Learn Hardcore Japanese: sinkokyuu toka sutoretti toka no tiisana syuukan ha, syuutyuuryoku ga otiruno wo yobousuruno ni mo kenkou no tame ni mo yakuni tatimasu. - Small habits like deep breathing or stretching are useful both for preventing your concentration from dropping and for your health.

小さい is a regular い-adjective.
- Before a noun: 小さい習慣
- As a predicate: 習慣は小さいです。
小さな is a special attributive form used only before nouns:
- 小さな習慣 (OK)
- But you cannot say 習慣は小さなです (✕)

Nuance:

小さな often sounds a bit more literary, soft, or expressive.
In practice, 小さい習慣 and 小さな習慣 mean the same thing here; the writer just chose the slightly more “story-like” or “gentle” expression 小さな.

Why is 習慣 marked with は instead of が in 小さな習慣は … 役に立ちます?

は is marking 小さな習慣 as the topic of the sentence:

“As for these small habits, they are useful for …”

If you used が:

小さな習慣が役に立ちます。
- This would emphasize “It is the small habits (and not something else) that are useful,” often introducing them as new, focused information.

With は, the sentence feels like a general statement or explanation about small habits, not a contrastive emphasis. That fits the idea of giving general advice about small habits.

Why is 集中力 followed by が in 集中力が落ちる? Would を ever be possible?

落ちる is an intransitive verb here (“to fall, to drop, to decline”), so the thing that declines is its subject, marked by が:

集中力が落ちる。
“Concentration falls/declines.”

You normally do not use を with intransitive verbs like this because there is no direct object. Compare:

雨が降る。 – “It rains.” (rain is the subject)
値段が下がる。 – “The price goes down.” (price is the subject)
テンションが上がる。 – “Energy/mood goes up.”

Same pattern: 集中力が落ちる → concentration is the thing that “falls,” so it takes が.

What is the の doing in 集中力が落ちるのを予防する?

This の turns the whole clause 集中力が落ちる (“concentration falls”) into a noun-like phrase so it can take を and become the object of 予防する.

Clause: 集中力が落ちる – “concentration falls / the concentration drops”
Nominalized: 集中力が落ちるの – “the fact that concentration falls / the dropping of concentration”
With を: 集中力が落ちるのを予防する
“to prevent the dropping of concentration”

So the pattern is:

[Sentence in plain form] + の + を + verb

You could often replace の with こと here:

集中力が落ちることを予防する – also grammatical, slightly more abstract.
の tends to feel a bit more concrete and is common in everyday speech.

Why is there another の in 予防するのに? What does 予防するのに mean?

Again, this の is a nominalizer. It turns the verb phrase 予防する (“to prevent”) into a noun-like chunk so that に can attach:

予防するのに ≈ “for preventing (it)” / “for the purpose of preventing it”

Structure:

集中力が落ちるのを予防する
“to prevent concentration from falling”
Nominalize that action: 集中力が落ちるのを予防するの
“the act of preventing concentration from falling”
Add に: 集中力が落ちるのを予防するのに
“for the purpose of preventing concentration from falling”

So, V-plain + のに here means “for ~ing / in order to ~”.

Note: there is another grammar V-plain のに meaning “although / in spite of,” but in this sentence the presence of も and the parallel with 健康のために clearly show the “for the purpose of” meaning, not “although.”

What does にも mean in 予防するのにも健康のためにも?

にも is a combination of:

に – “for, to, in”
も – “also, too, even”

So:

予防するのにも – “also for preventing it”
健康のためにも – “also for (the sake of) health”

The pattern:

A にも B にも役に立ちます。
“It is useful both for A and for B.”

Without も, it would be:

予防するのに役に立ちます。 – “It is useful for preventing it.”
健康のために役に立ちます。 – “It is useful for your health.”

Adding も to both emphasizes “both A and B.”

Why is 健康 followed by のために instead of just に? What does 健康のために mean exactly?

健康のために literally means “for the sake of health” or “for your health / for health reasons”.

The pattern is:

N のために – “for the sake of N, for N, for the benefit of N”
- 家族のために働く – “work for the sake of one’s family”
- 将来のために勉強する – “study for the future”

So:

健康のために – “for (the sake of) health”

If you just said 健康に:

健康に often means “in a healthy way” or “to become healthy,” e.g.
- 健康に暮らす – “live healthily”
- 体を健康にする – “make the body healthy”

Here, we’re talking about purpose/benefit, so 健康のために is the natural choice.

What does 役に立ちます literally mean, and why is に used there?

役に立つ literally means “to stand (立つ) into a role/use (役)”, so figuratively:

“to be useful / to be helpful / to be of use”

The pattern is:

N に役に立つ – “be useful for N”
- 日本語の勉強に役に立つ本 – “a book that is useful for studying Japanese”
- 仕事に役に立つ経験 – “experience that is useful for work”

So in the sentence:

… 予防するのにも健康のためにも役に立ちます。
- “(They) are useful for preventing it and for your health.”

The に marks the target or area where something is useful.

Also note:

役に立つ (plain) → 役に立ちます (polite form)
Synonyms:
- 役立ちます – shorter, often written
- ためになります – “good/beneficial for (you)” (more about personal growth)

Why are 深呼吸 and ストレッチ used as nouns here? How would you say “to take a deep breath” or “to stretch”?

In Japanese, many actions are expressed as noun + する:

深呼吸する – “to take a deep breath”
ストレッチする – “to stretch (do stretching exercises)”

In the sentence, they appear as nouns inside a bigger noun phrase:

深呼吸とかストレッチとかの小さな習慣
- “small habits like deep breathing or stretching”

So we’re naming the kinds of habits, not directly saying “do deep breathing” or “stretch” as verbs.

Examples as verbs:

朝起きたら、深呼吸をします。 – “When I get up, I take deep breaths.”
運動の前にストレッチをしたほうがいいです。 – “You should stretch before exercising.”

Can you summarize the main grammatical structure of the sentence in simple chunks?

Yes. Broken into parts:

深呼吸とかストレッチとかの小さな習慣は、
“Small habits like deep breathing or stretching,” (topic)
集中力が落ちるのを予防するのにも
“also for preventing your concentration from falling,”
健康のためにも
“also for your health,”
役に立ちます。
“are useful / are helpful.”

So the core frame is:

A は、 B にも C にも役に立ちます。
“A is useful both for B and for C.”