|I had "pain behind the knee" back in high school. I did the following with a theraband wrapped around the foot and knee while sitting on a table (a towel might work also).... pain went away after 2 days of doing the exercise (~had been in pain for 3 months)! I've kept the article all these years, so hope this helps.:)
Behind Problem Knees: The Popliteus Muscle
By James P. Kotorac, D.C.
The popliteus is a small muscle that runs behind the knee. Due to its small size compared to the hamstrings above and the calf below, it is often overlooked in knee and lower leg injuries. It also isn't a very strong muscle, which adds to its relative obscurity. It is, however, of paramount importance to athletes. The popliteus has three basic motions. It helps to flex the knee, in fact, it begins the motion of knee flexion, actually unlocking the knee from full extension. In relation to this motion, a tightness or shortening of the popliteus inhibits full extension of the knee, leaving the knee unable to fully straighten.
Another motion is laterally rotating the upper leg on the lower leg when the foot is planted.For a runner, this becomes critical as a balanced gait is only achieved when this muscle is functioning properly. The final motion is medially rotating the lower leg under the upper leg. In running this would occur when the foot of that leg is in the air, powering toward the next foot strike. Shortness of this muscle would lead to an improper foot plant and excess
Injury occurs in two ways:
Any acute sprain/strain to the knee will involve the popliteus muscle.
Chronic overuse/ imbalance stress will also injure the muscle.
When the lateral hamstrings are stronger than the medial hamstrings, the popliteus muscle will weaken. Overpronation or running in worn shoes will cause excessive lower leg rotation and overstress the popliteus. A common practice among runners is hanging out or walking around in old running shoes. While you may be running in a good neutral position, the rest of the day you can be adding stress to the popliteus and the rest of your body as well.
The most effective treatment to an injured popliteus is manually applied trigger point therapy and ultrasound. While many muscles respond well to self-applied rubbing or kneading, the popliteus muscle should be approached with care. It overlies the popliteal fossa which is loaded with sensitive blood vessels and nerves where damage via too much pressure is possible.
The popliteus muscle is slightly stretched when the hamstrings are stretched. To strengthen the muscle, sit on a high chair with your legs dangling off the ground. Using elastic tubing anchored at one end, wrap the other end around the inside of your foot and rotate your foot and lower leg inward. Use low resistance and high repetition, remembering that this is not a powerful muscle.
Examination and, if necessary, treatment, therapy and strengthening of the popliteus should occur after any knee or ankle injury, lower leg break, or after any knee surgery.
Here the popliteus' lack of strength is an advantage. Treatment restores this muscle to normal in a relatively short time compared to other larger and stronger ones. But donít let its size and strength fool you. A popliteus problem can cause severe enough knee pain that running can become impossible.