13 ms·

If the heart is a muscle, why doesn't it ever get tired?

431 points by zem 7y ago

jaked89 7y ago
https://pubmed.ncbi.nlm.nih.gov/29798816/ https://pubmed.ncbi.nlm.nih.gov/29798816/
- 01100011 7y ago
  Yes. Also this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ It may be that the heart is multi-functional. It may serve as a regulator, a pump, or some combination of the two.
docbrown 7y ago
As we were told during high school biology: cardiovascular muscle contains vast amounts of mitochondria as compared to other muscle types. Mitochondria are good. Therefore, more and stronger mitochondria = more efficient working muscle tissue. One of my favorite professors holds a PhD in kinesiology (exercise physiology concentration) and wrote his dissertation on the mitochondria. As he stated many times in class: if you want to have a superhuman composition, acquire more mitochondria. he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria.
- chrisco255 7y ago
  I wonder what the trade-offs would be if you could amplify mitochondria in skeletal muscle?
  - bamboozled 7y ago
    I'm pretty sure this is what happens if you're a weight lifter?
    - usrusr 7y ago
      Weight lifting isn't an endurance sport. If you want mitochondria obsession, look for anything long distance.
      - labawi 7y ago
        Non-repetitive weight lifting wouldn't be a good example, but neither is anything in 10s of km. Mitochondria produce ATP as energy. You can't store much¹ ATP, therefore mitochondria must be capable of producing ATP at your near peak output (say 10s average). I'd look at anything with high >10s peak power (probably a bonus if it's aerobic). Many bodybuilding exercises would qualify. ¹ Lactic acid is a byproduct of ATP production, therefore ATP supplies surely last less, than what it takes to start producing lots of lactic acid.
  - DoreenMichele 7y ago
    As a guess: You would be unable to rest without utter exhaustion, and possibly even not then. You might need to keep flexing your muscles constantly.
    - smabie 7y ago
      Why would that be?
      - DoreenMichele 7y ago
        I'm basing it off of this comment: https://news.ycombinator.com/item?id=22643333 https://news.ycombinator.com/item?id=22643333 And this follow-up comment sort of agrees with my inference -- at least the first part of my inference: https://news.ycombinator.com/item?id=22644577 https://news.ycombinator.com/item?id=22644577 Edit: I will add that I am also, no doubt, basing it off of background knowledge about cell function. For example, mitochondria change and develop greater capacity to process X if you consume a lot of it, which is part of the addiction process and part of why withdrawal is a thing. If you consume a lot of, say, alcohol, you need to ramp down gradually so that the body can make changes at the cellular level to adjust to the lesser amount of alcohol and this is part of why cold turkey is so very hard and it is generally recommended that you taper off. I used to ask smart people with PhDs and the like a lot of questions about cell function and read what I could get my hands on that could be followed by a lay person because I have a genetic disorder that impacts cell function.
    - hobofan 7y ago
      There are other cell types that have a strongly increased amount of mitochondria like brown adipose tissue. They also don't have a "need" to perform some work constantly. As with any cell function how much work mitochondria perform is highly regulated. Just because you have a lot of them doesn't mean you can't turn their function down.
      - DoreenMichele 7y ago
        Nadia Commenci was recruited as a gymnast at age five because she was too active and breaking the furniture at home. She made the first ever perfect 10 score in the Olympics. They didn't have a way to display it. It got displayed as 1.00 because they only had three spaces on the sign. Her best friend became a professional ballerina. I have heard that Chuck Norris does two workouts a day and if he skips one, he makes everyone around him crazy. If he does two per day, he's calm, cool and collected and fine to be around. If he doesn't, welp, he can't sit still and he can't control his mouth and he bounces off the walls and everyone can't stand him. I also talked about the addiction process and mitochondrial function in a different comment.
  - ChuckMcM 7y ago
    You become more chimp like.
  - gameswithgo 7y ago
    you would need more red blood cells to feed them, and at sone point that puts you at risk for a heart attack because your blood is too thick
    - nradov 7y ago
      That's not a realistic risk unless you have some rare medical condition or are doping with a PED like EPO.
  - PeterisP 7y ago
    The cells would consume more energy, so you'd need more food, so in conditions of food scarcity (i.e. 99% of our [pre]history) you would be at a severe disadvantage as your tribe would starve to death in conditions when more efficient homo sapiens would still survive.
    - EamonnMR 7y ago
      Also require more oxygen and produce more heat.
- justinator 7y ago
  Mitochondria are the powerhouse of the cell.
  - charles_f 7y ago
    Mitochondria are the powerhouse of the cell x2 in the heart
  - rootsudo 7y ago
    I love this meme.
    - stjohnswarts 7y ago
      It's not a meme, it's an analogy.
      - falcor84 7y ago
        Well, it definitely is a meme as defined by Dawkins[0]. In general, I would say that analogies and metaphors like this one have a huge impact on normal science, and are one of the main things that change during a paradigm shift. I recall a great example in how 150 years ago people thought of the body's physiology as analogous to a steam engine with downstream effects due to pressure building up, contrasted to how in today's computer age, we tend to think of physiology in terms of signal processing. [0] https://en.wikipedia.org/wiki/Memetics https://en.wikipedia.org/wiki/Memetics
        lioeters 7y ago
        I agree, the imagery that we use in metaphor (in speech, visually, or in conception) influences how we think about things - and a popular analogy like that about the mitochondria is certainly a meme, a "cultural information transfer". As you pointed out, a fairly recent meme is "the brain is the computer of the body", and maybe "the Internet is the brain of humanity".
- hyperdunc 7y ago
  Then I guess the obvious question a non-physiologist would ask is, why don't all our muscles already have vast amounts of mitochondria? If it's that beneficial with no major downsides then surely evolution would have stumbled on that configuration already?
  - ivalm 7y ago
    Mitochondria do produce a lot of free radicals. Probably energy expensive to maintain cells like that.
    - rolph 7y ago
      not only energy expensive but free radicals do genetic damage, and a this requires the second budget for a set of enzymes to counteract the damages and scrub out FR's
      - lumost 7y ago
        Why isn't Heart Cancer more common if it's producing so many free radicals? Are there other mechanisms blocking genetic damage?
