When you have bad knees, it can be difficult to find weight loss exercises that accomplish the goal you want but don't hurt your knees. Conditions like osteoarthritis can make weight-bearing exercises difficult, as can acute injury or knee replacement. Avoid impact exercises like running or sports that have fast changes of direction, and you can still perform weight loss exercises with a high degree of intensity.
Warmups are an important part of any exercise routine, maybe even more so if you have bad knees. A proper warmup helps to loosen stiff muscles and get your blood flowing. To get your body ready for the exercises that lie ahead, do some brisk walking or other light activity that doesn't hurt your knees until you break a sweat. Then, perform some static stretches to loosen the muscles and ligaments before you begin. Take 10 to 15 minutes to thoroughly warm up your body, or follow a specific routine as set down by your physical therapist, if you have one.
Swimming takes most of the gravity out of the equation and is gentle on all your joints. You can perform most of the swimming strokes to swim laps of the pool, tread water or just move around as you please to exercise without impact on your knees. Avoid any strokes that cause discomfort, and swim continuously for at least 20 minutes so your heart rate is elevated and the fat burning effects of the exercise take hold.
Riding a bike is another non-impact exercise that is beneficial to weight loss. Riding a bike utilizes your quadriceps, hamstrings, calves and glutes to propel you forward without any pounding on your joints. If you've recently had surgery, you may have to wait until riding a bike is comfortable. To get a quality weight loss workout, ride your bike off road or on the road, or use a stationary bike at the gym. Stay away from steep hills to protect your knees; riding on flatter surfaces doesn't require as much intensity.
Despite some people's belief that weight training is for building big muscles, it's also a beneficial weight loss exercise that someone with bad knees can use. Leg exercises like heavy squats, leg presses and leg extensions will likely have to be avoided, but you can still get a good calorie burn with others. The bench press, shoulder press, rowing movements, biceps and triceps exercises and abdominal work helps to build lean muscle, which helps burn fat. Set up a series of exercises in a circuit to increase the calorie burn even more. Use caution with leg exercises and lift your feet off the floor if you turn while holding a weight so you don't twist your knee.