The influence of shoulder abduction and external rotation on throwing arm kinetics in professional baseball pitchers

BACKGROUND

The relationships between shoulder abduction and external rotation with peak kinetic values at the shoulder and elbow in professional baseball pitchers are not well established.

METHODS

Professional pitchers (n = 322) threw 8-12 fastballs under 3D motion analysis (480 Hz). Pitchers were stratified into quartiles by shoulder abduction and external rotation at distinct timepoints. Regression analyses were performed to quantify associations between shoulder position and kinetics.

RESULTS

Shoulder abduction remained relatively consistent throughout the pitch (foot contact-ball release: 85.5 ± 11.1-90.7 ± 8.4°); shoulder external rotation increased dramatically (foot contact-ball release: 30.8 ± 24.6-165.2 ± 9.7°). For every 10° increase in maximum shoulder rotation, shoulder superior force increased by 2.3% body weight (p < 0.01), shoulder distraction force increased by 5.9% body weight (p < 0.01), and ball velocity increased by 0.60 m/s (p < 0.01). Shoulder abduction was significantly associated with shoulder superior force at all timepoints but not with ball velocity (p > 0.05). For every 10° increase in shoulder abduction at ball release, shoulder superior force increased by 3.7% body weight (p < 0.01) and shoulder distraction force increased by 11.7% body weight (p < 0.01).

CONCLUSION

Increased shoulder abduction at ball release and increased maximum shoulder external rotation were associated with greater superior and distraction forces in the shoulder. Pitchers can consider decreasing shoulder abduction at later stages of the pitch to around 80° in order to minimize shoulder superior force, with no impact on ball velocity.

The Relationship Between Maximum Shoulder Horizontal Abduction and Adduction on Peak Shoulder Kinetics in Professional Pitchers

BACKGROUND

Repetitive horizontal shoulder abduction during pitching can cause increased contact between the posterosuperior aspect of the glenoid and the greater tuberosity of the humeral head, theoretically putting baseball pitchers at increased risk of shoulder internal impingement and other shoulder pathologies.

HYPOTHESIS

Increased shoulder horizontal abduction is associated with increased shoulder anterior force, while increased horizontal adduction is associated with increased shoulder distraction force.

STUDY DESIGN

Descriptive laboratory study.

LEVEL OF EVIDENCE

Level 4.

METHODS

A total of 339 professional baseball pitchers threw 8 to 10 fastball pitches using 3D motion capture (480 Hz). Pitchers were divided into 2 sets of quartiles based on maximum shoulder horizontal abduction and adduction. Elbow flexion, shoulder external rotation, and peak shoulder kinetics were compared between quartiles with post hoc linear regressions conducted for the entire cohort.

RESULTS

At maximum shoulder horizontal abduction, there was no difference in ball velocity between quartiles (P = 0.76). For every 10º increase in maximum shoulder horizontal abduction, shoulder anterior force decreased by 2.2% body weight (BW) (P < 0.01, B = -0.22, β = -0.38), shoulder adduction torque decreased by 0.5%BW × body height (BH) (P < 0.01, B = -0.05, β = -0.19), and shoulder horizontal adduction torque decreased by 0.4%BW × BH (P < 0.01, B = -0.04, β = -0.48). For every 10º increase in maximum shoulder horizontal adduction, shoulder anterior force increased by 2%BW and ball velocity decreased by 1.2 m/s (2.7 MPH).

CONCLUSION

Professional pitchers with the least amount of maximum horizontal adduction had faster ball velocity and decreased shoulder anterior force. Pitchers with greater maximum shoulder horizontal abduction had decreased shoulder anterior force, shoulder adduction torque, and shoulder horizontal adduction torque. To maximize ball velocity as a performance metric while minimizing shoulder anterior force, pitchers can consider decreasing maximum shoulder adduction angles at later stages of the pitch.

CLINICAL RELEVANCE

Identifying risk factors for increased throwing shoulder kinetics (ie, shoulder anterior force, shoulder adduction torque) has potential implications in injury prevention. Specifically, mitigating shoulder anterior forces may be beneficial in reducing risk of injury.

Increased Knee and Meniscal Injury Incidence in Professional Baseball Pitchers With Wider, Positive Stride Width

BACKGROUND

Professional baseball pitchers sustain 75% of knee injuries while at the pitcher's mound, yet no pitching motion has been associated directly with such injuries. Stride width is a potential, modifiable risk factor worth investigating.

HYPOTHESIS

Increased stride width in both the positive and negative directions (deviations from neutral stride width) would correlate with increased incidence of knee injury in pitchers.

STUDY DESIGN

Descriptive laboratory.

LEVEL OF EVIDENCE

Level 5.

METHODS

Professional pitchers (n = 199) were evaluated with motion capture (480 Hz) while pitching. Injury history over 10 years was recorded at face-to-face interviews with pitchers. Players were subsequently grouped into stride width tertiles, compared for previous injury incidence of the lower extremities. Regressions were performed to observe performance benefits of stride width with ball velocity, accuracy, or consistency in pitch location as secondary outcomes.

RESULTS

Of the 40 lower extremity injuries reported, meniscal injury (27.5%) was the most common, followed by foot stress fracture (20.0%). Significant differences in injury incidence were noted between the least and most positive stride width tertiles: lower extremity (10.4% vs 25.8%, respectively; P = 0.03), knee (3.0% vs 15.2%, respectively; P = 0.02), and meniscal (0.0% vs 12.1%; P = 0.00). Stride width of pitchers with meniscal injury in the lead (32.6 ± 7.1 cm, n = 5; P = 0.02) and stance leg (33.5 ± 10.6 cm, n = 5; P = 0.03) was significantly more positive than that of uninjured pitchers (21.1 ± 11.5 cm, n = 164). No significant relationships were established between stride width and ball velocity (P = 0.54) or pitch location metrics (P > 0.05).

