Two differing widths of PVC tubing from the local building shop.
Resting the ankle on the smaller tube and relaxing the limb to help passively extend the knee.
The larger PVC tube creates greater passive force.
How to perform a passive extension stretch
Simple PVC tubes allow a simple passive stretch exercise. Laying an ankle weight on the knee during these passive stretch sessions can further improve the stretch.
The influence of electromyographic biofeedback therapy on knee extension following anterior cruciate ligament reconstruction: a randomized controlled trial. Christanell F, Hoser C, Huber R, Fink C and Luomajoki H. Sports Med Arthrosc Rehabil Ther Technol. 2012; 4: 41.