Questions & Answers about Я поднимаюсь в лифте на восьмой этаж, чтобы взять книгу.
Because the base verb is подниматься (to go up / to ascend), which is a reflexive verb in Russian. Here -ся / -сь is not “I lift myself” in a literal English sense; it’s just how Russian forms this meaning: to rise / to go up (stairs, elevator, etc.).
Non‑reflexive поднимать means to lift (something) up: Я поднимаю книгу = “I’m lifting the book.”
- Я поднимаюсь… (imperfective) = “I’m going up / I’m in the process of going up” (right now, ongoing).
- Я поднимусь… (perfective) = “I’ll go up / I will go up (and reach the top)” (a completed, one-time action in the future).
So your sentence uses поднимаюсь to focus on the process of riding upward.