CONCLUSION

Pitchers with increased positive, stride width had significantly higher incidence of lower extremity injury (knee and meniscus). Wider, positive stride width may increase the degree of external rotation on the lead knee in a loaded state, which can place the medial side of the knee (and meniscus) at higher risk of injury.

CLINICAL RELEVANCE

Decreasing stride width may be beneficial for professional pitchers to reduce the rate of lower extremity injury, while also preserving performance metric outcomes.

Increased Elbow and Olecranon Injury History in Professional Pitchers With Increased Elbow Flexion at Ball Release

BACKGROUND

Elbow flexion at late portions of the pitch has been associated with increased elbow varus torque, a kinetic surrogate associated with injury risk. Direct examinations of injury incidence with elbow flexion angles have not been conducted in professional pitchers.

PURPOSE

To compare elbow and shoulder injury incidence among professional baseball players stratified by degree of elbow flexion at ball release (BR).

STUDY DESIGN

Descriptive laboratory study.

METHODS

Professional pitchers (N = 314) were instructed to pitch between 8 and 12 fastballs while being evaluated using motion capture technology. Upper extremity injury incidence was recorded upon interview. Pitchers were subsequently subdivided into 3 groups based on increasing elbow flexion at BR. Analysis of variance was used to compare participant characteristics and kinematic and peak kinetic variables. An odds ratio (OR) was calculated to determine the risk of having a previous upper extremity injury based on the degree of elbow flexion at BR.

RESULTS

A total of 116 pitchers (132 documented injuries) had a previous upper extremity injury, with elbow injury (76 injuries; 57.6%) being the most common. Evaluation of kinetic values showed that pitchers with the smallest elbow flexion at BR had significantly less peak elbow flexion torque than did those with greatest elbow flexion at BR (3.8 ± 0.5 vs 4.1 ± 0.6 %weight × height; P = .003). Pitchers who demonstrated a greater than average degree of elbow flexion at BR when pitching were more likely to have a history of elbow injury (OR, 1.97; 95% CI, 1.14-3.40; P = .015) and olecranon spur formation or stress fracture (OR, 5.79; 95% CI, 1.25-26.85; P = .025).

CONCLUSION

Pitchers with greater elbow flexion at BR had significantly higher odds of previous injury of the elbow and olecranon. Increasing elbow flexion has been shown to place the medial elbow in a position to carry a greater amount of load, which may be exacerbated during the final moments of the pitching motion. Professional pitchers can consider decreasing elbow flexion at BR as a potential, modifiable risk factor for elbow injury, in particular for olecranon spur formation and fracture.

CLINICAL RELEVANCE

This study attempts to associate injury incidence with a modifiable, kinematic variable for an at-risk population.

Kinematic and kinetic analyses of professional pitchers with history of core or groin injuries: A propensity-score matched analysis

Background

Core injuries in professional baseball pitchers have been linked to both diminished performance and time missed during the season injury was sustained. It is currently unclear how a history of a core injury may affect the future pitching performance and mechanics of professional baseball pitchers.

Purpose

To compare kinetic and kinematic variables between professional baseball pitchers with prior core/groin injuries and those without prior injury.

Study design

Descriptive laboratory study.

Methods

Professional baseball pitchers with a history of core injury pitched 8-12 fastball pitches while evaluated with 3D-motion capture (480 Hz). Inclusion criteria necessitated that the core injury occurred within one to four-years prior to biomechanical evaluation and that the core injury required time off from professional play for a minimum of 2 weeks and maximum of 3 months. These pitchers were 4:1 propensity-scored matched by age, height, weight, and handedness to pitchers with no prior injury history (control). Twenty kinematic and eleven normalized and non-normalized kinetic parameters were compared between groups using appropriate parametric testing. Sub-analysis of pitchers with distinct core muscle and spinal injuries were also analyzed.

Results

The No Prior Injury (NPI) subgroup (n = 76) had significantly less elbow flexion at ball release (31 ± 5° vs. 35 ± 6° respectfully, p = 0.044) compared to the Core Musculature/Soft Tissue subgroup (CM/ST, n = 10), with no significant difference in kinematics for other injury groups (p > 0.05). The General Core/Groin injury group (GCG, n = 19) had significantly greater normalized elbow anterior force (43.9 ± 4.7 vs. 40.0 ± 5.2 %BodyWeight[BW], p = 0.006) and elbow flexion torque (4.3 ± 0.5 vs. 3.8 ± 0.5 %BWxBodyHeight[BH], p = 0.001) than the NPI pitchers. CM/ST had significantly greater normalized elbow anterior force (p = 0.031), elbow flexion torque (p = 0.002), and shoulder adduction torque (p = 0.007) than NPI pitchers.

Conclusion

Professional baseball pitchers with prior core/groin injuries demonstrated increased elbow anterior force and elbow flexion torque compared to pitchers with no prior core injuries. One possible explanation for this finding includes inadequate recruitment and utilization of the lower extremities as a component of the kinetic chain leading to compensation at the level of the throwing arm. Whether these kinetic differences arise as a consequence of injury or present a risk for such warrants additional investigation.