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An Objectivist Analysis of Heavy Duty
by: John Thomson

Few individuals in contemporary bodybuilding have fuelled such intense debate as the late Mike Mentzer. His Heavy Duty system contradicted almost every popular training principle of the time and, probably more importantly, the training practices of the renowned and charismatic Arnold Schwarzenegger.

Ironically but unsurprisingly, Mentzer’s attempt to establish a rational approach to bodybuilding did not result in intelligent debate of accepted training theory. Instead, with all of the relevance of a bicycle to a fish, Mentzer’s character was constantly attacked while his theories only received passing criticism for being different.

Proof to the validity of the Heavy Duty system didn’t arrive until Dorian Yates took hold of the Mr Olympia title for most of the 1990’s. During Yates’ reign popular interest in Heavy Duty soared. The whole intelligent, logic ‘thing’ was suddenly in vogue such that anyone not using Heavy Duty was ridiculed for their obvious lack of intellect.

During all of this time, still nobody questioned the underlying principles of Heavy Duty as isolated absolutes. Heavy Duty has been compared to every training system devised, but the inherent contradictions within the system itself have never been addressed. Let us address those contradictions now.

Heavy Duty Philosophy

Mentzer was a devout proponent of Ayn Rands Existentialist Philosophy, which he drew from when developing his Heavy Duty principles. Somehow though, Mentzer failed to recognise one of existentialisms’ primary principles: contradictions cannot exist.

Anecdotally, Heavy Duty is obviously and severely flawed. It dismisses the possibility of significant muscular growth arising from anything other than brief, infrequent, maximal exertions. In practice however, most successful bodybuilders develop their physiques doing almost exactly the opposite.

Ayn Rand asserts that when you think you have encountered a contradiction, you should check the premises upon which it is based. There she tells us you will find the error. And certainly, it is a flawed premise that underpins the entire Heavy Duty philosophy. The error that cascades down through every principle of Mentzer’s training system is his definition of intensity.

When developing his principles for hypertrophy Mentzer defined and measured intensity as the percentage of one’s momentary muscular ability. He was wrong. Intensity is weight.

Intensity Redefined

Consider the fact that muscles perform only one active task: they contract. In basic terms, an intense contraction can only be a forceful contraction; a muscle cannot do anything else by which it can be measured. If a load is applied against a muscle such that its greatest possible contractile capacity can only barely hold it, then it is true that the intensity of that contraction is 100% of that muscle’s ability. However, the intensity is measured by the force output which is equal to the load applied; the WEIGHT!

To draw an analogy, consider intensity in terms of light. The intensity of light is its brightness and is measured in Lumens. An intense light has a high lumen measurement. It is not measured by how severely it pains any one specific—i.e. subjective—pair of eyes.

Get Sick to Grow

There are several other contradictions inherent to Mentzer’s definition of intensity (actually it was Arthur Jones’ definition, originally). Consider that if intensity is the percentage of available momentary muscular ability, then the more malnourished and physically incapacitated you were, the more intense you are training. In fact, if you were sick enough, merely twitching your fingers would activate 100% of your momentary muscular ability and therefore, by Mentzer’s reckoning, “turn on the growth machinery inside your cells.”

Clearly not.

However, if intensity is defined as the amount of weight used– which is how it should be defined – training with maximal intensity requires you to be in peak physical condition. Sounds a bit more like it, hey?

Increasing Intensity

Yet another problem with Mentzer’s definition of intensity is that the concept of training with ever-increasing intensity is simply not possible. Performing a forced rep or drop set does not exceed 100% of your muscle’s momentary muscular ability; your muscle is still generating only 100% of its maximal contractile force at that time. Once you reach failure you have reached 100% of your momentary muscular ability. And you can do that during your very first workout. It is not possible to increase intensity – by Mentzer’s definition – beyond failure.

