
Mental fatigue impairs physical performance in humans (2009) - jimsojim
http://jap.physiology.org/content/106/3/857
======
paulojreis
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).

~~~
Laaw
Why is this kind of comment (a la "no duh, scientists!") always highly praised
on the Internet and in general, even from otherwise intelligent, thinking
folks??

Since _when_ have we been okay with "no duh" being our source of information?
Come on guys, we have to figure shit out before we get to say "no duh", and
then instead of saying "no duh" (which is another word for "common sense",
which we all laugh heartily about in other contexts) we get to cite the
studies and the research that provides a strong correlation.

~~~
paulojreis
I was a scientist until a few months ago (until I finished my PhD,
essentially), so - believe me - I know the value of studies which "state the
obvious", even when the conclusion seems "small" (which isn't the case,
anyway).

My previous comment wasn't meant as a "no, duh", really. I'm sorry it came out
that way. I'm highly favourable to studies which prove "common sense" (or
disprove: those I live even better!). The comment was just to share my
opinion: the fact that this kind of studied is shared (here, and in other
media) highlights how dualism is still basically the common sense view.

~~~
hvfhhvv
I know. God we, as a species, are very dumb.

------
amelius
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.

~~~
gxespino
From a personal experience: my best days are when I get a good morning workout
in. I feel energized the rest of the day. I think the sense of early
accomplishment helps in a way.

~~~
melted
There's workout, and then there's workout. Try squatting 405lbs or deadlifting
495lbs for reps (or whatever your limits are when it comes to maximum
exertion). That stuff wears you out pretty good. I wouldn't recommend doing it
in the morning. Cardio, light lifting, sure, but that doesn't really tax the
CNS that much.

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

------
PaulHoule
Weightlifters have known about this a long time.

~~~
lubonay
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
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
> _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.

------
dahart
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?

------
kazinator
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.

------
tetrep
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
Caffeine is pretty popular for pre-workout drinks.

------
swehner
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
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/...](https://www.researchgate.net/profile/Mehis_Viru/publication/8367555_Cortisol
--essential_adaptation_hormone_in_exercise/links/5448da0d0cf22b3c14e336b4.pdf)

------
6d6b73
This must be directly from the "No Shit, Sherlock" Department

~~~
dang
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.

------
dawnbreez
In other news, sky proven to be blue.

~~~
nickthemagicman
Has this been peer reviewed?!

------
bitwize
This new finding from the most recent issue of the medical journal _Duh_.

------
seaghost
This is very logical.

~~~
Elte
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
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.

------
funkdobiest
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
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?

