Vanjske tipkovnice pomažu kod problema kao što je napetost mišića.

Because tipkovnica is a feminine noun, and the adjective vanjski must agree with it in gender, number, and case.

Here we have:

• tipkovnica = keyboard
• tipkovnice = keyboards
• vanjska tipkovnica = external keyboard
• vanjske tipkovnice = external keyboards

In this sentence, vanjske tipkovnice is the subject, so it is in the nominative plural.

Pomažu means help and is the 3rd person plural present tense form of pomagati.

It matches the plural subject vanjske tipkovnice:

• Vanjska tipkovnica pomaže = An external keyboard helps
• Vanjske tipkovnice pomažu = External keyboards help

So the ending shows that the subject is they.

Yes, kod often means at someone's place / by / near, but here it has a different, very common meaning:

• kod problema = for problems, with problems, in cases of problems

So in this sentence, kod is being used in a more abstract sense, especially common in medical or practical contexts.

Examples:

• kod prehlade = for a cold / in cases of a cold
• kod bolova u leđima = for back pain
• kod problema sa spavanjem = for sleep problems

So pomažu kod problema means something like help with problems.

Because kod requires the genitive case.

The noun problem therefore changes form:

• nominative singular: problem
• genitive singular: problema
• genitive plural: problema

Notice that for this noun, the genitive singular and genitive plural look the same. That is very common in Croatian.

In this sentence, problema is usually understood in a general/plural sense:

• kod problema kao što je... = for problems such as...

Because the example that follows is singular:

• napetost mišića = muscle tension

So Croatian uses:

• kao što je ... for a single example
• kao što su ... for multiple examples

Compare:

• problema kao što je napetost mišića = problems such as muscle tension
• problema kao što su bolovi i grčevi = problems such as pains and cramps

Even though problema refers to more than one possible problem, the verb in kao što je agrees with the example being named, not with problema.

Kao što is a very common expression meaning such as, like, or as depending on context.

In this sentence:

• kao što je napetost mišića = such as muscle tension

It is best to learn kao što je as a chunk when introducing an example.

Other examples:

• voće kao što su jabuke i kruške = fruit such as apples and pears
• problemi kao što je umor = problems such as fatigue

Napetost mišića literally means tension of muscles or more naturally muscle tension.

Here:

• napetost = tension
• mišića = of muscles

So mišića is in the genitive, because Croatian often uses a genitive noun after another noun to show a relationship like of in English.

This pattern is very common:

• bol leđa = back pain
• upala zglobova = inflammation of the joints
• napetost mišića = muscle tension

Formally, mišića can be:

• genitive singular of mišić = of a muscle
• genitive plural of mišić = of muscles

The forms are identical.

In this sentence, the meaning is normally understood as plural/general:

• napetost mišića = muscle tension / tension in the muscles

So context tells you the intended meaning.

Because Croatian does not have articles like English a/an/the.

So:

• tipkovnice can mean keyboards, the keyboards, or sometimes some keyboards, depending on context.
• napetost mišića can mean muscle tension or the muscle tension, depending on context.

English speakers often look for an article, but in Croatian you usually understand definiteness from the situation or from word order and context.

Yes. Croatian word order is more flexible than English word order.

The original sentence is natural:

• Vanjske tipkovnice pomažu kod problema kao što je napetost mišića.

But you could also move parts around for emphasis, for example:

• Kod problema kao što je napetost mišića, vanjske tipkovnice pomažu.

That puts more focus on the type of problem first.

The original version is probably the most neutral and straightforward.

This sentence sounds natural. Croatian often expresses this idea with a prepositional phrase rather than a direct object.

So:

• pomažu kod problema = help with problems

That is more idiomatic here than trying to map the English structure word-for-word.

You may also hear other patterns in Croatian, but kod problema is very common in advice, health, and ergonomic contexts.