Чтобы улучшить выносливость, я бегаю по утрам в парке.

Here чтобы means in order to or so as to. It introduces a purpose:

Чтобы улучшить выносливость = In order to improve endurance

In Russian, чтобы is very commonly used to show why someone does something.

Улучшить is the perfective form, while улучшать is imperfective.

• улучшить = to improve, with focus on the result
• улучшать = to be improving / to improve in a general ongoing sense

After чтобы, Russian often uses the perfective infinitive when the goal is to achieve a result. Here, the goal is to get better endurance, so улучшить sounds natural.

It is in the accusative case because it is the direct object of улучшить.

The dictionary form of выносливость is nominative singular, but for many feminine nouns ending in -ь, the accusative singular looks exactly the same:

• nominative: выносливость
• accusative: выносливость

So the form does not change, even though the case does.

This is a very common question.

• бегаю means I run in the sense of a habit, repeated activity, or general routine
• бегу means I am running right now, usually in one specific direction

So:

• Я бегаю по утрам = I run in the mornings / I go running in the mornings
• Я бегу в парк = I am running to the park right now

Because this sentence describes a regular habit, бегаю is the correct choice.

These two verbs are related, but they are used differently:

• бегать = to run regularly, repeatedly, in different directions, or as a general activity
• бежать = to run right now, in one direction, as a single action in progress

In this sentence, the speaker is talking about a routine, so Russian uses бегать → бегаю.

По утрам is a set expression meaning in the mornings or every morning / generally in the mornings.

• утром = in the morning, often referring to one morning or simply morning time
• по утрам = in the mornings, habitually

Since the sentence describes a repeated habit, по утрам fits very well.

Утрам is dative plural.

That is because after по in time expressions like this, Russian often uses the dative:

• по утрам = in the mornings
• по вечерам = in the evenings
• по выходным = on weekends

So this is a useful pattern to memorize.

Because this sentence describes location, not movement into a place.

• в парке = in the park → prepositional case
• в парк = to the park / into the park → accusative case

Here the speaker runs in the park, so Russian uses в парке.

Yes, the comma is standard here.

Чтобы улучшить выносливость is a purpose clause placed before the main clause:

Чтобы улучшить выносливость, я бегаю по утрам в парке.

Russian normally separates that kind of clause with a comma.

Yes. Russian word order is fairly flexible.

For example, you could also say:

Я бегаю по утрам в парке, чтобы улучшить выносливость.

Both versions are correct. The difference is mostly in emphasis:

• Чтобы улучшить выносливость, ... emphasizes the purpose first
• Я бегаю по утрам в парке, чтобы ... starts with the action first

Russian often leaves out possessive words like my when the meaning is obvious.

So улучшить выносливость naturally means something like:

• improve endurance
• improve one’s endurance
• improve my endurance

If the speaker really wanted to stress my, they could say мою выносливость, but in this sentence that is not necessary.

You could, but it changes the nuance.

• чтобы улучшить выносливость = in order to achieve improvement, with focus on the result
• чтобы улучшать выносливость = in order to be improving endurance, with focus on the ongoing process

In this sentence, the perfective улучшить is more natural because the speaker is talking about a goal.

It is very close. Выносливость can mean:

• endurance
• stamina

In a fitness context, both are good translations. Endurance is often the most neutral choice, while stamina can sound a little more informal in English.