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Using Center of Pressure Data to Coach the Squat

T
he importance of center of pressure in the squat pattern is often considered, but rarely used as coaching tool in a gym setting due to the cost of force plates. Enter BodiTrak and BODITRAK DASH.

The purpose of this article is to investigate the relationship between center of pressure and squat mechanics, demonstrating how BODITRAK DASH can help provide insights into both. BODITRAK advisors Sasho Mackenzie and Jason Glass share how they’ve incorporated vertical force and center of pressure in their coaching and how they use DASH as a biofeedback tool.

Squats are a staple in virtually every exercise program.  The problem is that a lot of us don’t understand the squat… You can film a squat, you can coach a squat, but if you don’t know what’s really happening, you’re just guessing… I hate guessing.” – Jason Glass

In many athletic movements (such as the golf swing), the center of pressure trace can look very different than horizontal motion traced out by the center of mass.  However, in exercises like weighted squats, there is a much tighter relationship between the two measures, or at least there should be.  During a squat, the center of pressure trace will show a similar overall pattern as the motion of the center of mass; however, it will cover more ground and dart between the center of mass projection and the edge of the base of support to keep the athlete in balance.

If an individual with relatively long thighs and a short torso performs a front squat while adhering to the NSCA guidelines, it’s highly probable that the center of mass will fall outside the base of support at the back of the athlete before the thighs reach parallel,” says Sasho.  “If you want to avoid falling over, your center of pressure needs to be able to move between your center of mass and the edge of your base of support.

A common cue for athletes is to “drive through the heels” when coming out of the hole.  While certainly well-meaning, this cue can easily be misinterpreted and negatively affect performance and technique.

As you stand up in the squat, plantar flexion occurs, observed by the shin becoming more vertical and the center of pressure shifting into the toes.  Plantar flexion is a key aspect of generating maximum vertical force in the squat.

During a squat, the CoP will be strongly related to ankle torque.  If there’s no plantar flexion torque at the ankle, then the CoP will be under ankle.  If you’re able to plantar flex, CoP will be closer to the toes.

Inability to plantar flex (and shift center of pressure into toes) may be related a limitation in ankle mobility (dorsiflexion) or calf strength.

2010 study looked at the relationship between squat action and dorsiflexion range.  The results indicated that “…when the range of ankle dorsiflexion is insufficient, CoP displacement is forced to move posteriorly in squatting, and when the dorsiflexion range is below a set limit, the action becomes impossible.”

Sasho explains further: “Hip flexion and dorsiflexion move the center of mass anteriorly.  Knee flexion moves it posteriorly. Removing or limiting dorsiflexion takes away one mechanism for preventing the athlete from falling backwards while squatting down.”

If an athlete cannot dorsiflex, they will be unable to move their center of mass anteriorly.  This is a critical move in the squat.  While the downward movement of the squat might be initiated by center of pressure moving posteriorly, CoP should move towards the toes as the athlete stands up.

The graph on the right represents how CoP moves horizontally throughout the squat (FYI: this is a beta version of a feature which will be added in future updates to the DASH app).

If you aren’t pushing from the balls of your feet after you initiate upward movement (observed by CoP shifting towards toes), you’re missing out on a key power source.  The athlete either doesn’t understand proper squat technique or they are burdened by a physical limitation – poor ankle dorsiflexion.

There are a number of effective screens for ankle dorsiflexion, including a breakout in TPI’s overhead deep squat test (see image ->).

 

Regardless of whether the limitation is related to calf strength or dorsiflexion, lack of plantar flexion will limit performance and, ultimately, transfer of the exercise to efficient, athletic movement.

We want weighted squats to transfer to a movement pattern.  Take jumping for instance.  If you’re jumping, a proximal to distal sequence (hip -> knee -> ankle) is most effective.  

Studies link squat training to performance in numerous athletic tasks, from vertical jump to sprinting.  Therefore, it’s a foundational exercise in many strength training programs.  Assuming they have the physical capability to squat safely, almost any athlete can benefit from using them to improve their ability to generate vertical force.

While sports like golf and baseball appear to favor the transverse plane, developing power in the sagittal plane through exercises like squats can improve rotational performance.  That’s why the fitness community was right to rejoice when Rory shut down Brandel Chamblee with his infamous tweet.  Bigger squat = more vertical force. More vertical force = more rotational power potential. More rotational power = drives like this.

Now that we’ve established that the squat is important and coaching the squat appropriately is even more important, BODITRAK advisor Jason Glass broke down how he uses pressure data to evaluate squats.