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Nextiles-Motion Pitching: Arm Velocity Validation

Study supported by John DeFazio, John Peters, and Dr. George Sun


Arm velocity for baseball athletes is a major driver of fatigue and key indicator for potential arm injury [1]. There is currently no reliable way to measure arm velocity outside a traditional sports lab setting. Therefore, the Nextiles Arm Sleeve was created to provide an easy to use, on-body method to reliably measure arm velocity and other arm kinematic markers. 

Similarly, there is also a performance need to track ball velocity; however, ball velocity is difficult to capture reliably with current technologies [2]. For example, a radar gun may be accurate but is cumbersome to use in training or in game. Other systems require installing camera vision technologies which are prohibitively expensive for a majority of training facilities and coaches. Finally, there are no wearable technologies that can measure off-body velocities without being directly embedded in the baseball.

Thus, in order to fulfill a technology gap we hypothesize the Nextiles Arm Sleeve can be used as a strong correlative measure for ball speed, thereby providing a fundamental performance metric in a single wearable platform. The research performed in this study was to analyze the arm’s transfer of momentum throughout a pitch to predict the ball release point and ball exit velocity, which accuracy was compared against a radar gun. The arm kinematics were measured through the Nextiles Arm Sleeve, and the ball’s velocity was measured by a Stalker Radar gun, considered to be the industry standard for ball velocity tracking in baseball. 


This experiment was set out to: 

  1. Model the velocity kinematics of the arm during a pitch using the Nextiles Arm Sleeve.

  2. Analyze the correlation between the Nextiles arm velocity metric and ball velocity, measured by a Stalker radar gun.


One athlete from Motion Pitching performed bullpen sessions over a three week period. The experiment included one male, 24 years of age. The athlete was 6’0” and 185 pounds. The athlete was right handed. The athlete performed 500 throws. The athlete wore the Nextiles Arm Sleeve connected with the Nextiles Performance App to extract and store raw data for later analysis. Afterwards, for every pitch, the arm velocity calculation was recorded against its ball velocity measured by a Stalker Radar gun.  


The majority of throws had an absolute difference of less than +/- 2 mph. The arm velocity and ball velocity readings for each throw had a fit of 0.98 with a statistically significant p-value of < 0.01. The data was also modeled against the Pearson correlation function that showed a 0.87 correlation, suggesting a very strong correlation between arm velocity and ball speed (0.8 - 0.9 are considered very strong to excellent correlation indicators) [3]. The raw data from the experiment can be found here.

Motion Pitching graph on Nextiles Arm Velocity against Stalker radar gun.
The data suggests a very strong correlation [3] of the Nextiles arm velocity measurement against ball velocity, potentially making the Nextiles Arm Sleeve a good proxy tool for a radar gun and similar velocity tracking technologies.


This Nextiles experiment demonstrates the consistency and reliability of the Nextiles Arm Sleeve to track arm velocity, and thereby is a strong correlate to ball velocity. Therefore it can be confidently assumed that the Nextiles Arm Sleeve can be used in substitute of a radar gun or more sophisticated camera vision technologies, if the requirement is to track arm and ball speed.

Further investigation is needed for additional pitch types and left handed pitchers, as this study mainly focused on standard pitching exercise.


[1] Dowling B, Hodakowski A, Olmanson BA, Cohn MR, Pauley PJ, Verma NN, Nicholson GP, Garrigues GE. Relationship Between Arm Path, Ball Velocity, and Elbow Varus Torque in Professional Baseball Pitchers. Orthop J Sports Med. 2023 Dec 1;11(12):23259671231202524. doi: 10.1177/23259671231202524. PMID: 38045766; PMCID: PMC10693215.

[2] Whiteside, David, et al. "Ball flight kinematics, release variability and in‐season performance in elite baseball pitching." Scandinavian journal of medicine & science in sports 26.3 (2016): 256-265.

[3] Akoglu H. User's guide to correlation coefficients. Turk J Emerg Med. 2018 Aug 7;18(3):91-93. doi: 10.1016/j.tjem.2018.08.001. PMID: 30191186; PMCID: PMC6107969.


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