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Throwing Biomechanics

Original Editor - Vinit Kothekar

Top Contributors - Vinit Kothekar, Ewa Jaraczewska, Jess Bell, Vidya Acharya, Kim Jackson, Olajumoke Ogunleye, 127.0.0.1, Rachael Lowe, Naomi O'Reilly, Wanda van Niekerk, WikiSysop and Claire Knott

Introduction

Throwing is among the fastest human motions, engaging the entire body. To accurately analyse throwing techniques, it is essential to understand the phases of throwing, the biomechanics of each phase, the integrated kinetic chain, and common throwing injuries.[1]

Basic Terminology

Right-handed pitchers throw with their right arm. Their left hand is their glove hand. Their right leg is their pivot leg (also called drive or stance leg) and it remains in contact with the pitching rubber. Their left leg is their stride leg (also called the lead leg). The stride leg steps towards the home plate.

Phases of Throwing

The phases of an overhead throw are:[2][1]

  • wind-up
  • stride
  • arm cocking
  • arm acceleration
  • arm deceleration
  • follow-through

Each phase plays an important role in creating or transferring energy through the body to the arm and the ball.[1]

The following video shows a baseball pitch in slow motion:

[3]

Wind-Up Phase

The wind-up phase helps to establish a rhythm to achieve correct timing for subsequent movements. During wind-up, the pitcher conceals the ball in their glove, distracts the hitter and positions their body to aid ball propulsion.[4]

Biomechanics Overview

About 50% of the ball's velocity during an overhead throw is generated from step and body rotation.[5] The wind-up phase begins with the pitcher's initial movement from a static stance and ends when the stride leg reaches its maximum knee height.[2] This end position is known as the "balance point".

During this phase, the pitcher's body weight shifts to their pivot leg, storing potential energy, and the pivot leg engages the posterior chain. The pitcher lifts their stride leg to reposition their centre of mass. Key muscles involved in this lifting action are iliopsoas, rectus femoris, pectineus, and sartorius.

Breakdown of the Wind-Up Phase Steps
  • Initial stance: the pitcher faces the batter with the baseball concealed in their glove. Both feet are in contact with the ground. This is known as the wind-up stance.[6]
  • Phase initiation: the wind-up phase begins with the initial movement of the stride leg lifting and ends when the stride leg reaches its highest point (balance point).[7]
  • Body rotation and leg positioning: the pivot leg and trunk rotate approximately 90°, while the hip and knee of the stride leg flex as they lift.[4]
  • Weight transfer: during the wind-up phase, energy is transferred to the pivot leg as the stride leg lifts.
  • Centre of gravity shift: the body’s overall centre of gravity is raised as the stride leg reaches its maximum height.
  • Minimal shoulder stress: minimal stress is placed on the shoulder during this phase,[8] as the throwing motion has not yet begun.
Muscle Activation During the Wind-Up Phase

At the start of the wind-up phase, the pitcher brings their hands overhead and lowers them to chest level. EMG studies show that the upper trapezius has a maximum voluntary isometric contraction (MVIC) of 18%, serratus anterior 20%, and anterior deltoid 15%. Because the level of muscle activity is quite low in this phase,[9][10] the risk of injury is also low.[2]

  • As the pitcher lifts and flexes their stride leg, their weight is transferred from the stride leg to the pivot leg—the hip abductors, adductors, and extensors of the pivot leg act as weight absorbers.[6]
  • The anterior deltoid and pectoralis major show minimal, preparatory activity.
  • Upper trapezius, serratus anterior and lower trapezius work to produce upward rotation of the scapula.
  • The abdominal muscles work to rotate and stabilise the trunk.

