What would be good cardio other than treadmill cuz I have bad knees?

That is a great question and one that comes up a lot. You definitely want to limit the amount of impact on the knee joint by doing low-impact activities. I would start with cycling whether outdoors or on a stationary bike. This takes the impact factor out of it. Also, you have the elyptical machine which functions similarly except does not give the same support as when seated. One of my favorites, for all joint issues, rehab, etc. is Water Aerobics or swimming. This eliminates the pressure on the joints as well as impact. It’s a great full-body exercise. If you do have to use a treadmill walking is best.

Another one I’m going to throw out there that is not discussed as much is the arm bike. This upper body cardio machine is usually ignored for the ‘higher calorie burning machines.’. Because you are using the upper body, the heart is working very hard and it is a great cardiovascular workout which is also used in cardiac rehab. However, since the arms are a much smaller area than the legs, the calorie burn is also lower.

Of course, I always recommend seeing your doctor or Physical Therapist for your specific issue so that you can know which exercises/motions to avoid and which are ok.