Whats a good type of cardio, if you have a bad knee?

Elliptical is fairly easy on the legs

Swimming is great cardio and easy on the knees

Swimming. Boxing. I'm only 21 & my knees are screwed. I do the 30 Day Shred & some other videos, generally right after doing them and the day or two after my knees are killing me, not the best idea to do any circuit training type of DVD's or anything [I'm a hypocrite, obviously...Lol]

definitely swimming. maybe try rowing, too, and see if that's too rough or not. the elliptical is generally pretty easy on your knees, too, since there's pretty much no impact.

I just had knee surgery, so my knee's will be good soon... hehe.

However, up until now I've been doing elliptical, walking on the treadmill, and cycling. I did a few low impact zumba workouts, but I didn't enjoy it really.

I had torn cartilage in my knee so I wasn't allowed to do anything high-impact, no stairs or inclines as exercise, and no squats and lunges.

During my recovery, I'm allowed 'gentle' walking, and once my wound has healed swimming.

Oh and I work out with a Personal Trainer once a week, and he tells me we are going to do sitting down boxing and upper body weights this week.

I have a bad knee that limits my running. I have found that swimming & biking take stress off my knee, and still give me a great cardio workout.

punching

I dislocated and broke my right kneecap in January of 2011. I had surgery to remove the bone fragments (well, chunks, really) in March of 2011.
Due to the nature of the break (I broke off the ridge on the back of the patella), my patella slips out of place now and then. I wear a brace (http://www.braceshop.com/productcart/pc/Breg-Patella-Stabilizer-Knee-Brace-303p370.htm) and completely avoid the treadmill. I use the elliptical and I'm pretty happy with that. Also, I have a pool at home and am really close to the ocean so when I can, I swim. That's the lowest-impact, of course.

Good luck!

I have bad knees that resulted from serious running injury. During my acute pain, I found the physical therapy exercises were too easy for me, so I did this DVD called "Strong knees." It has really help me over come pain. Since then, I still have knee issues depending on the weather, depending of being sedentary for prolong periods of time, or just over doing it on exercise.

The best thing to do is warm up your muscles with some type of exercise and stretch those muscles. Tone muscles all around your knees so it supports your knee alignment. This can be done with yoga, pilates and or weight training. Do this daily to prevent knee pain.

As far as cardio burn exercises, I like Billy Blank's Tae Bo DVDs (uses your hips,) boxing, biking, swimming and just walking (prefer soft surfaces with cushioned shoes to prevent impact on the knee joints.) If your knees aren't that bad, I recommend Jackie Warner's Power Circuits DVD because explains proper form in that particular DVD. But many circuits can be hard on your knees like jumping jacks and please stay away from jump lunges - they are knee killers. I do "modified" jumping jacks and modified jumping rope.

Speaking of proper form, if you do squats or knee lunges, make sure your knee does not got past your toe. That can injury your knee.

After my treadmill dies (hope not any time soon as I spent a lot of money on it, ) I think I will buy an elliptical since I heard that is easier on your knees.

Swimming, elliptical, and lots of Icy Hot and Advil PM if it gets too bad. I'm 47 and never been on a treadmill in my life but just started using one about 4 months ago. So IH and Advil are my new best friends some nights.

I do th elliptical, and my knee gives me problems at times. After a few minutes the pain goes away, however at a speed of 3.5-3.7mph at an 8 incline on the treadmill is good on my knees and feels great!