If you sit at a desk all day, don't perch on the edge of your seat at work trying to sit up straight.

如果你要在桌子旁呆一整天，工作时别坐在椅子的边缘，要尽量坐直。

youdao

When I sit on the commode, I can no longer sit up straight.

当我坐在便桶上时，我怎么也坐不直身子。

youdao

Se?or, just sit up straight as much as possible.

在座位上尽量坐直身体。

哈佛公开课 - 幸福课课程节选

Just like they told you for your school photo, sit up straight, wet your lips and lean forward just a bit.

FORBES: 8 Ways To Get A Better Driver's License Photo

"Yeah, thatta girl, " he said, pulling back to sit straight again.

NPR: Excerpt: 'The Assassins Gallery'

The trick is to cycle at maximum speed until the point of overtaking, and then sit back in the saddle as you pass, looking straight ahead as if the mere breeze is carrying you forward.

BBC: NEWS | UK | Magazine | Cycle warriors