A challenge to the masses: CNS fatigue

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Karky

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I hear a lot of people talk about the CNS in relation to fatigue on here.. I've done it myself, too, but lately I haven't said it. There is a reason for that and this thread has the same reason.

I figured I'd post this to give a lot of people here some food for thought:

Can anyone tell me what CNS fatigue is? Why does low rep and explosive work give you more CNS fatigue than high rep? How does the CNS fatigue?
How do you know you've got CNS fatigue.. how do you measure it, how do you know it's in the CNS?.. Do you know what the CNS is?
Short term effects (within one workout) long term effects (CNS fatigue between workouts)? Most on here talk about long term CNS fatigue.. I.E, not that it's a part of you having to stop working out, but rather a part of how long you need to wait until you can work out again.
 
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Karky said:
Do you know what the CNS is?
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That's only question on there I can answer, and I know what it does from a strictly physiological standpoint (not related to training), which is why I have never used the term CNS fatigue in my life. An explanation would be awesome though.
 
my whole point about making this thread is that there's very little out there on CNS fatigue in the long term. There is a bit in the short term.. not being able to activate muscles fully as the workout goes on, etc, but I've never seen anything that lasts over days.. which really sucks :(
 
My understanding of the chronic is that you feel so overwhelmed, that you don't want to go back to the workout that initiated it. It can have some severe psychological consequences in addition to the physiological.

I've mildly overtrained when I skipped rest days and each workout felt like diminishing returns characterized with worsening weakness. An extended rest period with a bulking diet reset my system.
 
I can't give you any studies, but I have an idea of what all those things are, after inducing CNS fatigue via trying to hit a new 1 RM everyday, heavy volume, little rest/food, etc. This lasted for at least three months before I finally backed off.

Basically I was really, really tired, all the time. A bit depressed, unable to focus on anything, low motivation, an intense feeling of "I don't want to do this" when lifting. I always had to take a dump when I was getting ready to lift. Even when I got myself to the gym and started lifting, I always wanted to just leave soon after.

I want to stay away from talking out of my ass on scientific matters, but aren't adrenal fatigue and CNS fatigue closely related? I'm sure recruiting motor units is tough work for the CNS, but that isn't the only thing going on. For instance, if you work yourself up, getting ready to hit a new PR, you're essentially pumping yourself full of adrenaline. Lifting in general stimulates the SNS. When overstimulated, the PSNS overcompensates to try and bring your body back down to a normal level.

I didn't see the end of this for another year or more. I mean, I would eventually come to lift less, but all that energy I was using for lifting just got divided into more physical activity.

To this day I feel like I was messed up so long that long terms effects of it are still felt today in my resulting circumstances and person in general.

But yeah, I just started lifting less and doing less. I saw/have been seeing better gains.
 
I figure it's got to be a neurotransmitter deficiency, the question is why. What would cause decreased Ach, NE, DA, 5HT or whichever one it is.. Decreased hydroxylases? Increased Km of their respective hydroxylases? Decreased precursors? There's so many things included in CNS, I think we need to narrow our search to really try to identify what's going on.. Got any good studies (even short term) karks?

EDIT* Hell it could even be downregulation of their receptors from consistent stimulation (at any point in the chain, even the NMJ).
 
I've typically only seen CNS fatigue in relation to severe overtraining, the kind of overtraining that causes lifelong athletes to go into depression and never return to sport. Pretty much everything Leiyunfat described.

But that typically takes an intense amount of (over)training, and usually isn't something that the average gym goer has to worry about.

As far as I've read, I think that there is some improvement in CNS pathway and signal efficiency, which would mirror the neuromuscular adaptation in the PNS, in response to exercise. Typically, the body does not improve itself unless it is (damaged) placed under stress. I guess that it would be logical to assume that there is some form of very short term "fatigue" on the CNS caused by exercise and other forms of activity and stress that spurs adaptation and improvement.

It's possible that such short term fatigue could segway to full-blown CNS fatigue and syndrome overtraining if inadequate rest, recovery, and variation isn't provided.

Again though, I'm just going off of what I've studied about CNS fatigue in relation to the long-term effects of continued overtraining, and hypothesizing on the intermediate short term CNS.

I could be way off... but hopefully I'm not. :) If someone can come up with links to any sort of research or text on this, I'd definitely be up for the reading.
 
Hoss said:
I figure it's got to be a neurotransmitter deficiency, the question is why. What would cause decreased Ach, NE, DA, 5HT or whichever one it is.. Decreased hydroxylases? Increased Km of their respective hydroxylases? Decreased precursors? There's so many things included in CNS, I think we need to narrow our search to really try to identify what's going on.. Got any good studies (even short term) karks?

