One of my clients has chondromalacia in both knees. Her doctor has encouraged her to exercise, but the knees are sensitive. Stair climbing causes her pain. She walks a lot, with no real issues. Beyond the exercises she was given at physical therapy 5 years ago (quad sets, lateral leg raises, stretches etc.), I am not sure how to proceed. Her doctor has forbidden “squats”, and isolated quad exercises often involve a lot of stress on the patella (e.g. TKE), yet it seems prudent to strengthen the quads. Which exercises might be useful for her without causing additional stress on the patella or harm to the joint?