Questions & Answers about Me duele el hombro derecho cuando levanto el brazo.
The grammatical subject is el hombro (derecho), not me.
- doler works like gustar:
- Me duele el hombro. = The shoulder hurts me / My shoulder hurts.
- Me gusta el libro. = The book pleases me / I like the book.
So:
- duele is 3rd person singular because it agrees with el hombro.
- me is an indirect object pronoun meaning “to me”.
Literally: El hombro (derecho) duele a mí. → The (right) shoulder is painful to me.
With plural things, doler becomes duelen:
- Me duele el hombro. – My shoulder hurts.
- Me duelen los hombros. – My shoulders hurt.
- Me duele el hombro y el cuello. – My shoulder and neck hurt.
- Me duelen el hombro y el cuello. – My shoulder and neck hurt. (also possible: plural verb because the logical subject is plural)
So the verb agrees in number with what is painful, not with the person who feels the pain.