Learn Hardcore Russian: Перед бегом я делаю короткую разминку, чтобы разогреть мышцы и выпрямить осанку. - Before running I do a short warm‑up to warm up my muscles and straighten my posture.

The preposition:
- перед = before, in front of (in time or space)
  It normally means “right before” something happens.
- до = up to / until / before (in time)
  It focuses more on the whole period leading up to something, not the immediate moment right before.
In this sentence, we mean right before running, so перед is very natural.
The case with перед:
- перед always takes the instrumental case.
- бег (run, running) in the instrumental is бегом.
- So перед бегом is required grammatically; перед бег would be wrong.

You could say до бега, but that sounds more like “at some time before the run (not necessarily right before it)”, and it’s less idiomatic in this exact context.

Why is it короткую разминку and not короткая разминка?

Because разминку is a direct object of the verb делаю.

The verb делать (to do, make) is transitive, so its object goes into the accusative case.
разминка is a feminine noun (nominative singular).
Feminine accusative singular (for an inanimate noun) has the same ending as the feminine nominative singular adjective -ую / -юю pattern:
- nominative: короткая разминка – a short warm-up (subject)
- accusative: делаю короткую разминку – I do a short warm-up (object)

So короткую разминку is accusative and agrees in gender, number, and case with the noun.

Could I just say Перед бегом я разминаюсь instead of я делаю короткую разминку?

Yes, you can. The meaning is very close, but there are nuances:

разминаться (imperfective, reflexive) = to warm up (oneself), to do warm‑up exercises
- Перед бегом я разминаюсь. – I warm up before running.
делать разминку = to do a warm‑up
- Перед бегом я делаю короткую разминку. – Before running, I do a short warm‑up.

Differences:

разминаюсь focuses on the process: I’m warming up.
делаю короткую разминку sounds a bit more like a specific “routine” or “set of warm‑up exercises”, and the adjective короткую stresses that it’s brief.

Both are natural and correct; the original just gives a bit more detail (short, a specific warm‑up).

What is the structure чтобы разогреть мышцы и выпрямить осанку? How does чтобы work here?

This is a purpose clause: in order to warm up the muscles and straighten (my) posture.

чтобы
- infinitive expresses purpose:
  - чтобы разогреть – in order to warm up
  - чтобы выпрямить – in order to straighten

The full structure:

делаю короткую разминку, чтобы разогреть мышцы и выпрямить осанку.
Literally: I do a short warm‑up in order to warm up (the) muscles and straighten (the) posture.

You can often translate чтобы here simply as to in English:

I do a short warm‑up *to warm up my muscles and straighten my posture.*

Why are the verbs разогреть and выпрямить in the perfective aspect here, not разогревать / выпрямлять?

With чтобы + infinitive of purpose, Russian almost always uses the perfective aspect, because the focus is on achieving a result:

разогреть (perfective) – to get (the muscles) warmed up, to bring them to a warmed state.
выпрямить (perfective) – to straighten (posture) so that it becomes straight.

If you used разогревать мышцы or выпрямлять осанку, it would sound like focusing on ongoing repeated processes, which doesn’t fit a one‑time purpose in this sentence.

So:

чтобы разогреть мышцы – to end up with warmed muscles.
чтобы выпрямить осанку – to end up with straight posture.

Why is there no “my” in мышцы and осанку? Shouldn’t it be мои мышцы, мою осанку?

Russian often omits possessive pronouns like my, your when the owner is obvious from context, especially with body parts and things closely associated with the person.

мышцы here clearly means my muscles.
осанку clearly means my posture.

Russian speakers will not normally say:

✗ чтобы разогреть мои мышцы и выпрямить мою осанку
That sounds too heavy and unnatural in this context.

They only add мой / моя / мои if there is ambiguity or you need emphasis:

Он массировал мои мышцы, а не его. – He was massaging my muscles, not his.

Can I change the word order, like Я перед бегом делаю короткую разминку or Я делаю перед бегом короткую разминку?

Yes, Russian word order is flexible, and these variants are grammatical:

Перед бегом я делаю короткую разминку...
– Neutral, slightly emphasizes the time frame before running.
Я перед бегом делаю короткую разминку...
– Also natural, keeps я at the start, then specifies when.
Я делаю перед бегом короткую разминку...
– Still okay, a bit more emphasis on what I do, and then when.

All three are acceptable; the original version is perhaps the most neutral and smooth in writing.

Why is there a comma before чтобы, but no comma before и in разогреть мышцы и выпрямить осанку?

Comma before чтобы
- Чтобы разогреть мышцы и выпрямить осанку is a subordinate clause of purpose.
- Russian punctuation normally puts a comma before a subordinate clause introduced by чтобы:
  - ..., чтобы разогреть мышцы...
No comma before и
Inside that subordinate clause, we have two infinitives joined by и:
- разогреть мышцы
- выпрямить осанку

They form a single complex purpose: to warm up the muscles and straighten the posture. This is a simple coordination of two infinitive phrases, so no comma is used before и:

чтобы разогреть мышцы и выпрямить осанку

What exactly does разминка mean? Is it always “warm‑up” in a sports sense?

Разминка primarily means warm‑up, often in a physical or sports context:

Сделай разминку перед тренировкой. – Do a warm‑up before the training session.
Команда вышла на разминку. – The team went out to warm up.

But it can also be used:

More broadly as any “warm‑up activity”:
- Небольшая разминка перед основным заданием. – A small warm‑up before the main task.
Sometimes metaphorically as “easy preliminaries” before something serious:
- Это была только разминка перед настоящей работой. – That was just a warm‑up before the real work.

In this sentence, it’s clearly the physical, sports‑related warm‑up.

What is the difference between разогреть мышцы and разогреться?

This is transitive vs. reflexive:

разогреть мышцы
- разогреть = to warm something up (transitive)
- мышцы = direct object (accusative plural)
- Focus: you actively bring your muscles to a warmed state.
- Я делаю разминку, чтобы разогреть мышцы.
разогреться
- разогреться = to warm up (oneself) (reflexive)
- No direct object; the subject itself becomes warm.
- Я делаю разминку, чтобы разогреться. – I do a warm‑up to warm up.

Both are common; the original emphasizes the muscles specifically, whereas разогреться is more general (the whole body / the athlete warms up).

Why осанку and not спину? What does осанка mean exactly?

спина = back (the physical part of the body).
осанка = posture (how you hold your body, especially your back, shoulders, head).

Выпрямить спину means to straighten your back literally. Выпрямить осанку means to correct/improve your posture, not just momentarily straighten your back.

So выпрямить осанку is slightly more abstract and sounds like:

stand or run with proper, straight posture, not slouching.

In a fitness context, осанка is very natural because good running form involves overall posture, not only the spine.

What are the genders and basic forms of the main nouns here (бег, разминка, мышцы, осанка)?

Here are the key details:

бег (run, running)
- Gender: masculine
- Nominative singular: бег
- Instrumental singular: бегом (used after перед)
разминка (warm‑up)
- Gender: feminine
- Nominative singular: разминка
- Accusative singular: разминку (after делаю)
мышца (muscle)
- Gender: feminine
- Nominative singular: мышца
- Nominative plural: мышцы
- Accusative plural (inanimate = same as nominative): мышцы (after разогреть)
осанка (posture)
- Gender: feminine
- Nominative singular: осанка
- Accusative singular: осанку (after выпрямить)