Learn Hardcore Polish: Kiedy dużo biegam pod górę, czuję zmęczenie w nogach i w brzuchu. - When I run a lot uphill, I feel tiredness in my legs and in my stomach.

In normal spoken Polish, learners are usually fine just using kiedy most of the time. Here, gdy would sound a little more bookish, but still natural.

Why is the verb biegam in the present tense if I’m talking about something that happens generally?

In Polish, the present tense of an imperfective verb (here: biegam, from biegać) is used both for:

Actions happening right now:
- Teraz biegam po parku. – I am running in the park now.
Habitual / regular actions:
- Kiedy dużo biegam pod górę, czuję zmęczenie… – Whenever I run uphill a lot, I feel…

So this sentence describes a general, repeated situation, not one single event. English often uses the simple present in the same way: When I run uphill a lot, I feel tired…

What is the difference between biegam, biegnę, and biegać / biec?

biegać – imperfective, to run (in general, habitually, back and forth)
- biegam – 1st person singular present: I run / I go running (regularly)
biec – imperfective, to run (in one specific direction, one instance)
- biegnę – 1st person singular present: I am running (now, in some direction)

In your sentence:

dużo biegam pod górę = I (regularly) run uphill a lot
This describes a kind of training habit, so biegam from biegać is appropriate.

If you said:

Teraz biegnę pod górę. – I am (currently) running uphill (right now).

That’s more about the single action happening at this moment.

Why is there a comma after pod górę?

The structure is:

Kiedy dużo biegam pod górę, – subordinate clause (introduced by kiedy)
czuję zmęczenie w nogach i w brzuchu. – main clause

Polish punctuation rule:
When a subordinate clause (starting with kiedy, gdy, że, ponieważ, etc.) comes before the main clause, you must use a comma between them.

So:

Kiedy dużo biegam pod górę, czuję zmęczenie… – correct
Czuję zmęczenie, kiedy dużo biegam pod górę. – also correct (comma still needed).

What exactly does pod górę mean, and how is it different from na górę or w górę?

pod górę literally: up (towards) the hill / uphill
It focuses on going against the slope, like running uphill.
na górę: (to) upstairs / onto the top / onto the hill
- Idę na górę. – I’m going upstairs / to the top.
w górę: upwards (in a general vertical direction)
- Patrzę w górę. – I’m looking up.

In running / cycling / hiking contexts, pod górę is the natural phrase to mean uphill. So biegam pod górę = I run uphill.

Why is it pod górę and not something like pod górą? What case does pod take?

The preposition pod can take either:

Accusative – for movement towards / under something
Instrumental – for location under something

Compare:

Idę pod most. (Accusative) – I’m going under the bridge. (movement)
Czekam pod mostem. (Instrumental) – I’m waiting under the bridge. (location)

In your sentence:

biegam pod górę – there is movement going up towards the hill / up the hill
So górę is in the Accusative (feminine singular).

If it were static location under the hill, it would be:

Mieszkam pod górą. – I live under the hill. (Instrumental)

Why is it dużo biegam, not bardzo biegam or wiele biegam?

All three words are related to much / a lot, but they’re used differently:

dużo – means a lot / much / many, and can modify:
- verbs: dużo biegam – I run a lot
- nouns: dużo wody – a lot of water
bardzo – means very, and modifies adjectives or adverbs, not verbs directly:
- bardzo zmęczony – very tired
- bardzo szybko – very fast
  You normally don’t say bardzo biegam.
wiele – more formal/literary for many / much, usually with nouns:
- wiele książek – many books
  With verbs it’s sometimes possible but sounds bookish: wiele biegam would be very unusual in speech.

So here, with a verb, dużo biegam is the natural choice.

Why does the sentence use czuję zmęczenie w nogach i w brzuchu instead of something like jestem zmęczony?