Stride Phase

The stride phase begins when the pitcher's stride leg is lifted and ends when the stride foot strikes the ground. It involves the coordinated action of the ankles, legs, pelvis, core, thoracic spine, and shoulders.[1][11]

During this phase, the athlete generates a ground reaction force for linear propulsion by pushing off their pivot leg while maintaining a hip hinge. The stride foot should land in line with the pivot leg, pointed slightly inward.[12] When the stride length exceeds 80% of the athlete's body height, it can reduce elbow torque.[13] [11] However, if the stride foot lands too far forward, pelvic rotation may be restricted, causing the pitcher to throw across their body.[11] Hip-shoulder separation occurs as the pelvis rotates independently of the torso.

To minimise injury risk, the throwing arm should achieve approximately 90° shoulder abduction, over 35° shoulder external rotation, and over 90° elbow flexion by the end of this phase.

Muscle Activation During Stride Phase

The action of several muscle groups is crucial for optimal performance during the stride phase.

Core and lower body stability:

  • The abdominal obliques contract eccentrically to prevent excessive lumbar hyperextension during upper torso rotation and flexion.
  • The gluteus maximus of the pivot leg is activated to maintain slight dominant-sided extension and provide stabilisation for the pelvis and trunk during the stride phase.

Clinical relevance: poor core muscle activation and stability can impact the throwing motion, potentially resulting in injuries or pain, including low back pain.[11]

Shoulder mechanics:

  • Infraspinatus and teres minor externally rotate the shoulder, correctly positioning the humeral head on the glenoid.
  • The serratus anterior and scapular retractors (middle trapezius, rhomboid, and levator scapulae) facilitate upward rotation and retraction of the glenoid, creating a stable base for humeral rotation.

Arm Cocking Phase

The arm cocking phase occurs from stride foot contact to maximum shoulder external rotation (150-180°).[2] This phase is divided into early and late cocking stages. During the cocking phase, significant kinetic energy is transmitted from the lower extremities and trunk to the throwing arm, preparing it for the explosive acceleration phase. The cocking phase is relatively long compared to the acceleration phase.[14][15][16]

Early Cocking Phase

The early cocking phase begins when the pitcher's stride foot contacts the ground and continues as their shoulder externally rotates towards maximum external rotation.[6][7] During this phase, the throwing arm is in a ‘semi-cocked’ position with the shoulder in approximately 90° abduction, 30° horizontal abduction, and 50° external rotation.[10]

Key Biomechanical Events During Early Cocking

The pitcher's centre of gravity lowers as they flex the knee of their pivot leg. The stride leg provides a stable base for upper-body rotation. Pelvic rotation begins, followed by trunk rotation. The pitcher's shoulder continues to externally rotate as the arm path progresses.[10][7]

Muscle Activation in the Early Cocking Phase
  • The hip extensors and abductors, knee flexors and ankle plantar flexors of the pivot leg work to propel the weight forward as the stride leg moves forward.
  • The hip extensors and abductors, knee extensors and ankle plantar flexors of the stride leg work eccentrically to control the lowering of the body’s centre of gravity.
  • The abdominal obliques work eccentrically to control excess lumbar extension.
  • Supraspinatus and deltoid work together to abduct the arm.[10][17]
  • For right-handed pitchers, the right extensor carpi radialis longus and brevis, extensor digitorum communis, gluteus maximus and left oblique assist to produce peak activity.[6] In addition, their left erector spinae and left gluteus maximus produce a strong contraction for trunk stability.
  • Trapezius, serratus anterior, and pectoralis are moderately active in positioning the scapula.

Late Cocking Phase

External rotation continues through the late cocking phase until maximal external rotation is achieved, ending this phase. During late cocking, the pitcher's trunk becomes perpendicular to the pitching direction, and the upper extremity position reaches its final pre-acceleration position.[6] Their pelvis reaches maximum rotation, but their upper torso continues rotating, and tilts forward and laterally.

The pitcher's scapula is elevated and upwardly rotated, ensuring adequate subacromial space. The shoulder is abducted to about 90°, with 10-20° horizontal adduction and about 175° external rotation. Their elbow is flexed to 90° and elevated to around shoulder height. Their wrist is in a neutral position.

