What are the considerations for the biomechanics of throwing to prevent injury?

Biomechanics of Throwing and Injury Prevention

Core Biomechanical Principles

The overhead throwing motion requires optimal transfer of forces through the kinetic chain—from lower extremities through the core, shoulder, arm, and hand—with breaks or deficits in this chain leading directly to injury and decreased performance. 1

The Six Phases of Throwing

The throwing motion consists of six distinct phases where specific biomechanical stresses occur: 1

• Windup phase: Establishes base of support and initiates energy generation from lower extremities 1
• Stride phase: Transfers energy from legs through pelvis and trunk 1
• Arm cocking phase: Maximum shoulder external rotation occurs, placing greatest torque on the shoulder 2
• Acceleration phase: Rapid internal rotation generates ball velocity; pain during this phase indicates rotator cuff pathology 2, 3
• Deceleration phase: Eccentric stress on posterior shoulder structures (supraspinatus, external rotators, scapular stabilizers) leads to fatigue and injury 2, 3
• Follow-through phase: Completes energy dissipation 1

Primary Injury Mechanisms

Muscular Imbalance and Fatigue

Weakened posterior shoulder musculature combined with overdeveloped anterior musculature creates the biomechanical environment for injury, as the decelerating arm propelled by strong anterior muscles overwhelms fatigued posterior stabilizers. 2, 4

• Repetitive eccentric stress during deceleration causes fatigue in the supraspinatus, external rotators, and scapular stabilizers 2
• This imbalance prevents the humeral head from staying centered in the glenoid fossa during arm motion 2, 4
• Scapular dyskinesis compounds the problem by failing to maintain proper humeral positioning 4, 3

Distance-Related Stress

Maximum distance throwing ("long-toss") increases shoulder torque significantly and should be avoided during rehabilitation, as longer throws produce greater shoulder torques in the arm-cocked position with increased maximum external rotation. 2

Evidence-Based Prevention Strategies

Pitch Count and Rest Restrictions

Strict adherence to age-specific pitch count limits is mandatory, with 75 pitches per game maximum for 11-14 year olds and mandatory rest periods between throwing sessions. 2

Age-specific guidelines from USA Baseball and Little League: 2

• Ages 13-14: Maximum 75 pitches/game, 125/week, 1000/season, 3000/year 2
• Ages 11-12: Maximum 75 pitches/game, 100/week, 1000/season, 3000/year 2
• Ages 9-10: Maximum 50 pitches/game, 75/week, 1000/season, 2000/year 2

Critical rest requirements: 2

• Avoid pitching when arm fatigue or pain is present 2
• Refrain from throwing activities at least 3 months per year 2
• Do not pitch on 3 consecutive days 2
• Do not play catcher after being removed as pitcher 2

Strengthening Programs

Off-season and preseason strengthening of external rotators and supraspinatus prevents in-season throwing-related injuries requiring surgical intervention. 2

Essential strengthening targets: 2

• Posterior shoulder muscles (external rotators, infraspinatus, teres minor) 2, 4
• Rotator cuff muscles (supraspinatus) 2
• Scapular stabilizers 2
• Core lumbopelvic region 2
• Lower extremity strength for kinetic chain foundation 2, 1

Post-Throwing Recovery

Immediate post-pitching recovery routines including stretching, cryotherapy, and global kinetic conditioning are essential to prevent cumulative injury. 2

Rehabilitation Protocol After Injury

Four-Phase Progressive Return

Complete rest from throwing is mandatory until the athlete is asymptomatic, followed by a structured four-phase rehabilitation program before any return to competitive throwing. 2, 5

Phase 1: Acute Phase

• Cryotherapy, iontophoresis, ultrasound, electrical stimulation 2
• Flexibility and stretching of posterior shoulder muscles 2
• Rotator cuff and scapular stabilization strengthening 2
• Dynamic stabilization exercises 2
• Absolutely no throwing during this phase 2

Phase 2: Intermediate Phase

• Focus on internal rotation and horizontal adduction stretching 2
• Progressive isotonic strengthening 2
• Initiate core lumbopelvic and lower extremity strengthening 2

Phase 3: Advanced Strengthening Phase

• Plyometric program initiation 2
• Endurance drills 2
• Short-distance throwing program begins 2

Phase 4: Return-to-Activity Phase

• Progressive interval throwing program 2
• Age-specific protocols that replicate game conditions progressively 2
• Return to competition only after completing functional program without symptoms 2, 5

Injury-Specific Return Timelines

The progression speed depends on injury severity, with tendon/ligament injuries requiring significantly longer advancement periods than bone injuries. 2

• Bone involvement: Advance every other day as soreness allows 2
• Mild tendon/ligament injury: Every other day for steps 1-3, every third day for steps 4-8, then every other day 2
• Moderate/severe/postoperative tendon/ligament injury: Advance maximum one step every 3 days with 2 days active rest for steps 1-8 2

Common Pitfalls to Avoid

Volume of sports activity is the most consistent predictor of overuse injury, making single-sport specialization before puberty a critical error. 2

Key mistakes that increase injury risk: 2, 5

• Returning to activity before complete symptom resolution 5
• Failing to address the entire kinetic chain in rehabilitation 5, 1
• Ignoring pitch count and rest guidelines 5
• Relying on pain medications without addressing mechanical issues 5
• Single-sport specialization before puberty (associated with more injuries and earlier dropout) 2

Special Considerations for Young Athletes

Adolescent throwers are predisposed to age-specific injuries due to skeletal immaturity, with secondary impingement from weak rotator cuff muscles and ligamentous laxity being more common than primary impingement. 2, 3

Youth-specific factors: 2, 3

• Skeletal immaturity with open physes creates unique vulnerability 2
• Secondary impingement (difficulty keeping humeral head centered) predominates over primary impingement 2
• Weakness in rotator cuff combined with ligamentous laxity is the primary pathology 2, 4
• Pain during arm cocking and acceleration phases indicates developing overuse injury 2, 3

Long-Term Management Strategy

Multi-sport participation with at least 3 months off from throwing annually prevents overuse injuries and maintains long-term athletic participation. 2

Essential long-term elements: 2, 5

• Participation in multiple sports annually to enhance general fitness and motor development 2
• Education about proper technique and biomechanics 5
• Regular monitoring for recurrence of symptoms 5
• Gradual progression of training intensity and volume 5
• Biomechanical assessment coordinated with coaches to identify abnormal motions 5