Poster P13 - Differences in Pitching Kinetics and Kinematics During Various Effort Level Pitching

Introduction: After surgery, pitchers need to demonstrate a normalized range of motion, strength, and scapular mechanics before safely moving on to a throwing plan to avoid re-injury. Return to throw programs, in the form of interval throwing progressions, are often used for players who are returning to sport from a throwing related injury. Interval throwing progressions begin with gentle throws, gradually increasing in intensity and distance until the thrower reaches maximum effort. During rehabilitation and early return to throwing phases, arm kinetics should be kept low to avoid re-injury. When the medial elbow undergoes high torques, the UCL structure has a potential to be at an increased risk of injury. Identifying poor mechanics could be instrumental to safe return to throw after an arm injury. However, 3D motion analysis evaluations are normally not conducted until a player is throwing at 100% effort as it is thought that 100% effort throwing represents a player’s true mechanics. This assumption is unproven, as there is no literature comparing kinematics at different effort levels. During a return to throw program, once a player is throwing at 100% effort, it may be more difficult to make mechanical adjustments and the player may have already incurred increased kinetics to their injured limb. If kinematics are similar at lower effort levels, biomechanical analyses could be conducted earlier in a player’s return to play program. The purpose of this study was to assess the differences in kinetics and kinematics during reduced effort pitching.

Materials and

Methods: A cross-sectional study had collegiate aged pitchers (n = 19) throw five fastballs at each effort level including 60%, 70%, 80%, 90%, and 100%. Kinetics and kinematics were recorded. Variables of interest included elbow varus torque, shoulder rotation at maximum external rotation (MER), elbow flexion at MER, maximum resultant shoulder force, peak pelvis rotation velocity, peak trunk rotation velocity, peak shoulder internal rotation velocity, peak elbow extension velocity, shoulder abduction at MER, maximum shoulder horizontal abduction, and maximum hand velocity. Three-dimensional motion capture data was collected on pitchers using a 8-camera marker-less motion analysis system (KinaTrax). Pitchers were told they would be throwing 3 fastballs at various effort levels including 60%, 70%, 80%, 90% and 100% levels. Before they stepped on the mound, they threw up to five warm up pitches in front of the mound to reacclimate their arm to throwing. Once they were ready for data collection, they were instructed which effort level to throw, starting with 60%, and progressively increasing in effort to 70%, 80%, 90%, and 100%. Pitches were averaged per participant and effort level prior to analyses. Descriptive statistics were calculated including mean (standard deviation), minimum, maximum, and median values and were visualized in whisker box plots. Four separate analyses of covariance (ANCOVA) tests were performed to assess the potential differences of various effort level fastballs on SR at MER, EF at MER, MRSF and MEVT. Tukey Honest Significant Difference (HSD) post hoc test was performed. All statistical analyses were performed in R 4.3.2

Results, Conclusions, and Discussions: Minimal kinematic and kinetic differences were found when throwing at various effort levels. Only Maximum Elbow Varus Torque demonstrated differences between effort levels, with only the 100% effort level compared to the 60% effort level showing a significant difference of 19.35 Nm. This large percentage of change shows the significant reduction in stress that the elbow experiences at 60% effort level compared to 100%. Shoulder kinetics, hand speed and other kinematics observed did not have significant differences between effort levels. Hand velocity showed no statistically significant differences between effort levels. Using hand velocity as a surrogate for ball velocity, these results are not consistent with previous literature that ball velocity decreases with decreased effort levels. There were no significant differences in shoulder distraction forces across observed effort levels. Due to the limited studies available on percent effort throwing there have not been any other studies observing shoulder distraction forces across various effort levels. All kinematic variables did not have statistically significant differences across the various effort levels. Melugin et al. found similar results when observing shoulder rotation at MER and found no differences across various effort levels. This study allows comparisons of future investigations that may aim to reduce throwing arm kinematics and kinetics via reduced effort throwing. Secondarily, although minimal kinetic and kinematic differences were observed, throwing at close to half effort showed decreased elbow varus torque, which was consistent with previous literature. Throwing at near half effort may be advised for pitchers as they begin interval throwing programs, particularly during recovering from elbow injury. It is inconclusive if throwing at lower efforts will protect shoulder injured tissue during return to throwing programs at this time. Since there were no differences in pitching kinematics between effort levels, pitching mechanics will be maintained even at low effort levels. Thus, lower percent effort throwing will allow for continued proper throwing technique, preparing pitchers for higher effort throws as they progress through rehabilitation and can be utilized to assess pitching mechanics at lower effort levels.

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