डम्बल उठाइए।

A natural pronunciation is roughly:

ḍambal uṭhāiye

Very approximate English-style guide:

• डम्बल = DUM-bul / DUM-bəl
• उठाइए = u-THAA-ee-yeh

A few sound notes:

• ड is a retroflex d, made with the tongue curled slightly back.
• ठ is a retroflex, aspirated t sound, so it is stronger than a plain t.
• ए at the end of उठाइए sounds like eh/ay depending on accent and speed.

उठाइए is a polite imperative form of the verb उठाना, which means to lift, to raise, or to pick up.

So grammatically, the sentence is a command/request:

• डम्बल = dumbbell
• उठाइए = please lift / lift (polite)

This form is commonly used when speaking respectfully, politely, or in instructional situations.

Both are imperative forms, but they differ in politeness level.

• उठाओ = informal command, used with tum
• उठाइए = polite/respectful command, used with aap

So:

• डम्बल उठाओ। = Lift the dumbbell. (informal)
• डम्बल उठाइए। = Lift the dumbbell, please. / Please lift the dumbbell. (polite)

In exercise instructions, teaching, announcements, or respectful speech, उठाइए is very common.

Here the verb is based on उठाना, not उठना.

The difference is important:

• उठना = to get up / rise / stand up
• उठाना = to lift / raise / pick up

So:

• मैं उठता हूँ। = I get up.
• मैं डम्बल उठाता हूँ। = I lift a dumbbell.

Since the sentence means lifting an object, उठाना is the correct verb.

Because in Hindi, a direct object does not always need को.

With many inanimate objects, especially in simple commands, को is usually omitted:

• डम्बल उठाइए। = Lift the dumbbell.
• दरवाज़ा खोलिए। = Open the door.
• किताब पढ़िए। = Read the book.

You can sometimes add को for emphasis or specificity:

• डम्बल को उठाइए।

But in this sentence, leaving out को is the most natural and normal choice.

Yes. डम्बल is a borrowed word from English dumbbell.

Hindi often writes modern objects, gym terms, technology words, and brand-like vocabulary using Devanagari spellings based on English pronunciation.

So डम्बल is basically the Hindi-script form of dumbbell.

You may also hear slight pronunciation differences depending on speaker and region, but the idea is the same.

It is polite or respectful, but not extremely formal.

Because of उठाइए, it sounds suitable for:

• a trainer speaking politely
• written instructions
• classroom or exercise guidance
• speaking to someone respectfully

It is less casual than उठाओ, but not stiff or unnatural.

Yes. Hindi polite imperatives often carry a sense similar to please, even when कृपया is not present.

So उठाइए can be understood as:

• Lift it
• Please lift it

If you want to make the politeness extra explicit, you can say:

• कृपया डम्बल उठाइए। = Please lift the dumbbell.

But डम्बल उठाइए। already sounds polite on its own.

Yes. You may see both:

• उठाइए
• उठाइये

Both are commonly used in writing, and both represent the same polite imperative.
In modern standard writing, उठाइए is often preferred, but उठाइये is also widely understood and seen.

Borrowed nouns in Hindi are usually treated as having grammatical gender, often masculine by default, though usage can vary.

For डम्बल, many speakers treat it as masculine. However, in this sentence, gender does not affect the form उठाइए, so you do not need to worry about it here.

That is why the sentence stays simply:

डम्बल उठाइए।

Whether the noun is masculine or feminine does not change this polite command form.