Original Editor - Vinit Kothekar
- 1 Introduction
- 2 Phases
- 3 Common Injuries
- 4 Resources
- 5 Presentations
- 6 References
Throwing, for example, baseball pitching, is one of the most intensely studied athletic motions. Although the focus has been more on the shoulder, entire body movement is required to perform the act of throwing. Throwing is also considered one of the fastest human motions performed, and maximum humeral internal rotation velocity reaches about 7000 to 7500°/second.
The phases of an overhead throw consist of a:
Wind Up Phase
The wind up phase is defined as the initial movement to maximum knee lift of stride leg . During the initial movements, the pitcher brings his or her hands overhead and lowers to chest level. During these simple movements consider the muscles proximally to distally. EMG studies show that the upper trapezius has a maximum voluntary isometric contraction (MVIC) of 18%, serratus anterior 20%, and anterior deltoid 15%. During this phase, the muscle activity is quite low and for these reasons risk of injury is low as well .
- The pitcher is facing the batter with the baseball concealed away from the batter and in the glove, and both the feet are in contact with the ground. This is known as the windup stance.
- For a right-handed pitcher, throwing arm is right arm, a gloved hand is left, lead/stride leg is left lower extremity and pivot/stance leg is right.
- The phase of windup begins with the initiation of the stride leg and ends when the ball separates from the glove and the stride leg reaches the highest point.
- The ipsilateral leg and trunk rotate approximately 90° and the contralateral hip and knee flex.
- During the windup phase, the energy is transferred from stride leg to pivot leg and winding up of the stride leg occurs. It is an important phase which is responsible for imparting the velocity which is driven to the point of ball release. It is reported that about 50% of the velocity of the ball during an overhead throw is generated from step and body rotation. The body’s overall center of gravity is raised and minimal stress is imparted on the shoulder during this phase.
- The purpose of windup is threefold:
- to establish a rhythm to achieve correct timing for subsequent movements,
- to conceal the ball and distract the hitter and
- to place the body in a position that may contribute to the propulsion of the ball.
- During this phase, there is minimal muscle activity and muscle fire at low intensity.
- As the stride leg is flexed, the weight is transferred from stride leg to pivot leg and hip abductor, adductor and extensors of pivot leg act as weight absorber.
- Anterior deltoid and pectoralis major work concentrically at the glenohumeral joint. Upper trapezius, serratus anterior and lower trapezius work to produce upward rotation of the scapula. The abdominal muscles work to rotate and stabilize the trunk.
The picture below depicts an overhead view of the alignment of the body during the acceleration phase of throwing. Note the 15-degree angle of the foot away from the center of the mound . The stride ankle also typically lands approximately 10cm away from the same midline with a distance from the rubber averaging 87% of the pitcher's height . Fleisig emphasizes the importance of these values by describing the change in force exhibited on the shoulder when they deviate from the norm. During the cocking phase, Fleisig reports a 3.0N increase in anterior force at the shoulder for every extra cm and a 2.1N increase in anterior force at the shoulder with every degree increase of foot angle. Please note that decreasing the distance away from the center or decreasing the angle did not result in an increased anterior force on the shoulder. So, because of the increased anterior force on the shoulder, it can be assumed that over time the anterior ligamentous structures to the glenohumeral joint may be compromised. This finding is consistent with the anterior glenohumeral instability found in many throwing athletes and emphasizes the importance of proper mechanics throughout the entire kinematic chain .
Arm Cocking Phase
The arm cocking phase can be defined as the beginning of lead foot contact and ends at maximum shoulder external rotation . A substantial amount of kinetic energy is transmitted to the shoulder, approximately 80% of body weight, from the lower extremities and trunk rotation. Due to the circumstances, the scapula and shoulder muscles are highly activated to promote and sustain movements of the shoulder, especially external rotation. Special focus on anterior instability in this phase is vital due to the high ranges of external rotation reached in this phase  . In a study of pitchers with chronic anterior instability, stimulation of mechanoreceptors within the glenohumeral joint excited and/or inhibited certain muscles. The biceps brachii and supraspinatus are shown to be initiated or excited by these mechanoreceptors and assist with the prevention of anterior instability. Over time the excessive utilization of the biceps brachii could lead to a superior labrum anterior to posterior (SLAP) tear. Simultaneously the pectoralis major, subscapularis, and serratus anterior are inhibited. These muscles decelerate shoulder external rotation in this phase. When these actions cannot be performed there is an increased likelihood of anterior instability of the glenohumeral joint .
