"I have heavy knees after I run."
Translation:Eu am genunchii grei după ce alerg.
It is redundant and awkward. We don't repeat the subject if this doesn't add anything to the message. Usually, we even skip the subject completely if it can be understood from the conjugation of the verb or from the context.
Am genunchii grei după ce alerg.
eu am ------ eu alerg
tu ai -------- tu alergi
el/ea are --- el/ea aleargă
noi avem --- noi alergăm
voi aveți ---- voi alergați
ei/ele au ---- ei/ele aleargă
I am not a teacher and I don't know if there is a rule according to which that sentence would be strictly incorrect. My guess is that if a rule regarding this situation would exist, it would at least recommend avoiding such use.
These two sound natural:
- Eu am genunchii grei după ce alerg. / Am genunchii grei după ce alerg.
These two don't sound natural at all:
- Eu am genunchii grei după ce eu alerg. / Am genunchii grei după ce eu alerg.
One exception is when I want to emphasize that "I have heavy knees after I run, not after you run." Then it is not unnatural to use the second pronoun: "Eu am genunchii grei după ce alerg eu, nu după ce alergi tu." Please note that in this case the second pronoun comes after the verb!