Muscle Activation in the Late Cocking Phase

During the late cocking phase, the hip extensors, knee flexors and calf muscles of the pivot leg work concentrically to transfer force up the kinetic chain and aid in force generation at the arm.

  • Serratus anterior and pectoralis major are maximally active as the shoulder approaches maximum external rotation.[9]
  • Infraspinatus and teres minor reach their peak concentric activity to externally rotate the shoulder.
  • Subscapularis produces a significant eccentric contraction to control and store potential energy.
  • Biceps brachii is maximally active during flexion of the elbow to limit anterior translation and compression forces of the humeral head.
  • The wrist extensors are maximally active as maximum wrist extension is achieved.[4]

Clinical relevance: repetitive throwing can lead to overuse injuries in the shoulder. However, repetitive throwing also causes adaptive changes, which allow for greater external rotation range and contribute to higher pitch velocities.[18]

Arm Acceleration Phase

The acceleration phase starts when the shoulder is in maximal external rotation and ends when the ball is released. During this phase, forward trunk flexion, internal rotation of the throwing arm, and elbow extension occur. Stored energy in the shoulder capsule and explosive power from internal rotators contribute to internal rotation of the arm, while elbow extension and wrist flexion further increase velocity.[11]

Rotation of the arm lags behind elbow extension. This reduces shoulder inertia and increases torque and angular velocity, with the arm achieving an average angular velocity of 7,000° per second at ball release (velocity does depend on level of play). Overhead throwing is, therefore, one of the fastest human movements.[11] During the arm acceleration phase, scapular stability must be maintained due to the forward acceleration of the arm.

Breakdown of the Steps of the Arm Acceleration Phase
  • Energy transfer: the trunk continues to rotate and tilt, and energy is transferred through the upper extremity.
  • Rapid shoulder internal rotation: the shoulder moves into horizontal adduction and internal rotation. It moves from a point of 175° of humeral external rotation to 100° of humeral internal rotation in about 42-58 milliseconds.[4]
  • Ball release: occurs during the transition from external to internal rotation.
  • Elbow movement: the elbow first moves to about 120° of flexion and then rapidly extends to about 25° of flexion at ball release.[4]
  • Wrist and forearm positioning: the wrist moves into flexion from an extended position and ends in neutral, while the forearm is in about 90° pronation at release.
Muscle Activation in the Arm Acceleration Phase

The arm acceleration phase is the most explosive phase of pitching:

  • The trunk achieves its greatest rotation speed, which leads to peak activity of the obliques.[4]
  • Latissimus dorsi becomes active during the late cocking phase as the arm reaches maximum external rotation and continues to contribute towards humeral internal rotation during the acceleration phase.[10][17]
  • Shoulder internal rotation occurs due to the concentric activation of the internal rotators. Gowan et al.[17] found that during the acceleration phase, the contraction of subscapularis, serratus anterior and latissimus dorsi was considerably higher in professional athletes than in amateur athletes.
  • The rotator cuff muscles, trapezius, serratus anterior, and levator scapulae stabilise the scapula and glenohumeral joint.[9]
  • Triceps brachii is most active during this phase as the elbow rapidly moves into extension and the arm moves across the body.
  • The wrist flexors move the wrist from hyperextension to a neutral position at ball release.

Clinical relevance: improper stabilisation of the scapula during this phase may increase the risk of shoulder impingement.[2] [16]

Arm Deceleration Phase

The arm deceleration phase begins at ball release and ends when the shoulder reaches maximum internal rotation. During this phase, the shoulder experiences significant compressive forces as the rotator cuff muscles work eccentrically to control the arm's momentum. At the end of this phase, the glenohumeral joint reaches 0° external rotation, with the shoulder positioned at 100° abduction and 35° horizontal adduction.[2][11]

Muscle Activation in the Arm Deceleration Phase
  • Teres minor, infraspinatus, and posterior deltoid contract eccentrically to slow shoulder motion and absorb forces. Teres minor reaches its peak eccentric activity during this phase as it resists anterior humeral head translation, horizontal adduction and internal rotation.[2][11]
  • Biceps brachii and brachialis eccentrically contract to slow elbow extension and forearm pronation.[11]
  • Trapezius, rhomboids, and serratus anterior stabilise the scapula during deceleration.[11]