Cocking phase is further divided into (a) early cocking and (b) late cocking.
Early cocking phase
- It begins with the end of the windup phase or when the stride leg reaches its maximum height and it ends when the stride leg contacts the mound/ground.
- During an ideal pitch, at this point the throwing arm is in ‘semi-cocked’ position. With the arm approximately in 90° abduction, 30° horizontal abduction, and 50° external rotation.
- As the ball is removed from the glove, the center of gravity is lowered by flexing the knee of the pivot leg and the stride leg gradually extends and moves towards the batter.
- Its main function is to allow a linear and angular motion of the trunk, which lands directly in front of the pivot leg with the toes pointing slightly in. The knee and hip of the pivot leg extend and initiate pelvic rotation and forward tilting followed by upper torso rotation.
Muscle activation in Early cocking:
- Hip extensors and abductors, knee flexors and ankle plantarflexors of the pivot leg work to propel the weight forward as the stride leg is moving forward. And hip extensors and abductors, knee extensors and ankle plantarflexors of stride leg work eccentrically to control the lowering of body’s center of gravity. Abdominal obliques work eccentrically to control excess lumbar hyperextension.
- In the early cocking phase, the supraspinatus and deltoid work together to abduct the arm with a peak activity . And later during the late cocking phase the activity of deltoid decreases.
- The other muscles which produce peak activity during early cocking phase are right extensor carpi radialis longus and brevis, extensor digitorum communis, right gluteus maximus and left oblique for right-handed pitcher. And the muscle which produces a strong contraction are left erector spinae and left gluteus maximus for right-handed pitcher. Whereas trapezius, serratus anterior and pectoralis are moderately active to position the scapula.
Late Cocking phase
- This phase begins from the point where the stride leg contacts the ground to the point of maximum external rotation of the throwing arm.
- During this phase, the trunk is perpendicular to the batter and upper extremity position is finalized. The pelvis reaches its maximum rotation and the upper torso continues to rotate and tilt forward and laterally.
- The shoulder is abducted about 90°, 10° to 20° horizontally adducted and laterally rotates to about 175°. The wrist is in neutral and the elbow is elevated to about shoulder height and is 90° flexed.
- During this phase, a varus torque of about 64 N-m is generated at the elbow and about 67 N-m internal rotation torque is generated at the shoulder. The scapula is elevated and upwardly rotated which provides adequate subacromial space to avoid impingement.
Muscle activation in Late cocking:
- During late cocking phase, the pivot leg hip extensor, knee flexor and calf muscles work concentrically to transfer the force up the kinetic chain and aide in force generation at the arm.
- Serratus anterior and pectoralis major produce their greatest activity during late cocking phase just before maximum external rotation.
- Infraspinatus and teres minor have their peak activity to externally rotate the arm concentrically and later on their activity is decreased to moderate levels during acceleration phase.
- Subscapularis produces significant eccentric contraction as the humerus passes neutral rotation to control the lateral rotation of the arm.
- Biceps brachii presents with peak activity during flexion of elbow in late cocking phase as it limits anterior translation and compression forces of humeral head. As the wrist extension reaches maximum, the wrist extensor are at its greatest activity.
Arm Acceleration Phase
The arm acceleration phase begins at maximum shoulder external rotation and ends at ball release . During this phase, it is vital to maintain scapular stabilization due to the forward acceleration of the arm which is equivalent of a peak internal rotation angular velocity of approximately 6500⁰/sec near ball release. Improper stabilization of the scapula may be the cause of increased risk of shoulder impingement in this phase. Coupled with the arm cocking phase this phase has also been hypothesized to be at increased risk of various shoulder injuries due to the high kinetic energy generated from the lower extremities  .
- The acceleration phase begins from the point of maximum shoulder external rotation to the point of ball release.
- The trunk continues to rotate and tilt, and energy transferred through upper extremity.
- During this phase, the shoulder moves into horizontal adduction and internal rotation. A rapid shoulder internal rotation takes place and shoulder moves from point of 175o of humeral external rotation to 100o of humeral internal rotation in about 42 to 58 milliseconds.
- Ball release takes place between 40o and 60o of humeral external rotation. The elbow first moves to about 120o of flexion and then rapidly extends to about 25o of flexion at ball release. At ball release elbow extension velocity peaks at approximately 2500o/sec. The wrist moves into flexion from extended position and ends in neutral, while forearm is in about 90o pronation at release.
