADED TO USE ON ANOTHER SITE OR IN ANOTHER FORM OF MEDIA, ELECTRONICALLY OR OTHERWISE.

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