A dor no meu joelho fica pior quando eu caminho muito.

In Portuguese, it is very common to use the definite article with general or specific nouns, especially when talking about something identifiable in context.

So A dor means the pain. In this sentence, it refers to a specific pain the speaker has.

Portuguese uses articles more often than English does, so where English might sometimes say just pain, Portuguese often prefers a dor.

No is a contraction of em + o, meaning in/on the.

• em o joelho → no joelho
• em + meu joelho still keeps the article in normal Brazilian Portuguese usage:
  • em o meu joelho → no meu joelho

So no meu joelho means in/on my knee.

Using em meu joelho is grammatically possible in some styles, but it sounds less natural in everyday Brazilian Portuguese. No meu joelho is the normal choice.

Actually, the article is still there, but it is hidden inside no.

• no meu joelho = em + o + meu joelho

So the full structure includes the article o before meu joelho, which is very common in Brazilian Portuguese.

This is one reason possessives in Portuguese can feel different from English: Portuguese often uses both an article and a possessive:

• o meu joelho = my knee

Fica comes from ficar, which often means to become, to get, or to end up being depending on context.

In this sentence, fica pior means gets worse or becomes worse.

So:

• A dor... fica pior = The pain... gets worse

This is very natural Portuguese. English often uses get in this kind of sentence, while Portuguese commonly uses ficar.

Yes, but the meaning changes a little.

• fica pior = gets worse / becomes worse
• está pior = is worse

So:

• A dor no meu joelho fica pior quando eu caminho muito. = The pain in my knee gets worse when I walk a lot.

• A dor no meu joelho está pior. = The pain in my knee is worse.

The original sentence emphasizes a change that happens under a condition: when the person walks a lot, the pain worsens.

Pior is the normal comparative form of ruim.

Just like:

• bom → melhor
• mau/ruim → pior

So:

• pior = worse

Although you may sometimes hear mais ruim in speech, pior is the standard and most natural form here.

Yes, eu can be omitted.

Portuguese often drops subject pronouns when the verb ending already makes the subject clear.

So both are possible:

• quando eu caminho muito
• quando caminho muito

Both mean when I walk a lot.

Including eu can add clarity, emphasis, or simply reflect a speaker’s style. In Brazilian Portuguese, subject pronouns are used more often than in some other varieties, so eu sounds perfectly natural here.

Caminho is the first-person singular present tense of caminhar.

• eu caminho = I walk

So:

• quando eu caminho muito = when I walk a lot

Be careful not to confuse this verb form with the noun caminho, which means path or way. Context tells you which one it is. Here, because it comes after eu, it is clearly the verb.

Here, muito means a lot and modifies the verb caminho.

So:

• caminho muito = I walk a lot

It does not mean very here. In Portuguese, muito can mean either much/a lot or very, depending on what it modifies.

Compare:

• eu caminho muito = I walk a lot
• a dor é muito forte = the pain is very strong

Quando means when, and it is used because the sentence describes something that regularly happens.

• quando eu caminho muito = when I walk a lot

This suggests a repeated or predictable relationship: walking a lot makes the knee pain worse.

You could sometimes use se for if, but that would frame it more as a condition:

• Se eu caminho/caminhar muito, a dor piora. = If I walk too much, the pain gets worse.

The original sentence uses quando because the speaker is presenting this as something that happens whenever that situation occurs.

Yes, but the nuance is a little different.

• a dor no meu joelho = the pain in my knee
• a dor do meu joelho = the pain of/from my knee

In many real contexts, both can work, but no meu joelho is very direct when talking about location in the body. It clearly points to where the pain is felt.

So for body pain, dor no... is extremely common:

• dor na cabeça
• dor nas costas
• dor no joelho

Yes, absolutely.

• A dor no meu joelho fica pior quando eu caminho muito.
• A dor no meu joelho piora quando eu caminho muito.

Both are natural and mean essentially the same thing.

The difference is mostly stylistic:

• fica pior = more conversational, literally gets worse
• piora = more compact, directly worsens

Both are good Brazilian Portuguese.

The original word order is the most neutral and natural:

• A dor no meu joelho fica pior quando eu caminho muito.

But Portuguese does allow some variation.

For example:

• Quando eu caminho muito, a dor no meu joelho fica pior.

This version puts the time/condition part first and sounds very natural too. It may slightly emphasize the trigger: when I walk a lot.

So the word order is flexible, but the original order is a standard, neutral sentence structure.