目的：探討不同年齡少棒內野手在下肢牽張能力與守備接傳週期的相關性和差異，也探討接球時不同腳步踩踏方式在守備接傳參數與傳球球速的差異。方法：招募29位少棒內野手為研究對象，進行內野守備及下肢爆發力的檢測，在內野守備檢測中，研究人員以手拋滾地球的方式，拋向守備員起始位置右方2公尺之位置。每位球員輪流以正手接球的方式完成接球並傳向一壘，每位球員都各進行2球有效球的測試，以Pocket Radar測速器記錄傳球球速，並以攝影機進行拍攝，以利後續進行接傳週期參數的記錄。在下肢爆發力的檢測中，以PASCO測力板對每位球員分別進行CMJ與SJ檢測各兩次，檢測後以pro-GRF力學分析軟體對下肢牽張收縮能力參數進行輸出及記錄。以接球後耗費不同腳步數分為2步組、3步組及4步組，以單因子變異數分析比較守備接傳週期參數、傳球球速之差異。以年齡分為9歲組、10歲組及11歲組，以單因子變異數分析探討三組在守備接傳週期參數、傳球速度及下肢牽張收縮能力參數的差異。將守備接傳週期參數、傳球速度分別與下肢牽張收縮參數做皮爾森積差相關的比對。以皮爾森積差相關探討接傳週期參數間、傳球球速的相關性。結果：11歲組下肢推蹬力峰值顯著大於9歲組，在守備接傳週期參數中9歲組、10歲組、11歲組三組無顯著差異，在10歲組與11組間發現持球時間皆與腳離地期產生相關相較於，相較於10歲組及11歲組，9歲組在傳球球速、接傳各分期時間之間的相關並未顯著，在9歲組和11歲組中傳球球速皆與向心功率峰值的PSAP有關，而與9歲組和10歲組相比，11歲組在傳球球速、接傳各分期時間與下肢牽張收縮能力的相關較為顯著，但有些顯著結果的發現不符合常理，根據過往文獻比對可以推論可能仍然與兒童的神經肌肉骨骼發展有關聯。本研究將未墊步的選手進行分析，結果發現，9歲組、10歲組與11歲組三組內野手在腳離地期佔持球時間比例無顯著差異，跨步期時間佔持球時間比例有顯著差異，其中10歲組顯著大於9歲組和11歲組，加速期時間佔持球時間比例有顯著差異，其中9歲組顯著大於10歲組和11歲組。結論：下肢肌力在高年級與中年級間的選手間是有所差距。而對於守備接傳週期參數來說，在9歲至11歲間，年齡可能不是會對於這些參數造成差異的因素。在10歲組與11歲組間持球時間皆與腳離地期產生相關，證實了接球後踏出的第一步所花費的時間會對於持球時間的多寡產生重大影響。欲在這些接傳週期參數間及傳球球速發現關聯性，研究對象須有一定的球技水平才能提高研究的準確性。接傳耗費2步的選手中，9歲組、10歲組、11歲組三組選手都在腳離地期花費了超過一半的時間，可以得知在未墊步的情況下，選手在接球後會延緩軸心腳著地的時間，來給予上肢做轉換的緩衝，而在剩餘的時間中，10歲組選擇將較多的時間分配在跨步期，9歲組則將較多的時間分配在加速期。意味著10歲組的選手在軸心腳著地後，會花費較多的時間在軸心腳蓄力，而9歲組則是花費較多的時間在前導腳的推蹬。

Purpose: To explore the correlation and differences between lower limb explosive strength and defensive relay cycle among infielders of different ages in youth baseball, and to investigate the differences in defensive relay parameters and throwing ball speed with different stepping methods during catching. Methods: Twenty-nine youth baseball infielders were recruited for the study. Testing was conducted for infield defense and lower limb explosive strength. In infield defense testing, researchers threw ground balls towards infielders positioned 2 meters to the right of the starting position using a hand-rolled method. Each player took turns catching the ball with an overhand grip and throwing it to first base. Each player underwent two valid tests, and the throwing ball speed was recorded using a Pocket Radar while filming with a camera for subsequent recording of relay cycle parameters. Lower limb explosive strength was tested using PASCO force plates, with each player undergoing CMJ and SJ testing twice. After testing, parameters of lower limb extension and contraction capacity were outputted and recorded using pro-GRF biomechanical analysis software.The relay cycle parameters and differences in throwing ball speed were compared using one-way analysis of variance among groups categorized by the number of steps taken after catching (2-step group, 3-step group, and 4-step group). Age groups (9-year-olds, 10-year-olds, and 11-year-olds) were compared using one-way analysis of variance to explore differences in relay cycle parameters, throwing speed, and lower limb extension and contraction capacity parameters. Pearson product-moment correlation was used to compare relay cycle parameters and throwing ball speed with lower limb extension and contraction parameters. Result: The peak lower limb pushing force of the 11-year-old group was significantly greater than that of the 9-year-old group. Among the defensive transfer cycle parameters, there were no significant differences between the 9-year-old, 10-year-old, and 11-year-old groups. However, between the 10-year-old and 11-year-old groups, it was found that the holding time was correlated with the period of the foot leaving the ground. In comparison to the 10-year-old and 11-year-old groups, the 9-year-old group did not show significant correlations between passing ball speed and various stages of receiving and passing times. Passing ball speed in both the 9-year-old and 10-year-old groups was correlated with peak concentric power of the lower limbs, whereas compared to the 9-year-old and 10-year-old groups, the 11-year-old group showed more significant correlations between passing ball speed, various stages of receiving and passing times, and lower limb extension contraction ability. However, some significant findings did not align with expectations, and it can be inferred from previous literature comparisons that they might still be related to the neuro-musculo-skeletal development of children. This study analyzed non-stepping players and found that there were no significant differences in the proportion of time spent with the foot off the ground during the holding period among the 9-year-old, 10-year-old, and 11-year-old infielders. There were significant differences in the proportion of time spent in the stride phase during the holding period, with the 10-year-old group significantly greater than the 9-year-old and 11-year-old groups. There were also significant differences in the proportion of time spent in the acceleration phase during the holding period, with the 9-year-old group significantly greater than the 10-year-old and 11-year-old groups. Conclusion: There is a difference in lower limb strength between players in higher grades and those in middle grades. For defensive transfer cycle parameters, age may not be a differentiating factor among ages 9 to 11. Holding time was correlated with the period of the foot leaving the ground between the 10-year-old and 11-year-old groups, confirming that the time spent taking the first step after catching the ball significantly influences holding time. To discover correlations between these transfer cycle parameters and passing ball speed, subjects need to have a certain level of ball skills to enhance the accuracy of the study. The lower limb explosive force utilized by youth infielders when throwing is related to the reflex ability of lower limb muscle extension contraction. Among stepping players, all three age groups spent more than half of their time during the foot-off period, indicating that players delay the time to land the axis foot after catching the ball to provide a buffer for upper limb conversion. In the remaining time, the 10-year-old group allocated more time to the stride phase, while the 9-year-old group allocated more time to the acceleration phase. This means that 10-year-old players spend more time storing energy on the axis foot after landing, while 9-year-old players spend more time pushing off with the leading foot.
Keywords: infield, stepping, extension-contraction, holding time, throwing ball speed

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