背景與目的：預期性姿勢控制（anticipatory postural control）指的是發生於主要動作之前身體姿勢的系列反應（如姿勢肌肉活化、身體壓力中心位移、身體旋轉力矩改變等），其目的為降低主要動作對身體穩定度可能造成的干擾，以增加執行動作時的身體穩定度。過去的研究結果顯示，預期性姿勢控制會隨動作對身體穩定度所造成的干擾程度的增大而隨之提早產生且控制幅度增加。然而以往的研究以探討動作速度或者是釋放重物等對身體穩定度所造成的干擾為主，甚少探討伸手距離對預期性姿勢控制的影響。此外，此預期性姿勢控制的能力是否會有年齡的發展效應，至今仍未有一致見解。本研究目的為探討伸手距離對預期性姿勢控制的影響，並探討5-12歲兒童之預期性姿勢控制的發展。方法：本研究共徵收63位受試者，依實際年齡共分為五組：5-6歲、7-8歲、9-10歲、11-12歲及成人。每位受試者皆依指令執行手臂前伸動作碰觸前方一燈鈕，燈鈕擺放位置依受試者的手長及最大前伸距離調整出四種距離：手長加最大前伸距離、手長加二分之一最大前伸距離、手長、手長減二分之一前伸距離。預期性姿勢控制反應則以身體壓力中心、旋轉力矩、手部動作反應時間及姿勢性肌肉反應來探討。統計分析使用二因子重覆變異數分析探討距離與年齡的主要效果與交互效應。結果：身體壓力中心與旋轉力矩所顯示之預期性姿勢控制反應的間值(latency)與最大量值(peak amplitude)皆因伸手距離與年齡不同而有顯著差異。當距離增加時，身體壓力中心向後位移與旋轉力矩的順時針方向的間值會增加且反應量值也增加；反應時間隨伸手的距離增加而增加、隨年齡的增加而減短，伸手距離與年齡之間沒有交互效應存在。同時預期性姿勢控制反應的間值與最大量值皆分別受手部動作反應時間與動作干擾影響，故本研究將預期性姿勢控制反應的間值與最大量值分別以手部動作反應時間與動作完成時最大干擾值作標準化，結果顯示標準化間值受伸手距離影響，隨距離增加而增加，但標準化間值與標準化最大量值並不受年齡的影響。至於姿勢肌肉之反應在兒童受試者間的變異性太大，看不出距離的影響與年齡的趨勢，但成人的姿勢肌肉反應清楚地顯示當伸手距離大於手長，前側肌肉活化提早；當伸手距離小於手長，則後側肌肉活化提早。結論：預期性姿勢控制會隨伸手距離對身體穩定度所造成的干擾程度之差異而有不同的控制表現，但此表現在5-12歲之間與成年人之間並無顯著差異。故我們認為預期性姿勢控制於5歲時就已發展至類似成人表現，會依伸手距離對身體穩定度所造成的干擾程度之大小而調控其身體反應。

Background and Purpose: Anticipatory postural control (APC) was defined as a series of postural adjustments in term of muscle activity, center of pressure (COP), and vertical torque (Tz) preceding a voluntary movement to maintain postural stability disturbed by forthcoming perturbation. The results of previous studies have shown that APC would be influenced by the magnitude of perturbation. However, studies that examined the effect of magnitude of perturbation were focus on the speed of arm-raising movement. There is a limited study of examining the effect of reaching distance on APC. Moreover, the age effect on APC was controversial and the developmental trend of APC was still unclear. The purposes of this study were to examine the effect of target distances on APC and to investigate the developmental trend of the effect of target distances on APC in a forward reaching task. Method: Sixty three children and young adults were recruited for the study. They were divided into 5 groups by age. Each subject was instructed to perform a forward reach to press a button which was placed at four distances adjusted by arm length and the maximal forward reach distance. The data of COP, Tz, reaction time (RT) and muscle activity were collected simultaneously. Main effects of group, reaching distance, and their interaction were tested using a two-way ANOVA with repeated measures. Results: The results showed that the latency of backward shift of COP and clockwise-direction of Tz increased as reaching distance increased and age decreased; the peak amplitude of backward shift of COP and clockwise-direction of Tz increased as reaching distance increased and age increased. RT was longer as reaching distance increased and age decreased. However, the latency and peak amplitude of APC were affected by RT and perturbation (the peak amplitude of forward shift of COP and counterclockwise-direction of Tz) respectively. Therefore, we normalized the latency and peak amplitude of APC by RT and perturbation respectively. The results showed the normalized latency and peak amplitude of APC were affected by reaching distance, not by age. The pattern of muscle activity was variable at the children, but consistent in adults. In adults, the ventral side muscles were activated earlier than dorsal side muscles when the reaching distance was longer than arm length. The pattern was just opposite when the reaching distance was shorter than arm length. Conclusion: According to the results of our normalized APC, APC is affected by reaching distance, but not influenced by age. The larger the distance is, the longer (onset earlier) the latency and the bigger the amplitude of APC will be. Children at the age of 5-year-old may have developed their APC in standing while performing a forward reach task to the similar level as young adults.

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