eojeneun eokkaega apaseo sonmok seuteurechingman jogeum haesseo.

는 here marks 어제 as the topic and adds a slight contrastive feeling.

So 어제는 is not just yesterday in a neutral sense. It often feels like:

• as for yesterday
• yesterday, at least
• yesterday, in that situation

In context, it can imply something like:

• Yesterday, my shoulder hurt, so I only did a little wrist stretching.
• maybe contrasting with today, usually, or some other day

If you said just 어제, the sentence would still make sense, but 어제는 sounds a bit more natural when setting the scene or contrasting yesterday with another time.

In 어깨가 아파서, the particle 가 marks 어깨 as the thing that hurts.

With body parts and physical conditions, Korean very often uses:

• X가 아프다 = X hurts

So:

• 머리가 아파요 = My head hurts
• 배가 아파요 = My stomach hurts
• 어깨가 아파요 = My shoulder hurts

Using 는 instead would shift the nuance. 어깨는 아파서 could sound contrastive, like:

• As for my shoulder, it hurt...
• maybe implying something like but my wrist was okay

So 가 is the normal, straightforward choice here.

아파서 is the -아서/어서 connective form of 아프다.

Here it means because it hurt or so it hurt, and as a result...

Structure:

• 아프다 = to hurt / to be painful
• stem: 아프-
• irregular change: 아파서

So:

• 어깨가 아파서 = because my shoulder hurt / my shoulder hurt, so...

It is not a separate past tense by itself. The time reference comes from the whole sentence and context, especially from 어제 and the final verb 했어.

This is because 아프다 is a ㅡ-irregular verb/adjective.

When a grammar ending beginning with 아/어 is added, the ㅡ usually drops.

So:

• 아프다
• remove 다 → 아프
• add -어서
• the ㅡ drops → 아파서

Other examples:

• 바쁘다 → 바빠요
• 크다 → 커요
• 슬프다 → 슬퍼요

So 아파서 is the correct natural form.

만 means only.

So:

• 손목 스트레칭만 했어 = I only did wrist stretching

It limits the action to that one thing. It implies that other exercise or stretching was not done.

Compare:

• 손목 스트레칭을 했어 = I did wrist stretching
• 손목 스트레칭만 했어 = I did only wrist stretching

In this sentence, it matches the idea that because the shoulder hurt, the speaker did something limited and less demanding.

조금 means a little and modifies 했어 here, meaning the speaker did only a small amount.

So the phrase breaks down roughly like this:

• 손목 스트레칭만 = only wrist stretching
• 조금 했어 = did a little

Together:

• I only did a little wrist stretching
• or more literally, I did only wrist stretching, and only a little of it

This word order is very natural in Korean.

Compare the nuance:

• 손목 스트레칭만 했어 = I only did wrist stretching
• 손목 스트레칭만 조금 했어 = I only did a little wrist stretching

The 조금 adds the idea of small quantity.

Because 만 often replaces the usual particle.

So instead of:

• 손목 스트레칭을 조금 했어

you often get:

• 손목 스트레칭만 조금 했어

Here 만 is attached directly to the noun phrase and takes over the slot where 을/를 might otherwise appear.

Sometimes Korean can stack particles, but with 만, dropping 을/를 is very common and natural.

했어 is the informal casual style, often called 반말.

It is used with:

• close friends
• younger people
• children
• people you are very familiar with

The more polite version would be:

• 어제는 어깨가 아파서 손목 스트레칭만 조금 했어요.

So the sentence is casual and conversational.

Yes, the subject is omitted, which is very common in Korean.

The sentence does not explicitly say I, but it is understood from context.

So the full idea is:

• Yesterday, my shoulder hurt, so I only did a little wrist stretching.

Korean often leaves out subjects like I, you, or we when they are obvious.

Also, in body-part sentences like 어깨가 아파서, Korean often just says the shoulder hurts rather than explicitly saying my shoulder. Possession is understood from context.

It generally means wrist stretching or wrist stretches.

In Korean, noun + noun combinations like this are very common:

• 손목 = wrist
• 스트레칭 = stretching

So 손목 스트레칭 means stretching related to the wrist. In natural English, that could be:

• wrist stretching
• wrist stretches
• stretching for the wrists

It is a borrowed-expression style phrase and sounds very natural in modern Korean.

Possibly, depending on context, but grammatically 어깨 is singular in form.

Korean nouns usually do not have to show singular vs. plural unless it matters. So 어깨가 아파서 could refer to:

• my shoulder hurt
• my shoulders hurt

if context makes that clear

However, without extra context, many learners will first understand it as my shoulder hurt. If the speaker really wanted to emphasize both shoulders, they might make that clearer in another way.

The structure is:

• 어제는 = as for yesterday / yesterday
• 어깨가 아파서 = because my shoulder hurt
• 손목 스트레칭만 = only wrist stretching
• 조금 했어 = did a little

So the pattern is basically:

time/topic + reason + limited action + final verb

A very literal breakdown would be:

• As for yesterday, because my shoulder hurt, I did only a little wrist stretching.

This is a very common Korean sentence pattern:

• setting
• reason
• result/action