- Acceleration phase is the most explosive phase of the pitching, and trunk achieves its greatest rotation speed which leads to peak activity of obliques.
- Strong activity of serratus anterior and pectoralis major continues into acceleration as the shoulder moves into horizontal forward flexion and scapula protracts.
- Latissimus dorsi becomes active during late cocking phase as the arm reaches maximum external rotation and continues to contribute towards humeral internal rotation during acceleration phase.
- Subscapularis at its greatest activity as it vigorously moves the arm into internal rotation during this phase. Study done by Gowan et al found that during acceleration phase, the contraction of subscapularis, serratus anterior and latissimus dorsi was considerably high in professional athletes compared to amateur athletes.
- Triceps is also at its greatest activity during this phase as the elbow violently moves into extension and across the body.
Arm Deceleration Phase
The arm deceleration phase begins at ball release and ends at maximum shoulder internal rotation . Typically the concern in this phase is safely decelerating the forward progression of the arm. Escamilla et al states that a shoulder compressive force slightly greater than bodyweight is generated to resist shoulder distraction, while a posterior shear force of 40-50% of bodyweight is generated to resist shoulder anterior subluxation. Due to the high forces generated in this phase, the posterior muscles are highly susceptible to tensile overload, undersurface cuff tears, labrum and bicep pathologies, capsule injuries, and internal impingement .
- It occurs from the point of ball release to maximal humeral internal rotation and elbow extension.
- Shoulder is abducted 100o, humeral rotation reaches 0o and arm is horizontally adducted to 35o.
- Greatest amount of joint loading is generated during this phase. Posterior shear force of about 400 N, inferior shear force of 300 N, 1090 N of compressive forces and about 97 N-m of horizontal abduction torque are generated during this phase after ball release.
- This is the most active phase for the muscles of shoulder girdle as they work eccentrically to decelerate the arm.
- Trapezius, serratus anterior and rhomboids produce high MVIC to assist in deceleration of shoulder girdle.
- Teres minor presents with its peak activity during this phase as it resists anterior humeral head translation, horizontal adduction and internal rotation.
- In addition to teres minor, infraspinatus, supraspinatus and deltoid also presents high MVIC to decelerate the arm in space as it moves forward.
- Biceps brachii and brachialis produces marked eccentric contraction to decelerate the elbow extension and forearm pronation.
- Follow-through is the phase where the body continues to move forward until the arm has ceased motion.
- The elbow undergoes a rebound effect and is approximately flexed to 45o.
- During this phase, the rest of the body catches up with the arm and it culminates with the pitcher in a fielding position.
- During follow-up phase, the trunk extensors work concentrically to bring the trunk in an upright position. And as the rest of the body catches up with the arm, the pivot leg hip flexors move the leg forward and the pitcher assumes a fielding position.
Injuries to the shoulder are most common baseball pitching and more particularly in late cocking and deceleration phase. Following is the list of potential shoulder injuries in different phases of pitching.
- Windup - No injuries are common
- Cocking - Anterior subluxation, internal impingement, glenoid labrum lesions, subacromial impingement.
- Acceleration - Shoulder instability, labral tears, overuse tendinitis, tendon ruptures.
- Deceleration - Labral tears at the attachment of long head of biceps, subluxation of long head of biceps by tearing of transverse ligament, lesions of rotator cuff
- Follow Through - Tear of superior aspect of glenoid labrum at the origin of biceps tendon, subacromial impingement.
Elbow injuries are second most common injuries in baseball pitching.
- Excessive valgus strain at the elbow during the late cocking phase can lead to medial elbow injuries such as muscle tear, avulsion fractures, ulnar nerve damage and most commonly UCL strain or tear . In addition to the valgus strain injuries also follow due to lateral compartment at the elbow such as avascular necrosis, osteochondritis dissecans, osteochondral chip fractures or any combination of these injuries .
- During acceleration phase, secondary to the excessive elbow extension peak velocity, olecranon can impinge against the medial aspect of the trochlear groove and fossa which may form posteromedial osteophyte and loose bodies formation leading to valgus extension overload syndrome.
|| The Biomechanics of Pitching: Maximum Velocity and Efficiency
In this presentation, created by ZenoLink LLC, ways to maximize throwing velocity while minimizing the risk of mechanical injury through improved biomechanics and throwing efficiency are discussed. View the presentation
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