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Squat Muscles

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What’s involved in a squat?

Why do you do a squat?  Most people know they are doing it to work the quads (quadriceps femoris) and the glutes (gluteus maximus). But some people say that the hamstrings are working. They are partially correct.

According to MRI studies and contrary to popular belief the hamstrings act as stabilizers to the knee and are not directly involved in the squat.  Since they cross both the hip and the knee joint they aren’t really doing much. On the down phase of a squat, the hamstrings are shortening at the knee joint (since the knee is bending), but they are elongating at the hip joint. This means the muscle is neither shortening nor lengthening during the squat.  So if it’s not doing that, it isn’t involved in squatting. At least not until the very last few degrees of hip extension.  On the up phase (standing portion) of a squat, the hamstrings work to extend the hip joint.

In fact, if there is excessive hamstring activation during your squat it can be detrimental to your technique.  The harder the hamstrings work on the knee joint the more quadriceps action you’ll get. This isn’t what you are going for in a squat.

The muscles involved in a squat are the vastus group which is part of the quadriceps femoris group. They operate the knee joint. As you go down into a squat they must slowly elongate to allow a controlled descent.   This is called an eccentric muscle action.

As you come up they contract to pull the knee into extension to allow you to straighten the knee and stand. This is called a concentric muscle action.
Because the hip is bent the fourth part of the quadriceps muscles (the rectus femoris) has only moderate involvement during a squat.

The soleus and gastrocnemius muscles work the ankle joint.

The gluteus maximus is the main muscle of the hip during a squat. Isn’t that, after all, why we do them?  On the down phase of a squat, they are all getting longer (an eccentric muscle action).  On the up phase the gluteus maximus are shortening (concentric) to pull the leg back (hip extension).

The gluteus medius and minimus at the lateral side of the hip stabilize the hip during the squat. Their job is to prevent the knees from buckling inwards. This is called Valgus knee position (or knock knees).  So you can say the “glutes” work when you do a squat, but you’d be more accurate to say that the gluteus maximus is the agonist (the main mover) and the gluteus medius and minimus are the stabilizers of the hip.

The adductors also play a large part in squatting. They prevent the legs from falling outward like you’ve been riding a horse for a long time. This is called Varus knees.   The adductor magnus (the largest of the group), also helps with hip extension. This explains why when you do some heavy squatting your inner thigh muscles become sore as well.

At no point is the hip flexor, the iliopsoas involved! This is a real misconception. It isn’t working to pull you down on the down phase, nor is it pushing you up on the up phase. The muscle working the hip is the gluteus maximus!

So, there you have it! Now you know all the muscles involved in a squat. 

Our next blog is on squat technique!

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