        dodobirdlord 7y ago
        Muscle cells don't replicate past early childhood development, they just get bigger and add more nuclei. So muscle cancers are extremely rare compared to cancers of other tissues.
        rolph 7y ago
        each nucleus contains a full genomic content. muscles are more of a "myosynsynctium" than a group of cells. there are cohorts of cells that are more prone to becoming cancer due to thier developmental origins and the complement of developmental mechanisms that can be reactivated. things such as cell adhesion, and cell migration through tissue dermal cells are good at this as they do these things over the course of development. muscles are built where they will live so these features are inhibited somewhat more completely and harder to "switch on or off"
- ramraj07 7y ago
  He would have lost his sons college thition then. Mitochondrial _inhibition_ is actually more correlated with longevity than the other way around. If more mitochondria meant more efficient working muscle tissue, then that's what we would have evolved, there's always a compromise. Are you sure you can keep the same power output for a given mass and volume of muscle if you keep increasing mitochondrial numbers? Even the reddit answer clearly says that the heart muscle is rate limited by oxygenation (they have more mitochondria but are also highly vascularized to power the mitochondria). More mitochondria===more power doesn't mean it's better for us, physiology is rarely that simple.
  - catalogia 7y ago
    > Mitochondrial _inhibition_ is actually more correlated with longevity than the other way around. Longevity is overrated. The light that burns twice as bright lives half as long. I'd rather be a superhuman for 40 years than feeble for 120 years.
    - TheSpiceIsLife 7y ago
      As I understand it, longevity in the life-extension sense is generally taken to mean years of good health. Edit: fixed a word.
    - goatinaboat 7y ago
      I'd rather be a superhuman for 40 years than feeble for 120 years. But that’s not a choice you can actually make, it’s out of your control. What if you could choose by taking a pill?
    - rubber_duck 7y ago
      Steroids let you control this trade-off
    - ci5er 7y ago
      Maybe yes, maybe no. But evolution didn't decide on the structure and behavior of our throw-away-cup bodies in order to make our puny minds sitting on top our puny brains happy. For better or for worse, in humans (we are not turtles, for example, they have their own success strategy), AVERAGE 2nd generation reproductive success is the measure of our existence. The collection of strategies to maximize that are different for human men and human women. But aligned. On average. 2nd-generation reproductive success is our "purpose" in a universe made mostly out of hydrogen. Nothing more - nothing less.
- jldugger 7y ago
  > he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria. Did he mention whether faculty get free family tuition or not?
  - ikeyany 7y ago
    His children will be made to forego college in order to trailblaze the up and coming trade of mitochondria hunting.
    - im3w1l 7y ago
      I read it as him claiming that investing in it would be a sure bet.
- hkmurakami 7y ago
  This just reminded me of the game Parasite Eve.
- heartisnt001 7y ago
  I am going to hijack this top comment. > If the heart is a muscle, why doesn't it get tired? Because it's illogical to assume muscles fatigue. They physically don't get to the point where they can no longer operate -- under normal everyday use and exercise. What does happen, that may seem like fatigue, is a gradual shifting of fuel sources by muscle cells depending on exertion levels. Suffice to say, it goes like this: - First: Creatine Phosphate is the first energy source in your muscles, the most powerful one, and the least plentiful. It's the first to go during exercise and is partly why you focus on 1-5 reps for strength-focused lifting (that's roughly how long it takes to get used up) - Second: Glycogen in your muscles and liver. This is fairly plentiful, fairly powerful, and rapidly mobilizeable. After your creatine phosphate stores are emptied, glycogen takes over. This is still a very powerful fuel source, but its metabolism creates a negative feedback loop on itself. You can only sustain moderate exertion (see: sprinting or 8-15 reps moderate weight) for around 60-90 seconds, before glycogen is no longer easily accessible (note: accessible, not depleted. It's almost impossible to deplete in a single workout) - Finally: Fat. Once you've exhausted glycogen, your body turns to fatty acid oxidation. This is the least powerful but most plentiful. In normal exercise you use a mix of fat and glycogen depending on how hard you exert yourself. Harder: more glycogen. Easier: more fat. If you want to know how it feels like to run on only fat: do a marathon -- then hit the wall. What you experience is literally the complete depletion of glycogen, and a transition into "low-power" mode as your body starts running on the only fuel source it has left: fat. You have months of this fuel source on your body, you won't run out. You can keep walking for days without having eaten anything or slept, but you won't be able to run at any pace that resembles a jog. I know, because I have. What's the point of all this? It's to illustrate that muscle "exhaustion" is a misnomer. Muscle exhaustion is, in reality, a depletion of power-generating fuels leading to a state of minimal exertion. Coincidentally, that's the mode the heart operates in 24/7. Coincidentally, the heart has an asinine amount of mitochondria to fuel non-stop fatty acid oxidation. The heart doesn't fatigue because it's not physically possible. It doesn't need creatine phosphate or glycogen (very very little) to pump blood. It's not a strenuous task. An aside: if you had as much mitochondria in all your cells, as you do in your heart's, you would waste away.
  - raidicy 7y ago
    Some anecdata but, I suffered from very bad muscle injuries from one summer in 2014. I skateboarded hard for two days in a row. Ran 3-ish miles on both days. Two days later I was exhausted but took two ibuprofen and I went to a beach with friends anyway. Where I skated hard at a park for a few hours, then swam, then ran. A day or so later, after not getting the best sleep, on an hour drive home, I pull both quads. The day after I had to call out for a week. I was exhausted and my obliques, core, quads, and arms were beyond sore. I laid around for most of the week. Your muscles may not get "exhausted" but it seems like there must be some breakdown in the cells that outpace recovery at some point.
- loeg 7y ago
  > he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737409/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737409/ aka https://en.wikipedia.org/wiki/SR9009 https://en.wikipedia.org/wiki/SR9009
  - lioeters 7y ago
