7 ms·

Mental fatigue impairs physical performance in humans (2009)

110 points by jimsojim 11y ago

PaulHoule 11y ago
Weightlifters have known about this a long time.
- lubonay 11y ago
  As an amateur weightlifter and professional programmer, I've definitely noticed reduced performance following a hard release cycle. What's interesting is that I usually hit PRs immediately after a mental fatigue, but a week or so afterwards it catches up with me and my performance in the wightlifting hall goes down.
  - gonzo 11y ago
    I also lift. You're not going to be able to maintain the peak required for PRs week over week. Don't even try. Take the gains as they come, focus on your training, diet and sleep. If you feel like you're not improving, change something. Weightlifting is mostly mental discipline, acquired via training. A very large percentage of the increased weight you can move is due to improved form and increased recruitment of the existing muscle tissue. (This is why newcomer gains are so large.)
    - pc86 11y ago
      > If you feel like you're not improving, change something. Just make sure you give it enough time to make sure it's truly a plateau (measured in weeks or months depending on how long you've been training). Bouncing around to a new barbell program every 2 weeks will do you little to no good.
blowski 11y ago
I think I learnt about this in biology class in 1995, and the converse that physical fatigue impedes mental performance.
seaghost 11y ago
This is very logical.
- Elte 11y ago
  Even so it's important to have been researched. Where exercise (or nutrition, for that matter) is concerned many statements floating around the internet in particular sound entirely logical - including a lot of false ones.
  - clock_tower 11y ago
    Absolutely; common knowledge becomes scientific knowledge (or is refuted) by experiment and reproducibility. You can go too far in rejecting old wives' tales (like how, in their discovery of vitamin A, the Japanese initially ignored the popular wisdom that buckwheat noodles prevent beriberi), but you can obviously go too far in accepting them as well.
6d6b73 11y ago
This must be directly from the "No Shit, Sherlock" Department
- mhb 11y ago
  Especially since it's from 2009.
- jacobolus 11y ago
  You saw the headline, but you might have missed the second sentence of the abstract: “Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated.” Even if the overall idea is obvious, these effects are good to validate and quantify. For instance, this is a bit less obvious: “[...] physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. [...] our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms.” It would be interesting to do follow-up studies with larger groups of participants to figure out how much variation there is in the effect between different people, or whether there are any ways to reduce the subjective impression of effort to mitigate the apparent throttling effect of mental fatigue. * * * The paper has been cited nearly 300 times in the past 6 years, so it’s probably not completely useless. https://scholar.google.com/scholar?cites=957481530281065221&as_sdt=2005&sciodt=0,5&hl=en https://scholar.google.com/scholar?cites=957481530281065221&...
- dang 11y ago
  Please don't post drive-by dismissals to Hacker News. Even if you're right and the article is worthless, it degrades the quality of the discussions here and signals the wrong things. And if you're wrong, i.e. if the article has value and you missed it, then you're really damaging the thread. In such a case, please either flag the article and move on, or post something substantive about its specifics.
tetrep 11y ago
Interesting. I started biking to/from work and was wondering why going home always felt harder. I suspected it was because my body was a bit tired just from being awake for the past ~8 hours (desk job, so not the work itself) but I never considered mental fatigue to play a part. I wonder if this extends into the positive as well, do cognitive boosting drugs (nootropics?) enhance your performance.
- adrianN 11y ago
  Caffeine is pretty popular for pre-workout drinks.
- agarden 11y ago
  > I wonder if this extends into the positive as well, do cognitive boosting drugs (nootropics?) enhance your performance. Yes. Dextroamphetamine is considered a PED and is banned in (some? all?) professional sports. The Orioles' slugger Chris Davis was suspended a couple years ago for using it. But it is a CNS drug; I believe it is most commonly prescribed to people with ADHD, to improve their focus.
paulojreis 11y ago
This shouldn't come as a surprise; "mental" and "physical" aren't distinct entities, our bodies function as a whole. Having to state this is, I think, a reflex of an ever-present dualist view of the body (in the Cartesian sense, i.e., mind vs. matter).
- magicmu 11y ago
  Cartesian dualism has been a plague on philosophy and psychology IMO. My favorite refutations of that logos come from J.L. Austin and Wittgenstein.
  - paulojreis 11y ago
