मैं फिट हूँ और थकी नहीं हूँ।

Because Hindi is really expressing two linked statements:

• मैं फिट हूँ = I am fit
• मैं थकी नहीं हूँ = I am not tired

The word और joins them, but each part still has its own हूँ. That is the normal, clear way to say it.

English often avoids repeating am in similar situations, but Hindi commonly keeps the copula in both parts.

थकी shows that the speaker is feminine.

In Hindi, words like थका / थकी / थके often agree with the gender and number of the person being described.

So:

• female speaker: मैं थकी नहीं हूँ
• male speaker: मैं थका नहीं हूँ

If a man were saying the full sentence, it would be:

मैं फिट हूँ और थका नहीं हूँ।

It is best understood as an adjective-like participle.

It comes from the verb थकना = to get tired, but in sentences like this it functions like tired in English:

• मैं थकी हूँ = I am tired

So even though it comes from a verb, it behaves like a describing word here, which is why it changes for gender.

Because फिट is a borrowed word from English, and in everyday Hindi it is usually treated as indeclinable here.

So both a male and a female speaker can say:

• मैं फिट हूँ

By contrast, थका / थकी is a Hindi word that does show agreement.

In Hindi, नहीं usually comes before the finite verb.

Here, the finite verb is हूँ, so:

• थकी नहीं हूँ = literally something like tired not am

That is the normal Hindi order. English says am not tired, but Hindi places not before the verb, not after it.

Yes, very often.

Because हूँ already tells you the subject is I, Hindi often drops मैं when it is understood from context.

So all of these can work:

• मैं फिट हूँ और थकी नहीं हूँ।
• फिट हूँ और थकी नहीं हूँ।

Including मैं makes the sentence a little clearer or more explicit, especially for learners.

It is very natural in modern everyday Hindi, especially in conversation.

Hindi uses many common English loanwords, and फिट is one of them. It often means fit, in shape, or doing well physically.

If you want a more traditionally Hindi option, you could use words like:

• स्वस्थ = healthy
• तंदुरुस्त = fit, healthy

But फिट हूँ is completely normal in speech.

In casual speech, sometimes yes. A speaker might say:

• मैं फिट हूँ और thकी नहीं

and the meaning is still understood.

But for clear, standard Hindi—especially for learners—the full version is better:

• मैं फिट हूँ और थकी नहीं हूँ।

Keeping the second हूँ makes the structure clearer and more natural in careful speech.

It is possible, but it is less clear.

The sentence मैं फिट हूँ और थकी नहीं हूँ is better because it clearly separates the two ideas:

• I am fit
• I am not tired

If you say मैं फिट और थकी नहीं हूँ, it can sound compressed, and for a learner it is easier to make mistakes with what exactly नहीं is negating. The fuller version is the safest one to learn first.