Many Shades of Grey

A discussion of spectra rather than all or nothing phenomena in health and performance

I have often written about the difference in understanding between the beginner and the expert. Similarly, I have discussed the simple falsehood (and it’s utility, especially for beginners) vs the complex (or nuanced) truth. The hope for this piece is that it aids readers to better understand the nuances in physiology via the description of what I am calling “the light switch fallacy” and use of a heuristic to combat it, in essence giving readers the metaphorical fishing rod, rather than any metaphorical fish.

The Light Switch Fallacy

As I have written previously the body is a complex system (not a simple or complicated system - more here for an explanation). Given this, it should stand to reason that the truth (or reality) in physiology is always a little more nuanced than ‘all or nothing’ which is akin to a light switch - hence “the light switch fallacy.” (™)

Simple Falsehoods

A light switch is a threshold phenomenon; it is black or white, on or off, all or nothing, there’s no half way or grey. This is how physiology is often discussed and understood. Again, to be fair, this is helpful in the earlier phases of learning physiology where ‘it depends’ makes things infinitely complex. Having said that, it can also be quite harmful or counterproductive at times.

Complex Truths

The dimmer switch, is one where the light be turned on, brightened and dimmed. This is a better analogy for physiology and the way things generally work in physiology. The dimmer switch is all about ‘the shades of grey’, it’s not an all or nothing phenomenon. An example of this is the discussion of whether walking is exercise, where the answer is a complex shade of grey largely determined by intensity. An amble looks physiologically more like sitting and fidgeting, whereas a brisk uphill walk carrying a heavy backpack probably looks physiologically similar to a jog in many ways.

Some Misconceptions Corrected

The following are a group of commonly discussed physiological situations where the “light switch fallacy” is regularly committed.

Fat Burning

The crux of this is that there is an intensity when you are burning only fat (or similar incarnations of this).

• When intensity is sufficiently low, you will burn fat, if it is too high you will eventually not burn fat per se as a substrate to fuel the activity.

• This intensity varies based on diet, training etc.

• People who’ve done more endurance training for longer will burn more fat.

• Diet, both habitual and recent (last meal) influence fat burning quite significantly.

• There is an intensity beyond which you burn exclusively carbohydrates, there is probably always some amount of carbohydrate burned (the exception may be a super low carbohydrate intake and a super low intensity of movement, in a trained individual).

• If your goal is body composition change, the substrate you are using to fuel your movement is not a particularly relevant factor.

From Wang et al 2003

Exercise Thresholds

To be clear, the existence of THREE distinct ‘zones’ with thresholds separating them is well established. However, the further subdivision of these zones is a tool for coaches (“all models are wrong, some are useful”), not based in physiology. Similarly, the thought that these thresholds are hard, easily visible, non-debated and stationary is patently false. As such, there is a range of physiology wherein a transition (aka threshold) occurs, it should stand to reason that this range itself and perhaps a little either side of it, is not immensely different. To be clear this is not to say that one should not view these zones as different but that it is closer to a spectrum than a distinct point where all physiology and adaptations to exercise change.

From Seiler and Tønnessen 2009

Energy Systems

Following on from the above thresholds discussion, energy systems as distinct and thus distinctly trainable at certain intensities as a concept is patently misunderstanding the physiology and its interplay.

The classical figure, below, shows contribution of systems at maximal efforts for different durations. Of note, there is NEVER 100% or 0% contribution of any system. I would suggest this is even more true if there has been an appropriate warm up prior to this (which in effect dictates metabolic rate and thus activity of different systems). Likewise when exercise is not truly maximal, this will vary slightly, as the figure below is with respect to all out exercise.

Thus, it should stand to reason that all training sessions have contributions from all systems - of course to varying degrees and the most benefit will be to intensities closer to those being trained. So your “VO2Max” or “threshold” type of training sessions will always impact all energy systems, and as a result you need not worry about keeping these stimuli distinct if you wish to mix them. Similarly, if you make some mistakes with pacing and intensity, all is not lost (as I have written before, the small details probably don’t matter as much as we think they do).

Relative energy system contribution to the total energy supply for any given duration of maximal exercise from Gastin 2001

Rep Ranges

No doubt readers have seen any number of tables with different repetitions with different end goals. Something like 1-6 reps for strength, 6-12 reps for hypertrophy and 12+ for endurance. Maybe, if you’re as old as me, you even saw that ‘endurance’ called ‘toning’ at some point (jeeez I am happy that word his died - really what people wanted when they said this was a low body fat).

Thankfully these tables are becoming less common and the appreciation for the cake (adaptations) that is a resistance training variable set (ingredients) is becoming more appreciated.
As is the appreciation of true drivers of adaptation;

• Strength and power look to be largely related to neural mechanisms, so intent (move the bar as fast as possible) with significant recovery (>2min) and no significant fatigue within the set (6 reps of less).

• Hypertrophy looks to be mediated largely by volume and to a degree by proximity to failure (though metabolic stress certainly play a roll as discussed in my series on blood flow restriction training here). Thus rest and rep ranges aren’t as relevant and serve more as variables related to logistics and enjoyment.

Where does endurance to fit in?
Using some logic and basics of physiology we can see a continuum emerge from something like a 1RM deadlift (one of a few indicators of true maximum strength) to an ultramarathon (a true feat of endurance). Of course as we add external resistance more strength is required, or as we reduce rests between sets, or increase repetition ranges things becomes more endurance focussed. That said, resistance training is probably not the modality you should be choosing for ‘endurance’ adaptations.

So you can see in the case of resistance training, it’s certainly a case of “more and less” not all or nothing/specific, stand alone adaptations. This should be liberating and allow for you to add variety in training rather than staunchly adhering to certain prescriptions.

Hopefully using the heuristic of physiology being a spectrum, you can avoid falling victim to the “light switch fallacy” and better understand health and performance. Specifically better navigating information and literature pertaining to health and performance.

References

1. Wang, Dizhi & Zhang, Peizhen & Li, Jin. (2023). Crossover point and maximal fat oxidation training effects on blood lipid metabolism in young overweight women: a pilot study. Frontiers in Physiology. 14. 1190109. 10.3389/fphys.2023.1190109.

2. Seiler, Stephen & Tønnessen, Espen. (2009). Intervals, Thresholds, and Long Slow Distance: the Role of Intensity and Duration in Endurance Training. SPORTSCIENCE · sportsci.org. 13. 32-53.

3. Yogev, Assaf & Arnold, Jem & Nelson, Hannah & Clarke, David & Guenette, Jordan & Sporer, Benjamin & Koehle, Michael. (2023). Comparing the reliability of muscle oxygen saturation with common performance and physiological markers across cycling exercise intensity. Frontiers in Sports and Active Living. 5. 10.3389/fspor.2023.1143393.

4. Gastin, P.B. Energy System Interaction and Relative Contribution During Maximal Exercise. Sports Med 31, 725–741 (2001). https://doi.org/10.2165/00007256-200131100-00003

5. Lecce, E., Romagnoli, R., Frinolli, G. et al. Exerting force at the maximal speed drives the increase in power output in elite athletes after 4 weeks of resistance training. Eur J Appl Physiol (2024). https://doi.org/10.1007/s00421-024-05604-1