Biomechanics of Throwing

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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

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Wind-up

• Begins with initiation of leg movement
• Ends when pitchers 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

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Arm Deceleration

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

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Follow-Through

• From max IR until pitcher reaches balanced
  fielding position
• Trunk and legs dissipate energy in the arm

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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

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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

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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

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Shoulder/Elbow

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

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Shoulder/Elbow

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

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Biomechanical Factors

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

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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

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Importance of Pitch Type

• Fastball
• High kinetics
• Fast arm speed and trunk rotation
• Forearm neutral
• Wrist from extension to flexion
• Ball speed high

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Importance of Pitch Type

• Change-up
• Low kinetics
• Slow arm speed and trunk rotation
• Forearm neutral
• Wrist from extension to flexion
• Ball speed low

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Importance of Pitch Type

• Curveball
• High kinetics
• Slow arm speed and trunk rotation
• Forearm supinated
• Wrist from radial to ulnar deviation
• Ball speed low

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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

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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

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Summary

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

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Summary

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

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• Marco Bosquez MD