Anyone knows how much tension does national player string on their racket?.?

there are 1000's national badminton players (pros) in the planet earth, and I'm not even counting ex-nationals.

Uhh, as cooler mentioned, there are many pro players there and they all use different tensions and whichever accelerates their game the best they'll use that. But pros use very high tension like 30 or so. Jonas said it's not very common to see them using a low tension.