Morten, why don't you just play tennis?
It won't hurt anything, and you only go down a level or so.
I've been windsurfing, playing tennis, snowboarding, and surfing on it, besides some construction work and gardening, so it's no biggie.
I can't come close to walking downhill since '08, or run. So what? So I'm a top level 3.5 singles player instead of a run of the mill 4.0. No biggie.