Caught Looking: May 2021

Here are three studies the R&D department at Driveline read this month.

Relationships Between Clinically Measured Upper-Extremity Physical Characteristics and Ball Spin Rate in Professional Baseball Pitcher

As the baseball community continues to put more emphasis on manipulating pitched ball flight and spin characteristics, various groups have looked into legal ways to improve spin rate. Many of those investigations have involved grip strength measurements and hand size measurements. What those studies have lacked for the most part is wrist flexion and extension strength. 

Wong et al. in a collaboration between the Texas Rangers, the University of Colorado Boulder, and the Texas Metroplex Institute did an investigation that included wrist strength to the typical measurements for these studies. With a sample of 90 professional pitchers, the following measurements were taken:

• Shoulder, elbow, wrist, and finger range of motion
• Arm and hand lengths
• Grip, finger, and wrist strengths
• Time to reach peak force for grip strength measurements
• Four seam fastball finger positioning
• Four seam fastball spin rate with a stadium TrackMan unit

A model using the wrist strength measures–including peak force and the time taken to reach that peak force–explained a significant amount of variance in spin rate. The two most significant predictors in this model were wrist extension strength and radial deviation strength. 

One thing to consider when interpreting these results is that the analysis was not controlled for fastball velocity. Since spin rate is positively related to velocity (as velocity goes up, so does spin rate), the results may lack some applicability for player development purposes. It’s possible that the relationship between wrist strength and spin rate was confounded by velocity, meaning the pitchers who had stronger wrists and higher spin rates may have also just thrown harder. If this were the case, it’s unlikely an athlete’s spin rate would increase just from gaining wrist strength without improving their velocity.

Nonetheless, these results definitely warrant a deeper look into the idea of wrist strength affecting spin rate. Coaches, athletes, and researchers for quite a while have been interested in how to improve spin rate without the use of foreign substances so the results from this study are very exciting for the world of pitching player development. 

Biomechanical effects of foot placement during pitching

In amateur baseball, starting position on the pitching rubber is something that pitching coaches and athletes tweak to hopefully improve some type of outcome for the pitcher. For myself, it was always to make an adjustment in my pitch location if I kept missing to the same side. It was also a way for me to avoid stepping in craters created from myself and other pitchers since high school pitching mounds aren’t also maintained very well. 

As the baseball community continues to find quantitative ways to become more deceptive and effective as a pitcher, specifically with pitch movement, starting position on the rubber can be added to the list of things for pitchers to use to their advantage. Depending on the way your pitches move, there could be advantages to adjusting the position on the mound that you pitch from. 

All of this to say that if starting from a different position on the rubber leads to adverse mechanical effects for pitchers who change their starting position that also could lead to a decrease in performance or health, it is probably not worth the change. Slowik et al. at ASMI looked at these biomechanical effects with a very large biomechanics database. They separated the sample into four groups–pitchers who:

• Stride open and start from the first base side of the rubber
• Stride open and start from the third base side of the rubber
• Stride closed and start from the first base side of the rubber
• Stride closed and start from the third base side of the rubber

These were all between-groups comparisons, meaning they didn’t study the change in mechanics of the same player when moving them from one side of the rubber to the other but instead just compared pitchers who exhibited the above characteristics. Each group had 36 pitchers

The authors found that shoulder horizontal adduction at ball release (how far out front the pitcher releases the ball) and maximum shoulder internal rotation velocity exhibited non-trivial (meaningful) difference between groups. Both effects were small, however. 

There was also an interaction effect (the combination of stride direction and rear foot positioning mattered) which could explain the difference in peak shoulder internal rotation velocity (since higher velo is associated with higher arm speed). A difference in shoulder horizontal adduction at ball release also makes sense, since those who stride closed, toward the third base dugout for righties and first base dugout for legites, the arm will have to be more out front at release to compensate for the stride direction. 

As with the spin rate study above, since these comparisons were not made within-subjects by measuring mechanics from the same person starting on both sides of the rubber, we can’t necessarily apply these findings to a situation when an athlete changes their starting position but in the grand scheme–there are very few mechanical differences from different starting positions on the mound. If it helps a pitcher be more successful in the game, it should definitely be considered as a reasonable strategic change. 

The trunk is exploited for energy transfers of maximal instep soccer kick: A power flow study

Energy flow between body segments in baseball pitching delivery have recently become more popular in applied biomechanics labs. Dr. Aguinaldo’s group at PLNU has done a lot of work with induced power analysis to decompose active and passive contributions to power in the arm. Dr. Oliver’s group at Auburn University, including one of our incredible sports science interns Kyle Wasserberger, has done a lot of biomechanical modeling of energy flow through various joints in athletic movements as well. When combining the results of these studies with some work we have done with rotational velocity and energy using our internal datasets, it has been made clear that trunk movement is very important in the throw. 

Diego da Silva Carvalho et al. in Brazil looked into power flow throughout an instep soccer kick. 18 soccer players were assessed for instep kicking using 3D motion capture and force plates. With some relatively complex biomechanical modelling, the authors were able to calculate the flow of power throughout the segments using joint torques and joint displacements (basically just doing some cool math) to study how power propagates throughout the body during the instep kick.

The reason I am discussing a soccer biomechanics study in this edition of Caught Looking is because of their conclusion. The authors found that the energy during the kick flows downward in the following order:

1. Upper trunk
2. Lower trunk
3. Pelvis
4. Lower limb (leg)

This is interesting because of the work that has been done in baseball biomechanics labs where it is clear the trunk is a very important part of generating and transferring power and energy throughout the movement. As with quite a few of the studies that we often highlight on this blog series, it won’t necessarily change the way we train athletes, but it absolutely highlights the importance of the trunk’s movement in explosive movements and should be treated appropriately when training as a player or when evaluating an athlete’s needs as a coach.