fiber optic strands are glass tubes and they bend.
[1] https://physics.stackexchange.com/questions/12913/hollow-tub...
[2] https://www.mtbiker.sk/forum/download/file.php?id=207637
Hollow air core fibre does exist and seems to be touted as the next big thing though.
https://www.optcore.net/hollow-core-fiber-introduction/#h-wh...
(From vague memory, stiffness is proportional to the cube of the thickness.)