Wzmacniam mięsień po wypadku.

Wzmacniam is the 1st person singular present-tense form of the verb wzmacniać.

So it tells you:

• the subject is I
• the tense is present
• the action is viewed as ongoing, repeated, or in progress because wzmacniać is imperfective

Depending on context, it can mean either:

• I am strengthening
• I strengthen

In Polish, the verb ending usually already shows who the subject is.

Here, -am in wzmacniam tells you it means I. So ja is not necessary.

You could say Ja wzmacniam mięsień po wypadku, but that would usually add emphasis, something like:

• I’m the one strengthening the muscle
• As for me, I’m strengthening the muscle

Because mięsień is the direct object here, so it is in the accusative case.

The noun mięsień is a masculine inanimate noun, and for many masculine inanimate nouns, the accusative singular looks the same as the nominative singular.

So:

• nominative: mięsień
• accusative: mięsień
• genitive: mięśnia

That is why you see Wzmacniam mięsień, not Wzmacniam mięśnia.

The dictionary form is wzmacniać.

That is the imperfective infinitive, meaning to strengthen.

A learner will often see:

• wzmacniać – imperfective, ongoing/repeated
• wzmocnić – perfective, completed

Because the preposition po in the sense of after takes the locative case.

The base form is:

• wypadek = accident

After po, it becomes:

• po wypadku = after the accident / after an accident

This is a very common pattern:

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

It can mean either one.

Polish does not have articles like a and the, so context decides.

So po wypadku could be:

• after the accident if the accident is already known in context
• after an accident if it is being mentioned more generally

It can correspond to both.

Polish does not divide the present tense in the same way English does. With an imperfective verb like wzmacniać, the present form can describe:

• a current action in progress: I am strengthening
• a repeated or regular action: I strengthen

So the exact English translation depends on context.

Because the sentence describes the action as an ongoing process, which fits the idea of rehabilitation or training.

Wzmacniam suggests:

• I’m working on it
• I’m in the process of strengthening it
• this may be repeated over time

The perfective partner is wzmocnić. Its future form wzmocnię would mean something more like:

• I will strengthen
• I will make it stronger as a completed result

So wzmacniam is the natural choice if the focus is on the process.

Yes. Polish word order is fairly flexible.

Wzmacniam mięsień po wypadku is a neutral way to say it.

But you could also hear:

• Po wypadku wzmacniam mięsień – puts more focus on after the accident
• Mięsień wzmacniam po wypadku – puts more focus on the muscle, often contrastively

Even though the order can change, not every version sounds equally natural in every context. The original sentence is a normal, straightforward choice.

Yes. The singular means one specific muscle.

If you wanted muscles, you would say:

• Wzmacniam mięśnie po wypadku.

So:

• mięsień = muscle
• mięśnie = muscles

The singular is perfectly natural if the speaker is talking about one injured or rehabilitated muscle.

Wypadek is a general word for accident.

It can refer to:

• a traffic accident
• a work accident
• a fall
• another harmful unexpected event

If you want to be more specific, Polish can add another word, for example:

• wypadek samochodowy = car accident

So by itself, wypadek is broad, just like English accident.