In contrast, when intensity is defined as ‘weight’ then there is no upper limit or relative measure. Intensity can always be increased. There is no way to measure a percentage of infinity, so there is no such thing as training with 100% intensity. This is another way of saying that when ‘Intensity’ is defined in terms of the amount of weight one uses, there is no finish line; there is always a heavier weight to lift and more growth to achieve.

Even with an incorrect definition of ‘Intensity’, Mentzer evolved his meaning of the term into something else again. Mentzer’s application of intensity began to focus more on the length of time a muscle is kept working at 100% of its ability than simply achieving 100% ability. And because ‘Momentary muscular ability’ is almost inseparable from subjective ‘pain’ and ‘effort,’ those techniques that increase pain and effort are touted as intense. Hence, drop-sets, forced reps and anything else ‘difficult’ that extends the length of time a muscle works at its maximum ability is considered ‘intense.’ This is ironic when one realizes that Heavy Duty’s original definition of intensity, when scrutinized, renders these techniques redundant.

Light Weights for Growth?

This leads us to another error in the Heavy Duty definition of intensity. Though Mentzer recommended lower reps with heavier weights, his definition of intensity did not. His definition does not exclude any lower limit of resistance or upper limit of ‘time under tension.’ In fact, by Mentzer’s definition, a marathon runner that collapses 10 feet before the finish line has successfully achieved 100% intensity and therefore induced growth. Now, we know that is not true, but it does qualify as true by Mentzer’s very flawed definition of intensity.

But once again, with intensity defined as ‘weight’, ridiculously high reps require light weights and therefore cannot be intense enough to induce meaningful and/or ongoing growth.

Continual Progress?

Mentzer asserts that as you develop your physique you need to train with ever increasing intensity while decreasing frequency, which he prescribes to facilitate the recovery induced by increased intensity. This would have actually been an accurate prescription when considered in the context of intensity as the amount of weight that is lifted. It makes perfect sense that as you get bigger and stronger you have to train with heavier weights to continue growing. And training with heavier weights requires more recovery time. We all know that.

But Mentzer’s Heavy Duty System explains that while weight is important, you have to use more in the way of drop sets, forced reps, super sets etc as you grow and develop. If anything, the opposite is true. As you get larger, your added strength means that you are training more intensely as a matter of course. As you continue to grow you would be best to hold back from training to failure. Just ask any 1000lb Squatter.

For a Powerlifter to increase his squat over 1000lb the last thing he will consider doing is a 1000lb triple drop set with forced reps and negatives, tri-setted with Leg Presses and Leg Extensions! If he lived, he’d need so long to recover that he’d never realize a gain. But by training with 40-80% of his max and always staying well within his capacity he will probably increase 20-50lbs every 3-6months.

Why Weight?

When you understand that intensity is ‘weight’ then a number of anecdotal observations are explained. Why do you think Squats and Deadlifts have always been considered such fantastic mass builders? Because no other exercises place so much intensity – so much weight – on so much muscle.

Why has Bench Press always been the king of chest movements? Because no other chest exercise lets you apply as much weight; no other chest exercise is as INTENSE.

Why are negatives such a shockingly effective technique? Because they are intense; you have just raised your training intensity – the weight – beyond anything you have trained with before.

Why are machines generally considered inferior to free weights for building muscle? Because generally less of your muscles are left to handle less weight; they are less intense. That is also why Hammer Strength machines are so highly regarded – they apply heavy loads; they are intense.


As you can see, the error in the definition of intensity is the major failing of all High Intensity, Heavy Duty training variants. Worse still, from the flawed definition has arisen an entirely different meaning. And the contradictions cascade through all such systems from thereon in.

Mentzer always maintained that all training systems cannot be right; there must be one consistent, underlying philosophy. As with so many aspects of his philosophy, he was right. But Heavy Duty is not it.

When you use the amount of weight you are lifting as your definition of ‘Intensity,’ then a single, consistent philosophy is established. And it is one that embraces the possibility that varying combinations of intensity, volume and frequency being equally effective.