I stepped downhill on uneven ground and twisted my knee to prevent myself from falling. This was years ago. Never had it seen to. Just recently I did the same thing to a much lesser degree. Not much pain, just knowing the feeling. Now when I use the stationary exercise bike, low resistance, slow speed, this knee burns like hell. I thought this would be a good controlled exercise to get it back into shape. Is the burn acceptable? Should I be doing a different exercise?