"Intensity"
Definitional Chaos
In past books and articles, I have sought to explain the meaning of intensity on several levels. We will review several usages before embarking into a deeper application that is fraught with pitfalls that we had assumed we previously avoided by our straightforward delineations.
Level I
At this level, I acknowledge the widespread usage of intensity to describe a state of elevated emotional tension or abnormality in nature. A few such examples:
A high-energy personality
Seething anger
A loud or rushed musical passage
A violent storm
This usage is general and colloquial.
For ease of manipulation, we later denote this level of meanings textually and graphically as I1.
Level II
At the next level, we encounter a technical usage whereby intensity is synonymous with force or the magnitude of light… I2
Level III
At this pseudo-technical level, the exercise physiologists garnered intensity as reflective of heart rate.
Another usage in the field of exercise—especially as exercise is confused with sports and athletic activity—is to apply intensity in different ways to indicate mechanical work… and probably to indicate power. For example, mileage per time (as a runner might use) is one loose usage. Another somewhat similar usage is to refer to a quantity of physical conditioning as an indication of how hard a subject trained or the severity of the training. (i.e., He trained very hard (intensely) to prepare for the Olympics… over eight hours daily for weeks.)
These usages are loaded with inconsistencies. Intensity and hardness (degree of effort or exertion) are used synonymously with quantity and dedication and besmirched of a sensitivity of quality.
Apart from the heart rate being an objective, although misapplied measurement, these other usages are also extremely subjective qualifiers. None of them approaches the objective application that is witnessed with the measurement of light (for example).
Although I don’t remember personally encountering it, I expect that work performed per time has also been expressed as intensity as another a loose expression of power. Of course, all of these applications are technically worthless to our pursuits in exercise. And the expression of power in exercise is crass and physically dangerous.
No doubt, intensity is used in many different disciplines to denote properties specific to those disciplines. I have a limited perspective on these varied usages due to their specificity. It’s as if the word, dog, has a different meaning in each of the hundreds of languages throughout the world. This I3 definition can be treacherous to navigate.
Level IV
When Nautilus founder, Arthur Jones, first used intensity, it was as if he had coined a new word rather than stipulated a new meaning for an old word. As one who was NOT at first firmly grounded in I1, I2, and I3, I could only latch onto Arthur’s meaning (I4) as he related it many times with explanations of exercise—specifically, intensity of effort by the exercise subject. The cruder expression for intensity was the hardness—how hard the subject efforted or how mightily he strained against a work load.
With this usage, Arthur greatly delimited the meaning. Intensity was no longer indicative of quantity or work or magnitude of force. In fact, high force and large work quantity often indicated low intensity of effort in exercise.
Still, the notion of intensity—a la Arthur—remained subjective and elusive. As Arthur explained I4, intensity was only measurable at zero and 100% effort. “If one desired to exercise at a 50% or 75% or 95% effort, how could one do this?” Arthur begged.
Arthur applied his definition in two veins simultaneously. The overall intensity of a workout was the degree of effort applied from its outset to its end—with an objective to eliminate as much rest between exercises as possible.
The other vein was specifically applied to each of the individual exercises performed in a workout.
These two veins were applied simultaneously.
Although for years, we acknowledged Arthur’s dictum that only zero and 100% could be assessed (not truly measurable) [Actually, only zero percent effort is measurable.], we became adept at observing and subjectively rating a subject’s overall workout or specific exercise performed by that subject as of low, moderate, high, or extremely high intensity.
These ratings of intensity were largely if not completely experiential. I say experiential because an instructor having no personal working experience with so-called high-intensity exercise could not convey it to a subject under tutelage. And when the instructor was extremely attuned to this concept of intensity, he often encountered extreme challenges to bridge his attunation to his subject? To convey his attunation, he often had to get his subject to experience it. And this was an arduous conveyance process.
A good instructor has a daunting task as the novice subject often fears the hard work experienced with high-intensity exercise. And the lingering concepts of I1, I2, and I3 continue to prey against the novice’s psyche.
The Sequalae
The major sequala of the several definitions of intensity and the misunderstandings of Arthur’s usage led to many perversions of Arthur’s concept to “train brief and train hard.” The phrase, high-intensity training, coined by Ellington Darden, PhD and now commonly abbreviated as HIT is spread across the fitness landscape to apply to almost anything promoted. Arthur and Ellington had propagated a winning phrase that won great appeal, but lost its unique meaning except to a few faithful practitioners.
Level V
Then Arthur (or the people around Arthur) stepped in—in a sense—to save us from definitional extinction by dilution. He noted—particularly with his MedX venture using equipment that could track and display inroad—the relationship between a subject’s effort and the rate of inroad. Zero effort produced zero inroad and thus zero inroad rate. And the greatest momentary effort produced the steepest (most fast) inroad. These relationships seemed unassailable.
Hence, Arthur propounded that intensity = inroad / time. We denote this as I5. And someone—perhaps Arthur—proposed that I4 was consistent with I5.
