Learn Hardcore Russian: После тренировки я чувствую усталость и радость. - After the training, I feel fatigue and joy.

после тренировки – after the training / after a workout (one training session, or training viewed as a single event or routine)
после тренировок (genitive plural) – after the trainings / after workouts (in general, repeatedly)

In the sentence После тренировки я чувствую усталость и радость, the speaker is talking about the state after a particular workout (or each single session viewed individually), so singular fits naturally.

Why is it я чувствую, and not something like я есть чувствую?

In Russian you never use есть as a separate word to form the present tense of normal verbs.

English: I feel
Russian: Я чувствую (not я есть чувствую)

The verb чувствовать is conjugated directly:

я чувствую
ты чувствуешь
он/она чувствует
мы чувствуем
вы чувствуете
они чувствуют

The word есть as “is/are” is normally omitted in the present tense:

Я устал. = I am tired. (literally “I tired.”)

Why is there no себя: why я чувствую усталость, not я чувствую себя усталым?

Both are correct but they are slightly different in structure and nuance.

Я чувствую усталость и радость.
- Literally: I feel tiredness and joy.
- чувствую
  - nouns (усталость, радость) as direct objects.
- Focuses on experiencing these states as things you feel in yourself.
Я чувствую себя усталым и радостным.
- Literally: I feel myself tired and joyful.
- чувствую себя
  - adjectives (усталым, радостным) describing “myself”.
- Focuses more on how you are rather than on the “substances” of tiredness/joy.

In everyday speech, both patterns are natural. Using the nouns (усталость, радость) sounds a bit more like naming the feelings themselves; using adjectives (усталым, радостным) is more like describing your state.

What case are усталость and радость in here?

Grammatically, they are in the accusative case, because they are direct objects of the verb чувствую:

(Я) чувствую что? → усталость и радость.

However, feminine inanimate nouns ending in -ь/-ость have the same form in nominative and accusative singular:

Nominative: усталость, радость
Accusative: усталость, радость

So they look like nominative, but function as accusative in this sentence.

Why use the nouns усталость and радость, not adjectives like усталый and радостный?

Both ways are natural, but they feel slightly different:

Я чувствую усталость и радость.
- Uses abstract nouns.
- Emphasizes the feelings as “things”: tiredness and joy are like two distinct sensations.
После тренировки я устал и рад.
- Uses short-form adjectives (устал, рад).
- Sounds very natural and conversational: I’m tired and happy after training.
После тренировки я чувствую себя усталым и радостным.
- Longer, descriptive; emphasizes your state.

The original sentence is perfectly correct and slightly more “bookish,” because of the abstract nouns усталость, радость.

Can I change the word order, like Я после тренировки чувствую усталость и радость?

Yes. Russian word order is fairly flexible. All of these are grammatically correct, with small differences in emphasis:

После тренировки я чувствую усталость и радость.
Neutral, common: After the workout, I feel tiredness and joy.
Я после тренировки чувствую усталость и радость.
Slight emphasis on “I (personally), after the workout, feel…”—still natural.
После тренировки я чувствую радость и усталость.
Emphasizes радость first, maybe suggesting joy is more important.

Very unusual or very shuffled orders can sound strange or poetic, but moderate changes like these are fine.

Why is the verb чувствую in the present tense and not something like почувствовал?

Чувствую is the present tense, imperfective of чувствовать:

я чувствую = I feel / I am feeling (now or generally)

If you said:

После тренировки я почувствовал усталость и радость.

then почувствовал is past tense, perfective, and it means:

After the workout, I (at some point) felt / noticed tiredness and joy.

So:

чувствую – focuses on the ongoing state right now or usually after workouts.
почувствовал – focuses on the moment you began to feel it (a single event in the past).

In the given sentence, the speaker is describing their state after training, so present imperfective is natural.

What do the endings -ость in усталость and радость tell me?

The ending -ость is very common for abstract feminine nouns in Russian, often derived from adjectives:

усталый (tired) → усталость (tiredness, fatigue)
радостный (joyful) → радость (joy)
серьёзный (serious) → серьёзность (seriousness)
новый (new) → новизна, but often -ость: скорый → скорость (speed)

So -ость often means something like “-ness” / “-ity” in English and usually forms feminine nouns.

Why is there no comma before и радость?

In Russian, as in English, you do not put a comma between two items joined by и (and) in a simple pair:

усталость и радость – no comma ✔

You would use commas in longer lists:

усталость, радость и удовлетворение
(tiredness, joy, and satisfaction)

So the punctuation in the sentence is correct.

Can I drop я and just say После тренировки чувствую усталость и радость?

Yes, that is possible and often done in informal speech.

Russian can omit the subject pronoun when it’s clear from the verb ending:

(Я) чувствую ⇒ the ending -ю already shows 1st person singular.

So:

После тренировки чувствую усталость и радость.
sounds a bit more conversational, like a comment or diary note.

Keeping я is also perfectly natural and maybe slightly more explicit or neutral.

Is there a more colloquial or shorter way to say the same idea?

Yes, several options, for example:

После тренировки я устал, но рад.
After the workout I am tired but happy.
После тренировки я устал и рад.
After the workout I’m tired and glad.
После тренировки приятно устать.
It’s nice to get tired after a workout.

The original После тренировки я чувствую усталость и радость is correct and clear; these are just stylistic alternatives you might hear in conversation.