Water-based activities like swimming build strength while being low impact, meaning they put less stress on the joints, including the knees. “Run” in the water to increase leg strength. Strap on a flotation belt and head to the deep end of the pool. Keep your body straight and alternate between high knees and marching for variety. Swim laps using different types of strokes to work different muscle groups; combined with kicking, this will exercise your whole body.
Ellipticals
Ellipticals offer low impact exercise opportunities, but if used incorrectly they can cause pain. Maintain correct posture and keep your core tight when using the machine. Start with a five-minute warmup at level 3 resistance. Increase to level 5 for five minutes, then level 6 for five minutes, then all the way up to level 8 or 9 resistance for 10 minutes. Move back down to level 6 for five minutes, then down again to level 3 or 4 for five minutes. If your elliptical trainer can be pedaled in reverse, do this to work your calves and hamstrings even more.
Body-weight Exercises
Try and increase your flexibility by stretching the muscles surrounding the knees and do basic body-weight exercises. Start with thigh, calf and hip stretches. Stretch your thighs by bending one leg behind you and pulling that foot to your rear. Stretch your calves by pushing against a wall with one foot back farther. Push that heel to the ground to work the calf muscle. Stretch your hips and IT band by sitting cross-legged on the floor, then pulling one knee toward your chest. Straight leg lifts will strengthen your quads, and these are done by lying on your back and lifting one leg at a time six to 12 inches off the floor. Hold for 10 seconds, then lower and repeat 10 times for each leg. Do a half squat to further strengthen leg muscles. From a standing position, lower and raise yourself slightly – using an 8- to 12-inch range -- to mimic riding a horse. Do 10 to 20 reps for five sets.