Thread by @Conor_Harris_

A thread on how you can use knee extension & flexion to help determine limitations in the lower body

The “screw-home mechanism” of the knee entails an overall external rotation of the knee, but with relative femoral internal rotation & tibial external rotation (Levangie, 2011).

In knee flexion, there is an overall internal rotation moment occurring at the knee with relative femoral external rotation and tibial internal rotation.

This is because locking-out, or extending, the knee requires segments within the femur, knee, and tibia to roll and glide

around each other in order to produce a tight seal of stability through the joint.

Therefore, if we had someone sit on a table and they couldn’t extend their knee all the way, that’s probably an indication that they have tight femoral external rotation muscles, limiting their

ability go into the necessary relative internal rotation.

These muscles are likely the:
- Biceps Femoris hamstring muscle
- Psoas
- Rectus Femoris quad muscle

The same principle could be applied for knee flexion. If they can’t flex their knee to about 135 degrees in a face-down

position, that means they’re likely tight in their femoral internal rotator muscles which is limiting their ability to go into the necessary relative femoral external rotation.

They might have tight:
- Adductors
- Inner hamstrings
- Tensor Fasciae Latae or IT Band

Summary:
- Lack of knee extension: Indication of internal rotation need at femur/pelvis
- Lack of knee flexion: Indication of external rotation needs at femur/pelvis

Ideally this would not be the only assessment we use, as cross-referencing multiple tests will give best results.

I think this is important because proper human movement entails all ranges of motion in different contexts.

If our goal is to develop robust athletes and humans, ensuring they have access to all necessary “movement options” is going to maximize their gains.