Epistemic spot checks used to be a series in which I read papers/books and investigated their claims with an eye towards assessing the work’s credibility. I became unhappy with the limitations of this process and am working on creating something better. This post about both the results of applying the in-development process to a particular work, and observations on the process. As is my new custom, this discussion of the paper will be mostly my conclusions. The actual research is available in my Roam database (a workflowy/wiki hybrid), which I will link to as appropriate.
This post started off as an epistemic spot check of Fatigue is a brain-derived emotion that regulates the exercise behavior to ensure the protection of whole body homeostasis, a scientific article by Timothy David Noakes. I don’t trust myself to summarize it fairly (we’ll get to that in a minute), so here is the abstract:
An influential book written by A. Mosso in the late nineteenth century proposed that fatigue that “at first sight might appear an imperfection of our body, is on the contrary one of its most marvelous perfections. The fatigue increasing more rapidly than the amount of work done saves us from the injury which lesser sensibility would involve for the organism” so that “muscular fatigue also is at bottom an exhaustion of the nervous system.” It has taken more than a century to confirm Mosso’s idea that both the brain and the muscles alter their function during exercise and that fatigue is predominantly an emotion, part of a complex regulation, the goal of which is to protect the body from harm. Mosso’s ideas were supplanted in the English literature by those of A. V. Hill who believed that fatigue was the result of biochemical changes in the exercising limb muscles – “peripheral fatigue” – to which the central nervous system makes no contribution. The past decade has witnessed the growing realization that this brainless model cannot explain exercise performance.This article traces the evolution of our modern understanding of how the CNS regulates exercise specifically to insure that each exercise bout terminates whilst homeostasis is retained in all bodily systems. The brain uses the symptoms of fatigue as key regulators to insure that the exercise is completed before harm develops.These sensations of fatigue are unique to each individual and are illusionary since their generation is largely independent of the real biological state of the athlete at the time they develop.The model predicts that attempts to understand fatigue and to explain superior human athletic performance purely on the basis of the body’s known physiological and metabolic responses to exercise must fail since subconscious and conscious mental decisions made by winners and losers, in both training and competition, are the ultimate determinants of both fatigue and athletic performance
The easily defensible version of this claim is that fatigue is a feeling in the brain. The most out there version of the claim is that humans are capable of unlimited physical feats, held back only by their own mind, and the results of sporting events are determined beforehand through psychic dominance competitions. That sounds like I’m being unfair, so let me quote the relevant portion
[A]thletes who finish behind the winner may make the conscious decision not to win, perhaps even before the race begins. Their deceptive symptoms of “fatigue” may then be used to justify that decision. So the winner is the athlete for whom defeat is the least acceptable rationalization
(He doesn’t mention psychic dominance competitions explicitly, but it’s the only way I see to get exactly one person deciding to win each race).
This paper generated a lot of ESC-able claims, which you can see here. These were unusually crisp claims that he provided citations for: absolutely the easiest thing to ESC (having your own citations agree with your summary of them is not sufficient to prove correctness, but lack of it takes a lot works out). But I found myself unenthused about doing so. I eventually realized that I wanted to read a competing explanation instead. Luckily Noakes provided a citation to one, and it was even more antagonistic to him than he claimed.
VO2,max: what do we know, and what do we still need to know?, by Benjamin D. Levine takes several direct shots at Noakes, including:
For the purposes of framing the debate, Dr Noakes frequently likes to place investigators into two camps: those who believe the brain plays a role in exercise performance, and those who do not (Noakes et al. 2004b). However this straw man is specious. No one disputes that ‘the brain’ is required to recruit motor units – for example, spinal cord-injured patients can’t run. There is no doubt that motivation is necessary to achieve VO2,max. A subject can elect to simply stop exercising on the treadmill while walking slowly because they don’t want to continue; no mystical ‘central governor’ is required to hypothesize or predict a VO2 below maximal achievable oxygen transport in this case.
Which I would summarize as “of course fatigue is a brain-mediated feeling: you feel it.”
I stopped reading at this point, because I could no longer tell what the difference between the hypotheses was. What are the actual differences in predictions between “your muscles are physically unable to contract?” and “your brain tells you your muscles are unable to contract”? After thinking about it for a while, I came up with a few:
- The former suggests that there’s no intermediate between “safely working” and “incapacitation”.
- The latter suggestions that you can get physical gains through mental changes alone.
- And that this might lead to tissue damage as you push yourself beyond safe limits.
Without looking at any evidence, #1 seems unlikely to be true. Things rarely work that way in general, much less in bodies.
