I was discussing this in another venue, tried finding some studies about it but my google-fu failed me (I’m not good at google-fu), but I’ll try to be brief:
When we perform a high intensity compound lift like a deadlift single we get pretty fatigued, i.e. our form is severely compromised if we try some more reps with a brief rest. Usually this is explained by fatiguing MUs. Alternatively, if we perform an activity that demands high focus and/or extreme motor refinement, usually in a non-repeating pathway (not knitting, but something more like surgery and some kinds of handcraft and body performances) we get a deep kind of “mental” fatigue along with little muscular fatigue, but usually it goes away with little rest.
Most of what I’ve seen shared in social media by Austin points to psychological factors regarding fatigue and exhaustion, the abstracts I’ve read point to muscular fatigue in the MU fatigue, and then the CNS just turns MUs on and off or changes the recruitment pattern in order to try to perform the task. So what is that “CNS fatigue”, “neural fatigue” that we see people claim?
My uninformed opinion tells me that the broscience “CNS fatigue” is bullshit, but that what we experience when training starts to get too fatiguing is actually a metabolic/endocrinological impact from all the inflammatory signals (cytokines, cortisol, etc.) and a psychological feedback loop akin to somatization. The one remaining factor that I couldn’t wrap my head around is the role of electrolytes (sodium, calcium, potassium, phosphorus) in the MU activation after they begin to fatigue. Again google-fu was too weak (maybe I need to do a Google-Fu LP?) and yielded no good results.
TLDR (not for you docs, but for readers): Is broscience CNS fatigue bullshit and “neural/mental fatigue” just result from the muscle fatigue/inflammation and psychological factors? Are the electrolytes related to a neural component of MU fatigue?