    Good stuff! > Activation of Rev-ErbA-α by SR9009 in mice increases exercise capacity by increasing mitochondria counts in skeletal muscle. > Some companies are selling SR9009 online for human use as a 'research chemical'. > "The drug [alters] the circadian rhythm (in mice) and we would need to assume in humans – and we don't know if it is beneficial or detrimental at this point." --- It has "several issues that make it unsuitable for human use". > Firstly, it has no oral bioavailability. I know the company selling this is indicating taking it orally is ok – but it doesn't even get into the blood. > SR9009 has some functional groups that are known to have potential toxicology liabilities and it would never be developed as a drug. > So bottom line – I would never recommend using this compound at this point. That being said – we are still working on improved compounds with one of the potential uses being sarcopenia – loss of muscle and strength due to aging.
- peter_retief 7y ago
  Aren't mitochondria captive cells from early evolutionary times? I googled and from nature.com "Mitochondria and chloroplasts likely evolved from engulfed prokaryotes that once lived as independent organisms. At some point, a eukaryotic cell engulfed an aerobic prokaryote, which then formed an endosymbiotic relationship with the host eukaryote, gradually developing into a mitochondrion."
bo1024 7y ago
I don't think any of the top answers are good at all. I suspect part of the reason is how poorly we understand muscle fatigue. Many answers talk about lactate and how it builds up in muscles but not the heart. However they don't say anything about how lactate is related to fatigue. A lot of the answers talk about the high mitochondria concentration in the heart. This allows it to use more oxygen and produce more ATP. That's fine, but again, what is the connection between mitochondria and fatigue? One example to show these answers are inadequate: You can walk or jog at an easy effort for a long time and eventually your muscles will get tired and sore, without ever going anaerobic or lactic -- i.e. without your leg muscles ever needing more energy than your mitochondria can provide or ever producing more lactic acid than your bloodstream can clear away immediately. So mitochondria and lactic acid can't be the full story. I don't know the true answer and I'm not a biologist, but I suspect the heart has evolved to never be the weakest link. Maybe exercise always strengthens the heart at a higher rate than the other muscles. Or maybe part of the answer is that we don't have nerves to feel soreness/tiredness in the heart? (I have seen research that the heart does experience temporary damage from e.g. marathons, so it does get tired in some sense. Of course then it gets stronger.)
- tachyonbeam 7y ago
  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.
  - travisjungroth 7y ago
    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.
akiselev 7y ago
Because all known multicellular organisms, with the exception of a few (<10 out of millions) microscopic species, use the electron transport chain to produce ATP and the animals whose primary organ responsible for supplying the entire body's metabolism suddenly stopped all died on the spot. Now, how those animals survived is a much more interesting question.
01100011 7y ago
I hate to spread a wacky idea, but I ran across something on Facebook the other day that I initially wanted to disprove but then started to seem plausible. The general consensus is that the heart is a pump and generally the sole driver of circulation in mammals. There is an alternative theory, which seems easy to disprove, that the heart is more of a regulator and operates more like a hydraulic ram. I can post more links later. Curious if anyone has heard of that and if there is a rebuttal to the idea. Edit: The paper I was thinking of, if anyone is interested, is here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ Edit #2, from the paper: "Gladwin et al. estimated that 25% to 30% of basal human blood flow can be attributed to red blood cell-induced production of nitric oxide by vascular endothelium."
- thaumasiotes 7y ago
  > The general consensus is that the heart is a pump and generally the sole driver of circulation in mammals. It's certainly not the general consensus that the heart is the sole driver of circulation in mammals. Your heart drives the flow of blood out through your arteries; it's much less effective at driving blood back through your veins.
  - TheSpiceIsLife 7y ago
    Veins contain one-way valves, so veinous return is aided by movement and muscle contraction. The lymphatic system doesn’t have a pump at all and is entirely driven by movement + muscle contraction + fluid pressure as a result of tissue integrity.
- deleted 7y ago
  [deleted]
- rzzzt 7y ago
  I always think of it as a peristaltic pump: big tube, squeeze one side, squeeze the other to circulate blood. This paper might be of interest: "A review of selected pumping systems in nature and engineering--potential biomimetic concepts for improving displacement pumps and pulsation damping" https://www.ncbi.nlm.nih.gov/pubmed/26335744 https://www.ncbi.nlm.nih.gov/pubmed/26335744
jxramos 7y ago
There's three types of muscles: smooth, skeletal, and cardiac. They share a lot in common but are very distinct to each other. Might not be an apples to apples comparison because fatigue is a notion taken from our experience of skeletal muscles which is not cardiac muscle. It would be interesting to compare the energy spend of each, or rather the power each is capable of. As enduring as the heart is its likely limited in its power output because its just circulating fluid against resistance and gravity. I don't know how much energy is required for that. Bench pressing a hundred pounds, what's the power in that and how many heart beats would equal that work?
- TheSpiceIsLife 7y ago
  Someone with more maths chops than me should be able to tell you how much energy it takes to lift 50kg 50cm over 5 seconds at Earth’s surface. I’d imagine it’s at least a magnitude of more than the heart would expend in 5 seconds.
  - drdeca 7y ago
    50 kg * 50 cm * 9.8 (m/s^2) PE = M g h
    - anticensor 7y ago
      245 joules
      - ORioN63 7y ago
        245J/5s == 49W This website [1] shows several sources. The range of estimated power outputs is between 1W and 5W. https://hypertextbook.com/facts/2003/IradaMuslumova.shtml https://hypertextbook.com/facts/2003/IradaMuslumova.shtml OP hypothesis seems to be correct.
        bagacrap 7y ago
        yes, but the original question was "how many heartbeats". First source in the link says 75bpm and 2w, 245J/2w = 122.5 seconds or ~2 minutes of 75bpm, 150 beats.
downerending 7y ago
It doesn't because it can't. Any hearts that got tired died, and their owners did not reproduce. It's like being Atlas--you're holding up the world. It's not a virtue, a flaw, a conceit, nor anything at all. It is because it must be.
- hadlock 7y ago
  This. Beating heart on an ultrasound is widely considered the first true sign of a healthy pregnancy. Almost before anything else, the heart develops and immediately begins beating, and does so until you die. There's a reason why the cliche X is the beating heart of Y.
