Learn Hardcore Croatian: Ona trenira u parku jer želi biti zdrava. - She trains in the park because she wants to be healthy.

to train / to work out / to exercise (physically) – e.g. going for a run, doing workouts
It can also mean to practice a sport in a more serious, athletic sense.

In this sentence, “Ona trenira u parku” is most naturally understood as:
“She works out / exercises in the park.”

If you just want the idea of “doing exercises” without the nuance of sports training, you might also hear vježbati (“to exercise / to practice”), but trenirati is very common for working out.

Why is it “Ona trenira” and not something like “Ona treniram / treniri / trenire”?

The verb trenirati is being conjugated in the present tense, 3rd person singular (he/she/it):

ja treniram – I train
ti treniraš – you train (singular)
on/ona/ono trenira – he/she/it trains
mi treniramo – we train
vi trenirate – you train (plural/formal)
oni/one/ona treniraju – they train

Because the subject is ona (“she”), you must use trenir*a → ona trenira.

Can I leave out “Ona” and just say “Trenira u parku jer želi biti zdrava”?

Yes. In Croatian it’s very natural to drop subject pronouns when the verb ending already shows who the subject is.

Ona trenira u parku jer želi biti zdrava.
Trenira u parku jer želi biti zdrava.

Both mean the same thing: “She trains in the park because she wants to be healthy.”
You usually keep ona only for emphasis or clarity (for example, to contrast with someone else).

Why is it “u parku” and not just “park” or something like “na parku”?

You need a preposition to express location. Croatian doesn’t say “she trains park”; it needs u (“in”).
The preposition u (“in”) here is used with the locative case to show where something happens:
- u + locative → u parku = in the park

The noun park is masculine. Its locative singular form is parku:

nominative: park (basic form)
locative: parku (after u for location)

Na parku would sound wrong here. For an open public place like this, you use u parku (“in the park”).

Why is there no word like “a” or “the” in “u parku”?

Croatian has no articles like a / an / the. The phrase u parku can correspond to:

“in a park”
“in the park”

Which English article you choose depends on the context, not on anything in the Croatian sentence. Croatian simply uses u parku, and the listener infers whether it’s “a” or “the”.

What exactly does “jer” mean, and how is it different from “zato što”?

Jer is a conjunction meaning “because”. It introduces a reason:

Ona trenira u parku jer želi biti zdrava.
→ She trains in the park because she wants to be healthy.

Zato što also means “because”, often with a bit more emphasis or formality:

Ona trenira u parku zato što želi biti zdrava.

Both are correct. In everyday speech jer is very common and sounds neutral and natural here.

Should there be a comma before “jer” in this sentence?

In modern standard Croatian, when the “jer”-clause comes after the main clause (as here), it is normally written without a comma:

Ona trenira u parku jer želi biti zdrava. ✅

You do use a comma if the “jer”-clause comes first:

Jer želi biti zdrava, ona trenira u parku. ✅

So the given sentence without a comma is correct and normal.

Why is it “želi biti” and not something like “želi da je zdrava” or “hoće biti”?

In Croatian, many verbs of wanting or needing are followed by an infinitive, just like English “wants to be”:

želi biti = wants to be
- želi – she wants
- biti – to be (infinitive)

So “želi biti zdrava” literally matches English structure: “wants to be healthy.”

You can say “želi da bude zdrava” (“she wants that she be healthy”), but:

it sounds more formal/structured,
and in this simple sentence “želi biti zdrava” is more natural.

Hoće also means “wants” in some contexts, but želi is safer and more neutral for learners here.

Why is “biti” in its basic form and not changed like “je”?

Croatian distinguishes:

biti – the infinitive: “to be”
je – 3rd person singular present of biti: “is”

In this sentence, biti depends on želi (“wants”) and acts like English “to be”:

želi biti – wants to be
želi je – would mean “wants her” (different grammar, je would be a pronoun, not a verb).

So the form biti is required here because it’s an infinitive after želi.

Why does the adjective end in -a: “zdrava” and not “zdrav” or “zdravo”?

Adjectives in Croatian must agree with the gender, number, and case of the noun (or pronoun) they describe.

Here the subject is ona = she, which is:

feminine
singular
nominative (subject of the sentence)

So zdrav (“healthy”) must match ona:

masculine singular: zdrav (On je zdrav. – He is healthy.)
feminine singular: zdrava (Ona je zdrava. – She is healthy.)
neuter singular: zdravo (Dijete je zdravo. – The child is healthy.)

Therefore “biti zdrava” is correct for ona.

How would the sentence change if we were talking about a man instead of a woman?

You change ona (she) to on (he), and the adjective to the masculine form:

On trenira u parku jer želi biti zdrav.
→ He trains in the park because he wants to be healthy.

The verb trenir*a and želi stay the same, because they’re both 3rd person singular; only the pronoun and adjective change.

Why is the adjective “zdrava” in the nominative after “biti”? In some languages it would use another case.

In Croatian, adjectives used as predicative complements after the verb biti (“to be”) are normally in the nominative, agreeing with the subject:

Ona je zdrava. – She is healthy.
On je umoran. – He is tired.
Oni su zadovoljni. – They are satisfied.

So in “želi biti zdrava”, the understood full structure is like “želi (da) ona bude zdrava” – “she wants (that) she be healthy”. The adjective agrees with ona in nominative: zdrava.

Can Croatian present tense here mean both “she trains” and “she is training”?

Yes. Croatian present tense usually covers both:

Ona trenira u parku can mean:
- “She trains in the park (regularly).”
- “She is training in the park (right now).”

Context tells you whether it’s a habit or something happening at the moment. There is no separate continuous form like English “is training”.

Can I change the word order and still be correct? For example, “Jer želi biti zdrava, ona trenira u parku.”

Yes, Croatian word order is flexible, especially with clauses:

Ona trenira u parku jer želi biti zdrava. (neutral, very natural)
Jer želi biti zdrava, ona trenira u parku. (emphasizes the reason at the beginning)

Both are grammatically correct. The difference is mostly emphasis, not meaning.