Vejrtrækningen bliver roligere, efterhånden som hun sidder stille efter træningen.

Danish makes compounds very freely, so what English might express as two words often becomes one word in Danish.

• vejrtrækning = breathing
• vejrtrækningen = the breathing

The ending -en is the suffixed definite article, so Danish usually says the by attaching it to the noun instead of putting a separate word before it.

So:

• en vejrtrækning = a breath / a breathing
• vejrtrækningen = the breathing

In this sentence, vejrtrækningen refers to her breathing in general.

Because bliver shows a change.

• bliver = becomes / gets
• er = is

So:

• Vejrtrækningen bliver roligere = Her breathing becomes calmer / gets calmer
• Vejrtrækningen er roligere would mean Her breathing is calmer, which describes a state rather than the change into that state.

Since the sentence is about her breathing settling down after exercise, bliver is the natural choice.

Roligere is the comparative form of rolig.

• rolig = calm / quiet
• roligere = calmer / quieter

Danish often forms the comparative by adding -ere:

• hurtig → hurtigere
• langsom → langsommere
• rolig → roligere

Here it means her breathing is getting calmer. In context, calmer is the best English equivalent.

Efterhånden som is a fixed expression meaning something like:

• as
• gradually as
• as ... goes on

It connects two things that happen progressively together.

So this part:

• efterhånden som hun sidder stille

means something like:

• as she sits still
• as she continues sitting still
• gradually, while she sits still

It suggests that the longer she remains still, the calmer her breathing becomes.

Not if you want the same nuance.

• mens = while
• efterhånden som = as / gradually as / in step with

Mens would only tell you that two things happen at the same time.
Efterhånden som adds the idea of gradual development.

Compare:

• Hun læser, mens han laver mad.
  = They are simply happening at the same time.

• Vejrtrækningen bliver roligere, efterhånden som hun sidder stille.
  = Her breathing changes progressively during that time.

So efterhånden som is more precise here.

Because sidder stille describes a physical state: she is sitting still, not moving around.

• sidder stille = sits still / is sitting still
• er stille = is quiet / is still, often more general and sometimes more about silence

In this sentence, the focus is on recovery after exercise. She has stopped moving, and as she sits still, her breathing settles. That makes sidder stille the natural choice.

This is a very common Danish distinction:

• sidder = is sitting
• sætter sig = sits down

So:

• Hun sidder stille = She is in the sitting position and remains still.
• Hun sætter sig = She moves into a sitting position.

The sentence describes an ongoing situation after the workout, not the moment she sits down, so sidder is correct.

Because it refers to a specific training session: the one she has just finished.

• efter træning can mean after training / after exercise in a more general sense
• efter træningen means after the training session / after the workout

In real usage, Danish often uses the definite form when the situation is specific and understood from context.

Not always. Træning can cover several English ideas, depending on context:

• training
• exercise
• workout
• sometimes practice

In this sentence, træningen most naturally means the workout or the exercise session, because the sentence is about breathing calming down afterward.

So a very natural understanding is:

• after the workout
• after exercising

The sentence has:

1. a main clause
   
   • Vejrtrækningen bliver roligere
2. a subordinate clause introduced by efterhånden som
   
   • hun sidder stille efter træningen

Inside that subordinate clause, the word order is straightforward:

• hun = subject
• sidder = verb
• stille = complement
• efter træningen = time phrase

So it is basically: subject + verb + rest.

If you put the subordinate clause first, the main clause would show the normal Danish verb-second pattern:

• Efterhånden som hun sidder stille efter træningen, bliver vejrtrækningen roligere.

That is a useful pattern to notice in Danish.

Because efterhånden som hun sidder stille efter træningen is a subordinate clause, and many Danish writers place a comma before that kind of clause.

So the comma marks the boundary between:

• the main clause: Vejrtrækningen bliver roligere
• the subordinate clause: efterhånden som hun sidder stille efter træningen

You may also notice some variation in Danish comma usage depending on which comma system is being followed, but the comma here is completely normal.

A few parts may be tricky for English speakers:

• æ in træningen is a front vowel, somewhat like the vowel in English cat, though not exactly the same.
• å in efterhånden is roughly like aw in law.
• The d in words like sidder and efterhånden is often a soft Danish d, not a strong English d.
• vejrtrækningen is a long compound, so it is often easiest to learn it in chunks:
  • vejr
  • trækning
  • -en

As with many Danish words, listening to native audio is much more helpful than trying to guess from spelling alone. Danish pronunciation is often less transparent than the spelling suggests.