Questions & Answers about Portante ĉi tiun sakon, mi sentas doloron en la brako.
Portante is the active present participle of porti (to carry). In this sentence, it means while carrying or when carrying.
So:
- mi portas ĉi tiun sakon = I carry/am carrying this bag
- portante ĉi tiun sakon = while carrying this bag
Esperanto often uses participles to make a short adverbial phrase. In English, we do something similar with carrying this bag in a sentence like Carrying this bag, I feel pain in my arm.
The person carrying the bag is mi (I).
In Esperanto, a participial phrase like Portante ĉi tiun sakon normally refers to the subject of the main clause. So the sentence means:
While I am carrying this bag, I feel pain in the arm.
It would sound wrong if the participle referred to someone else. In other words, portante must match the doer of sento here, which is mi.