The Relationship Between Ankle Mobility and Sway in Hitting

Fri Oct 2, 2020 by OnBaseU

We can all agree that rotational athletes need to be able to use the ground efficiently to generate maximum power, so shouldn't we be evaluating their ability to do this?  

One of the keys to using ground reaction force for rotational power is the ability to create a stable platform with the back leg that allows a hitter to load into their trail side and drive their weight to their front side in an efficient manner.  A common inhibitor associated with this move is a hitting characteristic we call Sway.

We define "Sway" as an excessive lower body lateral movement away from the pitcher during the negative move.  If the back knee moves outside the back foot, a hitter will have a difficult time generating a consistent and repeatable stride. 

In our last Q&A Webinar we demonstrated how we evaluate different hitting characteristics.  Here's an example of how we identify "Sway."  

This is an example of the Body-Hitting Connection.  If we would've looked at the OnBaseU screen results first, we would've predicted there would be a high probability for this kind of pattern in the swing.

As Don Slaught mentioned, Sway not only can reduce power, but also consistency.  If a hitter's weight shifts to the outside of their back foot, their timing can be affected.  

Sway can be the product of inefficient technique, but it's commonly the result of a lack of mobility, especially in the ankle.  If a hitter can't evert their back side ankle, they may resort to moving their center of mass to "load."  

How do you know if ankle mobility is a contributor to this issue?  We don't guess, we assess.  Here's how:

The goal of our screen and our system is to take advantage of what a coach might have access to at their field: high speed video, a bat, a plate, a bucket or a chair.  Therefore, in our webinars/seminars we teach coaches to identify Sway by looking at the center of mass on 2D video, but Sway can also be evaluated by looking at center of pressure on a force plate.

Here's Liam Mucklow from Baseball Performancel Lab discussing how they used force plates to diagnose Sway in one of the hitters who was training at their facility in Baton Rouge (and here's a deeper dive with BPL's Micah Gibbs into how/why they use screens to optimize set up).  

You probably don't have a research-grade force plate in your cage, but this example underscores why a lack of ankle mobility can be a problem even if Sway isn't easily identified in 2D analysis.  Think about it this way: If you were coaching an athlete to cut laterally, would you teach them to push off of the outside of their foot or the inside of their foot?  If a hitter can't evert their back ankle, they may be unknowingly using the outside of their foot.

The ankle rocking test takes about 10 seconds. If your hitter passes, it doesn't necessarily mean that they will load into their trail side efficiently, it just means that ankle mobility shouldn't prevent them from doing so.