system
Given the following post, respond as if you're commenting on Reddit:
human
How can fish swim their entire lives?

I know that not all fish need to keep moving in order to prevent suffocation, but that some fish do. For the ones who do - how are they able to swim their entire lives? I realise that fish are perfectly adapted for life in the water, and that they probably use very little energy by swimming, but surely even then their muscles must get fatigued eventually? If I was to leave my house now and walk an infinite distance, I'd get far, but at some point I'd have to stop and rest my muscles. Don't fish have this problem?
gpt
How do you breath all your life? Your diaphragm muscles must surely tire of pulling air in all the time, if you spend all your life breathing. Or your heart, which pumps blood nonstop your whole life.

Some muscles don't tire because they can't. They're too important.