Grepsstyrken kommer fra underarmen.

Because Norwegian normally writes compound nouns as a single word.

So:

• grep = grip
• styrke = strength
• grepsstyrke = grip strength

Then the definite ending is added:

• grepsstyrken = the grip strength

This is very common in Norwegian. English often uses two words where Norwegian uses one.

The -s- is a linking sound used in many Norwegian compounds.

So the structure is:

• grep
• • s (linking element)
• • styrke
• = grepsstyrke

It does not mean possession here. It is just part of how the compound is formed. You will see this in many other words too.

Because -en is the definite ending, similar to English the.

• grepsstyrke = grip strength

• grepsstyrken = the grip strength

• underarm = forearm
• underarmen = the forearm

In Norwegian, the definite article is usually attached to the end of the noun instead of being a separate word.

Yes. In this sentence, underarmen means the forearm.

This is important because English speakers may think of underarm as the area near the armpit, but Norwegian underarm usually means the lower arm, that is, the forearm.

If you want to say armpit in Norwegian, the usual word is armhule.

Kommer fra literally means comes from, and here it expresses source or origin.

So:

• Grepsstyrken kommer fra underarmen = the grip strength comes from the forearm

This is natural when talking about where something originates physically or functionally.

A few comparisons:

• kommer fra = comes from / originates from
• er fra = is from, often used for place of origin, as in Han er fra Bergen
• stammer fra = stems from / originates from, often a bit more formal

So in this sentence, kommer fra is a very natural choice.

Because the sentence refers to the forearm as the relevant body part.

In Norwegian, just like in English, you usually need a definite or indefinite form here:

• fra underarmen = from the forearm
• fra en underarm = from a forearm

Using just fra underarm would not sound right in normal Norwegian.

The definite form works well because the sentence is identifying the forearm as the source.

This is standard Norwegian main-clause word order:

• Grepsstyrken = subject
• kommer = verb
• fra underarmen = prepositional phrase

So the pattern is:

subject + verb + other information

Norwegian main clauses also follow the V2 rule, which means the finite verb is in the second position. If you move another part to the front, the verb still stays second:

• Fra underarmen kommer grepsstyrken.

That version is possible, but it sounds more marked or stylistic.

Yes, you could, but the nuance changes slightly.

• Grepsstyrken kommer fra underarmen = the grip strength comes from the forearm
• Grepsstyrke kommer fra underarmen = grip strength comes from the forearm

The version without -n sounds more general, like a general statement about grip strength as a concept. The version with -n sounds more definite and context-based.

In practice, both can make sense depending on context.

Yes. Kommer is the present tense of å komme.

Here are a few forms:

• å komme = to come
• kommer = comes / is coming
• kom = came
• har kommet = has come

In this sentence, the present tense is used for a general fact:

• Grepsstyrken kommer fra underarmen. = Grip strength comes from the forearm.

Yes. It sounds natural, especially in a context like anatomy, exercise, climbing, physiotherapy, or strength training.

It gives a factual explanation of where grip strength mainly comes from. A native speaker might also say similar things like:

• Mye av grepsstyrken kommer fra underarmen. = Much of the grip strength comes from the forearm.
• Grepsstyrke sitter mye i underarmen. = Grip strength is largely in the forearm.

So the sentence is both grammatical and natural.