Learn English – idiom for “if you are not improving, you are deteriorating”

idioms

Is there an idiom or expression for "if you are not improving, that means you are deteriorating"

Thank you

use it or lose it

Here's an example of usage:

For several decades, people have used the term "use it or lose it" to aptly describe the best way to off-set the problems that come with aging.

In other words: use your brain, or lose your brain.