- avoz 7y ago
  I'd actually be interested to know how many mitochondria are there in the heart of other species when compared to humans, because the mere assertion that the heart doesn't get tired because otherwise we would die does little to explain the mechanisms behind it.
- naasking 7y ago
  > It doesn't because it can't. Any hearts that got tired died, and their owners did not reproduce. They're asking why the heart can't get tired. You answered why we evolved such that the heart can't get tired, which is not the same question.
  - downerending 7y ago
    True. My answer was more of a cri de coeur.
herbstein 7y ago
This isn't suuuuper relevant, but the title instantly made me think of one of my favorite folk-punk songs by Ramshackle Glory called "Your heart is a muscle the size of your fist". The album version is really good[0], but I do vastly prefer the energy of this phone-recorded live version[1]. [0] https://youtu.be/pC3IrqUpm9U [1] https://youtu.be/ubX9JaaqBXo
- milofeynman 7y ago
  Not: Your Heart Is a Muscle by Carly Rae Jepsen?
luc_ 7y ago
Wow. Incredibly reasonable question that I've never given much thought to. Thanks for sharing!
ummonk 7y ago
Isn't a heart attack basically the heart muscle getting too fatigued to keep going? It doesn't seem to ben the only muscle that doesn't get tired - e.g. if it weren't for sleeping I suspect the neck muscles could hold up the head indefinitely. The diaphragm obviously never gets tired either, unless you have asthma. I can also type pretty much indefinitely without feeling muscle fatigue in my fingers. climbing on the other hand will exert them enough to quickly fatigue them.
- 01100011 7y ago
  A heart attack is caused by an interruption in the supply of blood to the heart muscle(or by an electrical problem, i.e. arrhythmia).
  - ummonk 7y ago
    Ah, TIL.
bad_user 7y ago
Missed from that first comment is that... the heart not getting tired is a problem. You can overwork your heart which can lead to lesions. Endurance athletes who exercise excessively can have heart problems. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538475/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538475/ That muscles get tired and sore is a feature because it prevents damage.
- hinkley 7y ago
  Atrial fib is no joke. I don't know who needs to hear this, but if you are considering becoming an endurance athlete, and especially if you are considering transitioning to ultra-endurance, go see a fucking doctor before, after and during. Source: father had a stroke 20 years later.
6510 7y ago
The heart does get tired eventually. Poor blood circulation will do terrible things. This is a pretty cool technology. https://billionsinchange.in/en/solutions/renew/ https://billionsinchange.in/en/solutions/renew/ It squeezes the legs to help the heart pump blood.
- elric 7y ago
  Wouldn't that increase mean arterial pressure? Would the heart reduce its output as a response to the external pressure? And what's with their claims of it clearing "trash" from your brain?
  - 6510 7y ago
    I honestly have no idea. The marketing material suggests old people show health improvements. I'm no expert but so far it seems officially it doesn't do anything but looks promising. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3021100/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3021100/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC385349/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC385349/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3383356/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3383356/
tummler 7y ago
Yogis would posit it's prana shakti.
- carapace 7y ago
  Aye. The heart is not really a pump for blood. There's a kind of signal that comes in from above through the Sun to the Earth and then up into each beings heart. The organ is more of a resonator or tuned waveform guide for this pulse, which then flows through the body moving the blood. There's a kind of meditation you can do that involves becoming aware of the pulse throughout your body. The subjective experience is very powerful, so much so that I've personally have not gone "all the way" as I fear it would dissolve me. Metaphorically, direct awareness of the blood pulse is like looking into the sun, it's too potent.
macawfish 7y ago
It does can get tired. This tiredness is just experienced differently from tiredness of other muscles.
macawfish 7y ago
Hasn't anyone here ever heard of a broken heart? A broken heart is a tired heart.
sebow 7y ago
Doesn't it though?As we grow older, the heart rate usually slows down.And since it is a muscle, it shows that working out can improve heart rate and other vascular conditions. "Tired" not as in the other muscles, but you can't function at 100% for long period of times.
aaaaarghZombies 7y ago
The heart does get tired, it can operate at very high levels but only for a short period of time. It also has a pretty good blood supply.
huffmsa 7y ago
Everybody always wonders about the heart and never about the intestines. Shit in shit out, day after day after day. If not for you guts never tiring, your heart wouldn't get any fuel, you'd get a fistula and die of sepsis, you'd back up like a lot of people's pipes this week because they're flushing unflushable wipes. So here's to the real unsung smooth muscles of the body. We salute you.
polytronic 7y ago
It does rest after every beat
yawaramin 7y ago
Oh hey, this reminds me of one of my favourite songs https://www.youtube.com/watch?v=Y5OpvDdVtYU https://www.youtube.com/watch?v=Y5OpvDdVtYU
ck2 7y ago
Any runner or cyclist knows your heart gets tired. A beat is not guaranteed volume, a rested heart can move more blood at the same heartrate than a tired one.
econcon 7y ago
Also, why heart doesn't get bigger/thicker walls through cardio? Like we can do enough reps and sets to achieve hypertrophy?
- science4sail 7y ago
  The heart does experience hypertrophy from exercise. https://en.wikipedia.org/wiki/Athletic_heart_syndrome https://en.wikipedia.org/wiki/Athletic_heart_syndrome
perlgeek 7y ago
Isn't it funny how many meanings the word "why" has? My first explanation, on hearing the question, was: because, evolutionarily speaking, no organism would have relied so heavily on the heart if it got tired easily. Or looking on it another way, if the heart was easily fatigued, we'd be all dead, or be very different.
- hinkley 7y ago
  There have been a few astrophysics shows where they talked about 'why are we here?', with varying definitions of 'why' or special emphasis on here (as opposed to elsewhere). In most of them, someone says words to the effect of "well if we weren't here, we wouldn't be having this conversation". Survivor bias, in a very literal sense.
  - perlgeek 7y ago
    ... also know as https://en.wikipedia.org/wiki/Anthropic_principle https://en.wikipedia.org/wiki/Anthropic_principle
havella 7y ago
It does. Try riding a bike above FTP at altitude for as long as you can. Then describe how your heart feels for the reminder of that day.

