Nakon trčanja volim se osvježiti tušem, pogotovo kad je vani trideset stupnjeva.

Because nakon always takes the genitive case.

The base noun is trčanje = running, and its genitive singular form is trčanja. So:

• trčanje = running
• nakon trčanja = after running

This is very common in Croatian:

• nakon posla = after work
• nakon škole = after school
• nakon ručka = after lunch

So here trčanja is simply the correct case form required by nakon.

It is a noun, not a finite verb form.

Trčanje is a verbal noun meaning running. Croatian often uses these verbal nouns where English uses -ing forms.

So in this sentence:

• nakon trčanja = after running

Even though it comes from the verb trčati = to run, it behaves grammatically like a noun and changes by case, which is why you get trčanja after nakon.

Yes. In Croatian, voljeti can be followed by an infinitive to mean to like/love doing something.

So:

• volim čitati = I like reading
• volim plivati = I like swimming
• volim se osvježiti = I like to refresh myself

This is very natural Croatian. English often uses like + -ing, but Croatian normally uses voljeti + infinitive in this kind of sentence.

Se is the reflexive particle. It shows that the action is directed back to the subject.

So:

• osvježiti = to refresh something
• osvježiti se = to refresh oneself / to freshen up

In this sentence, the speaker is refreshing themself, not something else, so se is needed.

This pattern is very common:

• odmoriti se = to rest
• obući se = to get dressed
• istuširati se = to take a shower

English often does not explicitly say oneself, but Croatian often does.

This is mainly about aspect.

• osvježiti (se) is perfective
• osvježavati (se) is imperfective

Here, osvježiti se means a single completed action: to freshen up / to get refreshed. That fits well after running.

With volim, both aspects can sometimes appear depending on meaning, but perfective is very natural here because the idea is: after running, I like to do this one complete act of refreshing myself.

Very roughly:

• Volim se osvježiti tušem. = I like to freshen up with a shower.
• Volim se osvježavati hladnom vodom. = I like refreshing myself with cold water / I like to keep cooling myself down.

So osvježiti se sounds like one concrete refreshing action.

Tušem is the instrumental singular of tuš.

Here the instrumental expresses the means or method:
with a shower / by means of a shower.

So:

• tuš = shower
• tušem = with a shower

This use of the instrumental is very common:

• ići autobusom = to go by bus
• pisati olovkom = to write with a pencil
• osvježiti se tušem = to freshen up with a shower

English uses with, but Croatian often just uses the instrumental case without a preposition.

Because Croatian does not always translate English with using s(a).

There are two different ideas:

1. Instrumental of means/method

   • tušem = by means of a shower / with a shower

2. s(a) + instrumental for together with or accompanied by

   • s prijateljem = with a friend

In this sentence, the shower is not a companion. It is the means used to refresh oneself. That is why plain instrumental tušem is the natural choice.

Pogotovo means especially, particularly, or above all.

In this sentence:

• pogotovo kad je vani trideset stupnjeva = especially when it’s thirty degrees outside

It highlights the following idea as even more true in that situation.

Its position is fairly flexible, but it is commonly placed before the part it emphasizes:

• Pogotovo kad je vani trideset stupnjeva.
• Volim se osvježiti tušem, pogotovo kad je vani trideset stupnjeva.

Other similar words are:

• osobito = especially
• naročito = especially
• posebno = especially / particularly

Pogotovo is very natural in everyday speech.

Because after numbers 5 and higher, Croatian normally uses the noun in the genitive plural.

So:

• jedan stupanj = one degree
• dva / tri / četiri stupnja = two / three / four degrees
• pet stupnjeva = five degrees
• trideset stupnjeva = thirty degrees

That is why stupnjeva is correct here.

This pattern is very important:

• pet minuta = five minutes
• deset godina = ten years
• dvadeset ljudi = twenty people

So trideset stupnjeva is just the normal number pattern.

Vani means outside or outdoors.

So:

• kad je vani trideset stupnjeva = when it is thirty degrees outside

It refers to the outdoor temperature, not the temperature inside a room.

You may also see:

• unutra = inside
• napolju / vani = outside

In standard Croatian, vani is very common and natural in everyday speech.

Because Croatian uses biti = to be in temperature statements like this.

So:

• Vani je trideset stupnjeva. = It is thirty degrees outside.

English uses it is, while Croatian uses je without a dummy subject like it.

Compare:

• Hladno je. = It is cold.
• Toplo je. = It is warm.
• Vani je trideset stupnjeva. = It is thirty degrees outside.

So the sentence is perfectly normal Croatian structure.

Yes, but the meaning changes slightly.

• volim se osvježiti tušem = I like to freshen up with a shower
• volim se tuširati = I like to shower / I like taking showers

The original sentence emphasizes the result or purpose: getting refreshed.
The alternative emphasizes the activity itself: showering.

So both are natural, but osvježiti se tušem is a bit more expressive in this context, especially because the sentence continues with hot weather: pogotovo kad je vani trideset stupnjeva.

Croatian word order is fairly flexible, but not completely free. The original sentence sounds natural and neutral:

• Nakon trčanja volim se osvježiti tušem, pogotovo kad je vani trideset stupnjeva.

You could also hear variations such as:

• Volim se nakon trčanja osvježiti tušem.
• Nakon trčanja se volim osvježiti tušem.

But some versions sound more natural than others depending on emphasis.

A useful point here is that the clitic se usually wants to be near the beginning of its clause, in the typical second-position area. That is one reason the original word order feels smooth and idiomatic.

So yes, some variation is possible, but the given version is a very good standard choice.