Clinical relevance: the high forces generated during the arm deceleration phase make the posterior musculature and posterior capsule highly susceptible to tensile overload. Repeated exposure to these forces can lead to rotator cuff tears, labral pathologies, biceps tendon injuries, and capsular injuries.[2] Together with the anterior capsule stretching that occurs during the late cocking phase, pitchers are at increased risk of developing glenohumeral internal rotation deficit (GIRD).[11][19]

Follow-Through

During follow-through, the pitcher's body moves forward until their arm stops moving.[20] During this phase, the elbow undergoes a rebound effect and is flexed to approximately 45°.[7] The appearance of this phase varies among athletes due to factors like arm slot and lower-body mechanics.[1]

Muscle Activation During the Follow-Through Phase
  • During the follow-through phase, the trunk extensors work concentrically to bring the trunk upright.
  • The pivot leg hip flexors move the leg forward, and the pitcher assumes a fielding position.

Clinical relevance: the follow-through phase is a "culmination of [the] kinetic chain delivering the pitch. [There is] a low risk of injury during this phase."[11]

Kinetic Chain

During throwing, athletes generate velocity through a sequential transfer of energy from the ground, through their legs, pelvis, trunk and upper extremity. Optimal performance and injury prevention rely on the efficient transfer of energy throughout the kinetic chain.[1]

A functional kinetic chain has three main components. These are: optimised anatomy (i.e., the strength, flexibility, and power of individual parts of the chain, like the feet, hips, trunk, and shoulder); sequential generation of forces; and efficient motor patterns. Dysfunction in any of these components can disrupt the kinetic chain.[1]

Clinical relevance: When the kinetic chain is dysfunctional, the upper extremity compensates, increasing injury risk.[1]

Assessment and Prevention of Kinetic Chain Dysfunction

It is important to evaluate the entire kinetic chain, considering range of motion, strength, coordination, and internal derangements at each link in the chain. Preventative training or rehabilitation programmes can then address specific issues.[21] Modern throwing analysis uses video motion capture to assess kinetic chain efficiency.

Common Throwing Pathomechanics

"Clinical evaluation of the shoulder joint complex in the injured throwing athlete should be comprehensive and systematic, following an evaluation pathway for proximal and distal causative factors and including observation of humeral motion."[22]

Because the kinetic chain is a closed system, an alteration in one area can create widespread changes. This catch-up phenomenon means that changes in interactive moments can alter the forces in distal segments. These increased forces place additional stress on the distal segments, often leading to pain or injury.

Altered mechanics during throwing can lead to a condition known as the disabled throwing shoulder (DTS). DTS is a broad term that encompasses the functional limitations experienced by symptomatic athletes who are having difficulty performing throwing or hitting actions.[23]

DTS often results from a series of injuries, where the demands of throwing or hitting trigger alterations throughout the kinetic chain. The legs, core, scapula and shoulder are the most commonly affected areas.[23][24]

Common Injuries

Shoulder Injuries

Shoulder injuries are common in baseball pitching, particularly in the late cocking and deceleration phase.[25][6]

  • Windup: not commonly associated with shoulder injuries.
  • Arm cocking: anterior subluxation, internal impingement, glenoid labrum lesions and subacromial impingement.
  • Arm acceleration: shoulder instability, labral tears, overuse tendinopathy and tendon ruptures.
  • Arm deceleration: labral tears at the attachment of the long head of biceps, subluxation of the long head of biceps and rotator cuff injuries.
  • Follow-through: tear of the superior aspect of the glenoid labrum at the origin of the biceps tendon and subacromial impingement.

