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What Causes Pain in Knee Cap and Runner’s Knee?

Pain in knee cap, “Runner’s Knee”, or more accurately Patellofemoral pain syndrome is a complex repetitive strain injury.


As a runner, you put extreme stress on your knee cap, especially on long runs.  Research has shown that a predictor for pain in knee cap is when there is weak extension of your leg.  However, the part that isn’t often discussed is why you have weak extension of your leg!

The Muscles That Cause Pain in Knee Cap:


Three of the four quadriceps muscles originate along your thigh bone (femur) and one important quadriceps muscle (rectus femoris)  originates on the tip of your pelvis.

All four quadriceps merge into the patella tendon that crosses over your knee cap inserting into your shin bone (tibia).  When your leg is bent your quadriceps are at their longest length.  In order to straighten your the quadriceps need to contract which pulls on your patella tendon.

What Happens When You Run For Miles:


If you run for multiple miles, your quadriceps are being repetitively strained.  This also causes an overload of toxins which creates muscle fiber knots (spasms) to form.  The spasms cause a shortening of the muscle fibers placing strain on the insertion point causing pain in your knee cap.

To eliminate pain in knee cap and for the muscle to have power, it needs to be at its longest length.


As your rectus femoris muscle shortens because of the repetitive strain of running for miles, it pulls down on your pelvis.  This causes your pelvis to rotate down in the front and up in the back.  This rotation causes your hamstrings to overstretch!

Your hamstrings feel tight, and they do have spasms, but the pelvic rotation has overstretched muscles that are already in spasm.  This causes your hamstrings to feel tight, and causing pain in knee cap, but to stretch these muscles without first releasing the spasms can potentially tear the muscle fibers.

Non-Muscular Causes of Pain in Knee Cap:


  • Cartilage in the knee joint may become worn and not provide the shock cushion for the leg bones.

  • The kneecap may dislocate if isn’t in proper alignment in the femoral groove.

  • Bow legs and other skeletal deformities put a severe stress on the knee, hip, and ankle joints.

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