The strongest pieces of evidence for #2 and #3 isn’t addressed by either paper: cases when mental changes have caused/allowed people to inflict serious injuries or even death to themselves.
- Hysterical strength (aka mom lifts car off baby)
- Involuntary muscle spasms (from e.g., seizures or old-school ECT)
- Stiff-man syndrome.
So I checked these out.
Hysterical strength has not been studied much, probably because IRBs are touchy about trapping babies under cars (with an option on “I was unable to find the medical term for it). There are enough anecdotes that it seems likely to exist, although it may not be common. And it can cause muscle tears, according to several sourceless citations. This is suggestive, but if I was on Levine’s team I’d definitely find it insufficient.
Most injuries from seizures are from falling or hitting something, but it appears possible for injuries to result from overactive muscles themselves. This is complicated by the fact that anti-convulsant medications can cause bone thinning, and by the fact that some unknown percentage of all people are walking around with fractures they don’t know about.
Unmodified electro-convulsive therapy had a small but persistent risk of bone fractures, muscle tears, and join dislocation. Newer forms of ECT use muscle relaxants specifically to prevent this.
Stiff-man Syndrome: Wikipedia says that 10% of stiff-man syndrome patients die from acidosis or autonomic dysfunction. Acidosis would be really exciting- evidence that overexertion of muscles will actually kill you. Unfortunately when I tried to track down the citation, it went nowhere (with one paper inaccessible). Additionally, one can come up with other explanations for the acidosis than muscle exertion. So that’s not compelling.
Overall it does seem clear that (some) people’s muscles are strong enough to break their bones, but are stopped from doing so under normal circumstances. You could call this vindication for Noake’s Central Governor Model, but I’m hesitant. It doesn’t prove you can safely get gains by changing your mindset alone. It doesn’t prove all races are determined by psychic dominance fights. Yes, Noakes was speculating when he postulated that, but without it his theory is something like “you notice when your muscles reach their limits”. When you can safely push what feel like physical limits on the margin feels like a question that will vary a lot by individual and that neither paper tried to answer.
Overall, Fatigue is a brain-derived emotion that regulates the exercise behavior to ensure the protection of whole body homeostasis neither passed nor failed epistemic spot checks as originally conceived, because I didn’t check its specific claims. Instead I thought through its implications and investigated those, which supported the weak but not strong form of Noake’s argument.
In terms of process, the key here was feeling and recognizing the feeling that investigating forward (evaluating the implications of Noake’s arguments) was more important than investigating backwards (the evidence Noake provided for his hypothesis). I don’t have a good explanation for why that felt right at this time, but I want to track it.
Levine's comments seem to be a bit of a strawman of Noakes' position... though, based on your second quote, he may also be a strawman of himself.
Whether sub-maximal oxygen transport ever occurs is entirely beside the point; the implication of the central governor model would be that maximal oxygen transport (or maximal muscle contraction, or whatever) occurs only under extreme circumstances, because the brain subconsciously detects potential for damage to the body and reduces exercise effort. A VO2 max is generally determined by running some exercise test "until exhaustion", with no mechanism in place for knowing how hard the athlete is trying. Presumably the only motivation is "this doctor just told me to keep going until I'm tired" or maybe "I want a good test score for bragging rights". It's definitely not "baby trapped under the car". In this situation the evidence for Noakes' hypothesis would be something like, measure VO2 max again while being chased by a bear (or during some kind of competition, if the IRB doesn't like the bear thing) and it should be higher the second time. If you can improve performance through increased motivation, up to the highest levels of motivation you're willing/able to measure, then common sense would say you still probably haven't reached the actual "maximum". Anecdotally, in at least one instance of extreme motivation I've been able to cycle so hard that in a period of about 30 seconds I gave myself a nasty cough lasting several days; I am unable to repeat this under normal circumstances.
Whether the performance limitation occurs primarily through pain or whether there's also some kind of hard limit is unclear. Limitation of exercise performance by fatigue is familiar to anyone who's tried running a mile in gym class. On the other hand, I've read that major league pitchers are often limited in pitching speed by the stress on their elbow ligaments, rather than by the ability of the muscles to contract harder. If true that means the brain is detecting potentially injurious muscle contractions and putting a damper on them, but without necessarily causing pain.
Following up on this because what I said about VO2 max is misleading. I've since learned that VO2 max is unusually useful as a measure of fitness specifically because it bypasses the problem of motivation. As effort and power output increase during the test, VO2 initially increases but then plateaus even as output continues to increase. So as long as motivation is sufficient to reach that plateau, VO2 max measures a physiological parameter rather than a combination of physiology and motivation.