спину

спину

The Russian word "спину" is the accusative singular form of "спина," which means "back" (the rear part of the body).

Here, "спину" (in its nominative form: "спина") refers to the physical part of the body, specifically the back area, and it is used in the accusative case to indicate 'my back.'

Я ощутил боль в спине после тренировки.

I felt pain in my back after the workout.

In this sentence, "спиной" (an instrumental case form of "спина") describes the manner in which the action is performed, showing the body part used in turning.

Он повернулся ко мне спиной, не сказав ни слова.

He turned his back to me without saying a word.

Here "спину" (in the accusative case) is used as a direct object of the verb 'выпрямить,' meaning 'straighten.'

За весь день я так и не смог выпрямить спину.

Throughout the day, I couldn't straighten my back.