Poslije treninga me bole lakat i rame, pa večeras neću igrati.

Because poslije means after and it requires the genitive case.

• trening = nominative, training
• treninga = genitive, of training / after training

So:

• poslije treninga = after training

A very similar alternative is nakon treninga, which also takes the genitive.

Me is the short accusative form of ja (I / me), and here it means me as the person affected.

Croatian uses boljeti differently from English. The thing that hurts is treated as the grammatical subject:

• Boli me glava. = My head hurts.
• literally: The head hurts me.

So in your sentence:

• me bole lakat i rame = my elbow and shoulder hurt

The body parts are the things doing the hurting, and me is the person who feels the pain.

Because the subject is plural in meaning: lakat i rame = elbow and shoulder.

With boljeti:

• boli = singular subject
• bole = plural subject

Compare:

• Boli me lakat. = My elbow hurts.
• Bole me lakat i rame. = My elbow and shoulder hurt.

Even though each noun is singular by itself, together they form a compound subject, so the verb goes into the plural.

Because they are the grammatical subject of bole.

In this structure:

• me = the affected person
• lakat i rame = the things that hurt

So lakat and rame stay in the nominative:

• lakat = elbow
• rame = shoulder

This is different from English learners’ first instinct, because you might expect something like my elbow hurts me, where elbow still acts like the subject.

Because with body parts, Croatian very often does not use a possessive adjective when the owner is already clear.

So instead of saying:

• moj lakat i moje rame

Croatian naturally says:

• me bole lakat i rame

The word me already shows whose elbow and shoulder we are talking about.

This is very common:

• Boli me glava. = My head hurts.
• Perem ruke. = I’m washing my hands.

Croatian often sounds more natural than English here if you leave out my.

Yes. Croatian word order is fairly flexible.

You can say:

• Poslije treninga me bole lakat i rame.
• Poslije treninga bole me lakat i rame.

Both are understandable. The version with me before the verb is very natural because short pronouns like me tend to appear early in the sentence.

So the original sentence is a very normal, natural word order.

Here pa means something like:

• so
• and so
• therefore
• sometimes just a natural spoken link between two ideas

In this sentence:

• ..., pa večeras neću igrati.
• ..., so I won’t play tonight.

It connects the pain with the consequence.

It is a very common everyday connector in Croatian and often sounds more natural in speech than a heavier word like zato.

Neću igrati is the future tense in the negative:

• ću = I will
• neću = I will not / I won’t
• igrati = to play

So:

• neću igrati = I won’t play

A useful comparison:

• igrat ću = I will play
• neću igrati = I won’t play

In standard Croatian, the affirmative future often places the auxiliary after the infinitive, but with neću the usual pattern is simply neću + infinitive.

Večeras is an adverb meaning tonight / this evening. It is the most natural everyday choice here.

So:

• večeras neću igrati = I won’t play tonight

You could express similar ideas in other ways, but večeras is short, common, and idiomatic.

No. A very common alternative is nakon.

So you could also say:

• Nakon treninga me bole lakat i rame, pa večeras neću igrati.

Both are correct. In this sentence, poslije treninga and nakon treninga are very close in meaning.

Because each body part is just one body part:

• lakat = one elbow
• rame = one shoulder

So the nouns stay singular individually. What becomes plural is the verb, because there are two subjects together:

• lakat i rame → two things
• therefore bole

This is just like English:

• My elbow and shoulder hurt

You would not make elbow and shoulder plural unless you meant both elbows or both shoulders.

Very often, yes. It is one of the most common ways to talk about something hurting.

Typical pattern:

• Boli me + singular noun
• Bole me + plural noun / two nouns

Examples:

• Boli me ruka. = My arm hurts.
• Bole me noge. = My legs hurt.
• Bole me leđa. = My back hurts.
  (Even though leđa looks plural, it is the normal Croatian word for back.)

So your sentence follows a very common and important pattern.

Not in standard Croatian here.

You need me, not mi.

• me = accusative me
• mi = dative to me

With boljeti, the affected person is normally in the accusative:

• Boli me glava.
• Bole me lakat i rame.

So mi would sound wrong in this sentence.