Eli5: Why some muscles in our body (like the heart) don’t need rest?


In the same note, why wouldn’t the entire body being made of such “unresting” tissues be a good idea? Wouldn’t it improve survival to have a small period of vulnerability?

In: 2

Because the heart is special. It’s literally made of a different kind of muscle than any other in your body, called “cardiac muscle”. It doesn’t need rest because heart muscles have 10x the amount of energy generators (mitochondria) that other muscles have.

Why don’t other muscles have all that mitochondria? Well think of how many people throughout humanity have died of starvation. Now think how many more would starve if *every* muscle needed 10x more energy than it currently does.

The heart can work all the time because it’s the only heart. If everything was as energy intensive as the heart, we wouldn’t have made it this far.

Life is a game of tradeoffs. Yeah, some things would be great to have way more of, but they’re just too energy inefficient to make more use of.

Think of a toy car that you like to play with. You might have fun running around with it, but after a while you would feel tired and need to rest, right? Now imagine if the toy car had a magic battery that never ran out of power. You could play with it all day long without ever feeling tired. Some of the muscles in our body have a magic battery like that. It is called “mitochondria” and it gives them lots of power all the time. The heart is one of those muscles, and it has to be strong and work all the time to keep us alive. So even when we feel tired from playing, our heart never feels tired because it has this magic battery that keeps it working all the time.