Reexamination of proximal to distal sequence in baseball pitching Norihisa FUJII Laboratory for Sport Biomechanics (LASBIM) University of Tsukuba, Japan

Proximal to distal sequence in human movements It is recognized that the joint movements occur with the sequential pattern from the proximal segment to distal segment of the body in ballistic movements. Vertical jump (squat jump) : the hip extensors become active first, and are successively followed by the knee extensors and the ankle extensors. ==> Proximal to distal (P-D) sequence in human movement

Proximal to distal sequence in throwing motion Herring and Chapman (1992) investigated the effect of timing of torque generation and torque reversal on throwing distance with the computer simulation technique. Kojima (1995) simulated the two-dimensional throwing motion with three torque generators. Two-dimensional throwing motion Internal rotation of shoulder, one of the most important movements in baseball pitching, was neglected.

Proximal to distal sequence in baseball pitching Three-dimensional throwing motion Fujii and Ae (1995) simulated the “three-dimensional” baseball pitching. It was inferred that the co-activation of the joint torques of horizontal adduction and internal rotation of the shoulder was more important than the sequential pattern of the peak torques of the shoulder. Since the joint torque of the previous report did not have the Hill-type characteristics, it is still open to question whether the P-D sequence is really important or not.

Purpose of study The purpose of this study is to reexamine the importance of the sequential pattern for pitching motion based on the three-dimensional model with the torque generators including Hill-type characteristics.

Linked segment model for 3-D pitching simulation

Hill type characteristics of torque generator Active torque = (maximum torque) × (active state) × f1(joint angle) × f2(angular velocity) 1.0 f1(joint angle) Joint angle Ratio to maximum torque Optimal joint angle Eccentric Concentric 1.0 f2(angular velocity) Angular velocity of joint Maximum angular velocity

Original active states of major torque generators Time, ms External (+) / internal (-) rotation of shoulder Extension (+) / flexion (-) of elbow Horizontal adduction (+) / abduction (-) of shoulder 1 -1 Active state 100 50 Stride foot contact Ball release

Modified active states for simulation 1 1 Extension of elbow condition 5 condition 6 Active state Active state Horizontal adduction of shoulder condition 1 condition 2 -1 -1 50 100 50 100 Time, ms Time, ms 1 Internal rotation of shoulder condition 3 condition 4 Original condition Shift earlier conditions Active state Shift later conditions -1 50 100 Time, ms

Simulation results Original condition Condition 3 Active state of internal rotation of shoulder was shifted earlier 20 ms.

Release velocities of simulated pitching motion Throwing direction component Original condition 27.6 m/s Simulation condition conditions shifted earlier shifted later Horizontal adduction 1 & 2 23.6 m/s 23.9 m/s Internal rotation 3 & 4 24.8 m/s 22.8 m/s Extension of elbow 5 & 6 26.3 m/s 26.6 m/s Resultant velocity Original condition 27.9 m/s Simulation condition conditions shifted earlier shifted later Horizontal adduction 1 & 2 24.0 m/s 26.9 m/s Internal rotation 3 & 4 26.8 m/s 23.2 m/s Extension of elbow 5 & 6 26.4 m/s 27.1 m/s

Active torques of torque generators 150 100 Extension of elbow Active torque, Nm Active torque, Nm Horizontal adduction of shoulder -100 -100 50 100 50 100 Time, ms Time, ms 50 Internal rotation of shoulder Original condition Condition 3 Active torque, Nm Condition 4 -100 50 100 Time, ms

Internal rotation of shoulder in condition 3 & 4 100 Limiting torque Joint angle 1 Joint angle, rad Joint torque, Nm Optimal joint angle 2 3 -100 50 100 50 100 Time, ms Time, ms 100 Original condition Condition 3 Condition 4 Angular vel, rad/s Angular velocity of joint -100 50 100 Time, ms

Importance of P-D sequence in baseball pitching With the Hill-type torque generators, the co-activation of the joint torques of the shoulder (horizontal adduction and internal rotation) is not effective. Further question: What is the reason why the horizontal adduction torque should be activated earlier than the internal rotation torque?

Combined condition for simulation 1 Active state -1 50 100 Time, ms Horizontal adduction (+) / abduction (-) of shoulder External (+) / internal (-) rotation of shoulder Extension (+) / flexion (-) of elbow

Active torques of combined condition 150 100 Extension of elbow Active torque, Nm Active torque, Nm Horizontal adduction of shoulder -100 -100 50 100 50 100 Time, ms Time, ms 50 Internal rotation of shoulder Original condition Combined condition Active torque, Nm Release velocity: combined condition: 22.6 m/s original condition: 27.6 m/s -100 50 100 Time, ms

Relation between P-D sequence and moments of inertia of upper limb in two-dimensional throwing Iwrist Ielbow Ishoulder Ishoulder > Ielbow > Iwrist ===> the shoulder torque should be activated first, and should be followed by the elbow torque and the wrist torque.

Moment of inertia of upper limb around the shoulder joint in three-dimensional throwing Iaa : Moment of inertia of upper extremity around the horizontal adduction/abduction axis Iaa Iie Iie : Moment of inertia of upper extremity around the external/internal rotation axis Iaa > Iie ===> horizontal adduction torque should be activated earlier than internal rotation torque.

Concluding remarks The simulation results suggest that in the three-dimensional pitching motion, the horizontal adduction of shoulder is considered as the proximal movement, and the internal rotation the distal movement, and the proximal to distal sequence of torque generators is important for the high release velocity.

Thank you for your kind attention!