Сначала я сел на велотренажёр, а потом перешёл к другому тренажёру.

Сел is the past tense of сесть, which means to sit down / to get onto something. It focuses on the completed action of changing position.

• сесть → сел = sat down, got on
• сидеть → сидел = was sitting
• садиться → садился = was sitting down / used to sit down

So in this sentence, the speaker first got onto the exercise bike, so сел is the natural choice.

Compare:

• Я сел на велотренажёр. = I got on the exercise bike.
• Я сидел на велотренажёре. = I was sitting on the exercise bike.

Because сесть describes movement onto something, and with that meaning на takes the accusative case.

• сесть на велотренажёр = to get onto the exercise bike
• сидеть на велотренажёре = to be sitting on the exercise bike

This is a very common Russian pattern:

• motion to a place/object → на + accusative
• location on a place/object → на + prepositional

So:

• Я сел на велотренажёр. = I got on the bike.
• Я был на велотренажёре. / Я сидел на велотренажёре. = I was on the bike.

Also, велотренажёр is inanimate masculine, so its accusative singular looks the same as the nominative: велотренажёр.

Сначала ..., а потом ... is a very common Russian structure meaning first ..., and then ...

Here, а does not mean a strong contrast like but in every case. It often links two stages or two parts of a sequence, especially when the speaker is moving from one thing to the next.

So this pattern sounds very natural:

• Сначала ... , а потом ...

You could sometimes hear и потом, but in this kind of step-by-step narration, а потом is more idiomatic.

Here перешёл к means moved on to or switched to.

It can be physical, but it often also suggests a change of activity or focus. So the idea is not just that the person walked somewhere, but that they finished one machine and then started using another.

• перейти к другому тренажёру = move on to another machine

This is why перешёл к works well here.

Some related verbs:

• подошёл к тренажёру = walked up to the machine
• сел на тренажёр = got onto the machine
• перешёл к другому тренажёру = switched/moved on to another machine

Because the preposition к requires the dative case.

Both the adjective and the noun have to change:

• другой тренажёр = another/different machine
• к другому тренажёру = to another/different machine

So:

• другой → другому
• тренажёр → тренажёру

This is standard agreement in Russian: the adjective matches the noun in case, number, and gender.

It can mean either, depending on context.

In this sentence, к другому тренажёру most naturally means:

• to another machine
• or to a different machine

Both work in English because the important idea is that it was not the same machine as before.

Russian often leaves that distinction looser than English does.

In the past tense singular, Russian verbs agree with the speaker's gender.

A male speaker says:

• я сел
• я перешёл

A female speaker says:

• я села
• я перешла

So the full sentence would be:

• Сначала я села на велотренажёр, а потом перешла к другому тренажёру.

Everything else stays the same.

Yes, Russian word order is flexible, and я can sometimes be omitted if the subject is already clear from context.

Possible variants:

• Сначала я сел на велотренажёр, а потом перешёл к другому тренажёру.
• Я сначала сел на велотренажёр, а потом перешёл к другому тренажёру.
• Сначала сел на велотренажёр, а потом перешёл к другому тренажёру. — possible if it is already obvious who is being talked about

One important point: Russian past tense does not show person, only gender and number. So сел by itself means sat down with masculine singular, but not specifically I sat down. That is why я is often kept for clarity unless the context already makes it obvious.

Yes.

• сел comes from сесть — perfective
• перешёл comes from перейти — perfective

Perfective verbs present the actions as completed whole events. That fits this sentence because the speaker is describing a sequence of finished actions:

1. got onto one machine
2. moved on to another

If you used imperfective forms, the meaning would change. For example, it might sound more like process, repetition, or background action.

Compare:

• Сначала я сел..., а потом перешёл... = first I got on..., then I moved on...
• Сначала я садился..., а потом переходил... = this would sound unnatural here unless you were describing repeated or habitual behavior

Yes, ё is important in pronunciation.

• тренажёр is pronounced roughly trena-ZHYOR
• тренажёру is roughly trena-ZHYO-ru

The stress falls on ё, and ё is pronounced like yo.

In many Russian texts, ё is often written as е, so you may sometimes see тренажер in print, but the correct pronunciation is still тренажёр.

For learners, it is very helpful to remember that ё is always stressed.