Learn Hardcore German: Jetzt weiß sie, dass eine kurze Dehnung nach den Liegestützen den Muskelkater deutlich reduziert. - Now she knows that a short stretch after the push‑ups clearly reduces the sore muscles.

In a main clause (independent clause), the conjugated verb must be in second position.
Here: Jetzt (1st element) weiß (2nd element) sie (3rd element).
In a subordinate clause introduced by dass, the conjugated verb goes to the very end of the clause.
In dass eine kurze Dehnung nach den Liegestützen den Muskelkater deutlich reduziert, the verb reduziert is the conjugated verb and therefore stands at the end.

So: main clause → verb in 2nd position, subordinate clause → verb at the end.

Why is there a comma before dass?

In German, subordinate clauses are almost always separated from the main clause by a comma.

Main clause: Jetzt weiß sie, …
Subordinate clause: … dass eine kurze Dehnung … deutlich reduziert.

The word dass always introduces a subordinate clause, so you put a comma right before it. Unlike English, where a comma is often optional before “that”, in German it is mandatory here.

What is the function of dass in this sentence?

dass is a subordinating conjunction that usually corresponds to English “that” as in “She knows that …”.

It introduces the content of what she knows:

Jetzt weiß sie – Now she knows
dass eine kurze Dehnung … den Muskelkater deutlich reduziert – what she knows

Because dass is a subordinating conjunction, it also forces the conjugated verb (reduziert) to the end of the clause.

Why is it eine kurze Dehnung and not something like ein kurzer Dehnung?

The noun Dehnung (stretching) is feminine in German: die Dehnung.

With feminine nouns in the nominative singular after the indefinite article, the pattern is:

eine (article, feminine nominative)
kurze (adjective, with the ending -e)
Dehnung (noun)

So you must say eine kurze Dehnung.

ein kurzer Dehnung is wrong because:

ein would be masculine/neuter, not feminine.
After ein with a feminine noun, the adjective would still get -e, but the noun’s article itself must be eine, not ein.

What case is eine kurze Dehnung in, and why?

eine kurze Dehnung is in the nominative case, because it is the subject of the subordinate clause.

In dass eine kurze Dehnung nach den Liegestützen den Muskelkater deutlich reduziert, you can ask:

Who or what reduces the muscle soreness? → eine kurze Dehnung
→ subject → nominative

The thing being reduced (den Muskelkater) is the object, so that one will be in the accusative case.

Why is it nach den Liegestützen and not nach die Liegestütze?

The preposition nach always takes the dative case.

The noun Liegestütze (push‑up) is feminine, and in the plural dative the article is den and the noun often gets an -n ending:

Nominative plural: die Liegestütze (the push‑ups)
Dative plural: den Liegestützen (after the push‑ups)

So nach den Liegestützen is:
nach (preposition + dative) + den (dative plural article) + Liegestützen (dative plural form).

Why is it den Muskelkater and not der Muskelkater?

Muskelkater is a masculine noun: der Muskelkater (nominative singular).

But here it is the direct object of the verb reduziert (reduces). Objects of this kind take the accusative case:

Nominative masculine: der Muskelkater (subject)
Accusative masculine: den Muskelkater (direct object)

Question test: “Reduces what?” → den Muskelkater → accusative → den.

Why is deutlich placed before reduziert and not after it?

German adverbs like deutlich usually stand directly before the verb or participle they modify in a simple sentence:

deutlich reduzieren – to reduce clearly / significantly
den Muskelkater deutlich reduziert – has clearly / significantly reduced the muscle soreness

Putting deutlich after the verb (reduziert deutlich) is possible in some contexts, but here den Muskelkater deutlich reduziert is the standard, neutral word order. It keeps the description of the verb action tight and natural.

Can the word order inside the dass‑clause be changed, for example dass den Muskelkater eine kurze Dehnung deutlich reduziert?

In theory, German allows some flexibility in the middle field (between clause‑initial element and final verb), but not all permutations sound natural.

Grammatically possible but strange:

dass den Muskelkater eine kurze Dehnung deutlich reduziert

Native speakers would strongly prefer:

dass eine kurze Dehnung nach den Liegestützen den Muskelkater deutlich reduziert

The usual order is:

Subject (eine kurze Dehnung)
Adverbials (nach den Liegestützen)
Object (den Muskelkater)
Adverb (deutlich)
Verb at the end (reduziert)

Reordering too much often sounds marked or awkward, even if not strictly “ungrammatical”.

Why does the sentence start with Jetzt? Could we also say Sie weiß jetzt, dass …?

Yes, you can say:

Jetzt weiß sie, dass …
Sie weiß jetzt, dass …

Both are correct. The difference is mainly emphasis:

Jetzt weiß sie, …
Emphasizes the time: Now she knows it (as opposed to earlier). The sentence starts with the new or important information.
Sie weiß jetzt, …
Slightly more neutral; focus is more on her knowing, with now as an added detail.

German main clauses must keep the verb in second position, but many different elements (time, place, object, subject) can be in the first position for emphasis.

Why is weiß used here and not kennt? What is the difference between wissen and kennen?

Both translate to “to know”, but they are used differently:

wissen = to know a fact, information, or that a statement is true
Example: Sie weiß, dass eine kurze Dehnung hilft. – She knows that a short stretch helps.
kennen = to be familiar with a person, place, thing, or situation
Example: Sie kennt diese Übung. – She knows (is familiar with) this exercise.

Here, she knows a fact (“that a short stretch after push‑ups reduces muscle soreness”), so German uses wissen → weiß.

Why is Liegestützen capitalized?

In German, all nouns are capitalized, regardless of where they appear in the sentence.

Liegestütze / Liegestützen is a noun (a thing, an exercise), so its first letter must be capitalized:

die Liegestütze (singular)
die Liegestützen (plural dative here)

Even after a preposition, in the middle of a sentence, the capitalization stays: nach den Liegestützen.

What exactly does Muskelkater mean? It’s not literally “muscle tomcat”, right?

Literally, Muskelkater looks like “muscle tomcat”, because Kater also means a male cat. But in this compound word, Kater is used in its other meaning: “hangover” or “aching, sore feeling”.

So Muskelkater is the normal German word for muscle soreness or stiff, aching muscles after exercise. It’s an idiomatic, fixed term: you don’t normally say “Muskel Schmerzen” for this.

Why is it kurze Dehnung and not kurzer Dehnung or kurzen Dehnung?

This is about adjective endings with a feminine noun in the nominative singular after eine.

Pattern:

Article: eine (feminine nominative)
Adjective ending: -e
Noun: Dehnung

So: eine kurze Dehnung.

Forms like kurzer or kurzen would correspond to other cases/genders (e.g. masculine genitive/dative), and do not match a feminine nominative subject.