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

2. 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

3. 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.

4. 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.

5. 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.

6. Linked segment model for 3-D pitching simulation

7. 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

8. 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

9. Modified active states for simulation1 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

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

11. 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

12. 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

13. 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

14. 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?

15. Combined condition for simulation1
Active state -1 50
100
Time, ms
Horizontal adduction (+) / abduction (-) of shoulder
External (+) / internal (-) rotation of shoulder
Extension (+) / flexion (-) of elbow

16. 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

17. 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.

18. 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.

19. 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.

20. Thank you for your kind attention!