本研究的目的是針對不同年齡層的投手做投球動作的比較，以找出投球過程中運動學、動力學及時間的參數的差異，及找出各年齡層影響球速的有效變數。本研究以國中、高中手及大學投手各10名（67±12kg，167±11cm；74±9kg，179±5cm；88±10kg，179±7cm）為研究對象，以兩塊測力板 (Kistler) 搭配動作分析系統 (Vicon MX13) (200Hz) 來收集投手對前方3m的網子全力投10球的影像。將最快的3球的參數平均，代表該受試者的參數，以單因子變異數分析(ANOVA)法來檢測3組投手的差異，並進行事後比較。再自各受試者中取6球，依不同年齡層分別進行迴歸分析，找出各個年齡層中影響球速的參數。。
研究結果發現，國中投手球速較高中和大學慢，高中和大學間無差異。在運動學和時間參數上，國中投手和其他兩組相比，在手臂加速期中的肩關節內旋範圍較大，加速時間較長。高中投手則是在著地瞬間的前導腳膝關節彎曲角度較小，加速期中的肘關節伸展速度峰值及肩關節內旋速度峰值較大，同時肩關節外旋角度峰值發生相對時間較晚，手臂加速期也時間較短。
在上肢動力學參數上，國中投手在手臂上舉期的肘關節前翻力矩、肩關節內旋力矩和手臂減速期的肘關節軸向力量、肩關節向後力量、肩關節軸向力量都低於其他兩組的值。在下肢動力學參數上，軸心腳的髖膝踝三關節軸向力量、髖關節內收力矩、膝踝兩關節的彎曲力矩值都有依年齡增加的趨勢，並且都在國中和大學間出現差異。前導腳則是在地面反作用力和膝踝兩關節軸向力量上有類似的差異，但髖關節軸向力卻未在三組間有任何差異。
在影響球速的因子中，國中投手分別是手臂上舉期肩關節內旋力矩峰值、跨步幅度和肘關節彎曲角度峰值等三參數影響較大。高中則是手臂上舉期肩關節內旋力矩峰值、球離手瞬間的前導腳膝關節彎曲角度、軀幹旋轉速度峰值和身高等四參數影響較大。大學是手臂上舉期肩關節內旋力矩峰值、前導腳著地瞬間前腳膝關節角度、肩關節外旋角度峰值和肘關節伸展速度峰值等四參數影響較大。
由結果得知，國中投手的投球動作和其他兩組大致相同，上、下肢的動力學參數都最小。到了高中，球速、身高、關節活動速度、上下肢動力學參數都變大。到大學時，體重和大部份下肢動力學參數變大，但球速和上肢動力學參數卻未增加。三組中的上肢力矩的參數對球速都很有影響力，據此推測造成台灣大學投手球速停滯的原因，可能是大學投手上肢的力矩不足。

The purpose of this study was to find the difference in pitching mechanics among various ages by comparing the kinematics, temporal and kinetics parameters. and investigate the relationship of biomechanical factors to baseball pitching velocity in each group. Ten pitchers of each level were served to be subjects (junior high school:67±12kg， 167±11cm；senior high school:74±9kg，179±5cm；college 88±10kg，179±7cm). Two forceplates (Kistler, 1000 Hz) and a 3-D motion capture system (Vicon MX13,200Hz) were used to collect kinetics and kinematics data. The subject threw to a target (40×60cm) which is 3 m in front of the force plates. Data from the 3 fastest successful trials were averaged for each subject. A one-way ANOVA was conducted for each parameter to identify differences among the three levels (junior, senior high school, college). Then 6 trails of each subject were chosen for regression analysis. Step-wise regression analysis was used to finding the relationship of biomechanical factors to baseball pitching velocity at each age level.
The result showed the ball speed of the junior high school pitchers (JHP) was slower than senior high school (SHP) and college pitchers (CP), and no difference existed in SHP and CP. At kinematic and temporal parameters, the JHP had more shoulder rotation range of angleand longer arm acceleration phase than the other two groups. The SHP had less lead legknee flexion at lead foot contact ground, more elbow extension and shoulder rotation velocity at arm acceleration time. In addition, their peak shoulder external rotation angle appeared later, and the arm acceleration phase time was shorter.
At upper limbs kinetic parameters, the peak elbow varus moment, peak shoulder internal rotation moment, peak elbow axis force, and peak shoulder poster force of JHP are lower than other two groups. At pivot foot kinetic parameters, the peak axis force in the three joints, hip adduction moment, ankle and knee flexion moments were existed a tendency to increase with age. At lead foot kinetic parameters, the ground reaction force and the axis force of knee and ankle increase with age, but no difference existed in the hip joint.
In JHP group, 3 biomechanical factors were associated with ball velocity. They were peak shoulder internal rotation moment in arm cocking phase, stride length, and elbow peak flexion angle. In SHP group, 4 biomechanical factors were associated with ball velocity. They were shoulder internal rotation moment in arm cocking phase, lead foot knee flexion angle at ball release, peak upper trunk angular velocity and body hight. In CP group, 4 biomechanical factors were associated with ball velocity. They were peak shoulder internal rotation moment in arm cocking phase, peak lead foot knee flexion angle at foot contact, peak shoulder external rotation angle and peak elbow extension angular velocity.
. As the result showed, the pitching mechanics kinematics of JHP are similar with other two groups. They have smallest upper and lower limbs kinetics. From JHP to SHP, ball velocity, body hight, upper limbs joint angular velocity, upper and lower limbs kinetics all increased. From SHP to CP, body mass and, lower limbs kinetics increased, but ball speed and upper limbs kinetics show no difference. The upper limbs kinetics was an important biomechanical factors associated with ball velocity in all three groups. We believe that the insufficiency of upperlimbs kinetic of CP cause their ball velocity similar with SHP.

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