Arthur seemingly had abandoned I4; however, it still had relevance. I then proposed that I4 served to refer to the overall effort applied to the general workout while I5 was to be used specifically to each particular exercise within that workout.
Even so, my suggestion remains somewhat contrived as I4 remains relevant in specific as well as in general. What’s more, I5 has relevance issues as well since inroad cannot be observed and measured without rare and expensive feedback equipment (and depending on how they are used, are extremely dangerous). To some degree, inroad can be visualized through discussion (i.e., Arthur’s The Harder It Seems, the Easier It Is presentation) and graphical presentation, but this remains elusive and widely unavailable information to instructors and their clients.
The Conflict Between I4 and I5
Despite the elegance of Arthur’s I5 (intensity >> inroad/ time), it does not always hold true. Not only is I5 sometimes inconsistent with I4, I5 is sometimes inconsistent within itself.
His I4 definition is not always consistent with his I5 definition although the consistency is good enough to be extremely useful. The estimation that I4:I5 (I5 is proportional to I4) aligns with what we can constructively communicate to subjects. [It’s best not to confuse the novice with these definitional inconsistencies. It’s too arcane for the ears and minds of all but the most advanced students.]
Below is a simplified schematic (Graph #1) to represent an inroad (green line) produced by a subject’s performance (gold line) on a feedback static (FS) exercise machine.
[Solid black lines represent the X (time under load or TUL = 90 seconds) and Y (force) axes and the blue dashed line represents the target load. Please refer to Transitioning from TSC to Feedback Statics for clarification. Greater insight is gleaned from Critical Factors for Practice and Conditioning.]
Graph #1
Note the brackets of time labeled T1, T2, and T3.
The target load is selected to enable the subject to attain approximately ⅔-¾ of the total time under load (TUL).
The solid red line is not a danger threshold. Instead, it is injury threshold. [By convention, a danger threshold is represented by a dashed red line.] The danger (probability of injury) increases as the performance line approximates it. Once the solid red line is attained, injury is frank.
Now, let’s examine and compare a few segments of the inroad curve:
With experience, we are assured that T1 fairly represents the essence of I5 as well as an agreement between I4 and I5. In other words, the subject loads to the target load and holds said target load for 5-10 seconds thus producing slight inroad with the devotion of a moderate intensity of effort. [Note that the green performance line begins very closely to if not on the danger line. This is my arbitrary selection to depict, but it may actually reside above the red line.] As with T1, T2 shows consistency with I5 and I4-I5 consistency. Greater intensity of effort yields greater inroad.
Again, this is noted by personal experience as I4 is subjectively estimated while I5 is truly measurable and recordable. And since one of these two phenomena is subjective, the relationship between them is, hence, subjective. Nevertheless, our perceptions are reliable enough to confirm the truth that greater intensity of effort yields greater inroad… at least at these time segments and at a less than 100% effort.
While I5 is completely measurable, it is not safe to do so above the target. I suspect that MedX has repeatedly done this and injured many subjects, so we have evidence to confirm Graph #1 in general.
But then we encounter T3. Here, on what I term the foot of the inroad curve, I5 becomes inconsistent with I4 as well as with itself. In other words, intensity of effort becomes extreme while inroad slows or stagnates. We have a kind of reciprocity failure and it’s a different kind of reciprocity failure than that Arthur Jones discussed in his early bulletins (1970, 1971). I have personally experienced this. And once the foot becomes too horizontal or last for more than a couple of seconds, the exercise must be terminated as the metabolic-cost/reward is exorbitant.
I am not unique with regard to this experience. Other instructors have observed the inconsistency of effort and inroad as displayed. But as far as I know, this is the first parsing of this observation.
Reciprocity Failure Revisited
Reciprocity failure (RF) is a subject known to serious photographers before the advent of digital cameras. The chemical reactions on the emulsion side of film occur at discrete light measurements that are controlled by two reciprocal factors: shutter speed and lens aperture (F-stop). If one doubled the other had to halve. If the other halved, the other had to double. This maintained the inverse relationship between light intensity and the duration of exposure.
The reciprocity observed with film emulsions is a strict multiplicative inverse (reciprocal) wherein the product is always 1. (2 x ½ = 1, 4 x ¼ = 1, etc.).
For a given film stock, this reciprocity is reliable up and down the continuum of shutter speeds and lens apertures, except at extremely slow (low-light intensity) shutter speeds. Since a camera can only open its lens so far, the only possible solution is to lengthen the exposure by more seconds, even minutes and hours in some cases. Different film stocks exhibit different reciprocity behaviors.
This is the photographic film reciprocity failure that Arthur was familiar with when he applied the same concept to exercise. After all, the body is a chemical factory and it runs chemical processes that have predicable reaction curves until encountering the extremes like in photography.
