Towel Drill vs Plyocare 7 oz ball


Pitchers from little league to the majors are always looking for ways to add velocity to their fastball. The towel drill and throwing of weighted Plyocare balls are two common approaches to improving fastball speed and mechanical efficiency. The common belief is that the Plyocare ball drills can create stress on the throwing arm, potentially leading to injury. While the Towel Drill is minimizing arm stress while also being able to work on throwing mechanics. Pitching experts are mixed in their opinions of the efficacy and safety each approach.

Research Question:

This study presents a first look at the effectiveness and safety of both approaches. We aim to gain insight into three important questions:

  1. Are pitchers able to generate more arm speed throwing a Plyocare ball or while completing the towel drill?

  2. Does throwing Plyocare balls or completing the towel drill create more stress on a pitcher’s arm?

  3. Is greater arm speed associated with higher levels of arm stress?

Research Method:

Nine pitchers were recruited to participate in the study. The players are all high school-aged players. Each of the nine is actively working to improve their fastball velocity.

Each pitcher was asked to complete five repetitions of the towel drill and five throws with a weighted Plyocare ball. This lead to a sample of 45 repetitions of the towel drill and 45 plyocare ball throws. During each towel drill repetition and Plyocare ball throw, the participants wore a Motus Arm Sleeve. The Motus device measured both the arm speed and the stress placed on the ulnar collateral ligament for each repetition and throw.  Each throw was “tagged” with the weight of throwing implements (ie. Towel = 3.68 oz and Plyocare ball = 7oz).  Of the 90 data points gathered in the study, one towel drill repetition and one Plyocare ball throw resulted in no score on the Motus device and the data for both was not used in our analysis.

We analyzed the data using paired t-tests with the assumption of non-equal variance. We adjusted our alpha levels using the Bonferroni method. All conclusions of significance are based on a 95% confidence level. We also calculated correlation coefficients to determine if there is a relationship between arm speed and stress.


First, we examined whether the average observed arm speed was higher during the towel drill repetitions or when throwing the weighted Plyocare balls. The average arm speed generated during the towel drill repetitions was 553.25 and the average arm speed when throwing Plyocare balls was 890.52. This was a statistically significant difference.

With respect to arm stress, we find that the towel drill generates significantly less stress than throwing plyocare balls. The average stress measured during the towel drill was 15.66. The average stress observed when throwing the weighted Plyocare balls was 24.14.

Finally, we examined whether greater observed arm speed was associated with higher levels of arm stress. Interestingly, we find no significant relationship between arm speed and arm stress for either the towel drill repetitions or throwing weighted plyo balls. The correlation between arm speed and stress for the towel drill was .0396 and -.0236 for plyo balls.


While certainly not a definitive study, we do present some interesting findings. First, it is not surprising that throwing Plyocare balls generates higher arm speed than the towel drill. We hypothesize that the towel drill creates wind resistance in the towel which would reduce arm speed. This does present a real positive for plyocare ball training in regards to training arm speed.

Our second significant finding is that the Plyocare ball training creates more arm stress than the towel drill. This is a very important finding. While throwing plyocare balls may help a pitcher to train with higher arm speed levels and possibly increase overall arm speed, it may also generate significantly more arm stress.

Taken together, these findings create a quandary for coaches and pitchers. Throwing weighted plyocare balls may well help a pitcher to generate greater arm speed than the towel drill, but does the increased arm stress lead to a higher likelihood of injury? Also, would training with the towel have a negative transfer once a 5oz (normal) baseball is introduced to the athlete. More research is clearly needed to settle this issue.

Finally, we find that there is not a significant relationship between higher levels of arm speed and arm stress for either the towel drill or throwing plyocare balls. This suggests that individual differences among pitchers, such as pitching mechanics, are more likely to predict arm stress than the level of arm speed that the pitcher generates. This is good news. Pitchers may be able to increase arm speed (and by extension velocity) and limit increases in stress on their arms. We recommend tracking all throws with the Motus Sensor to monitor safety of all throwing drills as it relates to each individual athlete. More research is needed to identify how gains in arm speed can be achieved without increasing arm stress.

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