Learn Hardcore Finnish: Pitkän työpäivän jälkeen selkää särkee, jos en venyttele. - After a long workday my back aches if I do not stretch.

use the partitive to show an ongoing, not clearly bounded state (the ache isn’t a single, complete event). This is similar to how the partitive is used for “incomplete” or “unbounded” actions and quantities.

Using nominative selkä here (Selkä särkee) would sound odd; native speakers naturally say selkää särkee.

How do I say explicitly “my back aches”? Where is “my” in selkää särkee?

In Selkää särkee, the possessor (my, your, etc.) is just understood from context (who is speaking).

If you want to make it explicit, you can say:

Selkäni särkee. – My back aches.
- selkäni = my back (selkä + -ni “my”)
Minun selkääni särkee. – literally It aches in my back.

All of these are natural:

Selkää särkee. – neutral, context decides whose back
Selkäni särkee. – clearly “my back” as the subject
Minun selkääni särkee. – emphasizes me as the experiencer

Is selkää särkee grammatically “impersonal”? Where is the subject?

Yes, this is an example of an impersonal-like construction.

The verb: särkee (3rd person singular)
The “thing affected”: selkää in the partitive

In traditional grammar terms, selkää is a partitive subject with a verb that describes a physical sensation or state. There is no explicit personal subject like I or you in the sentence.

So:

Selkää särkee.
≈ There is back-ache (in me). / My back aches.

Finnish very often leaves the “experiencer” implicit or marks it only with a possessive suffix, instead of a pronoun.

Can I change the word order, e.g. say Selkää särkee pitkän työpäivän jälkeen?

Yes, that is perfectly grammatical.

Both are fine:

Pitkän työpäivän jälkeen selkää särkee, jos en venyttele.
Selkää särkee pitkän työpäivän jälkeen, jos en venyttele.

The difference is emphasis and flow:

Starting with Pitkän työpäivän jälkeen emphasizes the time frame: After a long workday… (what happens?)
Starting with Selkää särkee emphasizes the symptom first: The back aches… (when? after a long workday.)

Finnish word order is fairly flexible, but the version with the time expression first is very typical in neutral narration: time – place – other details – verb.

What exactly does särkee mean, and how is it different from sattuu or on kipeä?

Särkee is the 3rd person singular of särkeä, which means to ache or to throb (with pain).

Common pain verbs and phrases:

särkeä – to ache, throb
- Päätä särkee. – I have a headache.
sattua – to hurt (often sudden or sharp pain, or as a general “it hurts”)
- Se sattuu. – It hurts.
koskea – close to sattua, also to hurt
- Kurkkua koskee. – My throat hurts.
olla kipeä – to be sore / in pain
- Selkä on kipeä. – The back is sore.

In this sentence, särkee suggests a more or less continuous ache rather than a quick sharp pain.

What is the nuance of venytellä compared to venyttää and venyä?

These three are related but not the same:

venytellä – to stretch (oneself), often a bit, here and there, habitually
- Venytellä is what you normally say for doing stretches as exercise.
- jos en venyttele = if I don’t (do my) stretching.
venyttää – to stretch something (transitive)
- venyttää lihaksia – to stretch (one’s) muscles
- venyttää paitaa – to stretch a shirt (make it longer/wider)
venyä – to stretch / lengthen by itself (intransitive)
- Kangas venyy. – The fabric stretches.

So in this sentence, venytellä is the natural choice: it describes the speaker habitually doing their stretching routine.

Why is it jos en venyttele and not something like a future tense?

Finnish does not have a separate future tense. The present tense is used for:

present time
habitual statements
the future, when context makes it clear

Here, jos en venyttele means:

if I don’t (usually) stretch
or if I don’t stretch (on that occasion)

The combination:

Pitkän työpäivän jälkeen selkää särkee, jos en venyttele.

is a general rule: After a long workday my back aches if I don’t stretch. Present tense in Finnish covers that habitual meaning.

How is en venyttele formed, and how would it look in other persons?

The verb is venytellä (type I verb). Present tense stem: venyttele-.

Finnish negation uses a separate negative verb (en, et, ei, emme, ette, eivät) plus the connegative form of the main verb (here: venyttele).

Present negative of venytellä:

en venyttele – I don’t stretch
et venyttele – you (sg) don’t stretch
ei venyttele – he/she doesn’t stretch
emme venyttele – we don’t stretch
ette venyttele – you (pl) don’t stretch
eivät venyttele – they don’t stretch

In the sentence we have jos en venyttele – if I don’t stretch.

Why is there a comma before jos in Finnish, when in English we usually don’t put a comma before “if” here?

Finnish comma rules are different from English ones.

Rule of thumb in Finnish:
A main clause and a subordinate clause (like a jos “if” clause) are normally separated by a comma, no matter which order they come in.

So:

Selkää särkee, jos en venyttele.
Jos en venyttele, selkää särkee.

Both get a comma between the two clauses. In English we might write My back aches if I don’t stretch with no comma, but Finnish spelling conventions are stricter here.

What kind of word is työpäivä, and why not työn päivä?

Työpäivä is a compound noun:

työ – work
päivä – day
työpäivä – workday / working day

Finnish strongly prefers compounds instead of “noun + genitive noun” for established concepts like workday, school day, etc.:

työpäivä – not usually työn päivä
koulupäivä – school day (not koulun päivä)

So pitkän työpäivän jälkeen literally: after a long workday (with työpäivä in the genitive: työpäivän).

Are there other natural ways to say the same thing in Finnish?

Yes, several variations are possible, for example:

Pitkän työpäivän jälkeen selkäni on kipeä, jos en venyttele.
– After a long workday my back is sore if I don’t stretch.
Pitkän työpäivän jälkeen selkäni särkee, jos en venyttele.
– same meaning, explicitly my back
Pitkän työpäivän jälkeen minulla on selkä kipeä, jos en venyttele.
– literally after a long workday I have back sore if I don’t stretch

The original sentence:

Pitkän työpäivän jälkeen selkää särkee, jos en venyttele.

is very natural and idiomatic, especially in spoken or informal language.