orae anja isseumyeon heoriga apayo.

오래 is an adverb meaning for a long time or long in duration.

In this sentence, it describes how long someone stays seated:

• 오래 앉아 있으면 = if you sit for a long time / when you stay seated a long time

A useful comparison:

• 오래 = adverb, so it modifies a verb
  
  • 오래 기다렸어요 = I waited a long time
• 오랜 = adjective form used before a noun
  
  • 오랜 친구 = a longtime friend

So here 오래 is correct because it modifies 앉아 있다.

Both are possible, but 앉아 있으면 is more natural here because it emphasizes remaining in the seated state.

• 앉다 = to sit down
• 앉아 있다 = to be sitting, to stay seated

So:

• 오래 앉으면 can sound like if you sit down for a long time
• 오래 앉아 있으면 clearly means if you stay sitting for a long time

In a sentence about back pain from posture, Korean often prefers 앉아 있다 because the issue comes from continuing to sit, not just the action of sitting down.

-으면 means if or when, depending on context.

Here:

• 앉아 있으면 = if you sit / when you sit
• more naturally in English: if you sit for a long time

It connects a condition to a result:

• 오래 앉아 있으면 = if you sit for a long time
• 허리가 아파요 = your lower back hurts

A small grammar note:

• after a verb stem ending in a consonant, use -으면
• after a vowel, use -면

Examples:

• 먹다 → 먹으면
• 가다 → 가면

Since 있다 has the stem 있-, it becomes 있으면.

In Korean, with body pain, the body part is often marked as the subject with 이/가, not as the object with 을/를.

So the normal pattern is:

• 허리가 아파요 = my back hurts
• 머리가 아파요 = my head hurts
• 배가 아파요 = my stomach hurts

Korean treats the body part as the thing that is in the painful state.

So:

• 허리 = lower back / waist
• 허리가 아파요 = the lower back hurts

Using 허리를 아파요 would be unnatural.

Korean often leaves out subjects or topics when they are obvious from context.

So 오래 앉아 있으면 허리가 아파요 can naturally mean:

• If you sit for a long time, your back hurts
• If I sit for a long time, my back hurts
• When people sit for a long time, their back hurts

The exact meaning depends on the situation.

This is very common in Korean. If needed, you can add a topic:

• 저는 오래 앉아 있으면 허리가 아파요.
  = If I sit for a long time, my back hurts.

But without it, the sentence still sounds natural.

허리 usually means waist or lower back, depending on context.

In this sentence, because it is talking about pain from sitting too long, 허리 is best understood as lower back.

So:

• 허리가 아파요 = my lower back hurts / my back hurts

If someone says 허리 통증, that means lower back pain.

아파요 is the polite present tense form of 아프다, which means to hurt or to be painful.

Forms:

• dictionary form: 아프다
• polite: 아파요
• casual: 아파
• formal: 아픕니다

So:

• 허리가 아파요 = my back hurts

Even though it is present tense, it can describe:

• something happening now
• a general tendency
• something that usually happens under certain conditions

It can mean either, depending on context, but it often sounds like a general tendency or habitual result:

• When I sit for a long time, my back hurts
• If you sit for a long time, your back hurts

Korean present tense is often used for general facts or repeated situations, not just what is happening at this exact moment.

If someone wanted to describe one specific past case, they might say:

• 오래 앉아 있었더니 허리가 아팠어요.
  = I sat for a long time, and then my back hurt.

Yes. 오랫동안 앉아 있으면 is also correct and means almost the same thing.

Comparison:

• 오래 앉아 있으면 = natural, simple, everyday
• 오랫동안 앉아 있으면 = also natural, a little more explicitly for a long period of time

Both work well. In conversation, 오래 is often the more common, lighter choice.

The sentence follows a very common Korean pattern:

condition + result

Breakdown:

• 오래 = for a long time
• 앉아 있으면 = if you are sitting / if you stay seated
• 허리가 = the lower back
• 아파요 = hurts

So literally, it is something like:

For a long time sitting if, the lower back hurts.

Natural English rearranges this as:

If you sit for a long time, your back hurts.

This is normal in Korean: the condition usually comes before the main result.

Yes, it is very natural.

It sounds like something someone would say in daily life when talking about physical discomfort or posture. It is polite but casual enough for normal conversation.

Very similar natural sentences include:

• 오래 서 있으면 다리가 아파요.
  = If I stand for a long time, my legs hurt.
• 오래 걸으면 발이 아파요.
  = If I walk for a long time, my feet hurt.

So this sentence is a very useful pattern to learn.