<story><title>If the heart is a muscle, why doesn&apos;t it ever get tired?</title><url>https://www.reddit.com/r/askscience/comments/fm2z8x/if_a_heart_is_a_muscle_why_doesnt_it_ever_get/</url></story><parent_chain><item><author>tachyonbeam</author><text>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&amp;#x27;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&amp;#x27;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&amp;#x27;s just that some core instincts really don&amp;#x27;t want me to spend energy liberally.</text></item><item><author>bo1024</author><text>I don&amp;#x27;t think any of the top answers are good at all. I suspect part of the reason is how poorly we understand muscle fatigue.&lt;p&gt;Many answers talk about lactate and how it builds up in muscles but not the heart. However they don&amp;#x27;t say anything about how lactate is related to fatigue.&lt;p&gt;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&amp;#x27;s fine, but again, what is the connection between mitochondria and fatigue?&lt;p&gt;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.&lt;p&gt;So mitochondria and lactic acid can&amp;#x27;t be the full story.&lt;p&gt;I don&amp;#x27;t know the true answer and I&amp;#x27;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&amp;#x27;t have nerves to feel soreness&amp;#x2F;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.)</text></item></parent_chain><comment><author>naasking</author><text>&amp;gt; Another part of the answer is that fatigue is largely in our heads.&lt;p&gt;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&amp;#x27;re untrained, your body doesn&amp;#x27;t actually know where this point really is.&lt;p&gt;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.&lt;p&gt;The heart does get fatigued though. You can run a horse into dying from a heart attack, for instance. Most people simply aren&amp;#x27;t fit enough to push it that far, as their other muscles would give out first.</text></comment>
<story><title>If the heart is a muscle, why doesn&apos;t it ever get tired?</title><url>https://www.reddit.com/r/askscience/comments/fm2z8x/if_a_heart_is_a_muscle_why_doesnt_it_ever_get/</url></story><parent_chain><item><author>tachyonbeam</author><text>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&amp;#x27;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&amp;#x27;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&amp;#x27;s just that some core instincts really don&amp;#x27;t want me to spend energy liberally.</text></item><item><author>bo1024</author><text>I don&amp;#x27;t think any of the top answers are good at all. I suspect part of the reason is how poorly we understand muscle fatigue.&lt;p&gt;Many answers talk about lactate and how it builds up in muscles but not the heart. However they don&amp;#x27;t say anything about how lactate is related to fatigue.&lt;p&gt;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&amp;#x27;s fine, but again, what is the connection between mitochondria and fatigue?&lt;p&gt;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.&lt;p&gt;So mitochondria and lactic acid can&amp;#x27;t be the full story.&lt;p&gt;I don&amp;#x27;t know the true answer and I&amp;#x27;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&amp;#x27;t have nerves to feel soreness&amp;#x2F;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.)</text></item></parent_chain><comment><author>travisjungroth</author><text>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.&lt;p&gt;It&amp;#x27;s the same with our body. Feeling tired is separate from being tired. Feeling hungry is separate from being hungry.&lt;p&gt;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.&lt;p&gt;But, sort of like you said, the signal comes really early. It&amp;#x27;s like a low fuel light that comes on when you get to a half tank.</text></comment>