Questions & Answers about У меня болит рука.
Why does this sentence use У меня instead of моя to say my arm?
In Russian, when talking about body parts aching or being injured, you typically use the possession structure У меня (literally: at me) rather than the possessive word моя (my). The sentence is literally saying: The arm hurts at me.
So what is the actual subject of this sentence?
The subject is рука (the arm). Even though the English translation starts with My arm, the Russian sentence is structured so that the arm is doing the action. That is why the verb болит (hurts) is conjugated in the he/she/it form to match the singular noun рука.
Does the word рука mean hand or arm?
It means both. The word рука covers the entire limb from the shoulder down to the fingertips. You rely on context to know if someone means hand or arm. While there are specific words for just the hand, рука is the everyday default.
How would this sentence change if both of my arms hurt?
Since the body part is the subject doing the hurting, you must make both the noun and the verb plural. You would say: У меня болят руки. Notice that the verb болит changes to болят (they hurt) to match the plural noun руки (arms).