THE CHANGES ON MECHANICAL WORK OF THE LOWER LIMB JOINTS DURING BASEBALL PITCHING IN A SIMULATED GAME / 体力科学

The purpose of this study was to investigate the changes on mechanical work of the lower limb joints during baseball pitching in a simulated game. One male college baseball pitcher threw 15 pitches in an inning for 9 innings (135 pitches) in an indoor pitcher's mound with two force platforms. Rest time between innings was 6 minutes. Three-dimensional positions of 47 reflective markers attached to subject were tracked by an optical motion capture system (Vicon Motion System 612, Vicon Motion Systems) with eight cameras (250Hz). For subject 75 fastball pitches (1st, 3rd, 5th, 7th, and 9th innings) were chosen for analysis.As the main results, the hip joint extension absolute and negative work of the stride leg decreased with increasing the number of pitches. The ankle joint extension absolute and negative work of the stride leg increased with increasing the number of pitches. These results suggest that the hip joint extension torque of the stride leg was needed to maintain for higher performance in baseball pitching.

JUMPER'S TIBIA ASSESSED ALONG 64 DIRECTIONS CENTERING CENTER OF GRAVITY OF THE BONE BY pQCT / 体力科学

Side to side difference in tennis players' mid-radius and cross-sectional study on mid-tibia of jumpers and sedentary controls suggest that the improvement of mechanical properties of cortical bone in response to long-term exercise is related to geometric adaptation and not to volumetric bone mineral density. In the present study, geometric and mechanical properties of right tibia were estimated along 64 directions centering center of gravity of the bone on cross-sectional peripheral quantitative computed tomography (pQCT) images. The tibias of 17 jumpers (7 females, 10 males) and 15 controls (8 females, 7males), aged 18-23, were scanned at mid site using pQCT. Periosteal and endocortical radius were larger, cortical thickness was thicker, and mechanical properties (moment of inertia of area and strength strain index) were greater in jumpers compared to those of controls. The differences in cortical thickness between the two groups were dependent on direction of measurement. Defined a direction from tibia's center of gravity to fibula's as 0°, difference in the cortical thickness between jumpers and controls was the greatest at around 240°. Along this direction, differences in mechanical properties were also the most significant, suggesting that the site-specific adaptation of bone to long-term exercise is due to geographical relation of bone to muscle.

Three-dimensional dynamics of elbow and shoulder joint throwing motion in relation to throwing arm movement and injury in baseball / 体力科学

This study was designed to clarify the causes of throwing injuries of the elbow and shoulder joints in baseball. Five varsity-skilled baseball players without pain in the elbow and shoulder joints were subjects for this study. They were fixed to a chair and asked to throw a baseball using three different throwing arm movements (T<SUB>0</SUB>, T<SUB>45</SUB>, and T<SUB>90</SUB>) . These movements were filmed using three-dimensional DLT videography. Linked rigid-body segment inverse dynamics were then employed to determine resultant joint force and torque at the elbow and shoulder joints. Peak varus torque at the elbow joint for T<SUB>90</SUB> was less than for the other movements during the acceleration phase. In the follow-through phase, however, a large anterior shear force (70 N) at the elbow, for elbow extension, was present for T<SUB>90</SUB>. These results indicate that T<SUB>90</SUB> was a high risk movement which leads to extension injuries rather than medial tension injuries. After the ball release, a large superior shear force (118 N) at the shoulder joint was present in all movements. This superior force may result from the subacromial impingement syndrome, except for critical zones of impingement caused by the different throwing arm movements. These findings suggest that the mechanisms of throwing arm injuries are closely related to differences in throwing arm movements.

A Three-dimensional analysis on mechanical energy flows of torso and arm segments in baseball throw / 体力科学

Twenty-four male university baseball players were each requested to throw a baseball, and filmed using the direct linear transformation method of three-dimensional (3D) videography. 3 D coordinates of landmarks were obtained. Resultant joint forces and resultant joint torques in the wrists, elbows, shoulders, neck, and upper torso joints were calculated using the inverse dynamics method. The mechanical powers caused by the resultant joint forces (joint force power) and by the resultant joint torques (joint torque power) of each segment were calculated, and the mechanical work was also obtained by integrating the joint torque powers with time. Peak values of energies of the upper torso, upper arm, forearm, hand, and ball appeared in sequence from the proximal segment to the distal segment. The joint force powers in any segment were markedly larger than the joint torque powers. Little joint torque power was produced in the wrist throughout the throwing motion. The negative joint force power and joint torque power at the proximal end of the upper torso were rapidly increased immediately after the foot contact stride. It was clarified that the appearance of the large energies in the distal throwing arm segments during the final phase of throwing motion were caused mainly by transfer of the energies produced by the motions of the torso and shoulder joints. This paper discusses the mechanical energy flows of the upper torso and upper limb segments during the motion of baseball throwing.