"It's a myth that squats hurt the knee," says Joe Hart, an assistant professor of kinesiology at the University of Virginia. "Squatting is very good for the knees, if you do the exercise right." To accomplish that, follow this protocol. Stand with your legs shoulder-width apart. Bend your knees until your thighs are almost, but not quite, parallel to the floor. Don't bend forward – you should always be able to see your toes. As you get stronger, use a barbell, held level near your chest, to add weight to the exercise. Do 20 to 30 reps three to five times per week.

Another great exercise for your knees? Leg lifts. This easy exercise works small muscles that help stabilize the knee. To do it, loop one end of a resistance band around the bottom of a door joint and the other around your ankle. Standing up straight and holding your stomach in to lengthen your spine, lift your leg to the side to work hip stabilizer muscles, straight behind you to strengthen gluteus and hamstrings, and straight in front of you to work quads and hip flexors. Repeat each lift 10 times on each leg, and increase reps over time. Do three to five times per week.