2 years post ACL - difficulties

I had my ACL reconstructed 2 years ago. It was injured when i was tackled to the ground and surgery was required using my hamstring to make the graft. Everything has been fine, i can run and walk with no problems, however, I returned to Karate classes last night and since i did so, my knee if painful and stiff and I cannot bend it properly. I can weight bare no problem and am unsure if the ACL is damaged or I just need to build up more specific muscles to cope with the twisting and kicking movements. Any advice would be thankfully received and faithfully applied.:D

Mufftie,
Karate is a more demanding sport activity than running. Damaging the ACL again should be diagnosed only via clinical assessment/examination. Try not to draw conclusions and go on with the lessons gradually. If you see that symptoms persist for more than a week, call your doctor or your physio.
ilias