Three Reasons Why a Slant Board Improves Squat Depth
Jan 30, 2022
Introduction:
It seems like the first modification that's made for someone with a limited squat is to elevate the heels. While this does improve range of motion, have you ever stopped to wonder why? Most people's go-to answer is that "it improves ankle dorsiflexion." Although this is true, there's a significant change happening throughout the entire body that we need to understand and appreciate. In this article, you'll learn why the slant board improves squat depth/technique and how to integrate it into your rehab or training. The three benefits that we'll discuss are as follows:
- Foot Biomechanics
- Pelvis Biomechanics
- Center of Mass
If you're a visual learner, click the video below to watch the same concepts as the article.
Before we dive into those topics, we need to understand that there's an inherent movement continuum that occurs during a squat. As a result, we can represent three distinct phases during a full range of motion squat. They can be categorized as the following:
0-60 Degrees of Hip Flexion: External Rotation Bias
60-90 Degrees of Hip Flexion: Internal Rotation Bias
>90 Degrees of Hip Flexion: External Rotation Bias
This ER --> IR --> ER concept was popularized by Bill Hartman but has also been discussed in the research. Newman et al reports that the piriformis possesses a 2.9 cm external rotation moment arm with the hip at 0 degrees of hip flexion, but a 1.4 cm internal rotation moment arm with the hip flexed to 90 degrees. This research demonstrates how the muscle's line of pull changes during the various positions of hip flexion.
Reason #1 - Foot Biomechanics:
Let's start with the most obvious impact the slant board has — the foot. When you place the entire foot on the slant board, it's going to be in a relative plantarflexed position. This position of the foot can sometimes create confusion as to how we increase dorsiflexion from a plantarflexed foot. To fully understand this, we need to differentiate between closed-chain dorsiflexion versus open-chain. Closed-chain dorsiflexion occurs when there's an anterior translation of the tibia on the talus. So, the position of the foot from the slant board is going to create a posterior starting point for the tibia. This further beginning point allows for more anterior translation to occur, thus increasing the available range of motion. As a result, we will see a more vertical squat trajectory, which is ultimately needed for a full range of motion squat.
Reason #2 - Pelvis Biomechanics:
To understand the impact on the pelvis, you need to first appreciate that certain motions in the human body are coupled together. This means that when specific motions occur at the foot, it will produce expected movements at the pelvis (and the entire body for that matter). To better understand this concept, let's look at the coupled motions of supination.
As you see from the above picture, supination is created by the contributions of the foot moving into plantarflexion, adduction, and inversion. Furthermore, we can categorize supination one step further by labeling the entire motion as external rotation or as having an external rotation bias. For your reference: pronation would be the opposite and be labeled as internal rotation or an internal rotation bias.
Here's what we need to understand: this external rotation bias doesn't just stop at the foot — it continues up through the tibia, femur, and pelvis. Just like the supination example, we'll see coupled motions and biomechanical expectations at the pelvis. These external rotation coupled motions are:
- Sacral Counternutation
- Innominate External Rotation
- Innominate Flexion,
- Innominate Abduction
This external rotation bias is advantageous and required for the squat for two main reasons. First, external rotation is going to increase the amount of space in the pelvis. Conversely, if we moved into an internal rotation bias, we would decrease the amount of space. Second, the increased amount of available space will produce a vertical trajectory during the squat. These two benefits of an externally rotated pelvis will directly contribute to the increased depth of the squat (and proper form)!
Now that we better understand the slant board individual foot and pelvis biomechanical benefits, let's put it all together.
1. The slant board places the foot in a plantarflexed position.
2. The plantarflexed position creates a bias towards supination.
3. Supination produces an external rotation bias through the tibia, femur, and pelvis.
4. Pelvis external rotation is going to create counternutation of the sacrum and move the innominate's into external rotation, abduction, and flexion.
5. These combined motions of the pelvis are required for vertical squat
6. A vertical squat without running out of space creates a full range of motion squat.
Reason #3 - Center of Mass:
Now that we have a better understanding of the biomechanics, we need to consider how our center of mass (COM) changes from using a slant board. To do this, let's keep things simple. When our entire foot is on the slant board with your heel elevated, it's going to naturally push our center of mass forward. You can also think of this as being similar to the late stance phase of gait. If you're struggling to comprehend that, put yourself in the heels-elevated position and see where it feels like you're biased towards.
The forward center of mass bias that is placed on the body allows it to move back easier. For example, when you squat – the cues you should be thinking of are pushing the knees forward and sitting straight down. If we had more of a posterior center of mass and tried to sit straight down, you'd most likely fall. Another way of looking at it is like one big game of tug of war. When two directional-pulls are met with even forces, there's little movement (vertical during a squat). If one side is stronger and has a bigger pull – you'll fall towards that direction (horizontal movement during a squat).
Who Will Benefit:
The quickest and most simple answer to this question — is everyone! Regardless of the positional bias (wide versus narrow ISA) that your patient or client has, they will feel improvements in their squat using a slant board. Now, if we had to get more specific – our patients and clients that have a wide infrasternal angle will benefit more. These individuals tend to move better in the horizontal direction (think hinged-based exercises). However, as we discussed throughout the article, the slant board is going to help create space to move into which produces a more vertical motion to occur. So, our wide ISA's are typically better at producing internal rotation and have a compressed pelvis anteriorly, but the slant board will aid in producing anterior expansion and providing them external rotation mechanics.
If you're unfamiliar with the wide vs narrow terminology or struggle with these biomechanical concepts – I encourage you to check out the Performance Redefined Online Course where this will be covered in extensive detail to simplify your approach to the human body.
Conclusion:
The slant board can be a very beneficial tool to have in your toolbox. It will work in your favor to increase available space to improve the biomechanics of a squat. However, it wouldn't be wise to choose a tool in your toolbox that you don't completely understand the pros vs cons. So, I encourage you to always raise your movement standards and seek to understand how a modification, or the tool, will impact the entire system and not just one part.
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