I have a knee problem and when at the Gym I do a variety of cardio vascular workouts that include the treadmill. I cannot run -I mean cannot as that would put so much pressure on the knees- they would give out- even on a treadmill. SO--- What I do is walk- Walk fast working up to 6 mph and up hills- the steepest hill on the machine. This will work the knees and hips and the muscle that takes the pressure is the calves. They really go through it when walking that fast- so give it a try.

And I still feel the best exercise is cycling. Whether on a trainer or out in the wind and the rain and the cold and working up those hills. Only thing is that when at the gym- I will also do a few weights to keep mobility into the upper body and the back. Still feel the best bit of Gym work is the Mixed Sauna at the finish.