Learn Hardcore Norwegian: Jeg bruker de gamle joggeskoene mine på trening, men styrketreningen på senteret gjør jeg ikke daglig. - I use my old sneakers for exercise, but I don’t do the strength training at the gym daily.

Both are grammatically correct. The version with the object first gives more emphasis/contrast to styrketreningen på senteret (as opposed to some other kind of training).

In that second clause, what is actually the subject and what is the object?

Grammatically:

Subject: jeg
Verb: gjør
Object: styrketreningen på senteret

Even though styrketreningen på senteret stands at the beginning of the clause, it is still the object of the verb gjøre. You can see this more clearly if you put the sentence in the neutral order:

Jeg gjør ikke styrketreningen på senteret daglig.

So word order in Norwegian is fairly flexible, but who does the action (subject) and what is done (object) are determined by the verb’s meaning, not just position.

Why is styrketreningen in the definite form (-en) when there is no article like den in front of it?

Norwegian usually marks definiteness on the noun itself with a suffix:

styrketrening = strength training (indefinite)
styrketreningen = the strength training (definite)

You only add a separate article (den / det / de) in double definiteness, i.e. when there is an adjective in front:

styrketrening
styrketreningen
den tunge styrketreningen = the heavy strength training

In styrketreningen på senteret, there is no adjective before the noun, only a prepositional phrase (på senteret), so simple definite with -en is correct and normal, and you do not add den.

What does de do in de gamle joggeskoene mine? Can we leave it out?

de is the definite plural article and is required here because you have:

a plural noun
in the definite form
with an adjective in front

Pattern for definite plural with an adjective is:

de
- adjective (plural/definite form)
  - noun + definite plural ending
    → de gamle joggeskoene

If you leave de out:

✗ gamle joggeskoene mine – incorrect in standard Norwegian.

So de is not optional here; it is part of the normal double definiteness pattern in Norwegian noun phrases with adjectives.

Why is the possessive mine placed after the noun in joggeskoene mine instead of before it?

Norwegian allows two positions for possessives:

After the noun (postposed):
- de gamle joggeskoene mine
Before the noun (preposed):
- mine gamle joggesko

Both are grammatically correct, but they differ in form and nuance:

Postposed possessive (after the noun):
- Uses the full definite form: de gamle joggeskoene
- Then adds the possessive: mine
- Sounds neutral and is the default in spoken Norwegian.
Preposed possessive (before the noun):
- No article and no definite ending: mine gamle joggesko (not mine gamle joggeskoene)
- Often adds emphasis or contrast: my old running shoes (as opposed to someone else’s).
- Slightly more written/formal or emphatic in tone.

So de gamle joggeskoene mine is the most natural, neutral way to say my old running shoes in this context.

Why is the adjective gamle and not gammel in de gamle joggeskoene mine?

Adjectives in Norwegian agree with the noun in number and definiteness.

gammel – singular, indefinite, common gender:
- en gammel joggesko = an old running shoe
gamle – used for:
- plural (both indefinite and definite)
- all definite forms with de or den/det/de:
  - gamle joggesko = old running shoes
  - de gamle joggeskoene = the old running shoes

Since joggeskoene is plural definite, you must use the plural/definite adjective form:

de gamle joggeskoene mine

Is joggesko singular or plural here, and how does its plural work?

joggesko is one of those nouns where the indefinite singular and indefinite plural have the same form:

en joggesko = a running shoe (singular)
joggesko = running shoe / running shoes (indefinite; context decides)
joggeskoene = the running shoes (definite plural)

In everyday speech, joggesko is usually understood as plural (a pair of sneakers). In the sentence, the form joggeskoene (with -ene) explicitly marks plural definite: the running shoes.

So:

de gamle joggeskoene mine = my old running shoes.

Why is it på trening and not til trening or i trening?

The preposition depends on the meaning:

på trening
- Used for being at / during a training session:
- Jeg bruker de gamle joggeskoene mine på trening. = I use my old running shoes when I train / at practice.
- Also used with movement:
  - Jeg skal på trening. = I’m going to training/practice.
til trening
- Focuses on the movement towards training:
- Jeg kjører bilen til trening. = I drive the car to training.
- Less idiomatic with bruke X til trening in this exact sense; that usually means use X for training (as a purpose), not at practice.
i trening
- Means in training / in (good) shape:
- Jeg er i trening. = I’m in training / in form.

In this sentence, we are talking about what shoes are used while training, so på trening is the natural choice.

Why is it på trening (without -en) but styrketreningen (with -en)?

This is a difference between indefinite, general activity and a specific, defined type of training:

på trening (indefinite):
- General activity: at training / when I work out / at practice (not one specific, defined training program).
- Comparable to English at work, at school.
styrketreningen på senteret (definite):
- A specific kind of training: the strength training at the center.
- The definite ending -en shows it is a particular, identifiable activity or program.

So:

på trening = in training, generally.
styrketreningen på senteret = that specific strength‑training routine at the gym.

What is the difference between daglig and hver dag? Could we say … gjør jeg ikke hver dag instead?

Yes, you can say:

… men styrketreningen på senteret gjør jeg ikke hver dag.

The difference is mostly style:

daglig
- Adverb meaning daily.
- Slightly more formal or concise.
- Often used in writing, or when summarising a habit:
  - Dette gjør jeg daglig. = I do this daily / on a daily basis.
hver dag
- Literally every day.
- Very common in everyday speech.
- Often feels a bit more concrete:
  - Jeg gjør det hver dag. = I do it every day.

In this sentence, both ikke daglig and ikke hver dag are natural; daglig might sound just a touch more formal or neutral-summary-like.

Does bruker mean use or am using here?

Norwegian has only one present tense, used for both English simple and progressive forms.

Jeg bruker de gamle joggeskoene mine på trening can be:
- I use my old running shoes at training (habitual)
- I am using my old running shoes at training (these days)

Context decides whether you understand it as a general habit or a current ongoing practice. The Norwegian verb form bruker itself doesn’t change.