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Squat Report Knee Flexion

  • by Admin
  • March 28, 2018

This month and next month we will be taking a look at what happens at the knee during a squat. I have split these two up because it really does take a lot of explanation.

During a squat a few interesting things happen when your knee flexes. One thing in particular is that we get external rotation across the tibial axis that causes eversion at the ankle (we covered this a few months ago). While this is happening the knee cap “drifts” laterally (towards the outside of the body). Also, the medial and lateral epicondyles (inner and outer head of the thigh bone) want to pop forward and slip off the tibial plateau. Please refer to the blog post a few weeks ago on Anatomy of the Knee to help you out with the terminology being used. The following picture depicts what I am trying to explain

As you can see the deeper you go into flexion the stronger your quadriceps have to be to make sure the knee cap stays in place which is to stop the femur (the thigh bone) from sheering off the tibial plateau. One thing that is not being shown here are the ligaments, the ACL, PCL, MCL, and LCL we will go into further discussion on the importance of these ligaments later on but for now we just need to know that during flexion the ACL and the LCL are the ligaments that have the most amount of stress as they are the ones acting as a brake to stop the knee from popping forward and inward. Please note that this is a last resort for the body if the musculature around the knee cannot take the load properly and we never want this to happen because the ligament threshold is far less forgiving than the muscles.
Now let’s get into the muscles that help the knee stay in place during flexion. We will start off with the muscles below the knee and end off with the muscles above the knee, just to make things flow better for next month.
The muscles below the knee are extremely weak knee flexors and act more of keeping the tibia and fibula together and helping them control them from splicing apart (you can find a more detailed explanation from last months blog post on the shin). The more powerful muscles of knee flexion are the hamstrings and quadriceps.
Above the knee is where most of the action happens. The distal (furthest from the body) aspect of the hamstrings (three in total semimembranosus, semitendinosus, and biceps femoris), and gracilis all contract and cause the knee to bend. Know in order for the knee not to pop out forward and laterally the distal aspect of the quadriceps, the TFL (tensor fascia latae), and the sartorius all have to contract in order to keep the knee cap from popping out and away which in turn the knee cap can hold the femur in place.

Now which one activates first and what is the correct order of firing pattern is hard to say. This is more of a co ordinated activation so that you can perform the knee flexion with ease, limited pain, and high quality of the repetition. When all these muscles fire correctly then you will get the maximum potential output for the task that you are asking out your body whether that be a leg curl, lunge, squat, leg press, run, walk or just getting out of bed. The good thing is that we already have these firing patterns ingrained into our subconscious, so we don’t have to think about doing them on a day to day basis. It’s only when we get hurt and have to come up with new firing solutions of these muscles that we have to be careful of and this is why we do what we do at Vio Fitness. We want those original firing solutions back to what they were, if at all possible.
Next month we will dive into the flip side of things and see how the knee acts while we go into extension.

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