創新之動態轉動慣量球棒對揮擊期間揮棒速度與肌肉活化之影響

Effects of innovative dynamic moment of inertia bat on swing speed and muscle activation during batting

目的：比較本研究創新之動態轉動慣量（dynamic moment of inertia, DMOI）球棒與正常球棒在跨步期、揮棒期、擊球瞬間、餘勢動作期等揮棒過程之揮棒速度與肌肉活化的差異。方法：大專甲組棒球隊8名野手為對象。利用紅外線動作捕捉系統（250Hz）及Biovision信號擷取系統（1000Hz），同步擷取球員在執行兩種不同球棒揮擊過程中的揮棒速度與肌肉活性。以相依樣本t考驗進行統計分析。結果：揮棒速度結果顯示，DMOI球棒在跨步期（0.91±0.32公尺/秒vs. 0.65±0.28公尺/秒）與揮棒前期（3.43±1.69公尺/秒vs. 2.84±1.61公尺/秒）顯著快於正常球棒；但正常球棒在揮棒中期（12.84±2.53公尺/秒vs. 11.19±1.64公尺/秒）、揮棒後期（22.54±2.15公尺/秒vs. 20.22±2.41公尺/秒）和擊球瞬間（23.09±1.91公尺/秒vs. 21.27±2.57公尺/秒）則顯著快於動態轉動慣量球棒。肌肉活化結果顯示，DMOI球棒在揮棒期的跟隨手屈腕肌（44.27±17.19%最大自主收縮maximal voluntary contraction [MVC] vs. 34.07±11.46%）及揮棒後期的前導手肱三頭肌平均肌電（92.57±40.66% MVC vs. 64.13±30.48% MVC）均顯著大於正常球棒。結論：使用DMOI球棒進行揮棒動作時，會有較高的揮棒初期速度，在揮棒中期隨著DMOI球棒的滑動塊移動至球棒最外側並產生碰撞，而增大球棒的轉動慣量，使揮棒後期與擊球瞬間的揮棒速度變慢，同時增加揮棒負荷使相關肌群有較高的肌肉活化。建議可在棒球揮擊訓練中使用DMOI球棒，以促進揮棒初期速度與揮棒後期的肌肉活化。

Introduction: To assess differences in swing speed and muscle activation during swinging, including the wind-up, swing, bat-ball contact moment, and follow through, between an innovative baseball bat with dynamic moment of inertia (DMOI) and a conventional baseball bat. Methods: Eight division-1 college baseball players participated in this study. The Motion Analysis System with 10 infrared cameras (250 Hz) and a biovision signal acquisition system (1000 Hz) were used to simultaneously record swing movement and muscle activity during the swinging of the DMOI bat and the regular bat. The dependent sample t-test was used for statistical analysis. Results: Significantly (p < .05) higher swing speeds during the stride phase (0.91±0.32 m/s vs. 0.65±0.28 m/s) and the pre-swing phase (3.43±1.69 m/s vs. 2.84±1.61 m/s) were achieved with the DMOI bat than with the conventional bat. However, the conventional bat was significantly (p < .05) faster during the mid-swing phase (12.84±2.53 m/s vs. 11.19±1.64 m/s), the late-swing phase (22.54±2.15 m/s vs. 20.22±2.41 m/s), and at the moment of impact (23.09±1.91 m/s vs. 21.27±2.57 m/s) than the DMOI bat. During the swing phase, average electromyographic (EMG) activity in wrist flexor in the trailing hand was significantly (p < .05) greater (44.27±17.19% vs. 34.07±11.46% maximal voluntary contraction [MVC]) and the leading arm's triceps brachii activity during the late swing phase was significantly (p < .05) higher (92.57±40.66% vs. 64.13±30.48% MVC) with the DMOI bat than with the conventional bat. Conclusion: Swinging a DMOI bat results in a higher initial swing speed. As the BMOI bat’s sliding block moves to the outermost part of the bat during the mid-swing phase and collides, it increases the bat’s moment of inertia, leading to a decrease in swing speed during the late swing phase and at the moment of impact. This also increases the swing load, resulting in higher muscle activation in related muscle groups. Incorporation of DMOI bats in baseball swing training is recommended to enhance initial swing speed and muscle activation in later stages.