Learn Hardcore Japanese: kyou ha undou no zikan wo sumaho ni kirokusimasita. - Today I recorded my exercise time on my smartphone.

Japanese often starts a sentence with what it wants to talk about (the topic), marked by は. The actual subject (like “I”) is omitted here but understood from context.

A fuller, very explicit version in English thinking would be:

（私は）今日は運動の時間をスマホに記録しました。
“(As for me,) today I recorded my exercise time on my smartphone.”

So:

今日 is the topic.
The implicit subject is 私 (“I”).
は does not equal “subject-marker” here; it’s “topic-marker.”

What does 運動の時間 literally mean? Why is の used between 運動 and 時間?

運動の時間 literally means “time of exercise” or “exercise time.”

Breakdown:

運動 = exercise, physical activity
時間 = time
の = connects two nouns in many ways (possession, “of,” “for,” etc.)

Here 運動の時間 can be understood as:

“the time for exercise”
“(my) exercise time”

の is used to link the two nouns instead of making a solid compound like 運動時間. 運動時間 does exist, but it sounds more technical or formal (e.g., in research, statistics). 運動の時間 sounds more natural in everyday speech.

Why is 運動の時間 marked with を? What is its grammatical role?

運動の時間 is the direct object of the verb 記録しました.

運動の時間を記録しました。
“(I) recorded the exercise time.”

In Japanese:

The thing that is directly affected by the action of the verb is marked with を.
Here, what did you record? → 運動の時間.
So it takes を.

Structure:

[運動の時間] を [記録しました]
direct object + を + verb

What role does に play after スマホ? Why スマホに and not something else?

に here marks the target/location where something is stored or recorded.

スマホに記録しました = “recorded (it) in/on the smartphone.”

Common uses of に:

destination: 学校に行く – go to school
place where something remains/exists or is put: 机に本を置く – put a book on the desk

Here, 運動の時間 is being put into / stored in the smartphone, so スマホに is natural.

What’s the difference between スマホに記録しました and スマホで記録しました?

The nuance changes:

スマホに記録しました
Focus: the place/target where the data is stored.
→ “I recorded it on the smartphone (that’s where the record now is).”
スマホで記録しました
Focus: the tool/means used to perform the action.
→ “I recorded it using my smartphone (as a tool).”

In everyday conversation, both could be used and often overlap, but:

Talking about where the record is saved → スマホに is more natural.
Emphasizing that the smartphone was the device you used → スマホで fits better.

What is スマホ exactly, and why is it written in katakana?

スマホ is the common short form of スマートフォン (“smartphone”).

スマートフォン → スマホ (abbreviation)
It’s written in katakana because it’s a loanword from English.

Japanese normally writes:

Native Japanese words in hiragana (and/or kanji)
Chinese-origin words in kanji
Foreign loanwords in katakana

Since “smartphone” is a foreign concept/word, it appears as スマートフォン / スマホ in katakana.

What is the dictionary form of 記録しました, and what does it mean?

The dictionary (plain) form is 記録する.

記録する = to record, to log, to keep a record of

Conjugation used in the sentence:

記録する → 記録します (polite, non-past)
記録しました (polite, past)

So 記録しました means:

“(I) recorded,” “(I) logged.”

The ました ending makes it polite past tense.

Where is the subject “I” in this sentence? How do we know it’s “I” who recorded it?

The subject is not explicitly stated, which is very common in Japanese.

The full, explicit version could be:

私は今日、運動の時間をスマホに記録しました。

But Japanese usually omits pronouns like 私 (I) when they are clear from context.

How do we know it’s “I”?

In a personal diary, app log, or casual conversation about your own habits, the default subject is usually the speaker.
Unless another subject is clearly introduced, listeners assume “I”.

So:

English needs “I recorded…”
Japanese is fine with just 記録しました, and context supplies “I.”

Can I change the word order? For example, is スマホに運動の時間を記録しました also correct?

Yes, that word order is correct and natural:

今日はスマホに運動の時間を記録しました。
今日は運動の時間をスマホに記録しました。

Both are fine. Japanese word order is flexible as long as:

Particles (は, を, に, の, etc.) stay attached to the right words.
The verb (記録しました) stays at the end.

Differences are mainly in slight emphasis:

運動の時間をスマホに記録しました。
More neutral; we’re just describing what was done.
スマホに運動の時間を記録しました。
Slightly more focus on スマホに (that’s where it went).

But in everyday speech, both sound normal.

Could I say 運動時間 instead of 運動の時間? Is there a difference?

You can say 運動時間, but the nuance is different:

運動の時間
Natural in daily conversation. Feels like “the time for exercise / exercise time” in everyday language.
運動時間
Sounds more technical/formal, like “exercise duration” as a statistic:
- Used in research papers, health data, charts, app labels, etc.

In a casual sentence like:

今日は運動の時間をスマホに記録しました。
運動の時間 is more natural.

If you were talking about data columns in a study, 運動時間 might appear.

Why is は attached to 今日 instead of 運動の時間? Could I say 今日運動の時間はスマホに記録しました?

You can move は to 運動の時間:

今日は運動の時間をスマホに記録しました。
“Today, (I) recorded my exercise time on my smartphone.”
今日、運動の時間はスマホに記録しました。
“Today, (as for) the exercise time, (I) recorded it on my smartphone.”

The difference in nuance:

今日は… → Topic is “today.” You’re talking about what you did today.
運動の時間は… → Topic is “the exercise time.” You might be contrasting it with something else, e.g.:
- 今日、運動の時間はスマホに記録しましたが、食事の内容はノートに書きました。
  “Today, I recorded my exercise time on my smartphone, but I wrote down what I ate in a notebook.”

So は can move, but it changes what you’re focusing or contrasting.

Are there more casual or alternative ways to say 記録しました in this context?

Yes, some common alternatives:

つけました
- 今日は運動の時間をスマホにつけました。
- つける (here) = to jot down, to keep a record (e.g., in a notebook or app).
  Sounds a bit softer and very natural in daily-life contexts like diaries or logs.
Plain (non-polite) form:
- 今日は運動の時間をスマホに記録した。
- Used in casual writing/speech with friends, or in a personal diary.
Progressive/ongoing nuance (if talking about a habit):
- 毎日、運動の時間をスマホに記録しています。
- “I record my exercise time on my smartphone every day.”
  しています implies an ongoing practice/habit.

In your original sentence, 記録しました is polite, simple, and perfectly natural.