Arthur observed that performing a greater quantity of exercise increased improvement in a novice subject for only a short while. Thereafter, increasing the intensity AND lessening the duration and/or frequency was required to continue said improvement. If the quantity (duration) and frequency was not reduced as the intensity was increased, the apparent reciprocity between quantity and improvement failed. In essence, the exercise subject’s improvement stopped or retrogressed.
[Note that what Arthur observed with exercise volume and intensity was not a strict multiplicative inverse as with photography, but it possessed a relationship that was certainly reciprocal.]
Within our examination of I4 and I5, we encounter another display of reciprocity failure (RF).
We expect a reciprocity wherein greater intensity of effort yields deeper and faster inroad. But with the deepest fatigue, this relationship fails. And this failure is NOT due to the subject’s lack of effort, mental focus, or general fatigue. The failure is specific to the localized fatigue of the particular muscle in a particular momentarily brief exercise.
I have both witnessed this RF phenomenon in subjects as well as experienced it myself.
Not only does the inroad slope decrease, but it eventually flattens—and in some cases reverses. In other words, although the subject provides ever-increasing intensity of effort during final seconds of the exercise bout, the body seems to maintain a seemingly impenetrable floor to the inroad process. Perhaps this is a kind of protection mechanism.
Graph #2 is my schematic notion of the performance curve when performed at 100% effort after a 10-second ramp.
Note that the maximum magnitude of force is slightly less than what I depict in Graph #1. This represents my appreciation that the ramping has caused some inroad before the subject attains greatest effort. This inroading occurs in the sub-maximum performance as well, but the preload, resting strength is presumed to be very close (slightly above or slightly below) to the red line in both scenarios. Also, the inroad line in Graph #2 is not truly synonymous with the performance line until the subject attains maximum effort.
Graph #2
Again, we see the T3 segment being inconsistent with I4 and the I4-I5 relationship.
I also suspect that the T1 segment—or parts of it—is inconsistent as well.
Is it possible that, although the subject is truly efforting at 100%, his innervation (recruitment) does not completely engage until he’s been at it for several seconds?... and that this further recruitment enables a flat inroad line for a short while?
High Intensity of Effort versus High Recruitment
or
High Intensity of Effort versus Injury
I used the following example when I first wrote my Walking Programs and Physicians article 40 years ago [I developed it into a book, Walking]. I will try to relate it to what I suggest in the previous paragraph.
As a thought experiment ONLY: First Part: While sitting at a desk, push one of your fists downward on the desk, powered only by the triceps of that hand’s arm. Increase your effort gradually, obtaining a 100% effort after 20 seconds and then sustain that 100% effort for another 20 seconds. Then relax. Your involved triceps is deeply fatigued. Your hand is uninjured.
Second Part of the thought experiment: Raise that same hand with your entire arm and slam your fist down on the table as hard as you can. Now your hand is shattered… perhaps your lower arm bones are broken. And your triceps is not fatigued at all.
I originally used this thought experiment to illustrate the difference between high-intensity muscular work and high-force generation, but here, I also want to illustrate the time required for muscular innervation and recruitment to build AFTER you begin with what you believe to be an 100% effort.
In the first instance, the triceps BOTH was allowed adequate time to recruit AND was isolated.
In the second instance, the triceps—although involved in extending the shoulder and in securing the elbow—was not allowed adequate time to recruit much beyond the instant required to provide rigidity to the collective arm.
Nor was the triceps isolated.
Most of the force was generated from the shoulder and was transmitted to the fist. Thus, the recruitment of muscle within the arm (i.e., triceps) was minimal.
Note that the insertion of the triceps on the olecranon was not injured in the least because the high angular speed of the limb nets a very high linear speed of that limb’s periphery, i.e., at the fist. And as this occurs, the force to the triceps is minimal.
Conclusion
At the time of this writing, I have not had access to feedback equipment for over five years. I defer to Gus Diamantopoulos to consider my foregoing assertions and to either confirm or deny their validity. His technical expertise as well as his experience applying novel feedback equipment to the workouts of a voluminous practice provides the basis for the best critique.
Please comment if you have constructive opinions about this topic.
I mentioned that 100% efforts are dangerous to apply in order to document the complete inroad curve. Here is a quote from The Midwestern Doctor regarding antibiotics like Levaquin and Ciprofloxacin:
“This is most well-known with the fluoroquinolone antibiotics, as the drugs (which have a high degree of toxicity to the mitochondria that fuel tissue buildup in the body) frequently cause tendon ruptures to occur over a month after the drugs are stopped.”
I suspect that I have instructed many subjects who never alerted me to the fact that they were on one of these drugs, or that they had been on one of these drugs. I also suspect that their doctors did not tell them of the dangers these drugs posed to their tendons. After all, I have used them and none of my doctors warned me.
This is all the more reason to avoid 100% efforts in the first ~20 seconds of any exercise.
If the inroad curve is taken all the way to zero, we will encounter the failure of the reciprocity regardless of the existence of the foot that occurs somewhat above zero.