Po treningu boli mnie stopa, więc odpoczywam w domu.

The preposition po often means after in time expressions, and it usually requires the locative case.

• trening = training
• po treningu = after training

So treningu is the locative singular form of trening.

A few similar examples:

• po pracy = after work
• po obiedzie = after lunch
• po meczu = after the match

Polish usually expresses pain with the verb boleć in a structure that is a bit different from English.

The natural pattern is:

• boli mnie + body part
• literally: the body part hurts me
• natural English: my body part hurts

So:

• Boli mnie stopa = My foot hurts

This is much more idiomatic than Moja stopa boli.
If you say moja stopa, it usually adds emphasis or contrast, not just neutral information.

Mnie is the accusative form of ja.

With boleć, the person who feels the pain is usually in the accusative, while the thing that hurts is the grammatical subject.

So in:

• boli mnie stopa

the roles are:

• stopa = subject
• mnie = the person affected

This is why Polish does not copy the English structure exactly.

Because the subject is stopa, which is singular.

• stopa = foot
• boli = singular form

If the subject were plural, the verb would also be plural:

• Bolą mnie stopy = My feet hurt

So the verb agrees with the thing that hurts, not with mnie.

In Polish, possessive words like mój / moja / moje are often omitted when the owner is obvious, especially with body parts, clothes, and other personal things.

So:

• Boli mnie stopa naturally means My foot hurts
• You do not need moja

If you do say moja stopa, it usually sounds more emphatic:

• Boli mnie moja stopa, nie kolano = My foot hurts, not my knee

Yes. That is also possible.

Polish word order is more flexible than English, so both of these are natural:

• Boli mnie stopa
• Stopa mnie boli

The difference is mostly about focus and emphasis.

• Boli mnie stopa sounds like a neutral statement
• Stopa mnie boli puts a little more attention on the foot

The original sentence sounds very natural.

Więc means so, therefore, or thus.

It connects the two parts of the sentence:

• Po treningu boli mnie stopa = After training, my foot hurts
• więc odpoczywam w domu = so I’m resting at home

It introduces a result or consequence.

Because in Polish, więc is normally preceded by a comma when it links two clauses.

So:

• Po treningu boli mnie stopa, więc odpoczywam w domu.

That comma is standard Polish punctuation.

Odpoczywam is the 1st person singular present tense of odpoczywać, meaning to rest.

Here, the present tense can mean:

• I am resting
• I rest
• I’m taking it easy

In this sentence, it most naturally means I’m resting because of the situation described.

So the idea is:

• My foot hurts after training, so I’m resting at home

Because the sentence describes what the speaker is doing now as a result of the pain.

• odpoczywam = I am resting / I rest
• odpocznę = I will rest

If you said więc odpocznę w domu, it would mean so I’ll rest at home, which shifts the meaning into the future.

The original sentence describes a current reaction.

W domu means at home or in the house/home.

The preposition w usually takes the locative case when it means location.

So:

• dom = house/home
• w domu = at home

This is a very common expression in Polish. Even though English often says at home, Polish uses w domu.

Yes. Polish allows quite a lot of flexibility in word order.

For example, you could also say:

• Boli mnie stopa po treningu, więc odpoczywam w domu.
• Po treningu stopa mnie boli, więc odpoczywam w domu.

These versions are understandable, but the original:

• Po treningu boli mnie stopa, więc odpoczywam w domu.

sounds smooth and natural. Putting po treningu first sets the time frame right away: after training.

Yes, in this sentence stopa means foot.

Its basic forms are:

• stopa = foot
• stopy = feet

So:

• Boli mnie stopa = My foot hurts
• Bolą mnie stopy = My feet hurt

Just remember that with boleć, Polish structures the sentence differently from English.