<b>The Spine</b>

In part 1 of this series we discussed the various types of squats that you may have experienced or come across and some of the aspects that may influence your decision on which squat is most appropriate to you. In part 2, I would like to discuss more specifically the bodies biomechanical effects on the spine during squatting movements both with and without resistance.

<b>The ‘Break Point’</b>

Stuart McGill refers to what he calls the ‘<i>break point’</i> which he explains is; during squatting, there is a loss of the ‘<i>neutral spine’</i>. This loss of neutral curvature is actually how our spines were designed to move while we were sitting on our haunches when cooking, eating or performing tasks on the floor. In some countries this is still the case and in fact these natives seem to have a very low incidence of low back pain.

You will see in the photo on the left an example of a break point whereas the image on the right does not have a break point:

<img class="alignnone size-medium wp-image-712" src="https://www.www.biomechanicseducation.com/wp-content/uploads/2016/04/Screen-Shot-2016-04-08-at-20.57.10-300x111.png" alt="Screen Shot 2016-04-08 at 20.57.10" width="300" height="111" />

We also know from McGill’s work, and others, that each of the facet joints in the lumbar region allow a range of 5-8mm of flexion/extension and 1-5 mm of lateral flexion. This gives a total of about 45-50<sup>0</sup> of forward flexion from a fully extended position that we could call safe at the lumbar spine when squatting without resistance. Once we add some resistance, a barbell for example, this adds a compressive load onto these facet joints, whose main role is to stop excessive movement of the spine. This movement restriction protects the discs, and reduces their vulnerability and their risk of wear and tear. Consider a healthy, symmetrically stacked and robust spine and this compressive load is pretty safe, now imagine if you have asymmetry, any mechanical dysfunction or improper technique affecting the spines movement capacity and the risk increases further.

So you can see how actually there is much to consider when performing the squat with any kind of load on the spine if we are to maintain a healthy trunk long term.

The images below should help to explain what the ‘break point’ might mean to you and your technique.

<img class="alignnone size-medium wp-image-713" src="https://www.www.biomechanicseducation.com/wp-content/uploads/2016/04/Screen-Shot-2016-04-08-at-20.57.18-300x114.png" alt="Screen Shot 2016-04-08 at 20.57.18" width="300" height="114" />

The image on the left shows that if there is a break point, or spinal flexion, during a weighted squat, the position of the bar/resistance in relation to the gravitational pull is too far forwards for the best balance through the feet i.e. maintaining efficient centre of gravity alignment. This increases the risk of damage to the intervertebral discs as the load on the front of the discs is disproportionate to the on the back.

With no break point, or spinal flexion (see right), the weight in relation to the gravitational pull is in a far more advantageous position for foot stability and the intervertebral discs and facets are stacked evenly and within safer ranges thus reducing the risk of incurring damage or injury.

When considering the forces imposed upon the spine McGill states that:

<i>“when a more neutral lordotic posture is adopted, the extensor musculature is responsible for creating the extensor moment and at the same time provides a posterior shear force that supports the anterior shearing action of gravity on the upper body and handheld load……Thus, using muscle to support the moment neutral posture rather than being fully flexed with ligaments supporting the moment greatly reduces shear loading” </i>

What McGill means is the shear force is the force that causes one vertebra to move forwards (or backwards) in relation to the one above or the below and increases the pressure on the intervertebral discs and facet joints. Therefore minimising these shear forces by correct alignment during squatting is more important.

“What does this mean when translated into my squat technique”? You might be thinking, well ultimately your own reason for squatting needs to be clear but here I will try to cover as many possibilities as I can starting with this example:

<b>Depth of squat</b>

This is a topic of much debate and yet all of the matters covered in this series must be considered before we can identify an individual’s <i>capacity</i> for which depth is appropriate. While there are many factors that should be taken into consideration, it is my opinion that there should be 2 main determining factors:

1). the pelvis &amp; spine, their health, functional capacity and safe degrees of spinal flexion, extension

2). the knee, its health, functional capacity and safe degrees of flexion (see The Squat part 3)

Ultimately if the aim of your squat is to optimise the development of gluteus maximus then they should be performed to full range as demonstrated by Caterisano’s work. Using EMG data it was concluded

that as the depth of squatting increases, gluteus maximus activity increases by 9-14% from partial range to full. It was also found that the bicep femoris does not appear to be more active suggesting that a deeper squat would not work this hamstring muscle more than a parallel squat. Bicep femoris shows no more than 2-3% more activity between a partial squat, parallel squat and full squat. (Casterisano et al, 2002)

If however the goal is to target quadriceps, then a squat depth of 90<sup>0 </sup>appears to be optimal, as shown in several of the studies I have come across Van Eijen et al (1987), Signoile et al (1995), Isear et al (1997), Wretenberg et al (2007). Quadriceps activity will gradually increase during the descent of the squat as the degree of knee flexion increases. However beyond this point the quads are unlikely to enhance their development. On an EMG it has been demonstrated that the 2 vasti muscles produce 40-50% more activity than rectus femoris (Escamilla et al). Narrow or wide stance has not shown to have any greater or lesser effect upon hamstrings and quadriceps activation. VMO activity does increase during greater knee flexion angles as compared to the VL. (McCaw &amp; Melrose, 1999, Signorile et al,1995).

To summarise on these points;

The rules for spinal alignment during the squat change when you introduce a barbell or resistance.

When asked a common question like “how deep should I squat?” we should really be asking a series of questions back before we can even begin to answer with any confidence, starting with ‘why are you asking and what are you trying to achieve?’. Understanding an individuals intrinsic biomechanics will also mean we have a more objective method of analysis to increase confidence in your exercise prescription.

Coming next….

<b>The squat part 3 - The knee</b>

Would you like to learn how to assess for spinal hinges and what causes them?

<b><a href="https://www.www.biomechanicseducation.com/workshop/spinal-biomechanics-2/">READ MORE HER</a>E</b>