    Have you read "Descartes' Error", by António Damásio (USC Neurology professor)? I must have recommended this a thousand times. Found it amazing. https://en.wikipedia.org/wiki/Descartes%27_Error https://en.wikipedia.org/wiki/Descartes%27_Error
    - theseatoms 11y ago
      I can attest to this book changing my thinking quite a bit. And it's short enough to read rather quickly.
    - magicmu 11y ago
      Wow that looks like a great read, I'll definitely check it out. Thanks for the recommendation!
- DarkTree 11y ago
  Is the idea that humans can consciously push themselves to keep going even when it feels like you can't a part of the dualism paradigm or no?
  - bchjam 11y ago
    in the sense that you tend to consciously reinforce perceived limits, yes
amelius 11y ago
This also works the other way around. For example, when doing heavy weightlifting in the gym, the central nervous system takes a huge blow, and most people will certainly feel some mental fatigue the hours and possibly even the days after a workout session.
- matwood 11y ago
  Correct. It's why it is hard to lift really hard past 45-60 minutes even if you are working different muscles. The CNS just wears down.
  - beachstartup 11y ago
    45 mins. is when i start hitting the wall. the muscles simply won't move!
    - matwood 11y ago
      Quite a few studies have shown, that unless you are 'chemically' enhanced, all work after about an hour does not do much more for strength or size.
- Silhouette 11y ago
  What constitutes heavy lifting in this case? I find that in a regular gym workout, if I'm doing some sort of circuits with moderate weights, I'll fatigue physically by the third or fourth circuit as you would expect. However, if anything I tend to feel more alert and mentally capable after a workout, at least by the time I've got home, showered and changed.
  - roflc0ptic 11y ago
    Anecdotal: I experienced this doing stronglifts 5x5, which is a program that systematically keeps you lifting near your 5 rep max. Squats in particular seem to mess up my CNS. Moderate weight lifting is awesome for my mood and cognition, heavy weightlifting is destabilizing.
funkdobiest 11y ago
This was shown in the last episode of Arrow. Oliver was so mentally distraught over Felicity breaking up with him that he couldn't physically beat Vandal Savage, and all of Central City was destroyed.
- Silhouette 11y ago
  Maybe he was, but you just totally spoiled it for everyone who doesn't get to see the latest episodes the moment they air. A lot of us outside the US don't even get the "current" season yet. Warning next time, please?
dahart 11y ago
Agree with the comments that this seems to confirm what was already known. (Though if there was no previously published confirmation, then the paper is still relevant.) Two things about the methodology leave me wondering. They gave a 50-pound prize to the top performer on the mental fatigue tests. Couldn't this work against the study as a demotivator? I'm thinking in particular of the other studies showing monetary rewards have a negative performance effect on demanding cognitive tasks. Second, why neutral mood documentaries? Neutral mood doesn't to me make something obviously not mentally demanding. It does sound relatively lower mental effort, but as a research paper methodology, it doesn't seem to prove it, and I feel like there are better options. Why not meditate, for example, or just lie down for an hour listening to soothing beach sounds or something like that?
bitwize 11y ago
This new finding from the most recent issue of the medical journal Duh.
dawnbreez 11y ago
In other news, sky proven to be blue.
- nickthemagicman 11y ago
  Has this been peer reviewed?!
swehner 11y ago
I think the title can be taken as misleading. From the conclusion at the end: "... mental fatigue limits exercise tolerance in humans through higher perception of effort ..." So, according to them, it's the perception that changes with mental fatigue, not because there is any physiological reason to be tired.
- cpncrunch 11y ago
  That is their assumption, but I'm not sure they really can say that. I notice that they didn't measure cortisol, which seems odd. When you exercise, the increase in cortisol results in a 50% increase in endurance compared to if there was no cortisol increase, at least in rat experiments [1]. Given that cortisol is involved in both mental alertness and physical endurance, it seems like it could be a plausible reason for this finding. 1. https://www.researchgate.net/profile/Mehis_Viru/publication/8367555_Cortisol--essential_adaptation_hormone_in_exercise/links/5448da0d0cf22b3c14e336b4.pdf https://www.researchgate.net/profile/Mehis_Viru/publication/...
kazinator 11y ago
This is quite different from something that is familiar to athletes, namely that low blood sugar can get you to lose mental focus and coordination to perform your best. Here, the test subjects were simply subject to some cognitive loading. Nothing "doh, obvious" about this. We know that there is a connection between mental alertness and muscle coordination and drive, but it's not obvious that these can be eroded simply by cognitive activity; essentially a "software" problem.

