Når stangen er for tung, bruger hun de lettere håndvægte i stedet.

In Danish, when a sentence begins with an adverbial clause like Når stangen er for tung (When the bar is too heavy), the finite verb in the main clause normally comes first, before the subject.

So:

• Når stangen er for tung, bruger hun ...
• not Når stangen er for tung, hun bruger ...

This is a very common Danish word-order rule, often called verb-second word order. The first position is taken by the whole Når... clause, so the main verb bruger has to come next, and then the subject hun follows.

A very literal structure would be:

• When the bar is too heavy, uses she the lighter dumbbells instead.

That sounds wrong in English, but it is normal in Danish.

Når usually means when and is often used for something that happens regularly, generally, or whenever a situation occurs.

Here, the sentence suggests a repeated or usual situation:

• Når stangen er for tung, bruger hun de lettere håndvægte i stedet.
• When the bar is too heavy, she uses the lighter dumbbells instead.

So the sense is something like whenever the bar is too heavy.

By contrast, hvis usually means if and sounds more hypothetical:

• Hvis stangen er for tung, bruger hun ...
• If the bar is too heavy, she uses ...

That version is possible in some contexts, but når is more natural if this is her usual response in that situation.

Yes, for can mean for, but in Danish it also has another very common use: too in the sense of excessively.

So:

• for tung = too heavy
• for dyr = too expensive
• for stor = too big

This is one of those small but important high-frequency words that has more than one meaning.

So in this sentence:

• stangen er for tung = the bar is too heavy

not:

• the bar is for heavy

Stangen is the definite singular form of stang.

• en stang = a bar
• stangen = the bar

The ending -en often marks the definite form for common-gender nouns in Danish.

So:

• stang = bar
• stangen = the bar

The sentence uses stangen because it refers to a specific bar, probably one already known from the situation.

Here, tung is a predicate adjective after er, and it agrees with the noun it describes.

Stangen is a common-gender singular noun, so the adjective stays in its basic form:

• stangen er tung = the bar is heavy

Compare:

• huset er tungt = the house is heavy
  because hus is neuter, so you use -t
• stængerne er tunge = the bars are heavy
  because plural takes -e

So in this sentence, tung is correct because stangen is singular common gender.

Lettere is the comparative form of let, which means light in the sense of weight.

So:

• let = light
• lettere = lighter
• lettest = lightest

In this sentence, de lettere håndvægte means the lighter dumbbells.

It does not mean easy here. Danish let can mean both light and easy, depending on context, just like English light and easy are different words. Here, because the topic is exercise equipment and weight, lettere clearly means lighter in weight.

De is the plural definite article here, meaning the.

So:

• håndvægte = dumbbells
• de håndvægte = the dumbbells

When a plural noun has an adjective before it, Danish usually puts the definiteness in the article:

• de lettere håndvægte = the lighter dumbbells

This is different from English because in Danish, when there is an adjective, you often get:

• de + adjective + noun

Compare:

• håndvægtene = the dumbbells
• de lettere håndvægte = the lighter dumbbells

Notice that with the adjective present, the noun itself does not take the definite plural ending -ne here.

The singular is:

• en håndvægt = a dumbbell

The plural is:

• håndvægte = dumbbells

So the sentence uses the plural because she is using dumbbells as a pair or as a group:

• de lettere håndvægte = the lighter dumbbells

This is a common plural pattern in Danish, though noun plurals are not always fully predictable, so it is worth learning håndvægt → håndvægte as a vocabulary item.

I stedet means instead.

It is a fixed expression:

• i stedet = instead
• often also i stedet for = instead of

In your sentence:

• bruger hun de lettere håndvægte i stedet
• she uses the lighter dumbbells instead

It is just the normal Danish way to express this idea. You should learn i stedet as a chunk rather than trying to translate each word separately every time.

Danish often uses the present tense in general statements and habitual actions, just as English does.

So this sentence describes a regular pattern:

• Når stangen er for tung, bruger hun de lettere håndvægte i stedet.
• When the bar is too heavy, she uses the lighter dumbbells instead.

This does not mean it is happening only right now. It can describe what she usually does.

The verbs are:

• er = is
• bruger = uses

Yes, in many contexts that is a very natural way to understand it.

Because når often gives a habitual sense, the sentence can feel like:

• Whenever the bar is too heavy, she uses the lighter dumbbells instead.

That is often closer to the real meaning than a one-time when.

So if you want to feel the nuance better, you can think of når here as:

• when
• or more specifically, whenever

depending on context.