Using K Vest to Compare Rotational Velocities During The Pitching Motion

Using K Vest to Compare Rotational Velocities During The Pitching Motion

          There are many aspects of the throwing motion that get talked about as being impactful to throwing velocity.  One such thing that has caught my attention lately is the idea of rotational velocities.  Clearly, baseball is a rotational sport and requires very fast rotational movements.  I was given access to a K-Vest for a few weeks so I wanted to collect a bunch of data to see if rotational velocities alone could give insight into throwing velocity. 

          K-Vest uses 4 sensors to capture data: a vest with a sensor on the upper back, a belt with a sensor on the tail bone, an upper arm strap with a sensor just above the elbow & a lower arm strap with a sensor on the wrist.  Rotational velocities of each show up as Pelvis, Torso, Upper Arm and Hand.  The measurements for each are Degrees Per Second. 

          I collected data on 10 different pitchers ranging in age from 10-21 years old.  2 are current college pitchers, 1 is an incoming college freshman, 3 are High School D1 commits, 2 are current High School Freshman and 2 are youth level players.  Each threw between 6&8 pitches while using the K-Vest.  Below are the average results for each pitcher, along with their peak indoor mound velocity and a ranking (1-10) in each individual category.

Current Level	Peak Indoor Velo (MPH)	Avg Pelvis Speed (deg/sec)	Avg Trunk Speed (deg/sec)	Avg Upper Arm Speed (deg/sec)	Avg Hand Speed (deg/sec)
D3 Junior (D1 Transfer)	90.7 (1)	835 (2)	1,220.2 (5)	1,357.8 (7)	2,768 (8)
HS Sr D1 Commit	90.3 (2)	598.7 (8)	944.3 (9)	1,489.5 (5)	2,953.8 (3)
D1 Junior	88.4 (3)	612.7 (7)	1,273  (4)	1,623.7 (3)	2,926.7 (5)
HS Sr D1 Commit	82.1 (4)	840.8 (1)	1,238.5 (3)	1,347.3 (8)	2,504 (9)
D3 Freshman	81.3 (5)	743 (6)	1,404.8 (2)	1,553.8 (4)	2,975.3 (2)
HS Sr D1 Commit	77.7 (6)	596.4 (9)	1,208.6 (7)	1,218.7 (10)	2,790 (7)
HS Freshman	71.9 (7)	795.2 (3)	1,149.2 (8)	1,447.5 (6)	2,855.5 (6)
HS Freshman	69.1 (8)	794 (4)	1,415.8 (1)	1,739.6 (2)	2,403.2 (10)
Youth Level	60 (9)	514.5 (10)	805.2 (10)	1,281.6 (9)	2,982.3 (1)
Youth Level	54.2 (10)	793.5 (5)	1,217.8 (6)	1,886.5 (1)	2,943.5 (4)

The chart below shows the correlation (R Value) between velocity and each rotational speed.  
     

Velocity vs Pelvis Speed	Velocity vs Trunk Speed	Velocity vs Upper Arm Speed	Velocity vs Hand Speed
.0136	.1683	-.3419	-.0513

Wrap Up

          From the charts above, it’s fair to say that there is no correlation between any of the 4 rotational speeds being directly linked to velocity.   

There are several thoughts that I have after conducting this test.  The K-Vest calculates K Angle, which is the difference between pelvis and trunk within the playback animation.  This should allow for actual numbers on shoulder/hip separation. I will go back and calculate each throws maximum K Value and compare that to throwing velocity.  That being said, the idea of shoulder/hip separation isn’t as cut and dry as just shoulder/hip separation at any part of the throwing motion.  The timing of it should be very important.  Also, the amount of bend in the trunk will impact shoulder/hip separation.  The K Vest also measures that, but I’m not certain on how to calculate it into a separation number.  When looking at other studies and trying to compare their findings with the data from the K Vest, I don’t know exactly how the measurements themselves differ.  This could lead to errors in comparison due to different ways the measurements are taken. I also don’t have anything to test its accuracy against. Even though there were no correlations to velocity, the K Vest has huge potential benefits for pitchers due to its ability to take the guesswork out of numerous angles throughout the entire delivery. 

Questions to Ponder

1.    Could the differences from metric to metric (pelvis to trunk, trunk to upper arm, upper arm to hand) give us real insight as to where guys are efficiently gaining their current velo and where they have inefficiencies?

2.    Does weight play a role in all of this?  If 2 guys have similar trunk rotational speeds but one weighs 200 pounds while the other weighs 150 pounds, will the 200 pound guy benefit more from that rotational speed?

3.    If there was a way to determine force into the ground while maximum rotational velocities were occurring, how much better would that insight give us into ball velocity?

4.    If we know when maximum negative trunk rotation occurs, would the K Value at that moment have a strong correlation with velocity?