110 points by jimsojim 11y ago

PaulHoule 11y ago

Weightlifters have known about this a long time.

lubonay 11y ago
As an amateur weightlifter and professional programmer, I've definitely noticed reduced performance following a hard release cycle. What's interesting is that I usually hit PRs immediately after a mental fatigue, but a week or so afterwards it catches up with me and my performance in the wightlifting hall goes down.
- gonzo 11y ago
  I also lift. You're not going to be able to maintain the peak required for PRs week over week. Don't even try. Take the gains as they come, focus on your training, diet and sleep. If you feel like you're not improving, change something. Weightlifting is mostly mental discipline, acquired via training. A very large percentage of the increased weight you can move is due to improved form and increased recruitment of the existing muscle tissue. (This is why newcomer gains are so large.)
  - pc86 11y ago
    > If you feel like you're not improving, change something. Just make sure you give it enough time to make sure it's truly a plateau (measured in weeks or months depending on how long you've been training). Bouncing around to a new barbell program every 2 weeks will do you little to no good.

blowski 11y ago

I think I learnt about this in biology class in 1995, and the converse that physical fatigue impedes mental performance.

seaghost 11y ago

This is very logical.

Elte 11y ago
Even so it's important to have been researched. Where exercise (or nutrition, for that matter) is concerned many statements floating around the internet in particular sound entirely logical - including a lot of false ones.
- clock_tower 11y ago
  Absolutely; common knowledge becomes scientific knowledge (or is refuted) by experiment and reproducibility. You can go too far in rejecting old wives' tales (like how, in their discovery of vitamin A, the Japanese initially ignored the popular wisdom that buckwheat noodles prevent beriberi), but you can obviously go too far in accepting them as well.

6d6b73 11y ago

This must be directly from the "No Shit, Sherlock" Department

mhb 11y ago
Especially since it's from 2009.
jacobolus 11y ago
You saw the headline, but you might have missed the second sentence of the abstract: “Although the impact of mental fatigue on cognitive and skilled performance is well known, its effect on physical performance has not been thoroughly investigated.” Even if the overall idea is obvious, these effects are good to validate and quantify. For instance, this is a bit less obvious: “[...] physiological responses to intense exercise remained largely unaffected. Self-reported success and intrinsic motivation related to the physical task were also unaffected by prior cognitive activity. [...] our study provides experimental evidence that mental fatigue limits exercise tolerance in humans through higher perception of effort rather than cardiorespiratory and musculoenergetic mechanisms.” It would be interesting to do follow-up studies with larger groups of participants to figure out how much variation there is in the effect between different people, or whether there are any ways to reduce the subjective impression of effort to mitigate the apparent throttling effect of mental fatigue. * * * The paper has been cited nearly 300 times in the past 6 years, so it’s probably not completely useless. https://scholar.google.com/scholar?cites=957481530281065221&as_sdt=2005&sciodt=0,5&hl=en https://scholar.google.com/scholar?cites=957481530281065221&...
dang 11y ago
Please don't post drive-by dismissals to Hacker News. Even if you're right and the article is worthless, it degrades the quality of the discussions here and signals the wrong things. And if you're wrong, i.e. if the article has value and you missed it, then you're really damaging the thread. In such a case, please either flag the article and move on, or post something substantive about its specifics.

tetrep 11y ago

Interesting. I started biking to/from work and was wondering why going home always felt harder. I suspected it was because my body was a bit tired just from being awake for the past ~8 hours (desk job, so not the work itself) but I never considered mental fatigue to play a part. I wonder if this extends into the positive as well, do cognitive boosting drugs (nootropics?) enhance your performance.

adrianN 11y ago
Caffeine is pretty popular for pre-workout drinks.
agarden 11y ago
> I wonder if this extends into the positive as well, do cognitive boosting drugs (nootropics?) enhance your performance. Yes. Dextroamphetamine is considered a PED and is banned in (some? all?) professional sports. The Orioles' slugger Chris Davis was suspended a couple years ago for using it. But it is a CNS drug; I believe it is most commonly prescribed to people with ADHD, to improve their focus.

paulojreis 11y ago

This shouldn't come as a surprise; "mental" and "physical" aren't distinct entities, our bodies function as a whole. Having to state this is, I think, a reflex of an ever-present dualist view of the body (in the Cartesian sense, i.e., mind vs. matter).

