It's hard to get a good workout out when most cardio is literally a pain in the knees. However, you don't have to subject your aching joints to the agony of high-impact activity, such as running or step aerobics. Low-impact cardio, like swimming, biking and the elliptical trainer, is just as effective in getting your heart rate up and the sweat flowing.
Your knees might hurt because of tight muscles, degenerating cartilage or patella strain, among other reasons. To get in your cardio without concern, look for workouts that take the stress off your knees.
Swimming and Water Workouts
Swimming takes nearly all the weight off your knees because of the buoyancy of the water, but it still burns an impressive number of calories — more than 250 calories in 30 minutes, simply doing a slow front crawl stroke.
However, you don't have to stick to swimming laps. Other water workouts, such as water walking and water aerobics, will get your heart rate up and work your muscles. Just make sure that you're not tensing your knees during a water workout.
When swimming, make sure you stay hydrated. You can't always tell how hard you're working because the water quickly washes the sweat away.
Grab a Bike
Biking burns a similar number of calories as running, says the New York Times Wellness section, but it's a lot gentler on your body because it's a nonweight-bearing activity. If you already own a bike, strap on a helmet and take a spin around the neighborhood.
If not, try out biking on a stationary bike in the gym. Once you're ready to kick it up a notch, enroll in a cycling class, which is a fast-paced, intense cardio workout that's done entirely on a spin bike.
Take a Walk
Walking is low-impact and, as long as your knees aren't completely shot, won't cause any pain. Start on a smooth, flat surface to avoid any pain, though you might be able to work your way up to hilly routes or trail hiking.
To make sure you're really getting your cardio in, aim to walk at a pace of at least 3 mph. Try out the talk test — you should be able to hold conversation, but not sing a song without running out of breath.
At the Gym
Make the most of your gym membership by doing cardio on the elliptical trainer or rowing machine. Both of these machines are low-impact, as they don't require your feet to leave the pedals, in the case of an elliptical, or the footrest on a rowing machine.
When you're on the elliptical, stand up straight and engage your core for a better workout. While you should hold onto the handles, because moving your arms helps raise your heart rate, you shouldn't lean on them — that simply makes the workout less effective.
On the rowing machine, focus on your form for the best workout. Hold the handles lightly, keeping your wrists straight and your shoulders relaxed but pulled back. Push your feet against the footrests and use your arms to pull the handles back until your hands are near your ribs. Release your elbows until they're straight and bend your knees to slide forward, completing the stroke.