"I'm looking for exercises to strengthen aging knees. I'm in my
late 60's, and I take part in dancing, wight lifting and yoga.
All this makes me feel good, gives me plenty of energy and helps me control my weight. But my knees hurt enough to make me wonder how long I can keep up with the workouts.Do you have any suggestions?" Reader Question . 865 votes.
You are already doing many things right, in terms of taking care of your aging knees. In particular, it sounds as if you are
keeping your weight under control.

Sturdy leg muscles, particularly those at the front and back of
the thighs, stabilize the the knee (as well as many ligaments and muscles around the knee).

An easy exercise to target these muscles is squat, which is quite good for for the knees, if you do the squats correctly.

Simply stand with your legs shoulder-width apart and bend your legs until your thighs are almost, but not completely, parallel
to the ground. Keep your upper body straight. Don't bend forward
since that movement can strain the knees. Try to complete 20 squats, using no weights at first. When that becomes easy, hold a barbell with weights attached. Or simply clutch a full milk
carton.

Straight leg lifts are also good for knee health. Sit on the floor with your back straight and one leg extended and the other bent toward your chest. In this position, lift the straight leg slightly off the gound and hold for 10 seconds.
Repeat 10 to 20 times and then switch legs.

From NY Times, by Gretchen Reynolds, Jan 25, 2013.

I hope this simple exercise or others like Han Baram's "move
legs up and down sitting on a chair with weighted leg bracelets
" will help all of your aging knees, and live in good health for your most precious remaining lives.