Po treningu boli mnie łokieć, ale na szczęście stopa już prawie nie boli.

Because the preposition po meaning after requires the locative case in this use.

• trening = training, workout
• po treningu = after the workout / after training

For masculine nouns like trening, the locative singular often ends in -u, so trening becomes treningu.

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

The pattern is usually:

boli + person affected + body part

So:

• Boli mnie łokieć = My elbow hurts
• literally, something like The elbow hurts me

Here:

• łokieć is the thing that hurts
• mnie is the person experiencing the pain

This is a very normal Polish way to talk about aches and pains.

Here mnie is the accusative form of ja.

With boleć, the person who feels the pain is often expressed in the accusative:

• boli mnie głowa = my head hurts
• boli cię ręka = your arm/hand hurts
• boli go ząb = his tooth hurts

So in boli mnie łokieć, mnie means me.

In Polish, possessive words like mój / moja / moje are often omitted with body parts when the owner is obvious.

So instead of saying:

• mój łokieć
• moja stopa

Polish usually just says:

• łokieć
• stopa

because it is already clear whose body part is being talked about from mnie or from the context.

This is very natural in Polish.

Because łokieć is the grammatical subject of boli.

Even though English says my elbow hurts, Polish structures it more like:

• The elbow hurts me

So:

• łokieć = nominative subject
• mnie = the person affected

The same is true in the second clause:

• stopa już prawie nie boli
• stopa is the subject

Because mnie is understood from the context and does not have to be repeated.

The fuller version could be:

...ale na szczęście stopa już prawie mnie nie boli.

But Polish often leaves out information that is obvious, especially when the same person is still being discussed.

So the shorter version sounds natural and efficient.

Na szczęście means fortunately or luckily.

It is a fixed expression:

• na = on
• szczęście = luck, good fortune

But you should learn it as a whole phrase meaning fortunately.

In this sentence, it shows a positive contrast:

• the elbow hurts,
• but fortunately the foot hardly hurts anymore.

It means something like already almost doesn’t hurt, which in natural English is usually:

• it hardly hurts anymore
• it almost doesn’t hurt anymore

The parts are:

• już = already / by now
• prawie = almost
• nie boli = does not hurt

So już suggests a change over time: earlier it hurt more, but now it is much better.

Polish word order is more flexible than English word order. This order sounds natural because it starts with the topic, stopa, and then gives the comment about it.

So:

• stopa już prawie nie boli = as for the foot, it hardly hurts anymore

You could see slightly different word orders in Polish, but this one is very normal.

Because the subjects are singular:

• łokieć = elbow
• stopa = foot

So the verb is singular:

• boli

If the subject were plural, you would use bolą:

• Bolą mnie nogi = My legs hurt
• Bolą mnie oczy = My eyes hurt

This is important because English leg and foot are separate words, and Polish is precise here too.

• stopa = foot
• noga = leg, but in everyday speech it can sometimes also refer more generally to the lower limb

In this sentence, stopa is used because it specifically means the foot, not the whole leg.

Yes. That is also correct.

Polish allows different word orders depending on emphasis.

Compare:

• Boli mnie łokieć — neutral, very common
• Łokieć mnie boli — puts more focus on elbow
• Mnie boli łokieć — possible, but may sound marked depending on context

So the original sentence is a very natural choice, but it is not the only grammatically correct one.

Ale means but.

It connects two contrasting ideas:

• Po treningu boli mnie łokieć = After training, my elbow hurts
• ale na szczęście stopa już prawie nie boli = but fortunately my foot hardly hurts anymore

So the contrast is:

• one body part still hurts,
• the other is getting better.