Changes in Ball Weight: A Method for Athlete Individualization

By Stephen Hart, Pitching Coordinator

Over the years, we’ve come to notice a trend among certain athletes, especially our amateur athletes: Many struggle to perform the pivot pickoff drill with the black Plyo Ball ®.  Anecdotally, our coaches often see or hear things like this:

“It feels like I’m just pushing it.”

“It just doesn’t feel smooth compared to the green ball.”

“It looks like you’re throwing darts.”

If that sounds familiar, keep reading…  

As a department, we knew we needed to create a solution that would allow athletes to throw more comfortably while still offering an overload constraint to help engrain new movement patterns.  

Introducing the 3 lb pink Plyo Ball ®. 

We tested it with a select few experienced athletes, and they gave it great praise and rave reviews, but we knew that we needed to test it more before we rolled it out to the whole gym. In particular, we needed to know how it differed kinematically from the black and green Plyo Ball ® within our drill set.

Investigation

Across 30 athletes, 142 pivot pickoff throws were collected in our motion capture lab for each ball type (green, pink, and black). The table below provides an overview of the descriptive statistics regarding the captures collected.

After the data collection phase of our investigation was completed, our sports science department examined kinematic and kinetic differences between ball weights in the following metrics:

• Maximum shoulder external rotation
• Shoulder abduction at max external rotation (MER)
• Max shoulder horizontal abduction
• Shoulder horizontal abduction at max external rotation (MER)
• Elbow flexion at max external rotation (MER)
• Maximum elbow varus moment

Maximum Shoulder External Rotation

Is there a significant difference between ball weights when it comes to maximum shoulder external rotation? In other words, when using the green, pink, and black balls, do athletes tend to achieve a significant difference in layback?  Admittedly, we hypothesized that athletes on average would achieve less layback with the black Plyo Ball ®, as it is fairly common for athletes seemingly to exhibit a ‘pushy’ arm action during pivot picks. 

However, it would seem the ol’ ‘eye test’ has failed once again. The data suggests, as seen in the density plot below, that there is no significant difference in layback between any of the balls.

Shoulder Abduction at Max External Rotation (MER)

When examining shoulder abduction (elbow height in relation to the shoulder joint) at MER, there was also no significant difference between any of the balls. This would suggest that, despite the increases in ball weight (of up to 4 lbs), on average an athlete’s shoulder rotation stays on plane with their upper body, relative to the other ball weights. Put more succinctly, athletes do not demonstrate any meaningful difference in elbow height relative to their body at MER.  

Max Shoulder Horizontal Abduction (SHA) and SHA at Max External Rotation (MER)

As a brief refresher, SHA, or scap retraction, is the angle of the humerus (upper arm) relative to the torso. Zero degrees of SHA would have your upper arm in line with your torso, while a positive number would indicate that your upper arm is behind your torso (as shown in the image below).

With this, we’ll first examine differences in max SHA (scap retraction, in layman’s terms).  Meaning, throughout the duration of the throw, how far behind the body does the athlete’s upper arm travel? From our dataset, max SHA is a very important metric and (one of many) strong predictors of throwing velocity.  A possible explanation for this is that an increase in max SHA, which likely creates an increase in SHA at foot plant, creates a greater stretch-reflex across the pectoralis and deltoid muscle groups and greater range of motion to accelerate the baseball.  

From our dataset, shown in the scatterplot below, on average athletes display an increase in throwing velocity as the amount of SHA (scap retraction) at foot plant increases.    

When examining max SHA across all ball types, we found a significant difference between all three balls. When looking at the density plot below, on average there was a gradual increase in max SHA as ball weight decreased. The average max SHAs for each ball type were 20, 25, and 29 degrees for the black, pink, and green balls, respectively.     

Next, let’s move on to SHA at MER. With this metric, we’re examining, in layman’s terms, the following question: When the athlete achieves max layback, how far behind their torso is their arm? We found some differences. Specifically, while there was no significant difference between the pink and black balls and no significant difference between the green and pink balls, we did find a significant difference between the green and the black balls. Such a significant difference can be seen in the density plot below.  

This would indicate that, on average, athletes performing pivot pickoffs with the green Plyo Ball ® have more SHA at MER than those throwing the black and pink Plyo Ball ®. While the value is still negative (upper arm in front of torso at MER), athletes throwing the green Plyo Ball ® exhibit a more favorable MER position when looking at SHA specifically. Oftentimes when athletes throw the black ball, they tend to exhibit a more elbow dominant (think throwing a dart) throw. This more negative SHA at MER value reinforces these observations..     