431 points by zem 7y ago

jaked89 7y ago

https://pubmed.ncbi.nlm.nih.gov/29798816/ https://pubmed.ncbi.nlm.nih.gov/29798816/

01100011 7y ago
Yes. Also this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ It may be that the heart is multi-functional. It may serve as a regulator, a pump, or some combination of the two.

docbrown 7y ago

As we were told during high school biology: cardiovascular muscle contains vast amounts of mitochondria as compared to other muscle types. Mitochondria are good. Therefore, more and stronger mitochondria = more efficient working muscle tissue. One of my favorite professors holds a PhD in kinesiology (exercise physiology concentration) and wrote his dissertation on the mitochondria. As he stated many times in class: if you want to have a superhuman composition, acquire more mitochondria. he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria.

chrisco255 7y ago
I wonder what the trade-offs would be if you could amplify mitochondria in skeletal muscle?
- bamboozled 7y ago
  I'm pretty sure this is what happens if you're a weight lifter?
  - usrusr 7y ago
    Weight lifting isn't an endurance sport. If you want mitochondria obsession, look for anything long distance.
    - labawi 7y ago
      Non-repetitive weight lifting wouldn't be a good example, but neither is anything in 10s of km. Mitochondria produce ATP as energy. You can't store much¹ ATP, therefore mitochondria must be capable of producing ATP at your near peak output (say 10s average). I'd look at anything with high >10s peak power (probably a bonus if it's aerobic). Many bodybuilding exercises would qualify. ¹ Lactic acid is a byproduct of ATP production, therefore ATP supplies surely last less, than what it takes to start producing lots of lactic acid.
- DoreenMichele 7y ago
  As a guess: You would be unable to rest without utter exhaustion, and possibly even not then. You might need to keep flexing your muscles constantly.
  - smabie 7y ago
    Why would that be?
    - DoreenMichele 7y ago
      I'm basing it off of this comment: https://news.ycombinator.com/item?id=22643333 https://news.ycombinator.com/item?id=22643333 And this follow-up comment sort of agrees with my inference -- at least the first part of my inference: https://news.ycombinator.com/item?id=22644577 https://news.ycombinator.com/item?id=22644577 Edit: I will add that I am also, no doubt, basing it off of background knowledge about cell function. For example, mitochondria change and develop greater capacity to process X if you consume a lot of it, which is part of the addiction process and part of why withdrawal is a thing. If you consume a lot of, say, alcohol, you need to ramp down gradually so that the body can make changes at the cellular level to adjust to the lesser amount of alcohol and this is part of why cold turkey is so very hard and it is generally recommended that you taper off. I used to ask smart people with PhDs and the like a lot of questions about cell function and read what I could get my hands on that could be followed by a lay person because I have a genetic disorder that impacts cell function.
  - hobofan 7y ago
    There are other cell types that have a strongly increased amount of mitochondria like brown adipose tissue. They also don't have a "need" to perform some work constantly. As with any cell function how much work mitochondria perform is highly regulated. Just because you have a lot of them doesn't mean you can't turn their function down.
    - DoreenMichele 7y ago
      Nadia Commenci was recruited as a gymnast at age five because she was too active and breaking the furniture at home. She made the first ever perfect 10 score in the Olympics. They didn't have a way to display it. It got displayed as 1.00 because they only had three spaces on the sign. Her best friend became a professional ballerina. I have heard that Chuck Norris does two workouts a day and if he skips one, he makes everyone around him crazy. If he does two per day, he's calm, cool and collected and fine to be around. If he doesn't, welp, he can't sit still and he can't control his mouth and he bounces off the walls and everyone can't stand him. I also talked about the addiction process and mitochondrial function in a different comment.
- ChuckMcM 7y ago
  You become more chimp like.
- gameswithgo 7y ago
  you would need more red blood cells to feed them, and at sone point that puts you at risk for a heart attack because your blood is too thick
  - nradov 7y ago
    That's not a realistic risk unless you have some rare medical condition or are doping with a PED like EPO.
- PeterisP 7y ago
  The cells would consume more energy, so you'd need more food, so in conditions of food scarcity (i.e. 99% of our [pre]history) you would be at a severe disadvantage as your tribe would starve to death in conditions when more efficient homo sapiens would still survive.
  - EamonnMR 7y ago
    Also require more oxygen and produce more heat.
justinator 7y ago
Mitochondria are the powerhouse of the cell.
- charles_f 7y ago
  Mitochondria are the powerhouse of the cell x2 in the heart
- rootsudo 7y ago
  I love this meme.
  - stjohnswarts 7y ago
    It's not a meme, it's an analogy.
    - falcor84 7y ago
      Well, it definitely is a meme as defined by Dawkins[0]. In general, I would say that analogies and metaphors like this one have a huge impact on normal science, and are one of the main things that change during a paradigm shift. I recall a great example in how 150 years ago people thought of the body's physiology as analogous to a steam engine with downstream effects due to pressure building up, contrasted to how in today's computer age, we tend to think of physiology in terms of signal processing. [0] https://en.wikipedia.org/wiki/Memetics https://en.wikipedia.org/wiki/Memetics
      - lioeters 7y ago
        I agree, the imagery that we use in metaphor (in speech, visually, or in conception) influences how we think about things - and a popular analogy like that about the mitochondria is certainly a meme, a "cultural information transfer". As you pointed out, a fairly recent meme is "the brain is the computer of the body", and maybe "the Internet is the brain of humanity".
hyperdunc 7y ago
Then I guess the obvious question a non-physiologist would ask is, why don't all our muscles already have vast amounts of mitochondria? If it's that beneficial with no major downsides then surely evolution would have stumbled on that configuration already?
- ivalm 7y ago
  Mitochondria do produce a lot of free radicals. Probably energy expensive to maintain cells like that.
  - rolph 7y ago
    not only energy expensive but free radicals do genetic damage, and a this requires the second budget for a set of enzymes to counteract the damages and scrub out FR's
    - lumost 7y ago
      Why isn't Heart Cancer more common if it's producing so many free radicals? Are there other mechanisms blocking genetic damage?
      - dodobirdlord 7y ago
        Muscle cells don't replicate past early childhood development, they just get bigger and add more nuclei. So muscle cancers are extremely rare compared to cancers of other tissues.
        rolph 7y ago
        each nucleus contains a full genomic content. muscles are more of a "myosynsynctium" than a group of cells. there are cohorts of cells that are more prone to becoming cancer due to thier developmental origins and the complement of developmental mechanisms that can be reactivated. things such as cell adhesion, and cell migration through tissue dermal cells are good at this as they do these things over the course of development. muscles are built where they will live so these features are inhibited somewhat more completely and harder to "switch on or off"
