If cardiac muscle is extremely hard to fatigue, why aren’t our skeletal muscles made of them to give us even better endurance?

Question

I know that the heart is made of cardiac muscle, why supposedly never fatigues or weakens. So why can’t our skeletal muscles also be made of cardiac muscle? It would give us a ton of endurance in life or death situations and make us even better runners to escape from predators.

In: Biology

Answer 1

Everything is a trade off. Cardiac muscle is hard to fatigue, but requires a ton of energy to maintain. Our bodies don’t like to waste energy hard to maintain things – energy was scarce, so conservation and efficiency were essential to survival.

Skeletal muscle gave us the right balance of enough strength and endurance to get the job done without the higher energy demands.