Both are correct, but they focus on different things:

Jestem zmęczony / zmęczona. – I am tired.
General state of the whole person.
Czuję zmęczenie w nogach i w brzuchu. – I feel tiredness/fatigue in my legs and in my stomach.
This is more specific: it says where in the body you feel the fatigue.

You could also say:

Męczą mi się nogi i brzuch. – My legs and stomach get tired.
Czuję zmęczenie w nogach i brzuchu. – without repeating w (also natural).

The original wording is a bit more descriptive, like I feel the fatigue in my legs and abs rather than just I’m tired.

Why is it w nogach and w brzuchu, not w nogi or w brzuch?

The preposition w can take two main cases:

Locative – for location inside / in something:
- w domu – in the house
- w szkole – at school
- w nogach, w brzuchu – in (my) legs, in (my) stomach
Accusative – for movement into something:
- Idę w góry. – I’m going to the mountains.
- Włożyłem książkę w torbę. – I put the book in the bag.

In w nogach / w brzuchu, you’re describing where you feel something, a location in the body, so Locative is used:

nogach – locative plural of noga (leg)
brzuchu – locative singular of brzuch (belly/abdomen)

Forms like w nogi or w brzuch (Accusative) would suggest movement into the legs/stomach (or sometimes hitting/impact), which doesn’t fit here.

Why nogach and not nodze? What’s the difference?

noga – leg
- Locative singular: nodze → w nodze – in the leg
nogi – legs
- Locative plural: nogach → w nogach – in the legs

In your sentence, w nogach means in my legs (both legs), so the plural locative form nogach is used.

If you wanted to say it for only one leg (less common in this context), you would say:

Czuję zmęczenie w nodze. – I feel fatigue in my leg.

Why is the personal pronoun ja (I) not used? Is Ja kiedy dużo biegam… wrong?

Polish is a pro‑drop language: subject pronouns (ja, ty, on, ona, etc.) are usually omitted because the verb ending already shows the person:

biegam → clearly I run
czuję → clearly I feel

So:

Kiedy dużo biegam pod górę, czuję zmęczenie… – natural.
Ja kiedy dużo biegam pod górę, czuję zmęczenie… – grammatically possible, but sounds heavy and only used for strong emphasis on “I” (e.g. contrast: I feel it, others don’t).

In normal, neutral speech, you drop ja here.

Does czuję change depending on the speaker’s gender?

No. Verb forms in the present tense do not change with gender in Polish.

(ja) czuję – I feel (same form for male and female speaker)
(ja) biegam – I run (same for everyone)

Gender shows up:

in past tense verbs:
- Byłem zmęczony. – I (male) was tired.
- Byłam zmęczona. – I (female) was tired.
and in adjectives / participles:
- zmęczony (m), zmęczona (f), zmęczeni (pl. people), zmęczone (neut./non-person plural)

So in your sentence, czuję is the same whether a man or a woman is speaking.

Could I say Kiedy biegam dużo pod górę instead of Kiedy dużo biegam pod górę? Does word order matter?

Yes, you can say:

Kiedy dużo biegam pod górę, …
Kiedy biegam dużo pod górę, …

Both are grammatical. The difference is mainly emphasis:

dużo biegam – slightly more natural here; mild emphasis on how much you run overall.
biegam dużo pod górę – can put a bit more focus on the uphill part of that running.

In everyday speech, Kiedy dużo biegam pod górę… is probably the most natural and neutral.

Why is it w nogach i w brzuchu instead of w nogach i brzuchu? Do I have to repeat w?

When you join two nouns that share the same preposition (w, na, z, etc.), you have two options:

Repeat the preposition:
- w nogach i w brzuchu
Use it only once:
- w nogach i brzuchu

Both are correct. Repeating w:

can sound a bit more careful or rhythmic,
sometimes avoids ambiguity in more complex phrases.

In a simple sentence like this, both versions are fine:

Czuję zmęczenie w nogach i w brzuchu.
Czuję zmęczenie w nogach i brzuchu.

Native speakers use both patterns.