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Biomechanics of Throwing

Biomechanics of Throwing. Marco Bosquez MD Round Rock Ortho and Rehab University of Texas Associate Team Physician Medical Director Danskin Triathlon. Goals. Stages of mechanics Forces acting at shoulder and elbow Relationship of faulty mechanics to injury

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Biomechanics of Throwing

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  1. Biomechanics of Throwing Marco Bosquez MD Round Rock Ortho and Rehab University of Texas Associate Team Physician Medical Director Danskin Triathlon

  2. Goals • Stages of mechanics • Forces acting at shoulder and elbow • Relationship of faulty mechanics to injury • Differences between children and adults • Different types of pitches

  3. Biomechanics • 6 Phases • Wind-up • Stride • Arm Cocking • Arm Acceleration • Arm Deceleration • Follow Through

  4. Wind-up • Begins with initiation of leg movement • Ends when pitcher’s lead leg has reached maximum height • Minimal kinetics and muscle activity in both shoulder and elbow

  5. Stride • Ends when lead foot makes contact • Arm abducted 90o, elbow flexed 90o • Arm externally rotated 30o-80o

  6. Arm Cocking • From foot contact until throwing shoulder reaches maximum external rotation • Pelvis and upper trunk rotate to face batter • Arm reaches maximum external rotation up to 180o • Gleno-humeral rotation • Scapulo-thoracic motion • Extension of spine

  7. Arm Acceleration • Lasts until ball release • Torques at shoulder at elbow produce rapid arm acceleration

  8. Arm Deceleration • Ball release to max internal rotation • Arm abducted at 90o regardless of style • Highest joint loads

  9. Follow-Through • From max IR until pitcher reaches balanced fielding position • Trunk and legs dissipate energy in the arm

  10. Shoulder • Late Cocking: • RTC peak compressive force of 650 N • Biceps begins to fire • Horizontal add.100 Nm, IR 70 Nm • Humeral head translates posteriorly

  11. Shoulder • Acceleration • Shoulder loads are minimal • Horizontal abduction returns to neutral • Humeral head recenters • Triceps early; pecs, lats, serratus ant. late

  12. Elbow • Late Cocking/Acceleration • Varus torque of 64 Nm at elbow during late cocking and early acceleration • UCL generates 54% (35 Nm) of this force • UCL failure strength = 32 Nm

  13. Elbow • Late Cocking/Acceleration • Valgus force and rapid elbow extension produce tensile stress to medial restraints • UCL: anterior bundle is primary restraint to valgus force from 30o to 120o of flexion • Flexor-pronator mass • Medial epicondyle apophysis • Ulnar nerve

  14. Elbow • Late Cocking/Acceleration • Compression of radial head and capitellum • Compressive forces of 500 N (125#) as elbow moves from 100o to 20o of flexion • Shear forces posteriorly

  15. Shoulder/Elbow • Release/Deceleration • Highest joint loads • Distraction at elbow and shoulder • Large proximal forces needed • Shoulder = 125% wt • Elbow = 100% wt

  16. Shoulder/Elbow • Release/Deceleration • Violent eccentric muscle contractions • Biceps contracts to stabilize shoulder compressive force of (1000N) • Biceps decelerates rapid elbow extension (60Nm)

  17. Biomechanical Factors • 50% of velocity attributed to mechanics • Top two factors • Timing of shoulder rotation and elbow extension • Trunk/Shoulder cocking and distance

  18. Biomechanical Errors • Lead foot too open • Lead foot pointed outward • Early shoulder rotation • Late shoulder rotation • Leading with elbow • Decreases ball speed, increases arm stress

  19. Importance of Pitch Type • Fastball • High kinetics • Fast arm speed and trunk rotation • Forearm neutral • Wrist from extension to flexion • Ball speed high

  20. Importance of Pitch Type • Change-up • Low kinetics • Slow arm speed and trunk rotation • Forearm neutral • Wrist from extension to flexion • Ball speed low

  21. Importance of Pitch Type • Curveball • High kinetics • Slow arm speed and trunk rotation • Forearm supinated • Wrist from radial to ulnar deviation • Ball speed low

  22. Age Differences • Ball velocity increases with age • Shoulder and elbow velocity increases with age • Shoulder and elbow distraction forces increase with body weight • No differences found in mechanics

  23. Summary • Children pitch with less force but similar mechanics to adults • Learning proper mechanics as early as possible is beneficial • Deviations from proper mechanics can lead to joint stress and potential injury

  24. Summary • The change-up is the easiest and safest off-speed pitch • The curveball is a difficult, stressful off-speed pitch

  25. Summary • Pitching is a kinetic chain • Good conditioning of all elements in the chain is critical • Good conditioning does not prevent overuse

  26. Marco Bosquez MD

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