“Your brain is like any other muscle,” people often say when they want to encourage you to use your brain a lot and keep it healthy.
Please don’t do that.
I know what you’re trying to say, but this isn’t it (unless you’re a complete idjit when it comes to understanding human anatomy).
The brain is not a muscle, and saying like any other implies that it is.
“Your brain is like a muscle; use it or lose it.” Now, that would be correct.
(Sorry, but “It’s a metaphor” doesn’t work here. Stick to the simile.)