magicmu 11y ago
Cartesian dualism has been a plague on philosophy and psychology IMO. My favorite refutations of that logos come from J.L. Austin and Wittgenstein.
- paulojreis 11y ago
  Have you read "Descartes' Error", by António Damásio (USC Neurology professor)? I must have recommended this a thousand times. Found it amazing. https://en.wikipedia.org/wiki/Descartes%27_Error https://en.wikipedia.org/wiki/Descartes%27_Error
  - theseatoms 11y ago
    I can attest to this book changing my thinking quite a bit. And it's short enough to read rather quickly.
  - magicmu 11y ago
    Wow that looks like a great read, I'll definitely check it out. Thanks for the recommendation!
DarkTree 11y ago
Is the idea that humans can consciously push themselves to keep going even when it feels like you can't a part of the dualism paradigm or no?
- bchjam 11y ago
  in the sense that you tend to consciously reinforce perceived limits, yes

amelius 11y ago

This also works the other way around. For example, when doing heavy weightlifting in the gym, the central nervous system takes a huge blow, and most people will certainly feel some mental fatigue the hours and possibly even the days after a workout session.

matwood 11y ago
Correct. It's why it is hard to lift really hard past 45-60 minutes even if you are working different muscles. The CNS just wears down.
- beachstartup 11y ago
  45 mins. is when i start hitting the wall. the muscles simply won't move!
  - matwood 11y ago
    Quite a few studies have shown, that unless you are 'chemically' enhanced, all work after about an hour does not do much more for strength or size.
Silhouette 11y ago
What constitutes heavy lifting in this case? I find that in a regular gym workout, if I'm doing some sort of circuits with moderate weights, I'll fatigue physically by the third or fourth circuit as you would expect. However, if anything I tend to feel more alert and mentally capable after a workout, at least by the time I've got home, showered and changed.
- roflc0ptic 11y ago
  Anecdotal: I experienced this doing stronglifts 5x5, which is a program that systematically keeps you lifting near your 5 rep max. Squats in particular seem to mess up my CNS. Moderate weight lifting is awesome for my mood and cognition, heavy weightlifting is destabilizing.

funkdobiest 11y ago

This was shown in the last episode of Arrow. Oliver was so mentally distraught over Felicity breaking up with him that he couldn't physically beat Vandal Savage, and all of Central City was destroyed.

Silhouette 11y ago
Maybe he was, but you just totally spoiled it for everyone who doesn't get to see the latest episodes the moment they air. A lot of us outside the US don't even get the "current" season yet. Warning next time, please?

dahart 11y ago

Agree with the comments that this seems to confirm what was already known. (Though if there was no previously published confirmation, then the paper is still relevant.) Two things about the methodology leave me wondering. They gave a 50-pound prize to the top performer on the mental fatigue tests. Couldn't this work against the study as a demotivator? I'm thinking in particular of the other studies showing monetary rewards have a negative performance effect on demanding cognitive tasks. Second, why neutral mood documentaries? Neutral mood doesn't to me make something obviously not mentally demanding. It does sound relatively lower mental effort, but as a research paper methodology, it doesn't seem to prove it, and I feel like there are better options. Why not meditate, for example, or just lie down for an hour listening to soothing beach sounds or something like that?

bitwize 11y ago

This new finding from the most recent issue of the medical journal Duh.

dawnbreez 11y ago

In other news, sky proven to be blue.

nickthemagicman 11y ago
Has this been peer reviewed?!

swehner 11y ago

I think the title can be taken as misleading. From the conclusion at the end: "... mental fatigue limits exercise tolerance in humans through higher perception of effort ..." So, according to them, it's the perception that changes with mental fatigue, not because there is any physiological reason to be tired.

cpncrunch 11y ago
That is their assumption, but I'm not sure they really can say that. I notice that they didn't measure cortisol, which seems odd. When you exercise, the increase in cortisol results in a 50% increase in endurance compared to if there was no cortisol increase, at least in rat experiments [1]. Given that cortisol is involved in both mental alertness and physical endurance, it seems like it could be a plausible reason for this finding. 1. https://www.researchgate.net/profile/Mehis_Viru/publication/8367555_Cortisol--essential_adaptation_hormone_in_exercise/links/5448da0d0cf22b3c14e336b4.pdf https://www.researchgate.net/profile/Mehis_Viru/publication/...

kazinator 11y ago

This is quite different from something that is familiar to athletes, namely that low blood sugar can get you to lose mental focus and coordination to perform your best. Here, the test subjects were simply subject to some cognitive loading. Nothing "doh, obvious" about this. We know that there is a connection between mental alertness and muscle coordination and drive, but it's not obvious that these can be eroded simply by cognitive activity; essentially a "software" problem.