jund in this 
t the grove 
ts direction 
de way, that 
und contact. 
abducted and 
t was flexed. 
g approached 
rated forward 
The elbow and 
al extension 
tation of the 
ontacted the 
y to end the 
es before the 
s began after 
he leg fixed 
ation of the 
yrward and the 
the external 
the shoulder 
rnal rotation 
re end of the 
mum external 
| which was a 
1lt (70 deg. ). 
tching was 50 
So, a lot of 
During this 
chialis, the 
) 
» (middle) 
(aft) 
  
Sapraspinatus 
-—— Pectoralis 
major(crav) 
-«- (chest) 
Coracabrachial 
  
is 
— Subscapularis 
Latissimus 
dorsi 
Teres major 
  
Infraspinatus(u 
pper) 
2.35 | (middle) 
c) 
  
ing pitching 
|toideus were 
| rotation and 
—- Deltoideus(fore 
  
  
the horizontal extension were increased in this phase, 
but this was not because of the muscle activities. It 
was because of the inertial force on the arm. 
After the maximum external rotation the acceleration 
phase began. The shoulder angle changed its direction 
to internal rotation, horizontal adduction, and 
adduction. The movement of the horizontal adduction 
stopped at the very instance of the ball release because 
of the reaction of the internal rotation to make forearm 
rotate forward. The ball was released at the end of the 
acceleration phase. The ball speeds which were 
calculated from the data were from 101 to 125 km/h. 
Those were from 71 to 87 * of the ball speeds during 
a real match for each subject. So, our data were 
  
upward direction of front direction of 
the humerus the humerus 
-2500 -500 1500 3500 -9500 
-2000 |, 
-4000 
—6000 HF 
-8000 + 
  
  
from the shoulder to the elbow 
direction of the humerus 
from the shoulder to the elbow 
direction of the humerus 
Fig. 6 calculated bone-to-bone force in the shoulder 
cons idered to be close to the situation of a real match. 
The average duration of the late cocking and the 
acceleration were 73 and 54 ms. These were similar value 
to the Papas' (1985b). In this acceleration phase the 
muscle activities increased very much. Especially the 
pectoralis major, the brachialis, and the latissimus 
dorsi showed the activity around 800 N. 
After the ball release, that was the follow through 
phase. Very large muscle activities were found. So, it 
was thought that muscle activities were required to 
make the body segment stop its movement. The 
supraspinatus, the deltoideus, the coracobrachialis 
the andpectoralis major enlarged its activities more 
than before the ball release. Peak force of the 
supraspinatus reached to 1500 N. Corresponding to the 
large muscle activities during the fol low through phase 
the force produced in the shoulder reached to 5000 N. 
The direction of the force was approximately along the 
upper arm. This bone-to-bone force was nearly 6 times 
of the body weight. 
4. CONCLUTION 
We applied the motion capture technique to a 
rehabilitation purpose. We could estimate the bone- 
to-bone force in a joint with motion captured data. In 
this method we could get into inside of our body without 
touching. The information obtained in this research 
will contribute the rehabilitation procedure of 
baseball players. The needs for this new method will 
increase in the future. 
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