MUSCULATURE OF THE OVERHAND BASEBALL PITCH
 
Sources include Glousman, R., Hancock, Robert E., Hawkins, Richard J, Dillman, Charles J., Fleisig, Glenn S., Andrews, James R.,  Jobe, Frank W., Radovich Moynes, Diane, Tibone, James E., Perry, Jacquelin, and Meister, Keith.

The goal of the motion is to sequentially develop a package of potential energy that is then converted to kinetic energy that can be imparted to the ball in an efficient and fluid manner (Meister).
Biomechanics:  Static limits of glenohumeral motion for all activities are imposed by the geometry of the articular components of the glenohumeral cavity as well as the soft tissue envelope.  The extremes of motion achieved during the normal throwing motion put all of these structures at risk.  Additionally, the speed with which the action occurs results in the extreme use of the dynamic stabilizing structures, increasing their vulnerability to injury (Meister).

WIND-UP
Concludes with the separation of the ball from the glove and involves no major muscle activity.

EARLY COCKING
Involves early activity of the deltoid muscle (all heads) for arm elevation with forward flexion and abduction of the humerus.  Late stabilizing activity is introduced by the supraspinatus, the infraspinatus, and the teres minor.  Generally concludes with the stride foot touching the ground with the upper body lagging behind to maximize the elastic energy available.  During this phase the loading of the lower body occurs.

LATE COCKING
Supraspinatus contracts eccentrically to elevate the humerus and draw the
humeral head toward the glenoid cavity to maintain joint stability. 
Infraspinatus contracts concentrically to externally rotate the shoulder.
Teres Minor contracts concentrically to externally rotate the shoulder.
Serratus Anterior contracts concentrically for upward rotation of the scapula.
Subscapularis contracts eccentrically to slow the external rotation of the
shoulder and protect the anterior joint.
Triceps contracts eccentrically to prevent excessive elbow flexion.

This phase generally concludes with the rotation of the lower extremities, the hips, and the trunk as they have accelerated and transferred their energy through a system of kinetic links to the cocked arm, which is now cocked at approximately 165 degrees.  The primary purpose of the supraspinatus is to provide joint stability of the glenohumeral joint and is used much more by amateur pitchers than by professionals leading to early fatigue and overuse injury.  The subscapularis and serratus anterior muscles fire extensively in normal shoulders during late cocking, however have considerably reduced activity in unstable shoulders and allow excessive external shoulder rotation.

ACCELERATION
Triceps contracts concentrically to extend the arm at the elbow.
Subscapularis contracts eccentrically to slow external shoulder rotation and
protect the anterior joint followed by concentric contraction for internal
shoulder rotation.
Serratus Anterior for internal shoulder rotation.
Pectoralis Major for internal shoulder rotation.
Latissimus dorsi for internal shoulder rotation.
This phase generally concludes with the release of the ball.  Professional pitchers use the subscapularis almost exclusively among the rotator cuff muscles during acceleration while amateurs use all rotator cuff muscles and the biceps during acceleration.  This further emphasizes the necessity for proper throwing mechanics to reduce or prevent shoulder muscle overuse and injury.  The proper, coordinated motion to the lower extremities, hip, trunk, shoulder, and elbow by the professional athlete renders the supraspinatus, infraspinatus, teres minor and biceps unnecessary for acceleration.  Repetitive activities such as pitching can lead to muscle strains and tendonitis.  Overuse syndromes may occur earlier and more often in the athlete who uses his muscle unnecessarily (Glousman, R.)

DECELERATION AND FOLLOW THROUGH
   Trapezius                              Supraspinatus                Subscapularis
   Serratus Anterior                   Infraspinatus                   Pectoralis Major
   Rhomboids                            Teres Minor
   Deltoids                                  Biceps

UPPER BODY OVERHAND THROWING MUSCLE ORIGINS AND INSERTATIONS 
DELTOID

Origin:  1) front outer 1/3 of the clavicle, 2) border of acromion, 3) lower edge
              of scapula spine.
Insertion:  deltoid tuberosity

SUPRASPINATUS
Origin:  supraspinous fossa
Insertion:  top of greater tubercle of the humerus

INFRASPINATUS
Origin:  below spine and lateral border of posterior scapula
Insertion:  greater tubercle of humerus (posterior side)

TERES MINOR
Origin:  below spine and lateral border of posterior scapula
Insertion:  greater tubercle of humerus (posterior side)

SUBSCAPULARIS
Origin:  anterior surface of subscapular fossa
Insertion:  lesser tubercle of humerus (anterior side)

SERRATUS ANTERIOR
Origin:  surface of upper 9 ribs at the side of the chest
Insertion:  costal aspect of whole length of the medial border of the scapula

PECTORALIS MAJOR
Origin:  1) inner ½ of anterior surface of clavicle, 2) anterior surface of costal
              Cartilages of first 6 ribs, 3) adjoining portion of sternum
Insertion:  flat tendon 2 to 3 inches wide to outer lip of intertubercular groove
                 of humerus 

LATISSIMUS DORSI
Origin:  1) posterior crest of ilium, 2) back of sacrum and spinous processes of
              Lumbar and lower 6 thoracic vertebrae, 3) slips from lower 3 ribs
Insertion:  medial side of intertubercular groove of humerus

TRICEPS
Origin:  1) long head- lower edge of the glenoid cavity of the scapula,
             2) lateral head- upper half of the posterior surface of the humerus
             3) medial head- lower two thirds of the posterior surface of the humerus
Insertion:  olecranon process of the ulna

TRAPEZIUS
Origin:  1) base of skull, 2) neck ligaments, 3) spines of seventh cervical and
              all thoracic vertebrae
Insertion:  1) outer clavicle, 2) acromion process, 3) spine of scapula

THROWING MUSCLE EXERCISES 

TRICEPS
pushdowns---reverse pushdowns---dumbbell tricep extensions (seated and prone)---tricep kickbacks---bench dips---back press---front press---bench press---incline bench press---push-ups--- parallel bar dips

DELTOIDS
back press---front press--- dumbbell press---front one arm and two-arm dumbbell raises---front barbell raises---low pulley lateral raises---low pulley front raises

TRAPEZIUS
bent-over lateral raises---low pulley bent-over raises---upright rows---standing lateral raises---chin-ups---lat pull downs---seated rows---one arm dumbbell rows—bent rows---T-bar rows---barbell shrugs

TERES MINOR
low pulley bent-over lateral raises---bent-over dumbbell lateral raises---dumbbell pullovers---bent rows

INFRASPINATUS
low pulley bent-over lateral raises---bent-over dumbbell lateral raises---bent rows---T-bar rows

PECTORALIS MAJOR
one arm dumbbell front raises---barbell front raises---front press---dumbbell press---bench press---incline bench press---push-ups---parallel bar dips---dumbbell flys---incline dumbbell flys---cable crossover flys---barbell pullovers---dumbbell pullovers

SERRATUS ANTERIOR
incline press---incline dumbbell press---dumbbell pullovers---barbell pullovers

LATTISIMUS DORSI
dumbbell pullovers---barbell pullovers---chin-ups---reverse chin-ups---lat pull downs (front and back)---straight arm lat pull downs---seated rows---one arm dumbbell rows---bent rows---T-bar rows

SUBSCAPULARIS
chin-ups---parallel bar dips---bent over rows---dumbbell pullovers---barbell pullovers---seated rows---one arm rows---bent rows

SUPRASPINATUS
same as deltoids