transitivity - I stretch after waking up

I have seen this question in an article:

Why do we stretch after waking up?

Consider the following sentences:

We stretch after waking up

I stretch after waking up

I (Subject) | stretch (Verb) | after waking up (Manner)

Do we need to add an "object" in the sentence above?

I stretch my body after waking up.

Answer

Complete Sentence As-Is

"I stretch after waking up." is a complete sentence and is perfectly understandable as is. Extending your sentence to "I stretch my body after waking up." is also correct, but adds length without detail.

Add Detail as Needed

If you only stretch one part of your body you could mention that to add more detail. For example:

I stretch my arms and legs after waking up.