The Association of Arm Speed, Ball Weight, and Sessions Performed on Elbow Varus Torque During Weighted Ball Throwing Exercises

Introduction: Due to the performance enhancements contrived from improved pitching velocity, the average pitch velocity has increased by 1.3 mph across all pitch types since 2008 in Major League Baseball. This has led to an emphasis on research initiatives and training to improve pitching velocity. Various forms of training have evolved to attempt to increase throwing velocity and keep injury risk low through strength training and throwing programs. One tool that has become common in pitch velocity training is weighted baseballs and subsequent throwing programs. For overload baseballs, (balls heavier than 5 oz) the proposed mechanism is similar to resistance training through overloading a muscle with greater resistance. Underweight baseballs (balls lighter than 5 oz) proposed mechanism is to help create overspeed throwing patterns to allow for maximal arm speed. However, even though these methods have been observed to be successful in improving pitch velocity, there is a concern that they also are associated with increased joint kinetics, potentially increasing arm injury risk. There is a critical need to further understand and define elbow varus torque values during plyometric drills. Wearable technology is a tool that has emerged to assess throwing kinetics in an on-field setting. By collecting biomechanical data and giving the user live feedback, wearable sensors may have several potential benefits and applications for injury prevention. Wearable technology also gives the athlete a unique opportunity to monitor throwing kinetics and kinematics independently of a biomechanics laboratory. This decreases cost and space while simultaneously allowing for live-on-field data collection.

Materials and

Methods: A prospective observational study had collegiate-aged pitchers (n = 19) perform weighted ball throwing exercises while wearing the Nextiles throwing sleeve. Weights of the balls included 3.5, 4.4, 5.25, 8, 12, 16, 18, 35, 53, and 70.5 oz balls. Four brands of weighted balls were utilized. MarvTraining (Marv Balls – Velo Set) weighted balls have seams on their weighted balls and consist of 3.5, 5, 7.5, 16 oz, and 32 oz. Driveline (PlyoCare Balls) weighted balls do not have seams and weigh 7, 3.5, 16, 53, and 70.5 oz. Arm strong weighted balls have seams on the ball and weigh 3, 5, 7, and 16 oz. Silverback (Ballistic Throwing Plyo Ball Set) weighted balls did not have seams on the balls and weighed 3.5, 5, 7, 9, 16, and 32 oz. Pitchers performed plyometric throwing exercises such as pivot pick-offs and reverse throws with these various weighted balls. Data was collected with the Nextiles arm sleeve while paired with the application. Pitchers then inputted their throwing exercise selected plyometric throws and entered the ball weight used. The pitcher started their session and began the throwing exercises.

Upon completion of data collection, a robust linear mixed effect model was performed with ball weight and arm speed as independent variables, time as an interaction term with peak arm speed, and peak varus torque as a dependent variable and then ran again while stratifying by ball weight.

Results, Conclusions, and Discussions: When holding ball weight equal, peak arm speed was found to have the highest association with peak varus torque while time had a slight increase in association with peak arm speed and peak varus torque. The 8 oz weighted balls were found to have the greatest association between peak arm speed and peak varus torque while the 35, 53, and 70.5 oz weighted balls had decreased peak varus torque values. These results suggest that the 8 oz balls may want to be avoided during weighted ball throwing and the 35, 53, and 70.5 oz weighted balls can be used when wanting to keep peak varus torque low. When session was added as an interaction term with arm speed a minimal positive association between arm speed and varus torque was observed. When stratifying by ball weight, different associations were found between various ball weights with the 8 oz ball resulting in the greatest positive association between arm speed and varus torque. The 3.5 oz, 16 oz, and 53 oz balls showed no association between arm speed and varus torque. Lastly, compared to the mean elbow varus torque that is calculated in the Wake Forest Pitching Lab with collegiate-aged pitchers, throwing weighted balls yields significantly less experienced stress in the elbow.

A positive, but minimal 0.004 Nm increase in varus torque was observed throughout multiple throwing sessions. For context, if a pitcher were to throw 40 sessions throughout a fall training season, this would result in a 0.16 Nm increase of varus torque. These findings imply that pitchers can enhance their arm velocity and pitch velocity throughout the fall season, with minimal rises in elbow kinetics. The majority of the weighted ball throws were performed with overweight baseballs (99.3%), and the minimal increase in varus torque throughout the fall could be occurring due to strengthening the periscapular and shoulder complex muscles overload principles in the form of resistance training.

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