Computational mechanisms underlying the dynamics of physical and cognitive fatigue, 2023, Matthews et al

Abstract

The willingness to exert effort for reward is essential but comes at the cost of fatigue. Theories suggest fatigue increases after both physical and cognitive exertion, subsequently reducing the motivation to exert effort. Yet a mechanistic understanding of how this happens on a moment-to-moment basis, and whether mechanisms are common to both mental and physical effort, is lacking.

In two studies, participants reported momentary (trial-by-trial) ratings of fatigue during an effort-based decision-making task requiring either physical (grip-force) or cognitive (mental arithmetic) effort. Using a novel computational model, we show that fatigue fluctuates from trial-to-trial as a function of exerted effort and predicts subsequent choices. This mechanism was shared across the domains. Selective to the cognitive domain, committing errors also induced momentary increases in feelings of fatigue. These findings provide insight into the computations underlying the influence of effortful exertion on fatigue and motivation, in both physical and cognitive domains.

Open access, https://www.sciencedirect.com/science/article/pii/S0010027723002378

 

I like that it's questioning everything that's "known" about fatigue. We don't really "know" anything about fatigue and fatigue-like states, so starting from scratch would be a good idea. I do feel that my "fatigue-like state" is derived from the neural/glial valuation and choice to exert, rather than a lack of ATP or other such physical limitations.

 

Is this not all stuff known for decades? Centuries even? Millennia?!

Because aside from the silly New age biopsychosocial stuff making fatigue about lack of motivation, all of this has been well-known for decades.

I guess there's the cognitive effort being similar that is not fully accepted, but again that's mostly a function of holding on to silly psychobehavioral stuff that would somehow have mental energy be its own separate thing from any other kind of effort. Which makes no sense. The body is an organism, it's not a fully separate set of organs operating in isolation. If this stuff is so obvious to me that I've been repeating it for years, damn, I don't know anymore. This profession is so amazing on some things, and completely messed up at other times.

All knowledge out of physical training, and it doesn't even have to be scientific, makes all of this pretty obvious about muscular recovery, and how training has its limits, how humans aren't machines and those processes can't be supplemented with simple chemical solutions, something that's been tried for millennia. How this isn't about willpower and motivation at all. The 20th century is filled with attempts at creating "super soldiers", all of which have failed miserably.

I really thought all this stuff was basic knowledge. But the prominence of BPS belief systems really does make it questionable. It's probably a good thing on the whole that basic stuff like this is being reaffirmed, but it shows that for all intents and purposes, medicine has basically made zero progress on the notion, definition and mechanism of fatigue, with most of this stuff already known back in Antiquity.

I guess the less is stop fooling around with psycho-mumbo-jumbo, but that's not about to happen any time soon, there's still quite a few years more with silly BPS nonsense left before they let go of it.