Getting started with knee strengthening exercises

What can you do to strengthen your knees?  What if you aren't up for doing lunges and squats quite yet?  Here is a video to get you started.  The target audience is anyone over 50 who is feeling a little unstable or occasionally experiences knee pain.  I recognized the first exercise from knee rehab.  I learned it during my first physical therapy session.

There are three exercises done on the floor and two standing exercises.  To do all the exercises, you need a foam roller or a mid-size ball, and a stability ball.