Baseball Pitchers’ Kinematic Sequences and Their relationship to Elbow and

Shoulder Torque Production

Scarborough DM1, Linderman SE1, Sanchez JE1, Berkson EM1,21Sports Medicine Service, Department of Orthopaedic Surgery, Massachusetts General Hospital;

2Harvard University Medical School, Boston, MA

No Disclosures to report.

Background & Purpose

• Kinematic Sequence = the sequential timing pattern of peak angularvelocities of body segments during a pitch

• Provides insight to segment position and motion control that drives thekinetic chain.

• Previous publications report an ideal Kinematic Sequence (KS) where thetiming of each body segment’s peak angular velocity occurs in a proximal-to-distal (PDS) pattern resulting in greater ball velocity and reduction in throwingarm injury risk.1,2

• A recent study revealed that baseball pitchers perform a variety of KSs.3

• High elbow valgus, external rotation and extension torques are associated withincreased vulnerability to joint injury, but to date there is no known investigationof the relationship of Kinematic Sequences and throwing arm joint torques.4,5

The purpose of this study was to:1) identify the number of different KSs performed by each pitcher and2) compare elbow valgus and shoulder external rotation (ER) and extension (Ext)

torques between the 3 primary KSs performed during the fastball pitch.

Subjects:• 14 male collegiate pitchers• Mean age 20.57± 1.91 yrs

Materials and Methods

Test Protocol:• Full body kinematics captured via Vicon MX 3D motion analysis system (360 Hz) • Each pitcher threw 10 - 12 fastballs from a standardized pitching mound the full

60’ 6“ length over home plate to strike zone target• A Stalker ATS 5.0 radar gun recorded pitch speed

Biomechanical calculations:• 15 segment 6 degree-of-freedom

model• Upper body segments were defined

in accordance with International Society of Biomechanics definitions6

Data Analysis

Kinematic Sequence The timing of peak angular velocities for 5 body segments (Pelvis, Trunk, Arm, Forearm and Hand) were recorded to generate each pitch’s Kinematic Sequence (Figure 1)

Figure 1. Altered distal upper extremity Kinematic Sequence

Pelvis Trunk Arm Hand Forearm

Kinematic Sequence NamingEach Kinematic Sequence was named in reference to the ideal PDS: The first segment noted out of order in the PDS sequence (Figure 2)

Pelvis Trunk Arm ForearmHand

Figure 2. Body positioning at the time of peak angular velocity for the 5 segments of the Altered distal upper extremity Kinematic Sequence.

Shoulder Variable Definitions:External Rotational torque: The required force to rotate the humerus about the vertical axis Externally (+) in the Z plane (N-m).

Extension torque: The required force to rotate the humerus about the frontal axis into Flexion (+) or Extension (-) in the X plane (N-m).

Data Analysis

Data:• Strike zone fastball pitch trials were included in analysis• Average fastball velocity = 34.51 m/s (± 1.99)• 119 fastball pitches (average of 8.5 ± 2.71 pitches per player) • Kinematic body segment position data calculated in Visual 3D™ (C-Motion)

Analyses:

ANCOVA statistical analyses were performed to compare joint torques across KS groups with ball velocity as a covariate.

0 5 10 15 20 25 30 35

AlteredProximalarmsegmentKS

AlteredDistalarmsegmentKS

Proximal-to-distalKS

Numberofpitches

Analyses of the 119 fastball pitches revealed:• 13 different Kinematic Sequences (KS)• An average of 3 ± 1.41 different Kinematic Sequences performed per pitcher• NONE of the kinematic sequences followed true ideal Proximal-to-Distal order• Three primary Kinematic Sequences were performed and named (Figure 3):

1. Altered Distal Upper Extremity (UE) KS

2. Altered Proximal Upper Extremity KS

3. PDS KS: closest KS to the ideal Proximal-to-Distal (PDS)

Results

Pelvis Trunk Arm Simultaneous Forearm & Hand

Pelvis Trunk Arm Hand Forearm

Pelvis Trunk Forearm Hand Arm

Figure 3. Number of pitches performed for three primary Kinematic Sequence patterns.

n= 11

n= 35

n= 20

Analyses of the 3 primary Kinematic Sequences (n= 66):Statistically significant differences across the sequences were noted for:• Elbow valgus torque [F(62,2) = 8.785, ɳ2 = .221, p < 0.00] • Shoulder external rotation (ER) torque [F(62,2) = 14.127, ɳ2 = .313, p < 0.00]• Shoulder extension (Ext) torque [F(62,2) = 13.237, ɳ2 = .299, p < 0.00] (Figure 4)

Results

Figure 4. Comparison of shoulder and elbow torques across the 3 primary KS sequences

Torq

ue (N

-m)

30405060708090100110120130

ElbowValgus ShoulderExt ShoulderER

Proximal-to-distal KS, n= 11 Altered Distal arm segment KS, n= 35Altered Proximal arm segment KS, n= 20

*

**

* p< 0. 05 established level of significance

• Our findings demonstrate that collegiate baseball pitchers performed anaverage of 3 different kinematic sequence patterns during fastballpitching.

• This is the first study to demonstrate a relationship between kinematicsequences (KS) and elbow and shoulder torque production.

• As anticipated, the PDS KSs, the sequence most similar to the idealproximal to distal sequencing, produced the least torque across the elbowand shoulder joints.

• The Distal Upper Extremity KS was most common and generated thegreatest shoulder extension torques.

• The Proximal Upper Extremity KS demonstrated the greatest elbow valgusand shoulder external rotation torques.

Conclusions

Discussion

• All fastball pitches are not the same. Each player throws different sets ofpitches with different timings. In the small sample in this study, an averageof 3 different timings (Kinematic sequences) were used for each player.

• Pitchers try to optimize the kinetic chain to harness power and efficiency.This is the first study to demonstrate that the concept of optimizing theKinematic Sequence is indeed efficient with lower torques. The KinematicSequence most similar to the proximal-to-distal Kinematic Sequenceproduce decreased torques in the shoulder and elbow.

• Despite this, the most commonly performed Kinematic Sequences were notthe ideal proximal-to-distal Kinematic Sequence and had greater associatedtorques.

• Further study of the influence of Kinematic Sequence patterns on jointtorques in the baseball pitch may provide insight into pitching injuries anddesign of injury avoidance programs

REFERENCES:1Putnam CA. Sequential motions of body segments in striking and throwing skills: Descriptions and explanations. J Biomech. 1993;26(SUPPL. 1):125-135. doi:10.1016/0021-9290(93)90084-R. 2Fortenbaugh D, Fleisig GS, Andrews JR. Baseball pitching biomechanics in relation to injury risk and performance. Sports Health. 2009;1(4):314-320. doi:10.1177/1941738109338546.3Scarborough DM, Bassett AJ, Mayer LW, Berkson EM. Kinematic sequence patterns in the overhead baseball pitch. Sports Biomech. 2018; Sep 14:1-18. 4Fleisig GS, Andrews JR, Dillman CJ, Escamilla RF. (1995). Kinetics of baseball pitching with implications about injury mechanisms. American Journal of Sports Medicine, 23, 233-239. 5Aguinaldo AL and Chambers H. (2009). Correlation of throwing mechanics with elbow valgus load in adult baseball pitchers. American Journal of Sports Medicine, 37, 2043-2048.6Wu G et al. ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion--Part II: shoulder, elbow, wrist and hand. J. Biomech. 2005 May;38(5):981-992.

References