Želim ne samo da vežbam nego i da ojačam mišiće.

It means not only ... but also ....

In this sentence, it links two things the speaker wants:

• da vežbam = to exercise
• da ojačam mišiće = to strengthen my muscles

So the structure is:

• ne samo X nego i Y
• not only X but also Y

A very close alternative is ne samo ... već i ..., which also means not only ... but also ....

In Serbian, after verbs like želeti (to want), it is very common to use:

• da + present tense

instead of an infinitive.

So:

• Želim da vežbam = I want to exercise
• literally: I want that I exercise, but naturally it just means I want to exercise

This is one of the most important patterns in Serbian. English uses to + verb, while Serbian very often uses da + present.

Because the sentence contains two coordinated actions:

• da vežbam
• da ojačam mišiće

Repeating da makes the structure clear and balanced:

• Želim ne samo da vežbam nego i da ojačam mišiće.

This is the most natural way to say it.

It mirrors English nicely:

• not only to exercise but also to strengthen my muscles

Because Serbian usually does not need the subject pronoun if the verb ending already shows who the subject is.

• želim = I want
• želiš = you want
• želi = he/she/it wants

So ja is unnecessary here unless you want emphasis:

• Ja želim... = I want... with extra stress on I

This pronoun-dropping is very normal in Serbian.

Because after da, Serbian uses a present-tense form, not the infinitive.

So:

• infinitive: vežbati = to exercise / to practice
• after da: da vežbam = that I exercise / to exercise

The same pattern appears with the second verb:

• infinitive: ojačati
• after da: da ojačam

This is mainly about aspect.

• vežbati is imperfective: it focuses on the activity/process
• ojačati is perfective: it focuses on reaching a result

So the sentence means something like:

• I want not only to do the activity of exercising
• but also to achieve the result of making my muscles stronger

That is why this combination sounds natural:

• vežbam = exercise, work out, practice the activity
• ojačam = become stronger / make stronger as a completed result

If you used jačam instead, it would sound more like an ongoing strengthening process rather than achieving the result.

Mišiće is accusative plural.

The noun is:

• singular nominative: mišić = muscle
• plural nominative: mišići = muscles
• plural accusative: mišiće

It is in the accusative because it is the direct object of ojačam:

• ojačam šta? = strengthen what?
• mišiće

So:

• da ojačam mišiće = to strengthen muscles

It can mean both, depending on context.

vežbati can mean:

• to exercise / work out
• to practice

In this sentence, because of mišiće and the idea of getting stronger, the meaning is clearly:

• to exercise / work out

If the context were language learning or music, vežbati could mean:

• to practice for example:
• Vežbam klavir. = I practice piano.
• Vežbam srpski. = I practice Serbian.

In the pattern ne samo ... nego i ..., nego i is the standard pairing.

So Serbian commonly says:

• ne samo ... nego i ... or
• ne samo ... već i ...

While ali means but, this sentence is not just a simple contrast. It is a fixed not only ... but also ... structure, so nego i fits naturally.

In other words:

• ne samo X nego i Y is a set expression you should learn as a whole

This word order is the most natural and easiest to understand:

• Želim ne samo da vežbam nego i da ojačam mišiće.

The paired expression works best when:

• ne samo comes before the first element
• nego i comes before the second element

That keeps the sentence balanced.

Serbian word order can be flexible, but for learners it is safest to keep this exact pattern when using not only ... but also structures.

A rough pronunciation guide:

• Želim ≈ ZHEH-leem
• ne samo ≈ neh SAH-moh
• da vežbam ≈ dah VEZH-bam
• nego i ≈ NEH-goh ee
• da ojačam ≈ dah oh-YA-cham
• mišiće ≈ MEE-shee-cheh

Two useful sounds here:

• ž sounds like the s in measure
• ć is a soft ch sound, softer than English ch

So:

• vežbam has that zh sound
• mišiće has the soft ć sound twice

Yes. That would mean:

• I want to exercise and strengthen my muscles.

It is perfectly correct, but it does not emphasize the not only ... but also ... idea.

Compare:

• Želim da vežbam i da ojačam mišiće.
  = I want to exercise and strengthen my muscles.

• Želim ne samo da vežbam nego i da ojačam mišiće.
  = I want not only to exercise but also to strengthen my muscles.

The second version gives stronger emphasis to the second goal.