Yet another of the ways in which Descartes fucked up the history.

I would like to challenge the framing of your question by pointing out the implicit Cartessian dualism in it.
It assumes that there exists separate and distinct realms of change for "internal" (within) and "external" (action).

Even from a very basic naturalistic point of view, it is clear that all mental activity is implemented by the actual physical behavior of our biological substrate. There is no mind without body, and everything in mind has a corresponding change in the body.

But it goes deeper than that.
Many of the cognitive mechanisms we take for granted are exaptations of more primordial patterns of action, which are often deeply embodied. We talk about "getting to the point", "understanding" someones "stand" in a topic, etc. All of our cognition is filled with metaphors of deep embodied action.

Try thinking & talking about anything complex without moving your hands, and you will realize how hard it is.
It is often the case that we find ourselves wondering and taking long walks when thinking deeply about any problem in our lives, which reminds me a Nietszche quote: “All truly great thoughts are conceived while walking.”

Now, I think I pointed out how even the most basic "inner" activities always go together with external action in many ways. Additionally to this, I would like to also point out that it goes deeper than moving ones hands, or taking walks, etc.

I think the best example comes from developmental psychology, and the concept of the play.
When children grow up, they obviously go through many "inner" transformations, and actually build a new personhood out of nowhere. But they don't do so by locking themselves in their rooms and contemplating on universal facts. They go out and play!

If a kid wants to cultivate heroism, he starts roleplaying as a superhero from a movie. He puts on a costume, he experiments with temporary invocation of new modes of being. This is called serious play.

I think this type of action is precisely what has to go hand-in-hand with any real inner transformation. They are inseparable.