At the start of week three of my physical therapy began an exercise in which while sitting was put on a device where I placed my foot in a stirrup and then used a hydraulic pump to gradually move the stirrup back toward my body which would flex the knee. The routine was to pump my foot back (increase the flex) until I could go no farther.....then hold for five minutes. Then repeat the process again. Interestingly.....when I got to the point that I could go no farther....after a couple of minutes was able to gradually pump more flex to the knee. Over the course of my physical therapy I substantially improved my flex. Did it hurt....hell yeah it hurt!!! After the ten minutes I would be drenched in sweat and did nothing but flexi my knee!! But I believe it was an extremely key exercise for me.
After complettion of this knee flex exercise I would then ride a bike for 20-30 minutes, then an elliptical trainer for 5-10 minutes, and then a stair master for 5 minutes. I firmly believe the forced flex and the motion exercise were the key factors in my successful therapy.
If you have the hydraulic knee flex device available at your physical therapy highly recommend the exercise.