Elbow Injuries

Elbow injuries are the 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 tears, avulsion fractures, ulnar nerve damage and ulnar collateral ligament strain or tear.[25]
  • Valgus strain injuries can lead to avascular necrosis, osteochondritis dissecans, osteochondral chip fractures, or any combination of these injuries.[6]
  • During the acceleration phase, rapid elbow extension can cause the olecranon to impinge against the medial aspect of the trochlear groove and fossa. This repetitive impact may lead to bone spur formation and loose bone fragments, resulting in valgus extension overload syndrome (also known as Pitcher's elbow).[26]

Resources

The first video discusses the biomechanics of throwing. The second video provides an example of throwing mechanics for a baseball athlete.

[27]
[28]

Presentations

https://www.youtube.com/watch?v=yzO_BVXkhE8
 The Biomechanics of Pitching: Maximum Velocity and Efficiency

In this presentation, ZenoLink LLC explored ways to maximise throwing velocity while minimising the risk of mechanical injury through improved biomechanics and throwing efficiency. View the presentation


References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Trasolini NA, Nicholson KF, Mylott J, Bullock GS, Hulburt TC, Waterman BR. Biomechanical Analysis of the Throwing Athlete and Its Impact on Return to Sport. Arthrosc Sports Med Rehabil. 2022 Jan 28;4(1):e83-e91.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Escamilla R, Andrews JR. Shoulder Muscle Recruitment Patterns and Biomechanics during Upper Extremity Sports. Sports Med 2009; 39 (7): 569-590.
  3. ↑ Zack Greinke Pitching Mechanics Slow Motion Baseball Instruction Analysis LA Dodgers MLB 1000 FPS. Available from: https://www.youtube.com/watch?v=iRPtVfEz4es
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 Pappas AM, Zawacki RM, Sullivan TJ. Biomechanics of baseball pitching: A preliminary report. The American journal of sports medicine. 1985 Jul 1;13(4):216-22.
  5. ↑ Toyoshima S, Hoshikawa T, Miyashita M, Oguri T. Contribution of the body parts to throwing performance. InBiomechanics IV 1974 (pp. 169-174). Palgrave, London.
  6. ↑ 6.0 6.1 6.2 6.3 6.4 6.5 6.6 Houglum PA, Bertotti DB. Brunnstrom's clinical kinesiology. FA Davis; 2012.
  7. ↑ 7.0 7.1 7.2 7.3 Seroyer ST, Nho SJ, Bach BR, Bush-Joseph CA, Nicholson GP, Romeo AA. The kinetic chain in overhand pitching: its potential role for performance enhancement and injury prevention. Sports Health: A Multidisciplinary Approach. 2010 Mar 1;2(2):135-46.
  8. ↑ Meister K. Injuries to the shoulder in the throwing athlete, part two: evaluation/treatment. The American journal of sports medicine. 2000 Jul 1;28(4):587-601.
  9. ↑ 9.0 9.1 9.2 Moynes DR, Perry J, Antonelli DJ, Jobe FW. Electromyography and motion analysis of the upper extremity in sports. Physical therapy. 1986 Dec 1;66(12):1905-11.
  10. ↑ 10.0 10.1 10.2 10.3 10.4 Park SS, Loebenberg ML, Rokito AS, Zuckerman JD. The shoulder in baseball pitching: biomechanics and related injuries--Part 1. Bulletin of the NYU Hospital for Joint Diseases. 2002 Dec 22;61(1-2):68-79.
  11. ↑ 11.00 11.01 11.02 11.03 11.04 11.05 11.06 11.07 11.08 11.09 11.10 11.11 Mayes M, Salesky M, Lansdown DA. Throwing Injury Prevention Strategies with a Whole Kinetic Chain-Focused Approach. Curr Rev Musculoskelet Med. 2022 Apr;15(2):53-64.
