There is one muscle in particular that causes the most problems at the knee. It’s name is the Rectus Femoris, but it is often called the “Wreck”us Femoris, because it causes so many problems.
The rectus femoris muscles begins at the front of the pelvis and attaches to the patellar tendon at the front of the knee, so just above the knee cap. The reason why the RF causes so many problems is because of its attachment to the pelvis and crossing in front of the hip, so it acts like a hip flexor. Because of its attachment points, the RF tends to become very tight on people, and this causes a lot of compressive forces at the knee cap as it slides on the femur (thigh bone).
Because we sit so much and the hips are therefore flexed, the hip flexor muscles will tend to shorten and causes extra tension at their attachment points. Also, if we do not stabilize our pelvis in the correct alignment with our lower rib cage, which is parallel to each other (see picture below), then the RF will act as a stabilizer for our pelvis, which is a task that it is not designed to perform, so it performs it poorly and creates too many tightness or tension at the knee.
There is an easy test to see if your RF is too tight. You lay on your belly on the floor or on a bed and try to take your heel to your butt. It is normal to get your heel pretty close or all the way to your butt. You can use a towel wrapped around your ankle to pull the lower leg if you have a hard time doing this test. If you cannot come close to bringing your heel to your butt, then you have a tight RF and it needs to be treated, especially if you have knee pain.
The good news is that a lot of knee pain is causes by this mechanical problem and getting the tension to reduce in the RF isn’t that hard. When you do get the tension or tightness reduced in the RF, your knees will feel a lot better!