The biomechanics of throwing/Carl W. NissenM.D./UCONN

Good article

The Biomechanics of Throwing: 2003
Carl W. Nissen, MD
UConn Sports Medicine

A) Introduction
Description of the basics
Attention to the shoulder and elbow mechanics and possible problems

B) What’s in a pitch?
Kinetic chain from foot to fingers
Translation of leg strength to ball velocity
Lower extremity provides the power
A majority of a pitch’s velocity (>60%) comes from the legs
Trunk rotation allows transfer of energy to shoulder and elbow
Importance of core stability obvious to allow transfer

C) Phases of a Pitch

D) Wind-up
Earliest phase
Perhaps the most underrated phase
Need solid, balanced pedestal position
Ends with hand separation and motion towards plate
Requires good balance and pelvic/trunk strength
Nolan Ryan epitomizes this phase
Legs and core work together to achieve ‘totem pole’ position
Relaxed upper body is goal

E) Early Cocking
Starts with hand separation and motion towards plate
Ends with foot plant
Requires good balance and patience
Early Cocking - Shoulder
Deltoid and supraspinatus muscles function together to elevate elbow above shoulder
Feltner & Dapena - Int J Sports Biomech - 1986
Early Cocking - Shoulder
Peri-scapular muscles work in coordinated fashion to adjust shoulder ball and socket position to match elbow elevation
Serratus anterior is primary scapular rotator
Early Cocking - Elbow
Positioning of elbow primarily a function of the shoulder and little elbow activity seen
Problems Found in Early Cocking
Poor balance in one leg stance allowing or forcing back lordosis or awkward leg kick to regain balance
Poor foot plant position blocking easy transfer of power from legs to trunk and arm

F) Late Cocking
Starts with foot plant
Need to achieve balanced, stable position
Stride should be no more than standing height in distance
Foot and stride should be towards the plate
Ends with maximal external rotation of shoulder
Late Cocking - Shoulder
Infraspinatus and teres minor are primary muscles functioning
External rotation of the shoulder ‘winds-up’ the shoulder
These posterior shoulder muscles help restrain anterior humeral head translation which is equivalent to shoulder instability
Serratus anterior positions shoulder socket (glenoid) appropriately
Allows maximal superior tilt of glenoid to allow maximal external rotation
Late Cocking - Shoulder
Subscapularis, pectoralis major, and latissimus dorsi muscles are functioning secondarily
They provide anterior capsular support
Subscapularis rotates to superior position on top of the humeral head
Late Cocking - Elbow
Joint should flex to 90 degrees
Flexor and extensor muscles work in coordination to control motion
Moderate valgus force across the elbow exists
Late Cocking
Problems in this stage include
Scapular dyskinesis (abnormal shoulder blade motion) leading to low elbow position
Anterior instability leading to internal impingement
Hyperangulation is the West Coast term to describe this problem
Glousman et al - AJSM - 1992

Late Cocking - Shoulder
Scapular motion irregularities include:
Lag or slow moving scapula, winging, asymmetric motion compared to other side
This abnormal scapular motion leads to elbow dropping necessarily due to decreases glenoid (shoulder socket) superior tilt
Late Cocking - Shoulder
Anterior instability (even in its subtlest form)
Pinching of infraspinatus and supraspinatus along with posterior glenoid labrum (i.e., Internal impingement)
Late Cocking - Shoulder
Anteriorly unstable shoulders show decreased dynamic anterior stabilizing effect of subscapularis and pectoralis major
Meaning that unstable shoulders have weaker stabilizing muscles as well as lax ligaments
Glousman - AJSM - 1992
Late Cocking - Shoulder
Tight posterior capsule can cause supero-anterior humeral translation
This is theorized to load postero-superior labrum and increasing risk of SLAP lesion (i.e., ‘Peel-Back’ mechanism)
Morgan and Burkhart
Late Cocking - Shoulder
Bony changes do exist that may explain ‘shift’ of arc of motion to increase in external rotation
In other words, the increased external rotation that pitchers have is equivalent to the decreased internal rotation they have
Andrews et al - AJSM - 1999
Osseous change may be protective
Problems Found During Late Cocking
Internal impingement (rotator cuff partial tears) with or without labral problems
Posterior SLAP tears

G) Acceleration
Starts with maximal external rotation of the shoulder
Ends with ball release

High angular (rotational) velocities occur in both shoulder and elbow
Shoulder internal rotation up to 7600 deg/sec
Elbow around 2500 deg/sec
Both joints also see significant joint compressive and tension loads
Acceleration - Shoulder
Pectoralis major and teres minor muscles are most active
High electrical activity within these muscles (i.e. the body is trying to make them work hard)
Work cooperatively to control internal rotation of the shoulder
Acceleration - Shoulder
Posterior deltoid and supraspinatus
Work to reduce posterior humeral translation which is a concern during this stage because of high muscle forces anteriorly
Acceleration - Elbow
Extensor muscles (triceps) allow rapid extension to 20 degrees
Valgus stress on medial structures (primarily the UCL) increase to 60 N
Failure strength of anterior band of UCL is 64 N
Flesig et al - AJSM -
Acceleration - Elbow
Restraint to valgus force at 90 degrees is primarily the UCL
Restraint at 20 degrees is UCL, anterior capsule, and lateral bony joint (radio-capitellar joint)
Morrey & An - AJSM - 1983
Acceleration - Elbow
Medial muscles (flexor-pronator mass including wrist flexors and pronator teres) are most active during this phase
DiGiovine et al - J Shoul Elbow Surg - 1992
Acceleration - Elbow
Wrist flexor muscles rest anatomically over the UCL and provide dynamic restraint to valgus force
Davidson et al - AJSM - 1995
Paradoxically the medial muscles are electrically quiet when UCL dysfunction exists

Problems Found During Acceleration
Mild rotator cuff impingement due to occult anterior instability
Posterior SLAP (labrum) lesions secondary to tight posterior capsule and the ‘peel-back’ mechanism
UCL sprains or ruptures
Flexor-pronator muscle strains
Compressive injuries on outside of elbow
H) Deceleration
Starts with ball release
Ends after one third of time till the end of arm motion
Deceleration - Shoulder
Teres minor muscle
Most active of all glenohumeral muscles
Controls deceleration of shoulder rotation
Other posterior shoulder muscles also assist in this motion control
Deceleration - Elbow
Flexors (anterior) muscles
Work to slow down the rapid extension of the elbow
Biceps and brachialis primarily
Problems Found During Deceleration
SLAP (labral) lesions due to increased tension and/or force on the biceps
Posterior compartment irritation of surfaces (i.e., posterior olecranon rubbing leading to bone spurs)
I) Follow Through
Starts after one third of terminal arm motion following ball release
Ends with the end of arm motion
Follow Through
More important for coaches as pitchers prepare to field a ball
Rarely a phase when injuries occur due to arm motion