OK, in this piece in the New York Times, Gretchen Reynolds doesn’t actually tell us how to strengthen knees, but she does tell us how to strengthen the muscles around knees, which is the best we can hope for. Squats are a no-brainer, easy to do and great for knees, and Reynolds also recommends straight leg lifts. The big value in this piece, however, is the accompanying video, which demonstrates four exercises that can stabilize less than stable knees.