Squat Report: Knee Extension
Last month we took a look at what happens to your knee when you are going into flexion during a squat.
This month we are going to look at the flip side of that equation and dive into knee extension and try to see what happens here. One note to take into heart here is that the muscles we are going to talk about here, today have dual roles. You see when your knee goes into extension during a squat it also causes hip flexion (we will discuss this next month when we look into hip extension)
Last month I used this picture to show how the bone structure plays a role in knee flexion
The same lies true for knee extension as well, however, during extension of the knee the force now comes from FQ and is transferred to FL from the quadricep muscle group and extending the knee.
One thing to take note here is the role of the hamstring is vital here as well, it must engage so that the posterior aspect (back part) of the femur (thigh bone) does not dislocate.
The Sartorius muscle also must engage to aid in knee extension as it is another muscle that helps in knee flexion as well as the Tensor Fascia Latae, and the Gracilis (the last two to a very lesser degree that the Sartorius). The following diagram will show a better indicator of what I am talking about
As you can see the quadricep group all “share” a common tendon that encapsulates the patella and inserts into the tibia. The Sartorius “wraps” around the front part of the upper leg and inserts to the inner part (medial aspect) of the tibia. These five muscles when called upon extend the knee. The other two weak extensors are the Tensor Fascia Latae which it’s long tendon attaches to the outside part (lateral aspect) of the head of the fibula and the gracilis which attaches to the medial aspect of the tibia. These two muscles provide support for the knee while going into extension and to a lesser degree aid in extension.
One muscle that I have not talked about yet is the Plantaris. The reason is that this does not flex, nor does it extend the knee. The purpose of this muscle is to unlock the knee when there load on the knee in a flexed position to start the process of extending the knee.