Mosjonsløpet kan fullføres bare løpeskoen passer.

Not quite. A native speaker would probably find it awkward as written.

The main issue is bare. In this sentence, Norwegian normally needs bare hvis or kun hvis to mean only if.

A more natural version would be:

Mosjonsløpet kan bare fullføres hvis løpeskoene passer.

or

Mosjonsløpet kan fullføres bare hvis løpeskoene passer.

The first version is usually the most natural in everyday Norwegian.

Mosjonsløpet is a compound noun:

• mosjon = exercise
• løp = race, run

So mosjonsløp means something like a recreational race, a fun run, or an exercise run.

The ending -et makes it definite singular:

• et mosjonsløp = a recreational race
• mosjonsløpet = the recreational race

Because Norwegian usually follows the V2 rule in main clauses: the finite verb comes in second position.

Here the sentence starts with the subject:

Mosjonsløpet + kan + ...

So:

• Mosjonsløpet = first element
• kan = second element

This is very normal Norwegian word order.

Because fullføres here is passive.

Compare:

• kan fullføre = can complete
• kan fullføres = can be completed

So:

• De kan fullføre løpet = They can complete the race.
• Løpet kan fullføres = The race can be completed.

This -s passive is common in Norwegian, especially in more formal or written style.

It comes from å fullføre, which means to complete, to carry through, or to finish.

In this sentence, fullføres means be completed.

So the structure is:

• å fullføre = to complete
• å fullføres = to be completed

Bare often means only or just.

But here, if the intended meaning is only if, then bare by itself is not enough for natural Norwegian. You normally need:

• bare hvis = only if
• kun hvis = only if

So the sentence as written sounds incomplete or odd.

Yes. As written, løpeskoen means the running shoe — singular, definite.

That is grammatically possible, but it sounds a bit strange in context, because people normally wear two shoes, or we talk about running shoes in general.

More natural alternatives would be:

• løpeskoene = the running shoes
• løpesko = running shoes / running shoe(s) in a general sense

So a more idiomatic sentence would probably use løpeskoene:

Mosjonsløpet kan bare fullføres hvis løpeskoene passer.

Here passer means fit.

The verb å passe can mean several things depending on context, such as:

• fit: Skoene passer. = The shoes fit.
• suit / be suitable: Det passer bra. = That works well / That suits well.
• look after: Jeg passer barnet. = I look after the child.

In this sentence, it clearly means fit.

That is exactly one reason the sentence feels unnatural.

English needs if in only if the running shoes fit, and Norwegian usually does too:

• hvis = if

So you would normally say:

... bare hvis løpeskoene passer.

Without hvis, the sentence sounds incomplete or nonstandard.

After hvis, Norwegian uses subordinate clause word order, which is different from main clause word order.

Main clause:

• Løpeskoene passer. = The running shoes fit.

Subordinate clause:

• hvis løpeskoene passer = if the running shoes fit

That looks the same here, but if you add an adverb, the difference becomes clearer.

Main clause:

• Løpeskoene passer ikke.

Subordinate clause:

• hvis løpeskoene ikke passer

In subordinate clauses, words like ikke usually come before the verb.

Both can work, but they feel slightly different.

• bare is very common in everyday Norwegian
• kun is a bit more formal or written

So both of these are possible:

• Mosjonsløpet kan bare fullføres hvis løpeskoene passer.
• Mosjonsløpet kan kun fullføres hvis løpeskoene passer.

In everyday speech, bare is often the more natural choice.

The most natural place is usually before the part it limits.

So:

Mosjonsløpet kan bare fullføres hvis løpeskoene passer.

This most naturally means:

The race can only be completed if the running shoes fit.

You can also say:

Mosjonsløpet kan fullføres bare hvis løpeskoene passer.

That is understandable, but many speakers would prefer the first version.

The clearest and most natural correction is:

Mosjonsløpet kan bare fullføres hvis løpeskoene passer.

If you want to avoid the singular løpeskoen, an even more idiomatic version is:

Mosjonsløpet kan bare fullføres hvis løpeskoene passer.

That is likely what a learner should remember.