Dr. says I have patellafemoral strain (runner's knees) what work out can be done safely?

A good form of exercise is swimming(the joints are cushioned in the water and it works muscles you are probably not used to using) Look to see if the fitness place has a pool.

I have had both knees operated on, my Achilles tendon ruptured, debrided and reconstructed, broke my ankle twice

and had countless sprains and strains.....

I get great, complete workouts on weight resistance machines

(think Bow Flex type) which are non-impact. Fantastic for

all-over cardio and muscular strength, building definition

and toning the heck out of what you have. Several weeks of

doing this type of work out and you will have "tightened" up considerably!

Ask a personal fitness trainer. It has to be specialized just for you.