I would imagine it would be a pretty good thing if we never tired out, even if it meant we weren’t quite as strong, or had to compromise elsewhere.
So why aren’t ALL our muscles the same way as the ones in our heart, where they’ll just keep working without aches, power loss or even all-out cramps and failure when they’re working hard?
Also, I do understand that even heart muscles can break down, e.g. in a heart attack, but we never get “heart cramps” even if we exercise all our other muscles to their limits and our heart is still working normally.
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Because the heart is very special, and very important, so it gets a *lot* of energy, second only to the brain. If every muscle in your body used that much energy, then our ancestors would have starved even more than they already did.
Plus, it requires incredible amounts of blood. Blood that is readily available at the heart, but less so literally anywhere else.
Your heart muscle cells have sacrificed everything else to be good at this one task. They can work tirelessly day after day because they’re completely gutted, removing any sort of repair or nutrition storage capacity in exchange for huge concentrations of mitochondria to drive them. They don’t replicate themselves at any useful rate and may only divide once in your lifetime.
For a cell that’s planning to be literally in your heart and first in line for all nutrition delivery and encased in a bony armored shell this is fine.
For skeletal muscle far from the heart and more exposed to injury it’s not so good. Storage and repair capabilities are necessary out there on the front lines, as is the ability to instantaneously apply enormous peak power rather than a more continuous pulse.
There’s a joke of a question “If the black box in a plane is indestructible, why isn’t the whole plane made out of a black box?” – it’s funny, but the realistic answer is that the plane won’t fly.
Your heart muscle doesn’t repair well, it takes a while to grow and your body prioritizes it above almost everything else for oxygen and nutrition. In contrast, your leg muscles repair fairly quickly, can grow with use if your lifestyle demands stronger legs, but can also shrink to conserve caloric need if you don’t particularly need large legs. Your heart is also very dense muscle for it’s size and need. Think about how easily a surgeon can manually pump a heart to keep a person alive. Imagine all those resources for that amount of strength?
What is the function of chordae tendinae? They’re the tendons which are inside the heart right?
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