ramraj07 7y ago
He would have lost his sons college thition then. Mitochondrial _inhibition_ is actually more correlated with longevity than the other way around. If more mitochondria meant more efficient working muscle tissue, then that's what we would have evolved, there's always a compromise. Are you sure you can keep the same power output for a given mass and volume of muscle if you keep increasing mitochondrial numbers? Even the reddit answer clearly says that the heart muscle is rate limited by oxygenation (they have more mitochondria but are also highly vascularized to power the mitochondria). More mitochondria===more power doesn't mean it's better for us, physiology is rarely that simple.
- catalogia 7y ago
  > Mitochondrial _inhibition_ is actually more correlated with longevity than the other way around. Longevity is overrated. The light that burns twice as bright lives half as long. I'd rather be a superhuman for 40 years than feeble for 120 years.
  - TheSpiceIsLife 7y ago
    As I understand it, longevity in the life-extension sense is generally taken to mean years of good health. Edit: fixed a word.
  - goatinaboat 7y ago
    I'd rather be a superhuman for 40 years than feeble for 120 years. But that’s not a choice you can actually make, it’s out of your control. What if you could choose by taking a pill?
  - rubber_duck 7y ago
    Steroids let you control this trade-off
  - ci5er 7y ago
    Maybe yes, maybe no. But evolution didn't decide on the structure and behavior of our throw-away-cup bodies in order to make our puny minds sitting on top our puny brains happy. For better or for worse, in humans (we are not turtles, for example, they have their own success strategy), AVERAGE 2nd generation reproductive success is the measure of our existence. The collection of strategies to maximize that are different for human men and human women. But aligned. On average. 2nd-generation reproductive success is our "purpose" in a universe made mostly out of hydrogen. Nothing more - nothing less.
jldugger 7y ago
> he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria. Did he mention whether faculty get free family tuition or not?
- ikeyany 7y ago
  His children will be made to forego college in order to trailblaze the up and coming trade of mitochondria hunting.
  - im3w1l 7y ago
    I read it as him claiming that investing in it would be a sure bet.
hkmurakami 7y ago
This just reminded me of the game Parasite Eve.
heartisnt001 7y ago
I am going to hijack this top comment. > If the heart is a muscle, why doesn't it get tired? Because it's illogical to assume muscles fatigue. They physically don't get to the point where they can no longer operate -- under normal everyday use and exercise. What does happen, that may seem like fatigue, is a gradual shifting of fuel sources by muscle cells depending on exertion levels. Suffice to say, it goes like this: - First: Creatine Phosphate is the first energy source in your muscles, the most powerful one, and the least plentiful. It's the first to go during exercise and is partly why you focus on 1-5 reps for strength-focused lifting (that's roughly how long it takes to get used up) - Second: Glycogen in your muscles and liver. This is fairly plentiful, fairly powerful, and rapidly mobilizeable. After your creatine phosphate stores are emptied, glycogen takes over. This is still a very powerful fuel source, but its metabolism creates a negative feedback loop on itself. You can only sustain moderate exertion (see: sprinting or 8-15 reps moderate weight) for around 60-90 seconds, before glycogen is no longer easily accessible (note: accessible, not depleted. It's almost impossible to deplete in a single workout) - Finally: Fat. Once you've exhausted glycogen, your body turns to fatty acid oxidation. This is the least powerful but most plentiful. In normal exercise you use a mix of fat and glycogen depending on how hard you exert yourself. Harder: more glycogen. Easier: more fat. If you want to know how it feels like to run on only fat: do a marathon -- then hit the wall. What you experience is literally the complete depletion of glycogen, and a transition into "low-power" mode as your body starts running on the only fuel source it has left: fat. You have months of this fuel source on your body, you won't run out. You can keep walking for days without having eaten anything or slept, but you won't be able to run at any pace that resembles a jog. I know, because I have. What's the point of all this? It's to illustrate that muscle "exhaustion" is a misnomer. Muscle exhaustion is, in reality, a depletion of power-generating fuels leading to a state of minimal exertion. Coincidentally, that's the mode the heart operates in 24/7. Coincidentally, the heart has an asinine amount of mitochondria to fuel non-stop fatty acid oxidation. The heart doesn't fatigue because it's not physically possible. It doesn't need creatine phosphate or glycogen (very very little) to pump blood. It's not a strenuous task. An aside: if you had as much mitochondria in all your cells, as you do in your heart's, you would waste away.
- raidicy 7y ago
  Some anecdata but, I suffered from very bad muscle injuries from one summer in 2014. I skateboarded hard for two days in a row. Ran 3-ish miles on both days. Two days later I was exhausted but took two ibuprofen and I went to a beach with friends anyway. Where I skated hard at a park for a few hours, then swam, then ran. A day or so later, after not getting the best sleep, on an hour drive home, I pull both quads. The day after I had to call out for a week. I was exhausted and my obliques, core, quads, and arms were beyond sore. I laid around for most of the week. Your muscles may not get "exhausted" but it seems like there must be some breakdown in the cells that outpace recovery at some point.
loeg 7y ago
> he was always willing to bet his kids entire college tuition funds if you could show him a pill that would produce more mitochondria. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737409/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737409/ aka https://en.wikipedia.org/wiki/SR9009 https://en.wikipedia.org/wiki/SR9009
- lioeters 7y ago
  Good stuff! > Activation of Rev-ErbA-α by SR9009 in mice increases exercise capacity by increasing mitochondria counts in skeletal muscle. > Some companies are selling SR9009 online for human use as a 'research chemical'. > "The drug [alters] the circadian rhythm (in mice) and we would need to assume in humans – and we don't know if it is beneficial or detrimental at this point." --- It has "several issues that make it unsuitable for human use". > Firstly, it has no oral bioavailability. I know the company selling this is indicating taking it orally is ok – but it doesn't even get into the blood. > SR9009 has some functional groups that are known to have potential toxicology liabilities and it would never be developed as a drug. > So bottom line – I would never recommend using this compound at this point. That being said – we are still working on improved compounds with one of the potential uses being sarcopenia – loss of muscle and strength due to aging.
peter_retief 7y ago
Aren't mitochondria captive cells from early evolutionary times? I googled and from nature.com "Mitochondria and chloroplasts likely evolved from engulfed prokaryotes that once lived as independent organisms. At some point, a eukaryotic cell engulfed an aerobic prokaryote, which then formed an endosymbiotic relationship with the host eukaryote, gradually developing into a mitochondrion."