  12. ↑ Dillman CJ, Fleisig GS, Andrews JR. Biomechanics of pitching with emphasis upon shoulder kinematics. Journal of Orthopaedic & Sports Physical Therapy. 1993 Aug;18(2):402-8.
  13. ↑ Fleisig GS, Escamilla RF. Biomechanics of the elbow in the throwing athlete. Operative Techniques in Sports Medicine. 1996 Apr 1;4(2):62-8.
  14. ↑ Douoguih WA, Dolce DL, Lincoln AE. Early cocking phase mechanics and upper extremity surgery risk in starting professional baseball pitchers. Orthop J Sports Med. 2015 Apr 22;3(4):2325967115581594. Erratum in: Orthop J Sports Med. 2015 Jun 26;3(6):2325967115595220.
  15. ↑ Wilk KE, Obma P, Simpson CD, Cain EL, Dugas JR, Andrews JR. Shoulder injuries in the overhead athlete. J Orthop Sports Phys Ther. 2009 Feb;39(2):38-54.
  16. ↑ 16.0 16.1 Whiteley R. Baseball throwing mechanics as they relate to pathology and performance - a review. J Sports Sci Med. 2007 Mar 1;6(1):1-20.
  17. ↑ 17.0 17.1 17.2 Gowan ID, Jobe FW, Tibone JE, Perry J, Moynes DR. A comparative electromyographic analysis of the shoulder during pitching professionally versus amateur pitchers. The American Journal of Sports Medicine. 1987 Dec 1;15(6):586-90.
  18. ↑ Thacher RR, Varady NH, Khilnani T, Camp CL, Dines JS. Current Concepts on the Management of Shoulder Instability in Throwing Athletes. Curr Rev Musculoskelet Med. 2024 Sep;17(9):353-364.
  19. ↑ Minhaj S, Afridi ZK, Rubab S, Qazi Z, Siddiqui M. Glenohumeral Internal Rotation Deficit and Risk of Upper Extremity Injury in Overhead Athletes: Systematic Review. Archives of Physical Medicine and Rehabilitation 2025;106(1):91-97.
  20. ↑ Diffendaffer AZ, Bagwell MS, Fleisig GS, Yanagita Y, Stewart M, Cain EL Jr, et al. The clinician's guide to baseball pitching biomechanics. Sports Health. 2023 Mar-Apr;15(2):274-281.
  21. ↑ Moiroux--Sahraoui A, Mazeas J, Delgado N, Le Moteux C, Acco M, Douryang M, Bjerregaard A, Forelli F. Prevention of overhead shoulder injuries in throwing athletes: a systematic review. Diagnostics. 2024 Oct 30;14(21):2415.
  22. ↑ Kibler WB, Sciascia AD, Grantham WJ. The shoulder joint complex in the throwing motion. J Shoulder Elbow Surg. 2024 Feb;33(2):443-449.
  23. ↑ 23.0 23.1 Kibler WB, Wilkes T, Sciascia A. Mechanics and pathomechanics in the overhead athlete. Clin Sports Med. 2013 Oct;32(4):637-51.
  24. ↑ Barfield JW, Bordelon NM, Wasserberger KW, Oliver GD. Preliminary Analysis of Closed Kinetic Chain Upper Extremity Stability Test Differences Between Healthy and Previously Injured/In-Pain Baseball Pitchers. Sports Health. 2023 Mar-Apr;15(2):290-294.
  25. ↑ 25.0 25.1 Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. Kinetics of baseball pitching with implications about injury mechanisms. The American journal of sports medicine. 1995 Mar 1;23(2):233-9.
  26. ↑ Stevens KJ, Chaudhari AS, Kuhn KJ. Differences in Anatomic Adaptation and Injury Patterns Related to Valgus Extension Overload in Overhead Throwing Athletes. Diagnostics (Basel). 2024 Jan 19;14(2):217.
  27. ↑ SPARK Physiotherapy, LLC. The Biomechanics of Throwing. Available from: http://www.youtube.com/watch?v=ERyWx46e7BQ [last accessed 15/06/16]
  28. ↑ Scotty Gilbertson. Sport Science: Aroldis Chapman. Available from: http://www.youtube.com/watch?v=yEpdoAZiHWQ [last accessed 15/06/15]
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