BackgroundImprovements in data processing, increased understanding of the biomechanical background behind kinetics and kinematics, and technological advancements in inertial measurement unit (IMU) sensors have enabled high precision in the measurement of joint angles and acceleration on human subjects. This has resulted in new devices that reportedly measure joint angles, arm speed, and stresses to the pitching arms of baseball players. This study seeks to validate one such sensor, the MotusBASEBALL unit, with a marker-based motion capture laboratory.HypothesisWe hypothesize that the joint angle measurements (“arm slot” and “shoulder rotation”) of the MotusBASEBALL device will hold a statistically significant level of reliability and accuracy, but that the “arm speed” and “stress” metrics will not be accurate due to limitations in IMU technology.MethodsA total of 10 healthy subjects threw five to seven fastballs followed by five to seven breaking pitches (slider or curveball) in the motion capture lab. Subjects wore retroreflective markers and the MotusBASEBALL sensor simultaneously.ResultsIt was found that the arm slot (R = 0.975, P < 0.001), shoulder rotation (R = 0.749, P < 0.001), and stress (R = 0.667, P = 0.001 when compared to elbow torque; R = 0.653, P = 0.002 when compared to shoulder torque) measurements were all significantly correlated with the results from the motion capture lab. Arm speed showed significant correlations to shoulder internal rotation speed (R = 0.668, P = 0.001) and shoulder velocity magnitude (R = 0.659, P = 0.002). For the entire sample, arm slot and shoulder rotation measurements were on a similar scale, or within 5–15% in absolute value, of magnitude to measurements from the motion capture test, averaging eight degrees less (12.9% relative differences) and nine degrees (5.4%) less, respectively. Arm speed had a much larger difference, averaging 3,745 deg/s (80.2%) lower than shoulder internal rotation velocity, and 3,891 deg/s (80.8%) less than the shoulder velocity magnitude. The stress metric was found to be 41 Newton meter (Nm; 38.7%) less when compared to elbow torque, and 42 Nm (39.3%) less when compared to shoulder torque. Despite the differences in magnitude, the correlations were extremely strong, indicating that the MotusBASEBALL sensor had high reliability for casual use.ConclusionThis study attempts to validate the use of the MotusBASEBALL for future studies that look at the arm slot, shoulder rotation, arm speed, and stress measurements from the MotusBASEBALL sensor. Excepting elbow extension velocity, all metrics from the MotusBASEBALL unit showed significant correlations to their corresponding metrics from motion capture and while some magnitudes differ substantially and therefore fall short in validity, the link between the metrics is strong enough to indicate reliable casual use. Further research should be done to further investigate the validity and reliability of the arm speed metric.

BackgroundWeighted-baseball training programs are used at the high school, collegiate, and professional levels of baseball. The purpose of this study was to evaluate the effects of a six-week training period consisting of weighted implements, manual therapy, weightlifting, and other modalities on shoulder external rotation, elbow valgus stress, pitching velocity, and kinematics.HypothesisA six-week training program that includes weighted implements will increase pitching velocity along with concomitant increases in arm angular velocities, joint kinetics, and shoulder external rotation.MethodsSeventeen collegiate and professional baseball pitchers (age range 18–23, average: 19.9 ± 1.3) training at Driveline Baseball were evaluated via a combination of an eight-camera motion-capture system, range-of-motion measurements and radar- and pitch-tracking equipment, both before and after a six-week training period. Each participant received individualized training programs, with significant overlap in training methods for all athletes. Twenty-eight biomechanical parameters were computed for each bullpen trial, four arm range-of-motion measurements were taken, and pitching velocities were recorded before and after the training period. Pre- and post-training period data were compared via post-hoc paired t tests.ResultsThere was no change in pitching velocity across the seventeen subjects. Four biomechanical parameters for the holistic group were significantly changed after the training period: internal rotational velocity was higher (from 4,527 ± 470 to 4,759 ± 542 degrees/second), shoulder abduction was lower at ball release (96 ± 7.6 to 93 ± 5.4°), the shoulder was less externally rotated at ball release (95 ± 15 to 86 ± 18°) and shoulder adduction torque was higher (from 103 ± 39 to 138 ± 53 N-m). Among the arm range of motion measurements, four were significantly different after the training period: the shoulder internal rotation range of motion and total range of motion for both the dominant and non-dominant arm. When the group was divided into those who gained pitching velocity and those who did not, neither group showed a significant increase in shoulder external rotation, or elbow valgus stress.ConclusionsFollowing a six-week weighted implement program, pitchers did not show a significant change in velocity, joint kinetics, or shoulder external rotation range of motion. When comparing pitchers who gained velocity versus pitchers who did not, no statistically significant changes were seen in joint kinetics and shoulder range of motion.

