ABSTRACT
To analyze the relationship of cause and effect between the onset of throwing disorders of the shoulder and decreased muscle strength, two studies were conducted at a baseball field. In study 1, shoulder joint muscle strength was measured when pain developed during practice and the relationship between pain onset and muscle strength was investigated. Decreased muscle strength was noted at the time of pain onset in 8.1% of players. Study 2 was a prospective study in which the relationship between changes in shoulder joint muscle strength from the start of pitching at the beginning of the season to one month later when competitive games began, and shoulder pain that appeared at the beginning of competitive games was analyzed. Based on the results, the possibility of shoulder joint muscle strength being a predictive factor for the onset of throwing disorders of the shoulder was investigated. However the pain group had greater muscle strength than the normal group at the beginning of the season. On the baseball field, the players’ throwing motions and joint function change daily, making it difficult to determine the reason for onset of disorders and injuries. These results suggest that onset of pain at the start of competitive games cannot be predicted from muscle strength at the beginning of the season.
ABSTRACT
The purpose of this study was to identify the angles of the shoulder complex which consist of glenohumeral joint, scapulothracic joint, and thoracic joint at the maximum external rotation (MER) of the shoulder complex during throwing in baseball players, and to analyze the correlation of each angle.The subjects were 19 collegiate baseball players. Throwing motion data was collected by three high-speed cameras and the three-dimensional (3D) coordinates of the shoulder complex were established by direct leaner translation method for the MER calculation. A 3D analysis was performed to obtain the external rotation (ER) angle of the glenohumeral joint, the posterior tilt angle of the scapula, and the extension angles of thoracic at MER of shoulder complex. The mean (±SD) value of the MER was 145.5±10.3°. The mean (±SD) values of the glenohumeral ER, the scapula posterior tilt angle and the thoracic extension angle at MER were 105.3±16.0°, 24.3±15.0°, and 9.1±7.2°respectively. Multiple linear regression analysis was used to relate the MER angle to each joint angle. The final linear regression model included the posterior tilting angle of scapula ( r=0.56, p＜0.05), and external rotation of the glenohumeral joint ( r=0.40, p＜0.05). Significant negative correlation was observed between the posterior tilting angle of the scapula and external rotation of the glenohumeral joint ( r=-0.52, p＜0.05). This finding suggested that scapula motion could be very important for the prevention of throwing injuries.
ABSTRACT
Anterior cruciate ligament (ACL) is the first restraint against anterior tibial translation (ATT) in the knee joint. Previous studies suggested that knee joint laxity might be increased by the repeated stress imposed on the knee joint. The purpose of this study was to demonstrate the effect of the repeated soccer ball kicking actions on the ATT in healthy knees. Forty female collegiate students volunteered for this study. KT-2000 knee arthrometer was used to measure ATT before and after the task. The findings demonstrated that the repeated kicking actions had no significant effect on the ATT in healthy knees. The maximum knee extension angle on the striking side was greater than the supporting side (p<0.05). Significant correlations between mean anterior translation and maximum knee extension angle were observed on both sides (p<0.05). The kicking force on a soccer ball resulted in no increase in the knee laxity.