bo1024 7y ago

I don't think any of the top answers are good at all. I suspect part of the reason is how poorly we understand muscle fatigue. Many answers talk about lactate and how it builds up in muscles but not the heart. However they don't say anything about how lactate is related to fatigue. A lot of the answers talk about the high mitochondria concentration in the heart. This allows it to use more oxygen and produce more ATP. That's fine, but again, what is the connection between mitochondria and fatigue? One example to show these answers are inadequate: You can walk or jog at an easy effort for a long time and eventually your muscles will get tired and sore, without ever going anaerobic or lactic -- i.e. without your leg muscles ever needing more energy than your mitochondria can provide or ever producing more lactic acid than your bloodstream can clear away immediately. So mitochondria and lactic acid can't be the full story. I don't know the true answer and I'm not a biologist, but I suspect the heart has evolved to never be the weakest link. Maybe exercise always strengthens the heart at a higher rate than the other muscles. Or maybe part of the answer is that we don't have nerves to feel soreness/tiredness in the heart? (I have seen research that the heart does experience temporary damage from e.g. marathons, so it does get tired in some sense. Of course then it gets stronger.)

tachyonbeam 7y ago
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.
- travisjungroth 7y ago
  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.

akiselev 7y ago

Because all known multicellular organisms, with the exception of a few (<10 out of millions) microscopic species, use the electron transport chain to produce ATP and the animals whose primary organ responsible for supplying the entire body's metabolism suddenly stopped all died on the spot. Now, how those animals survived is a much more interesting question.

01100011 7y ago

I hate to spread a wacky idea, but I ran across something on Facebook the other day that I initially wanted to disprove but then started to seem plausible. The general consensus is that the heart is a pump and generally the sole driver of circulation in mammals. There is an alternative theory, which seems easy to disprove, that the heart is more of a regulator and operates more like a hydraulic ram. I can post more links later. Curious if anyone has heard of that and if there is a rebuttal to the idea. Edit: The paper I was thinking of, if anyone is interested, is here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215277/ Edit #2, from the paper: "Gladwin et al. estimated that 25% to 30% of basal human blood flow can be attributed to red blood cell-induced production of nitric oxide by vascular endothelium."

thaumasiotes 7y ago
> The general consensus is that the heart is a pump and generally the sole driver of circulation in mammals. It's certainly not the general consensus that the heart is the sole driver of circulation in mammals. Your heart drives the flow of blood out through your arteries; it's much less effective at driving blood back through your veins.
- TheSpiceIsLife 7y ago
  Veins contain one-way valves, so veinous return is aided by movement and muscle contraction. The lymphatic system doesn’t have a pump at all and is entirely driven by movement + muscle contraction + fluid pressure as a result of tissue integrity.
deleted 7y ago
[deleted]
rzzzt 7y ago
I always think of it as a peristaltic pump: big tube, squeeze one side, squeeze the other to circulate blood. This paper might be of interest: "A review of selected pumping systems in nature and engineering--potential biomimetic concepts for improving displacement pumps and pulsation damping" https://www.ncbi.nlm.nih.gov/pubmed/26335744 https://www.ncbi.nlm.nih.gov/pubmed/26335744

jxramos 7y ago

There's three types of muscles: smooth, skeletal, and cardiac. They share a lot in common but are very distinct to each other. Might not be an apples to apples comparison because fatigue is a notion taken from our experience of skeletal muscles which is not cardiac muscle. It would be interesting to compare the energy spend of each, or rather the power each is capable of. As enduring as the heart is its likely limited in its power output because its just circulating fluid against resistance and gravity. I don't know how much energy is required for that. Bench pressing a hundred pounds, what's the power in that and how many heart beats would equal that work?

TheSpiceIsLife 7y ago
Someone with more maths chops than me should be able to tell you how much energy it takes to lift 50kg 50cm over 5 seconds at Earth’s surface. I’d imagine it’s at least a magnitude of more than the heart would expend in 5 seconds.
- drdeca 7y ago
  50 kg * 50 cm * 9.8 (m/s^2) PE = M g h
  - anticensor 7y ago
    245 joules
    - ORioN63 7y ago
      245J/5s == 49W This website [1] shows several sources. The range of estimated power outputs is between 1W and 5W. https://hypertextbook.com/facts/2003/IradaMuslumova.shtml https://hypertextbook.com/facts/2003/IradaMuslumova.shtml OP hypothesis seems to be correct.
      - bagacrap 7y ago
        yes, but the original question was "how many heartbeats". First source in the link says 75bpm and 2w, 245J/2w = 122.5 seconds or ~2 minutes of 75bpm, 150 beats.

downerending 7y ago

It doesn't because it can't. Any hearts that got tired died, and their owners did not reproduce. It's like being Atlas--you're holding up the world. It's not a virtue, a flaw, a conceit, nor anything at all. It is because it must be.

