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Comment by tachyonbeam | Hacker News Reader

Another part of the answer is that fatigue is largely in our heads. Your body wants you to minimize energy spending, probably because in cavemen days food was so hard to obtain. You will feel tired long before you hit real physical limits. If you've ever taken amphetamines, it becomes obvious. Suddenly, you can spend all night dancing more energetically than you ever did without feeling tired, work longer than ever, etc. Not suggesting that this is in any way sustainable long-term, it isn't, but for me, it really highlighted how my body is physically able to go several times beyond the point where I feel tired and uncomfortable. It's just that some core instincts really don't want me to spend energy liberally.

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> Another part of the answer is that fatigue is largely in our heads.

Not in our heads, but in our nervous system. Some types of fatigue are due to feedback into our central nervous system that reduces muscle activation signals from your brain in order to avoid damaging the muscle. But if you're untrained, your body doesn't actually know where this point really is.

Most strength and endurance gains when you first start training are neurological, where the effect of this feedback loop is pushed back as your body learns the true threshold for muscular damage.

The heart does get fatigued though. You can run a horse into dying from a heart attack, for instance. Most people simply aren't fit enough to push it that far, as their other muscles would give out first.

My guess is that the heart rests between each beat.

Like a jazz musician.

like a serverless function

The concept that helped me most understand my own body was realizing the signal and the system are separate. In your car, the oil light is almost entirely separate from the actual oil system.

It's the same with our body. Feeling tired is separate from being tired. Feeling hungry is separate from being hungry.

Drugs work like putting electrical tape over a low oil light. Amphetamines and even caffeine are good at blocking out the signal. The underlying issue is still there.

But, sort of like you said, the signal comes really early. It's like a low fuel light that comes on when you get to a half tank.

>Drugs work like putting electrical tape over a low oil light. Amphetamines and even caffeine are good at blocking out the signal. The underlying issue is still there

That's only true for some drugs, those that mask pain. Those that stimulate the mind are like feeding an engine nitrous...and sometimes similarly dangerous!

Completely incorrect. Amphetamine releases massive amounts of norepinephrine, which is the direct precursor to epinephrine (adrenaline). This causes a cascade of physical effects, including suppression of insulin, increased blood glucose and a massive boost in cellular energy production.

That’s a far cry from “all in your head”. It’s a systemic response that affects every part of the body.

This looks like the so called Central Governor model. https://en.wikipedia.org/wiki/Central_governor

This makes sense "evolutionary", because it means that even if you're tired after a long day, you actually still have reserves for sudden fight/flight situations.

I'm pretty sure that you'd get rhabdomyolysis if you continued jogging because amphetamines prevent you from feeling tired.

> Another part of the answer is that fatigue is largely in our heads.

Military schools like the Ranger Indoctrination Program really emphasize this point. The body will go on far past the point you think it will stop.

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