Elbow Flexion at Max External Rotation (MER)

Elbow flexion is used to describe how bent an athlete’s throwing arm is. Making a right angle with your elbow is 90 degrees. Performing a bicep curl action increases the angle to over 90 degrees, while straightening the elbow decreases the angle to under 90 degrees. Not surprisingly, elbow flexion at MER is describing how bent the athlete’s elbow is at max layback. When looking at the data, we found no significant difference between the pink and the black balls. However, there was a significant difference between the green and pink and between the green and black balls. This means that athletes on average exhibited a higher degree of elbow flexion at MER with the black and pink balls compared to the green ball.

It should be noted that while there may be a significant difference between the green and pink/black balls, this difference may be negligible in terms of throwing velocity performance. When we look at max elbow flexion as it relates to mound throwing velocity across ranges of 70 – 96+ mph, there seems to be a sweet spot somewhere between 105 – 125 degrees. From the image below, we can see a slow taper of throwing velocity as max elbow flexion is below 105 and greater than 125.  

It should be noted some pitchers who throw at an elite velocity may fall outside of these elbow flexion ranges, but on average the majority of elite throwers seem to fall within somewhere between 105 – 125 degrees.  

So, while it may seem that on average throwers exhibit less max elbow flexion at MER with the green ball compared to the pink and black balls, the amount of elbow flexion they do create at MER seems to be within a desired range, nonetheless.   

Maximum Elbow Varus Moment

The maximum elbow varus moment describes the amount of medial torque (measured in newtons) the elbow joint is exposed to throughout the throw (usually occurring around MER).  When looking at the data, there seems to be a significant difference in max elbow varus moment between the green and black balls, while we found no significant difference between the pink and black and between the green and pink. 

It is possible this significant difference between the green and black balls may be explained by the increase (~ 2lbs) in ball weight.  

Discussion and Implications

We had quite a few surprises and takeaways when we examined this data. First and foremost, our initial hypothesis seemed to be wrong in that MER, or max layback, on average was unaffected and not significantly different between all three balls. Naturally, there will be some athletes who may struggle to achieve layback with any ball, based on variables such as strength levels and familiarity with each ball or drill, but it seems incorrect to assume that an athlete will exhibit a ‘pushy’ arm action with less layback by throwing a ball 2 lbs or heavier. I think we could reach a similar conclusion regarding shoulder abduction, or elbow height, at MER.

I believe an interesting discussion could be had regarding SHA (maximally and at MER), elbow flexion, and maximum elbow varus moment.  

When discussing max SHA, or scap retraction, athletes on average achieved a greater degree maximally as ball weight decreased. This may indicate that athletes who struggle to achieve an adequate degree of scap retraction may benefit more from throwing the green ball as compared to the pink and black. In the future, I believe these results may warrant further investigation to identify if this relationship between scap retraction and ball weight within the pivot pick drill continues while throwing the lighter Plyo Ball ® balls (blue, red, yellow, and gray). This could have further implications for program individualization.

Furthermore, this investigation showed that athletes throwing the green Plyo Ball ® held their scap retraction a bit longer into MER when compared to the pink and black balls. In other words, athletes throwing the green ball displayed less of an elbow dominant (think dart throw) type throw. This relationship can likely be partially explained by athletes achieving a higher degree of maximal scap retraction with the green ball. 

When discussing max elbow flexion in isolation, as mentioned previously, athletes throwing all three balls exhibited elbow flexion within desirable ranges. That is to say, regardless of ball weight, presentations such as forearm flyout did not seem to occur. That being said, because on average athletes throwing the black and pink balls did present with greater flexion than the green, I think there could be an argument made that athletes who severely struggle with getting into proper elbow flexion positions could benefit from throwing the pink and black, slightly more than the green ball. A possible explanation could be that the heavier pink and black balls allow athletes to feel that more flexed position slightly more clearly than they can with the 2 lb green ball.  

When examining maximum elbow varus moment, we found a significant difference between the green and black balls, specifically. One can likely argue that this finding could have some rehabilitation and on-ramp implications for athletes. Perhaps there is some benefit to limiting the amount of black ball exposure for athletes in the early stages of rehab and on-ramping, as the varus torques seem to be lower for the green and pink balls. Then, potentially later on in the program, you could gradually expose them to the higher torques imposed by the black ball as a means of throwing or torque progression. 

Application

Based on the findings of this investigation, the following table may be used as a ‘cheat sheet’ for prescribing ball weights for the pivot pickoff drill based on specific athlete presentations. As a reminder, these are just recommendations that can be used as a starting point. Individual athlete responses may warrant certain ball weight prescriptions.

Conclusion

The results from this investigation are really interesting. To me, I think it really exemplifies that athlete individualization does not have to come in the form of 30+ drills or drill variations.  Sometimes athlete individualization can simply come down to ball weight used. The table above, when used as a starting point, shows that there is utility for all ball weights. And, like all things, each ball is a tool that deserves a place in our coaching tool box.