Write an article based on this "Go swimming for a low-impact cardio exercise. Work out with a rowing machine for a knee-safe cardio exercise. Exercise on an elliptical for a knee-friendly cardio workout. Ride a bicycle to get your heart rate up without hurting your knee."
Swimming can help you burn calories without risking your knee injury getting worse. Try swimming laps and doing different strokes, like the butterfly stroke and the backstroke.  You can also try jogging in the water since you won’t be putting as much stress on your knees.  You can burn 350-570 calories an hour by swimming, depending on the level of intensity. Rowing is a low-impact exercise that can help you get cardio without aggravating your knee. Rowing may not be recommended for all knee injuries, so be sure to consult your physical therapist or doctor before adding it to your daily exercise routine. You can burn between 400-800 calories using a rowing machine for 1 hour, depending on your weight and the intensity level you're using. Ellipticals are safer for a knee injury than a treadmill because your feet stay on the pedals, which limits the impact put on your knees. If you want to burn calories and get your heart rate up, spend time on an elliptical at home or at the gym.  Start with 5-10 minutes on the elliptical after your injury, and work up toward 20-30 minutes, increasing your time by 1-2 minutes at a time. Keep a slow, steady pace and a low elevation, especially at first. 30 minutes on an elliptical can help you burn 170-320 calories, depending on your weight and intensity level. Similar to an elliptical, riding a bicycle is a great cardio exercise that will put less strain on your knees than running. Stick with stationary or recumbent bicycles since a regular bike may be too hard on your knee.  You can burn 250-700 calories riding a stationary bike for 30 minutes, depending on your weight.  Make sure you’re not riding on an incline or you could make your knee injury worse. Most stationary bikes have different intensity settings you can choose from. Start out with a low-intensity setting and gradually increase the level of intensity so you don't strain your knee.