Тренер сказал, что выносливость растёт, когда пульс после бега быстро приходит в норму.

Сказал is the masculine singular past-tense form of сказать (to say / to tell).

In Russian, past tense agrees with the subject in gender and number:

• он сказал — he said
• она сказала — she said
• оно сказало — it said
• они сказали — they said

Here the subject is тренер, which is masculine singular, so you get тренер сказал.

The -л is the normal past-tense marker in Russian.

This is very normal in Russian.

Russian does not usually shift tenses backward the way English often does. In English, after a past reporting verb, you might say:

• The coach said that endurance increases...
• or The coach said that endurance was increasing...

In Russian, if the statement is still generally true, the present tense stays present:

• Тренер сказал, что выносливость растёт...

So Russian often keeps the original tense of the reported statement, especially for general truths, facts, and ongoing situations.

Что introduces a subordinate clause and means that.

So:

• Тренер сказал — The coach said
• что выносливость растёт... — that endurance is increasing / improves...

This is one of the most common uses of что in Russian.

Compare:

• Я знаю, что он дома. — I know that he is home.
• Она сказала, что придёт. — She said that she would come.

The sentence has two layers of subordination:

1. что introduces what the coach said.
2. когда introduces the condition/time situation inside that statement.

Structure:

• Тренер сказал, [что выносливость растёт], [когда пульс после бега быстро приходит в норму].

So:

• что = that
• когда = when

In this kind of sentence, когда can often feel like when / whenever in English, because it describes a general pattern rather than one single event.

Russian uses commas very consistently to separate subordinate clauses.

So:

• Тренер сказал, что...
• ...растёт, когда...

Each new clause introduced by что or когда is set off by a comma.

This is more regular than in English, where comma usage can be less strict in some similar sentences.

Выносливость is in the nominative case because it is the subject of растёт.

• выносливость растёт — endurance grows / increases

Even though выносливость ends in -ость, it is a feminine noun, and in the nominative singular it keeps that dictionary form.

A lot of abstract nouns in -ость are feminine:

• скорость — speed
• молодость — youth
• смелость — courage

Literally, yes: растёт means grows.

But in Russian, just like in English, grow can be used more abstractly. Here выносливость растёт means:

• endurance increases
• endurance improves
• stamina gets better

So it is not about something physically getting taller; it is about a quality developing.

This is a very natural way to say it in Russian.

Because the preposition после requires the genitive case.

The noun бег (running) is masculine, and its genitive singular is бега.

So:

• после
  • genitive
• после бега — after running

Other examples:

• после урока — after the lesson
• после работы — after work
• после тренировки — after training

Пульс is in the nominative case because it is the subject of приходит.

Inside the clause:

• пульс ... приходит в норму — pulse/heart rate returns to normal

So пульс is the thing doing the action.

Because приходить в норму is a very common Russian expression meaning:

• to return to normal
• to normalize
• to settle back to normal

It is idiomatic and very natural.

Breakdown:

• приходить — to come
• в норму — into the norm / into a normal state

So literally it is something like comes into normality, but naturally translated as comes back to normal or returns to normal.

You will hear this structure a lot:

• давление приходит в норму — blood pressure returns to normal
• температура приходит в норму — temperature returns to normal
• состояние приходит в норму — the condition returns to normal

This is a very useful case contrast.

With в, Russian can use:

• accusative for motion/change toward something
• prepositional for location/state in something

Here we have a change of state:

• приходит в норму — comes into a normal state

So норма becomes норму (accusative singular).

Compare:

• Пульс уже в норме. — The pulse is already normal.
  Here it is a state/location idea, so в норме.

• Пульс приходит в норму. — The pulse is returning to normal.
  Here it is movement/change toward that state, so в норму.

Приходит is imperfective present, and it fits because the sentence describes a general repeated pattern, not one single future event.

The idea is:

• endurance improves when the pulse returns to normal quickly after running

This is like a general rule or sign.

If you used придёт, that would be perfective future:

• когда пульс придёт в норму — when the pulse has returned / will return to normal

That would sound more like a specific future situation, not a general physiological principle.

So приходит is the natural choice here.

In this sentence, вы is not actually present. The sentence does not contain вы; it contains выносливость.

This is a common thing for learners to notice because выносливость begins with вы-.

So:

• вы = you
• выносливость = endurance / stamina

They are completely different words.

The word order is natural, but Russian allows some flexibility.

The original order:

• Тренер сказал, что выносливость растёт, когда пульс после бега быстро приходит в норму.

This is neutral and clear.

You could also hear variations such as:

• Тренер сказал, что, когда пульс после бега быстро приходит в норму, выносливость растёт.

This puts more focus on the when clause first inside the reported statement.

Or:

• Тренер сказал, что выносливость растёт, когда после бега пульс быстро приходит в норму.

This is also possible; it just shifts the placement of после бега.

So the sentence is not rigidly fixed, but the original version is smooth and standard.

The most useful stresses are:

• тренЕр
• сказАл
• что вынОсливость растёт
• когда пульс
• после бЕга
• быстро прихОдит в нОрму

A few especially important ones for learners:

• вынОсливость — not вынослИвость
• растёт — stress on ё
• бЕга — stress on the first syllable
• нОрму — stress on the first syllable

Also remember: ё is always stressed when written.

Not directly, but in this kind of general statement it can feel close to English when or whenever, and sometimes the logic overlaps with if.

Russian когда still literally means when. The sentence expresses a sign or condition associated with increasing endurance.

So the best translation is still based on when:

• endurance improves when the pulse returns to normal quickly after running

If you translated it with if, you would be changing the nuance slightly. Russian chose когда, so it presents this as a timing/pattern relationship rather than a pure hypothetical condition.

Literally, пульс means pulse. In real usage, especially in health, sports, and fitness contexts, it often corresponds to what English speakers call heart rate.

So in this sentence, an English translation might naturally use either:

• pulse
• heart rate

depending on style.

Russian commonly uses пульс in this kind of context, and it sounds perfectly normal.