Hip-Driven vs Trunk-Driven

When we squat, our ankles, knees, and hips flex, as our pelvis and spine extend as seen in the drawing on the right. [1] When our lower limbs can function and flex, our hips drive the squatting motion as our upper body stays upright.

When our lower joints can’t flex, we make up for that “missing flexion” by flexing our pelvis and spine as seen on the left.

This puts us in a “trunk-driven” motion because we aren’t able to move the lower joints well anymore.

The function we have affects the position of our body, and the position of our body affects the way we function.

In 2016 a study was done to further learn how our trunk position affects our lower back, thigh, and butt muscles. The study had individuals squat with 3 different trunk angles, 0, 15, and 30 degrees. [2]

This study found that when the trunk leans forward, the thigh muscles are less active, and the lower back muscles become more active.

In a 30-degree forward trunk position, more like the drawing on the left, the lower back muscles contracted under length which exponentially increased the load and stress on the lower back muscles and greatly increased the pressure within the disc.  [2,10,20]

When the trunk position remained at 0 degrees, meaning it was upright as shown in the drawing on the right, the thigh muscles, mainly the rectus femoris, became more active while the lower back and hamstring work reduced to normal levels.

This study was effective in showing how position affects function, but it only looked for correlation, not causation.

All the participants had a capacity to squat with an upright trunk.

Most people currently only have the option to throw their trunk forward due to lack of function in the ankles, knees, hips, and pelvis, which increases the risk of a back injury and pain.

If your body functions more like the drawing on the left with limited joint motion so you have to recruit excessive movement and flexion from your pelvis and spine, then just back exercises or hip stretches won’t help much – if they help at all.

This squatting Trunk-Driven movement is a great example of showing why usually where we hurt is never where the real problem is.

If your back has to involuntarily hijack your movement in the first place due to the body not functioning well as a single unit anymore – the back isn’t the problem. It’s the victim, and the criminal is what the rest of your body is doing…

What I don’t want is for anyone to read this and force themselves upright – if your body could, it would.

Let’s look at why it isn’t naturally upright and work on things from there.

So if you’re someone whose squat just doesn’t feel “right”, or you experience pain while doing this motion – let’s not target what hurts. Let’s show your ankles, knees, hips, pelvis, spine, and shoulders how to work better together and watch what happens to how you’re moving and feeling while squatting now.

If you are interested in learning how to move and feel better, click through our website more – I recommend starting off by clicking How It Works in the navigation menu to learn more about how we can help before you enroll in our Online Program. 

Remember, if you join, you won’t find any area-specific pain exercises, because we aren’t here to teach you how to continue chasing symptoms – we are here to help you go after what’s creating symptoms in the first place.

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[2]  Tae-Sik Lee, Min-Young Song, Yu-Jeong Kwon J, Activation of back and lower limb muscles during squat exercises with different trunk flexion. Phys Ther Sci. 2016 Dec; 28(12): 3407–3410. 2016 Dec 27.

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