STRIDE LENGTH COMPENSATIONS AND THEIR IMPACTS ON BRACETRANSFER

STRIDE LENGTH COMPENSATIONS AND THEIR IMPACTS ON BRACE-TRANSFER GROUND FORCES IN BASEBALL PITCHERS Crotin RL 1, 2 and Ramsey DK 1 1 Department of Exercise and Nutrition Sciences, University at Buffalo, NY 2 Baltimore Orioles, Baltimore, Maryland Improper baseball throwing mechanics, repetitive stress, and physical immaturity increase a pitchers’ vulnerability to orthopedic injury. “Pitching-fatigue” is considered a primary mechanism for throwing arm injuries and may impact lower body biomechanics and power generation. In order to maintain peak ball velocities, compensatory throwing mechanics are adopted. The brace-transfer phase is initiated at stride foot contact (SFC) and ends at maximal external shoulder rotation (MER). Brace-transfer ground reaction forces have the potential to be impacted by compensatory adaptations, possibly affecting the kinetic chain. We propose reduced stride length can affect brace-transfer forces despite maintaining ball velocity. Consequently, in support of current pitch count standards, the evaluation of ground reaction force profiles can offer greater injury protection in monitoring “pitching fatigue” and its association to stride length compensation. METHODS - continued RESULTS – GROUND REACTION FORCE DATA GAME-SIMULATED MOTION CAPTURE • 8 camera VICON F 20 (240 Hz), 2 Kistler force plates (960 Hz)) • Two highest velocity pitches in the first (pitches 1 -20) and last inning of simulated play (pitches 61 -80) analyzed • Joint angles & ground reaction profile derived using rigid body analysis (Visual 3 D) GAME-SIMULATED PITCHING VELOCITY • Jugs Radar Gun Pro with LED Feedback Display (Jugs Sports) recorded ball velocity for analysis of 3, 040 pitches HYPOTHESIZED STRIDE LENGTH COMPENSATION TO MAINTAIN BALL VELOCITY (REDUCED STRIDE = LOWER BODY EXERTION) (INCREASED STRIDE = THROWING ARM EXERTION) STRIDE LEG PURPOSE To demonstrate the impact of stride length changes on bracetransfer ground reaction forces. Exertion can impact stride length and affect typical bracing strategies in competitive baseball pitchers. As a result of atypical bracing, the risk for throwing arm injury may be exacerbated by stride length compensations. OVERSTRIDE UNDERSTRIDE P value GRFZ 0. 20 ± 0. 142 N/kg 0. 31 ± 0. 198 N/kg P=0. 056 GRFY -0. 011 ± 0. 142 N/kg 0. 05 ± 0. 627 N/kg P<0. 001 IMPZ 70. 8 ± 0. 857 Ns 66. 2 ± 0. 857 Ns P<0. 001 IMPY 25. 0 ± 0. 857 Ns 20. 0 ± 0. 255 Ns P<0. 001 FORCE/IMPULSE OVERSTRIDE UNDERSTRIDE P value GRFZ 0. 95 ± 0. 384 N/kg 0. 69 ± 0. 411 N/kg P=0. 056 GRFY -0. 57 ± 0. 245 N/kg -0. 34 ± 0. 198 N/kg P=0. 002 IMPZ 7. 84 ± 5. 34 Ns 6. 30 ± 5. 29 Ns P=0. 372 IMPY -4. 60 ± 3. 30 Ns -3. 11 ± 0. 267 Ns P=0. 123 SUMMARY and CONCLUSION SUBJECTS • 19 high level pitchers from high school and collegiate baseball programs were recruited to throw two, 80 -pitch games. • Ball velocity, 3 D kinematics, and ground reactions forces were recorded throughout each inning (20 pitches thrown per inning). BRACE-TRANSFER GROUND REACTION FORCES • Ground reaction forces normalized to body mass and synched with time normalized pitching trials for 80 -game pitches. • Stride foot contact (SFC) considered at 5%BW upon footstrike. • Time normalized shoulder kinematics identified (MER). FORCE/IMPULSE Ground reaction forces; GRFZ (vertical), GRFY (anterior+/posterior- shear), IMPZ (vertical impulse), IMPY (anterior+/posterior- impulse) METHODS PITCHING PROTOCOL • Warm-up throws at desired stride length for normalizing stride length. • Cross-over design used to randomly assign subjects to ± 25% of their desired stride. This equated to an understride at 50% body height and overstride at 75% body height for sim-games. • Pitches thrown in a ratio of 3 fastballs to 1 change-up. DRIVE LEG BACKGROUND Stride length compensations maintained linear hand ball velocities despite impacting brace-transfer ground reaction forces. RESULTS – SIMULATED GAME VELOCITIES Increased Stride • Increased drive impulse (increased time and force application) • Increased bracing ground reaction forces. SUBJECT CHARACTERISTICS Age: 18. 74 ± 1. 56 yrs Height: 1. 84 ± 0. 05 m Weight: 81. 95 ± 8. 10 kg BMI: 24. 35 ± 2. 58 kg/m² LINEAR HAND VELOCITY FASTBALL VELOCITY OVERSTRIDE: 20. 58 ± 1. 56 m/s (46. 04 mph) OVERSTRIDE: 126. 29 ± 8. 46 km/h (78. 5 mph) UNDERSTRIDE: 20. 13 ± 1. 50 m/s (45. 03 mph) UNDERSTRIDE: 126. 32 ± 7. 66 km/h (78. 5 mph) P= 0. 367 Reduced Stride • Reduced drive impulse (reduced time and force application) • Reduced bracing ground reaction forces. P= 0. 984 BENEFITS At present, pitch count measures are unable to delineate discrete occurrences where stride length variations influence ground reaction forces. Ground reaction force monitoring may be an efficacious way to detect changes in exertion for competitive pitchers. If unmonitored, injurious consequences can arise when high effort pitches are thrown consistently with altered, or less then optimal ground reaction force profiles.