I have had many joint injuries to both knees and ankles, but my left ankle has gone through three bad sprains. Tearing ligiments and tendons. Now is swells up walking or turning it the wrong direction. Because of this I have gained a lot of weight, not being able to exercise and get a high cardiovascular workout. Running is definately out of the question and walking has a roofing in weight loss in my case, because I am used to walking 26 miles with 40lbs strapped to my back. What cardio can I do to loose weight without being mobile and on my feet?