Learn Hardcore German: Nach dem Laufen mache ich eine lange Dehnung für Beine und Rücken. - After running I do a long stretch for legs and back.

In German, when you turn a verb into a noun, you:
- Capitalize it: Laufen
- Often use an article: das Laufen, beim Laufen, nach dem Laufen
das Laufen = the act of running / running (as an activity)

So nach dem Laufen literally means “after the running”, i.e. after (I have been) running.

Why do we say nach dem Laufen and not nach Laufen or nach zu laufen?

Three points here:

The preposition “nach”
- When nach means “after (in time)”, it is followed by a noun in the dative case.
- So you can’t follow it directly with a bare infinitive verb.
We need a noun-like form
- English can say “after running” using a gerund.
- German usually needs a noun or nominalized verb:
  - nach dem Laufen (after running)
  - nach dem Essen (after eating)
  - nach der Arbeit (after work)
“nach zu laufen” is ungrammatical here
- zu laufen is an infinitive construction (e.g. anfangen zu laufen = “to start running”).
- It does not work after nach in the temporal sense.

So nach dem Laufen is the standard, correct structure for “after running.”

What case is dem Laufen, and why that case?

dem Laufen is in the dative case.

The preposition nach (in the sense after, following in time or space) always takes dative.
das Laufen in the nominative becomes:
- dem Laufen in the dative (neuter singular)

Pattern:

nach
- dative → nach dem Laufen (after running)
Other examples:
- nach der Schule (after school)
- nach dem Training (after training)
- nach dem Essen (after eating / the meal)

Can I also say Ich mache nach dem Laufen eine lange Dehnung? Does the word order change the meaning?

Yes, you can say:

Nach dem Laufen mache ich eine lange Dehnung …
Ich mache nach dem Laufen eine lange Dehnung …

Both are correct and mean the same thing.

The difference:

Putting Nach dem Laufen at the beginning emphasizes the time frame:
- As for after running, that’s when I do a long stretch…
Starting with Ich mache is a more neutral, default word order.

In both cases, the finite verb (mache) must be in second position in the main clause, which is respected in both versions.

Why is it eine lange Dehnung and not ein langer Dehnung or einen langen Dehnung?

This is adjective and article agreement with a feminine noun in the accusative case.

Dehnung is feminine: die Dehnung.
In the sentence, Dehnung is the direct object of mache → accusative.
Feminine accusative singular has the same form as feminine nominative singular:
- Article: eine
- Adjective ending: -e → lange

So:

(Nominative) Eine lange Dehnung ist wichtig.
(Accusative) Ich mache eine lange Dehnung.

ein langer Dehnung / einen langen Dehnung are wrong because:

Dehnung is feminine, so you can’t use ein or einen, and the adjective ending -er / -en would be for masculine, not feminine.

Why is it lange and not langen in eine lange Dehnung?

This is about adjective declension after the indefinite article eine with a feminine noun in the accusative:

Feminine singular accusative (after eine) → adjective ending -e:
- eine lange Dehnung
Compare with other genders/cases for contrast:
- Masculine accusative: Ich mache einen langen Lauf.
- Neuter accusative: Ich mache ein langes Training.
- Plural accusative (no article): Ich mache lange Dehnungen.

So lange is exactly the ending you expect:
eine (feminine acc.) + adjective → lange + Dehnung.

What’s the difference between Dehnung and dehnen / mich dehnen? Could I say Nach dem Laufen dehne ich mich lange?

Yes, you could absolutely say:

Nach dem Laufen dehne ich mich lange.
(After running I stretch for a long time.)

Difference:

die Dehnung = the stretch / stretching (as a noun, the exercise itself)
- eine lange Dehnung machen = to do a long stretch
(sich) dehnen = to stretch (oneself) as a verb
- Ich dehne mich. = I stretch.

Both are natural and common. The original sentence chooses the noun + machen structure (eine Dehnung machen), which is very typical in German for sports and exercises:

Liegestütze machen (to do push-ups)
Dehnübungen machen (to do stretching exercises)

Why is it für Beine und Rücken and not für die Beine und den Rücken?

Both are possible:

für Beine und Rücken
für die Beine und den Rücken

Main differences:

Articles optional for body parts in a general sense
- Without articles (für Beine und Rücken) sounds a bit more general:
  - for legs and back (in general)
- With articles (für die Beine und den Rücken) sounds a bit more specific, like:
  - for the legs and the back (implicitly: your legs and your back)
Style and brevity
- In sports/fitness language, Germans often drop articles to sound shorter and more neutral:
  - Übungen für Rücken und Bauch
  - Training für Beine

Both versions are grammatically correct; the article-less version is just slightly more “exercise-manual style.”

What case do Beine and Rücken have after für, and why don’t they change visibly?

für always takes the accusative case.

So underlyingly we have:

für
- die Beine → accusative plural
für
- den Rücken → accusative masculine singular

In the sentence für Beine und Rücken:

Beine: plural accusative of das Bein → die Beine (but article omitted)
Rücken: accusative den Rücken (article omitted)

Because the articles are omitted, and the plural/singular forms already look similar or identical to other cases, you don’t see an obvious case ending:

Plural Beine looks the same in nominative and accusative.
Singular Rücken also looks the same in nominative and accusative; only the article (der → den) changes, but it’s not present here.

How would I say “for my legs and my back” in German, and why do the endings change?

You’d say:

für meine Beine und meinen Rücken

Explanation:

für → accusative case
meine Beine:
- Beine is plural → plural accusative of mein is meine
meinen Rücken:
- Rücken is masculine singular → masculine accusative of mein is meinen

Patterns:

mein (masc. nom.): mein Rücken
meinen (masc. acc.): für meinen Rücken
meine (plural nom./acc.): meine Beine, für meine Beine

So the full phrase becomes:
Nach dem Laufen mache ich eine lange Dehnung für meine Beine und meinen Rücken.

Does Laufen here mean running, jogging, or just walking?

In most contexts:

laufen = to run
In everyday speech in Germany, laufen gehen often implies jogging for exercise:
- Ich gehe laufen. = I’m going for a run / I’m going jogging.

For walking, German more typically uses:

gehen – to go / walk
spazieren gehen – to go for a walk

So nach dem Laufen in a sports/stretching context will almost always be understood as after running/jogging, not just after casually walking.