投球フォームとボール・リリース時の肩関節負荷

Abstract

The shoulder and elbow joint of a baseball pitcher are frequently overused by the repetition of throwing. The overuse causes throwing injuries of the shoulder or the elbow joint. To prevent the injuries or find them as soon as possible at an early stage, it is important to understand and evaluate each individual’s baseball pitching motion exactly. Therefore, we are developing an analysis system of the baseball pitching motion for clinical use.The pitching motion is classified into four major pitch styles, as follows: overhand, three-quarter, sidearm, and underhand. In the long-term clinical experience in Nobuhara Hospital, we have expected that one of the causes of throwing injuries is related to the pitch styles. A previous paper reported that different pitch styles produced different kinematic and kinetic results of pitching motion analysis (Matsuo, 2000). The difference of pitch styles will influence analysis results of the pitching motion.The classification, however, was performed qualitatively by a person having baseball experience. There is no standard method to classify the pitch styles quantitatively. The pitch styles also have to be classified quantitatively in order to investigate various factors of injuries. The aim of this study was to classify baseball pitchers of various levels into four pitch styles quantitatively and compare the kinematic and kinetic parameters.We measured the pitching motions of the baseball pitchers, using a motion-capture system at 500 Hz. Ages of the 104 subjects of this experiment ranged from 10 to 38 years. We suggested four kinematic parameters in order to classify the pitch styles. The measured pitching motions were then classified into four pitch styles, using multivariate discriminant analysis. The correct answer rate was 89.4%.ANOVA revealed significant differences of the antero-posterior direction of resultant force at the time of ball release among four classified pitch styles. The A-P force vector had high correlation (r=0.82) with horizontal adduction angle of the upper arm. The shear force on the shoulder is one of causes of injury during pitching. To reduce the risk of shoulder injuries, we believe it is necessary to reduce shear forces on the pitcher’s shoulder. Our results showed that the sidearm group had 50% lower shear force than the other groups.In conclusion, we suggested four kinematic parameters in order to classify the pitch styles. This result shows that these parameters are appropriate for classifying the pitch styles without relation to age or skill differences. The results of kinematic and kinetic parameters showed the significant differences between four pitch styles. Our next task is to increase the number of subjects, especially sidearm and underhand pitchers.