Force Plate Trends
(With A Wii Balance Board)
"There is no challenge more challenging than the challenge to improve yourself." -- Anonymous
Assessing athletes is a must if you truly want to help them get better. The purpose of obtaining data from an assessment is so we can better prescribe workouts and throwing programs for our athletes. The truth is though, we are only as good as our assessment. We must continue to update, critique, and monitor that assessment process to make sure we are doing our job and actually making them better. So during my last fall with the Montana State Club Baseball team, I implemented some force plate assessments to see if there were any trends that could be used to help the continuous perfection of the assessment process.
Background Information
A Wii Balance Board (WBB) was used to take the measurements; Standing, Jumping, Laying-Y, Laying-T, Internal Rotation (IR), External Rotation (ER), Front Leg, and Back Leg forces. Six subjects completed all eight measurements, while an additional subject took part in six of the eight measurements having not measured Back and Front Leg force. How this was set up is detailed in my "Doing It Club Style" article.
Before we get any deeper, it is important to note this is an extremely small sample size with unknown reliability in the instrument taking the measurements (although the WBB seems pretty close). So this shouldn't be treated as an end all be all, but more of an exploratory measure to see if something more precise should be pursued. It can be assumed a bigger sample size with validated technology will be used in any sort of revised experiment.
With such a small sample size, I decided to look further into what defines a strong correlation to help figure out what really matters. A good starting point of reference for what can be considered a strong correlation comes from the Director of Athletic Performance for the CSUN Matadors, Kyle Rogers. When the numbers were ran for his assessments (while still with Driveline Baseball), the strongest correlation was 0.4. It can be assumed there was a large sample size for this, though. So I dove a little deeper and found the Dummies website (basically, Statistics for Dummies). They make the point that "Most statisticians like to see correlations beyond at least +0.5 or -0.5 before getting too excited about them.", although they say +/-0.5 is moderate, and +/-0.7 is a strong correlation. Because of the small sample size, having stricter parameters on what defines a strong correlation is the way to go.
Using those references and parameters along with a little bit of our intuition, I think we can make some sense of the data even though the sample size is not ideal. So let's dive in a little further now.
The Data
The strongest correlation to velocity was the jump force measurement coming in with a correlation coefficient (CC) of 0.838, which is pretty darn good. On the other end of the spectrum, the correlation between ER force and velocity was the weakest with a CC of 0.285. I have my hypothesis on why there is not a correlation here, but I will dive into that a little later. The ER force CC and standing force CC were the only ones to be under the 0.5 mark with standing force coming in at 0.460 (just missed out).
In what Dummies has as the moderate range are IR force (0.523), Back Leg force (0.578), and Front leg force (0.617). In the strong correlation range with Jump force, is Laying-T force (0.763) and Laying-Y force (0.711).
Key Takeaways and Hypothesis That Might Be Worth Pursuing
There are major and minor correlations within the data, so what does it all mean? Here are some thoughts I developed from looking at the data that I think might be worth looking more into.
Front Leg force might be related to Lead Leg Block/Knee Extension
Throwing and landing on a WBB is not the easiest and most natural thing in the world. Being able to design a way for a pitcher to land on the force plate without altering their delivery would produce better results. With more accurate data, we could see more of a correlation. Having a good Lead Leg Block allows for energy to transfer up the kinetic chain more efficiently. So, if this allows us to quantify and monitor Lead Leg Block or Knee Extension, then it could be helpful in determining where a pitcher's programming needs are.
Jump Force is possibly a big predictor
I honestly don't know why this is so correlated, I am going to have to ask someone on this. I do have some good guesses as to why it. Newton's 3rd Law states that every reaction has an equal and opposite reaction. So if the pitcher is putting more force into the ground then they should be jumping higher because the ground is exerting that force back. If Front and Back Leg force are correlated to higher velocities because of that reaction from putting force in the ground getting transferred up the kinetic chain, then Jumping force would be another way to quantify one's overall ability to put force into the ground.
ER force might not matter
We see little correlation with ER force and velocity. My thinking on this is related to Active and Passive Range of Motion (ROM). During an Active ROM test, athletes normally will have less ROM compared to a Passive ROM test. During Active tests, the athlete is conducting the joint movement themselves. Muscles will then have to contract to make this movement which stiffens up the muscles. Because of this stiffness, less ROM can be achieved. Whereas during Passive tests, the examiner will put the athlete through the movement with the muscles in a relaxed state. Another way to put this difference is to think about when you grab your coffee cup by the handle. In this situation, your hand represents the muscles around your joint while the coffee cup handle is the joint cavity. A loose grip (passive ROM, muscles relaxed) allows for the cup to move quite a bit, but if you take a super firm grip (active ROM, muscles contracted), that cup will hardly move.
When we look at a six month average from athletes at Driveline, they had a mean Max ER of 159.3 degrees, well beyond the normal active or passive ROM. Maybe in order to reach that extreme ROM, the arm possibly needs to be more relaxed and not necessarily putting force behind it.
I would like to have two force plates to measure Front and Back Leg force at the same time
I think it would be interesting to watch the shift in force from back to front leg during a single pitch. It could help us understand Center of Gravity (COG) movement and uncover more relations to that.
Laying-T force would make sense if truly correlated
Recently at Driveline, there was an article published looking at biomechanical averages from their pitchers in a six month period. In that article, they talk about position at Ball Release (BR):
"On the mechanics side, we now know that the average thrower at Driveline releases the ball at about 90 degrees of shoulder abduction and about 0 degrees of shoulder horizontal abduction. This means that the throwing arm is raised neutrally out to the side, similar to a t-pose."
So being able to produce force in this position would seem to be beneficial, right? Honestly it seems too easy, but it is plausible so far.
Throwing out the Laying-Y test might be the best
Stated in the last point, the pitcher is normally in the T position at BR. So do we really care what they can do in the Y position? I don't think so, but really who knows.
Most tests can be designed better
With different force plates and with a different set up, better measurements will be able to be taken. This was the first time I have ever ran these tests and the tool definitely was not ideal. Only improvements can be made and I already have ideas.
Conclusion
So what do we ever really know? The point of this was more of a self discovery into if we can improve our assessment process and have another way to judge our pitchers than to prove something. We did learn that there was enough of a correlation in some areas that it may be worth monitoring in order to gather a bigger database. Then if they truly correlate, the real fun begins as we can then look into ways of increasing force production within those tests. For now, the research continues.