hadlock 7y ago
This. Beating heart on an ultrasound is widely considered the first true sign of a healthy pregnancy. Almost before anything else, the heart develops and immediately begins beating, and does so until you die. There's a reason why the cliche X is the beating heart of Y.
avoz 7y ago
I'd actually be interested to know how many mitochondria are there in the heart of other species when compared to humans, because the mere assertion that the heart doesn't get tired because otherwise we would die does little to explain the mechanisms behind it.
naasking 7y ago
> It doesn't because it can't. Any hearts that got tired died, and their owners did not reproduce. They're asking why the heart can't get tired. You answered why we evolved such that the heart can't get tired, which is not the same question.
- downerending 7y ago
  True. My answer was more of a cri de coeur.

herbstein 7y ago

This isn't suuuuper relevant, but the title instantly made me think of one of my favorite folk-punk songs by Ramshackle Glory called "Your heart is a muscle the size of your fist". The album version is really good[0], but I do vastly prefer the energy of this phone-recorded live version[1]. [0] https://youtu.be/pC3IrqUpm9U [1] https://youtu.be/ubX9JaaqBXo

milofeynman 7y ago
Not: Your Heart Is a Muscle by Carly Rae Jepsen?

luc_ 7y ago

Wow. Incredibly reasonable question that I've never given much thought to. Thanks for sharing!

ummonk 7y ago

Isn't a heart attack basically the heart muscle getting too fatigued to keep going? It doesn't seem to ben the only muscle that doesn't get tired - e.g. if it weren't for sleeping I suspect the neck muscles could hold up the head indefinitely. The diaphragm obviously never gets tired either, unless you have asthma. I can also type pretty much indefinitely without feeling muscle fatigue in my fingers. climbing on the other hand will exert them enough to quickly fatigue them.

01100011 7y ago
A heart attack is caused by an interruption in the supply of blood to the heart muscle(or by an electrical problem, i.e. arrhythmia).
- ummonk 7y ago
  Ah, TIL.

bad_user 7y ago

Missed from that first comment is that... the heart not getting tired is a problem. You can overwork your heart which can lead to lesions. Endurance athletes who exercise excessively can have heart problems. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538475/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3538475/ That muscles get tired and sore is a feature because it prevents damage.

hinkley 7y ago
Atrial fib is no joke. I don't know who needs to hear this, but if you are considering becoming an endurance athlete, and especially if you are considering transitioning to ultra-endurance, go see a fucking doctor before, after and during. Source: father had a stroke 20 years later.

6510 7y ago

The heart does get tired eventually. Poor blood circulation will do terrible things. This is a pretty cool technology. https://billionsinchange.in/en/solutions/renew/ https://billionsinchange.in/en/solutions/renew/ It squeezes the legs to help the heart pump blood.

elric 7y ago
Wouldn't that increase mean arterial pressure? Would the heart reduce its output as a response to the external pressure? And what's with their claims of it clearing "trash" from your brain?
- 6510 7y ago
  I honestly have no idea. The marketing material suggests old people show health improvements. I'm no expert but so far it seems officially it doesn't do anything but looks promising. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3021100/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3021100/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC385349/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC385349/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3383356/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3383356/

tummler 7y ago

Yogis would posit it's prana shakti.

carapace 7y ago
Aye. The heart is not really a pump for blood. There's a kind of signal that comes in from above through the Sun to the Earth and then up into each beings heart. The organ is more of a resonator or tuned waveform guide for this pulse, which then flows through the body moving the blood. There's a kind of meditation you can do that involves becoming aware of the pulse throughout your body. The subjective experience is very powerful, so much so that I've personally have not gone "all the way" as I fear it would dissolve me. Metaphorically, direct awareness of the blood pulse is like looking into the sun, it's too potent.

macawfish 7y ago

It does can get tired. This tiredness is just experienced differently from tiredness of other muscles.

macawfish 7y ago

Hasn't anyone here ever heard of a broken heart? A broken heart is a tired heart.

sebow 7y ago

Doesn't it though?As we grow older, the heart rate usually slows down.And since it is a muscle, it shows that working out can improve heart rate and other vascular conditions. "Tired" not as in the other muscles, but you can't function at 100% for long period of times.

aaaaarghZombies 7y ago

The heart does get tired, it can operate at very high levels but only for a short period of time. It also has a pretty good blood supply.

huffmsa 7y ago

Everybody always wonders about the heart and never about the intestines. Shit in shit out, day after day after day. If not for you guts never tiring, your heart wouldn't get any fuel, you'd get a fistula and die of sepsis, you'd back up like a lot of people's pipes this week because they're flushing unflushable wipes. So here's to the real unsung smooth muscles of the body. We salute you.

polytronic 7y ago

It does rest after every beat

yawaramin 7y ago

Oh hey, this reminds me of one of my favourite songs https://www.youtube.com/watch?v=Y5OpvDdVtYU https://www.youtube.com/watch?v=Y5OpvDdVtYU

ck2 7y ago

Any runner or cyclist knows your heart gets tired. A beat is not guaranteed volume, a rested heart can move more blood at the same heartrate than a tired one.

econcon 7y ago

Also, why heart doesn't get bigger/thicker walls through cardio? Like we can do enough reps and sets to achieve hypertrophy?

science4sail 7y ago
The heart does experience hypertrophy from exercise. https://en.wikipedia.org/wiki/Athletic_heart_syndrome https://en.wikipedia.org/wiki/Athletic_heart_syndrome

perlgeek 7y ago

Isn't it funny how many meanings the word "why" has? My first explanation, on hearing the question, was: because, evolutionarily speaking, no organism would have relied so heavily on the heart if it got tired easily. Or looking on it another way, if the heart was easily fatigued, we'd be all dead, or be very different.

hinkley 7y ago
There have been a few astrophysics shows where they talked about 'why are we here?', with varying definitions of 'why' or special emphasis on here (as opposed to elsewhere). In most of them, someone says words to the effect of "well if we weren't here, we wouldn't be having this conversation". Survivor bias, in a very literal sense.
- perlgeek 7y ago
  ... also know as https://en.wikipedia.org/wiki/Anthropic_principle https://en.wikipedia.org/wiki/Anthropic_principle

havella 7y ago

It does. Try riding a bike above FTP at altitude for as long as you can. Then describe how your heart feels for the reminder of that day.