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  • Neurological/CNS "Fatigue"

    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?

  • #2
    Fatigue is

    1) Really, really complex
    2) Really, really interesting

    Start here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5035715/
    IG / YT

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    • Murelli
      Murelli commented
      Editing a comment
      Great article, thanks!!! What are your thoughts on RTS TRAC tool (qualitative questionnaire, not the orthostatic HR stuff) and using bar speed as a proxy for fatigue/readiness?

      The idea of TRAC is a self-reported multi-factorial (psychological and physical fatigue) qualitative fatigue measurement that aids in the decision making of adding/taking out a set to make the most out of lifting. I've used it since Jun/2017 and like it very much. It only told me to add a set twice and to take a set out 2-3 times. It's already understood that one can't "out-TRAC" bad programming, but in my experience, if fatigue is constantly high/low and one is writing their own programming (let's not enter the merits of this) we have a good indication that programmed stress is not matching recovery and something must be done about it. It resonated a lot with the perceived part of the fatigue (Figure 2 of the article).

      OTOH, RPE accounts for the performance part, and bar speed is a great proxy for RPE and an even better measure of performance. So maybe using a qualitative perceived fatigue rating and a quantitative (bar speed) performance rating could be the greatest non-Blade Runner/Cyberpunk level of fatigue assessment we can get.

    • Austin Baraki
      Austin Baraki commented
      Editing a comment
      I don't have enough personal experience with the system to have an informed opinion on the matter, unfortunately.

      From your description (and what I've heard) - that combination seems to reflect the concepts described in the article, though!

    • PatrickD
      PatrickD commented
      Editing a comment
      This is a great paper. Thanks for posting it.

  • #3
    Originally posted by Murelli View Post
    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.
    I can make an interesting observation, (which is completely anecdotal, and I don't have the muscle-fu to understand everything you are talking about so I don't know if it has any bearing.)
    I spend my days working on tiny very complicated mechanical watches. The better my muscles have become through my barbell training the less mental AND physical fatigue I have doing these tasks and the quicker I can recover my "brain power" and my focus.

    I have no idea if this is true but it seems like when you are doing a repetitive focused task with weak muscles you get sore neck, back, shoulders etc. When you perform with strong muscles you don't get sore. Or maybe it is just that not being a lazy fat ass I have less inflammation over-all. Anyway I find it interesting and it definitely helps motivate me to train.
    Keep Getting Stronger!

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