If you have knee pain you should check this relationship. The Popliteus and Rectus femoris are functional opposites to each other. Meaning they do different actions. The rectus femoris extends the knee joint and the popliteus flexes the knee joint and medially (internally) rotates the bent knee (Unlocks the knee).
The rectus femoris is often weak and inhibited playing an inefficient role of flexing the hip and extending the knee. Why? Well sitting all damn day isn't helping! Your rectus femoris gets shortened at the hip joint and lengthened at the knee joint. It’s a two jointed muscle with a long lever. The longer the lever the more likely for disaster to occur.
As a result the popliteus drives more knee flexion, preventing the lower leg from taking full advantage of the elastic recoil of fascia from the foot to the glute. Torque on the knee from the medial tibial rotation causes pain and discomfort when walking, running, or walking up the stairs. Sometimes you may even feel the knee lock up.
Even if you have quads like the quadfather that doesn't mean they are functional and efficient for movement. That’s like having a Ferrari in the driveway that won’t start. If you have had an ACL injury no matter how long ago you can pretty much bet this relationship exists.
WHAT TO DO ABOUT IT?
Sit and feel for the popliteus just medial and behind the fibular head. It will run diagonal across the knee down towards the tibia. You will know when you hit it because it usually really hurts. Be careful in the posterior knee because there are lots of delicate structure sitting back there. Stay more lateral towards the fibula and you should be ok. To ensure you are on the popliteus resist knee flexion while internally rotating your tibia and it should pop into your fingers.
Massage that little guy for 1-2 minutes and then lie in your back and activate your rectus femoris by contract your quad and raising your leg up in the air holding the contraction at the top and bottom for 4 seconds repeat this for 10-20 Reps or until neural fatigue (see below).
OTHER MUSCLES RESPONSIBLE FOR A FACILITATED POPLITEUS
It is important to look at the body holistically as well, by paying attention to the kinetic chain you may be able to find some funky compensation patterns going on.
In the superficial back line, there is a chain that goes from the bottom of the foot, through the calf muscles, through the popliteus, into the hamstrings, and the gluteus maximus. In the extension phase of gait, these muscles work together. Inhibition of one or more of these muscles may cause another muscle in this chain to become facilitated (tight). For example, the popliteus may become facilitated due to inhibition of the gluteus maximus.
The popliteus can also become facilitated due to inhibition in the superficial front line. Inhibition of the extensor hallucis longus (your big toe), rectus femoris (quad), and psoas (hip flexor see previous post) commonly cause facilitation of the popliteus.
In internal rotation of the tibia, inhibition of the medial head of the gastrocnemius (calf) may cause facilitation of the popliteus.
In external rotation of the femur, inhibition of the biceps femoris (hamstrings) may cause facilitation of the popliteus.
Inhibition of the neck extensors, flexors, and rotators may also be caused by a facilitated popliteus.