Long-term training effects of weighted ball throwing programs have been well documented. However, the mechanisms by which these effects are facilitated are poorly understood due to the difficulty of measuring biomechanics in the baseball throwing motion. The purpose of this study is to replicate previous methods investigating within-session effects of throwing overload and underload baseballs to provide mechanistic evidence for weighted baseball training methods. We hypothesized that varying the pitched ball weight between three, four, five, six, and seven ounces will affect pitched ball velocity, upper body kinematics, lower body kinematics, kinematic velocities, and throwing arm joint kinetics during a maximum intent throwing workout. Twenty-six collegiate and professional level baseball pitchers ages 20-30 (mean age 23.5 ± 2.7 years) participated in a pitch velocity and biomechanical evaluation while pitching a series of leather weighted baseballs from a regulation pitching mound. A one-way repeated measures ANOVA was used to evaluate the within-subject effect of ball weight on a total of 15 parameters: pitch velocity, five kinematic positions, four kinematic velocities, and five kinetics. We found that as ball weight increased, pitch velocity, maximum elbow flexion, maximum pelvis rotation velocity, maximum shoulder internal rotation velocity, and maximum elbow extension velocity decreased, while anterior trunk tilt at ball release increased. Training with three- to seven-ounce baseballs can be used to work on increasing pitching velocity without increasing throwing arm joint kinetics or changing pitching mechanics in a practically significant way.

Long-term training effects of weighted ball throwing programs have been well documented. However, the mechanisms that facilitate these effects are poorly understood. The purpose of this study is to investigate within-session effects of throwing overload and underload baseballs to provide mechanistic evidence for weighted baseball training methods. Twenty-six collegiate- and professional-level baseball pitchers aged 20–30 years (mean age 23.5 [2.7] y) participated in a biomechanical evaluation while pitching a series of leather weighted baseballs. A 1-way repeated-measures analysis of variance was used to evaluate the intrasubject effect of ball weight on a total of 15 kinematic, kinetic, and performance parameters. Ball weight significantly affected pitch velocity, maximum elbow flexion, maximum pelvis rotation velocity, maximum shoulder internal rotation velocity, maximum elbow extension velocity, and anterior trunk tilt at ball release. None of the measured arm joint kinetics were significantly affected by ball weight. Training with 3- to 7-ounce (85- to 198-g) baseballs can be used to work on increasing pitching velocity without increasing throwing arm joint kinetics.

The purpose of this study was to examine differences in varus arm stress between baseball pitch types — fastballs versus a breaking ball of choice—with MotusBASEBALL’s motion capture arm sleeve. Twenty-eight males between the ages of 18 and 36 (21.4 ± 4.3) were asked to throw ten pitches of each pitch type — fastballs (n = 28), curveballs (n = 14), sliders (n = 14), and changeups (n = 18). Every subject threw fastballs and a breaking ball of their choice, and some subjects threw additional changeups. Sliders had the highest arm stress (54.6 ± 12.9 N·m) while curveballs had the lowest (46.8 ± 16.3 N·m). Fastball arm stress was 50.1 ± 16.8 N·m and changeup arm stress was 51.3 ± 15.5 N·m. There was no statistically significant difference between pitch types and arm stress (p-value range 0.08-0.92), although the proportion of outlier readings for arm stress was significant for sliders (proportion of outliers: 34%, p-value: 0.009 versus change-ups; p-value: 0.014 versus curveballs). In addition, pitch type was significant only in determining the velocity reading from the Motus App (p-value &lt;.0001), and was not significant in determining arm speed, arm slot, or shoulder rotation.