EDIT* Hell it could even be downregulation of their receptors from consistent stimulation (at any point in the chain, even the NMJ).
Click to expand...

KM? No abbreviations please, I need to be able to google your worlds :p

I've seen stuff indicating that ammonia might play a part (limited evidence, but increased ammonia levels are associated with fatigue)

I haven't read the entire article yet.

Increased tryptophan (precussor to 5HT) entry into the brain which causes an increase in 5HT.. Theoretical basis on this is pretty good, IMO, but studies supplementing with BCAAs, which decrease tryptophan entry into the brain, show mixed results on performance.

I've also heard stuff about the neuromuscular junction (NMJ). I've also heard stuff about the CNS itself not being able to fire the MUs properly.
here's one on the motor cortex:
I've only read the abstract, because lately my VPN thingy isn't working.. so I can't connect to the uni's subscriptions from home :(

Another interesting hypothesis is the central governor hypothesis.
Basically somewhere there is a system that senses if the heart (maybe other important organs too) is getting enough blood and oxygen. So if the muscles take up so much blood and oxygen that the heart might suffer (there would also be built in a reserve, so the heart wouldn't have to be in danger, but would have to be close to being in danger), the brain won't recruit as many motor units. This will result in the muscles using less oxygen so more oxygen can go to other vital tissues. The evidence they use for this is that under hypoxia, people will get tired without having a high lactate production.. so they get tired without the peripheral side of things. They also use some EMG stuff to see that muscles are less active as training under hypoxia goes on.



But all of this is short term, within one work out.. not between work outs. Someone must have done some studies on muscle activation before training compared with 1-2 days after training.. but I can't find any.

I also wonder if there could be anything that's calcium related.. that would probably go under peripheral fatigue, but still.. Fatigue is a really interesting subject.
 
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Km is the disassociation constant, basically referring to affinity of a substrate to its receptor or protein (something tells me you knew this but didn't recognize Km).

"Data synthesis: 1 The increase in γ -aminobutyric acid is one of the reasons for sports fatigue. Animal experiments have proved that the increase in γ -aminobutyric acid has a close correlation with the central inhibition in sports fatigue. 2 Dopamine plays an important role in controlling sports. The central fatigue may be correlated with the decrease in dopamine during sports. 3 Choline supplement could regulate acetylcholine levels and center conduction of excitation, which is helpful to delay sports fatigue. 4 Studies have proved that the increase in 5-hydroxytryptamine in some encephalic regions is related to central fatigue during sports. At present, the researches on nutrition intervention often focus on the influence of glucose and amino acids supplement on 5-hydroxytryptamine. Conclusion: The changes in partial neurotransmitters are related to fatigue during sports. But to get more reliable results, we still need further researches."
 
yeah, a small Km means you need only a little substrate to reach the maximum velocity of the reaction, while a high Km means the opposite. I remember reading about all sorts of different constants in chemistry some time ago, I had to google to remember which one this was, though :p That's the thing about reading as much as I do.. I'm amazed sometimes about how much I know (bragging, yes), but I'm even more amazed when I think about how much I've forgotten :p
 
A teacher once told us that's when you're educated: when you realize you know tons, yet barely anything.
 
lol, yeah, that's so true. The more I read and the more I learn the less I can actually answer because I know things are so complicated (specially when it comes to the human body). One year ago I would answer questions directly with a certain answer that I wouldn't be able to answer today, because I know how many factors actually play in.

This made me think about something funny. I live in a collective; i share kitchen with 6 other people. One of them is a mathematician and he always keeps asking me very concrete questions, and thinks that me not being able to tell him exactly how long he will be sore after his karate training is unacceptable and a sign that I'm bad at what I do :D

he also thinks I should be able to use what I know about the human body to calculate who will win a tennis match. I usually just tell him that I have put up an equation, but there aren't good enough mathematicians in the world to actually complete it :D
 
Karky said:
How applicable is research on horses to humans?
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the first paragraph:cool3:

Overtraining is an imbalance between training and recovery leading to symptoms associated with a neuroendocrine dysbalance called the overtraining syndrome, a disease characterized by behavioral, emotional and physical symptoms similar with depression. Although the prevalence of overtraining is high in human and equine athletes, at present no sensitive and specific test is available to prevent or diagnose overtraining. Nowadays, it is believed that combination of different (hormonal) parameters appear to be the best indicators of overtraining. Therefore, this review provides a summary of previous literature examining the response of the HPA axis and the GH-IGF-I axis to acute and chronic exercise as well as overtraining in humans and horses. The exercise induced hormonal responses seem to be equal for the equine as well as the human athlete, which makes comparisons possible.
 
that speed reading is no good i do it to much myself :).
 
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