姿勢控制是一個複雜的過程，包含接受與組織感覺輸入，計畫並經由促動協同的姿勢反應來執行動作以達到維持平衡之目標，也就是在所處的感覺環境中控制重心於支撐底面積內。姿勢干擾是指突然的改變狀態使個案偏離平衡狀況，姿勢干擾可包括生理性干擾、訊息性干擾及力學干擾。力學干擾可經由對個案之身體如頭、軀幹或肢體等部位施加外力以干擾其平衡，而臨床或實驗中最常見的力學干擾是支持面的干擾，也就是移動個案之站立支撐底面積，以引發維持平衡的姿勢反應。這些支持面干擾正如個案滑倒、絆倒、站在不規則地面或站在車子裏突然的加速或減速。
已有數種提供支持面干擾之平衡台被設計來進行平衡反應的研究，給予的干擾包括前/後平移、趾向上/向下(踝背屈/蹠屈)旋轉、多方向平移與旋轉干擾及連續性正弦曲線平移與旋轉干擾等。本實室設計了一個三自由度動作之姿勢干擾平衡台，提供前/後平移、上/下旋轉及左/右旋轉，以進行平衡評估及訓練。為了確保此平衡台可以做為提供姿勢干擾之平衡台，必須檢驗其精密度與準確度。旋轉與平移為兩種干擾型式，且向前平移與向上旋轉造成身體向後擺動，向後平移及向下旋轉造成身體向前擺動，不同干擾型式及不同身體擺動方向如何影響姿勢反應仍然未知。相較於大量平移及上下旋轉干擾的研究，左右旋轉干擾的研究較少。
所以，本研究目的在：1)檢驗三自由度動作之姿勢干擾平衡台的精密度與準確度，2)進行平移及上/下旋轉干擾之運動學姿勢反應的初步研究，3)探索平移及上/下旋轉干擾的姿勢反應，以檢驗干擾型式及擺動方向對姿勢反應的影響，及4)探索左/右旋轉干擾的姿勢反應，以檢驗旋轉速率與大小及向左/向右旋轉與張眼/閉眼旋轉對姿勢反應的影響。本研究利用肌電圖及運動學分析法檢驗正常青年針對各種支持面干擾的姿勢反應，我們相信了解維持平衡所需要的肌電圖及運動學因素將有利於設計增進姿勢平衡的治療方法及預防跌倒的策略。
研究結果顯示：1) 三自由度姿勢干擾平衡台為一個提供可靠及準確姿勢干擾的工具，2) 初步的檢驗平移與上/下旋轉干擾之運動學反應結果符合文獻中相關之研究結果，3) 平衡台干擾型式(前後平移或上下旋轉)與身體擺動方向對姿勢反應造成影響，平移型式及身體後向擺動造成較大的上身不穩定以引發快速肌肉反應與快速及較大的髖及膝關節動作；平移及垂直重心移動時間與大小也受平衡台干擾型式影響。4) 左/右旋轉干擾的速率及大小對肌肉反應的時間及大小沒有影響，但對關節動作及重心位移的時間與大小都有影響。肌肉反應、關節動作與重心位移等大部分變項在左/右旋轉或張眼/閉眼兩種情境下沒有顯著差異。本研究結果讓我們了解平衡評估與訓練時，平衡台干擾特性與反應策略，且提供我們正常個案平衡反應數據以作為與平衡異常病人比較之基礎。

Balance is a complex process involving the reception and organization of sensory inputs, planning and execution of movement by activating postural response synergy, to achieve a goal requiring upright posture. It is the ability to control the center of gravity over the base of support in a given sensory environment. Postural perturbation is a sudden exposure to conditions that displace the body away from equilibrium. These perturbations could consist of physiological, informational and mechanical perturbations. Mechanical perturbations can be applied on any body part such as push to the trunk, head or limbs. The most common experimental approach is to perturb the support surface, which displaces the base of support upon which a subject is standing. These support surface perturbations are like a slip, trip or acceleration or deceleration of support surface during vehicular motion.
Several types of support surface perturbation techniques have been developed to elicit subjects' balance reaction, including toe-up/down rotation, anterior/posterior translation, continuous sinusoidal translation and rotation, and multidirectional surface translation and rotation. In our laboratory, we have designed and built a moveable platform with three-DOF movements that can provide forward/backward translation, upward/downward rotation (pitch rotation), and right/left rotation (yaw rotation) for balance assessment and training. To ensure the usefulness of the instrument for providing postural perturbations, the precision and accuracy of the newly developed moveable platform have to be examined. Platform translation and rotation are two types of biomechanically different perturbations. Forward translation and upward rotation cause posterior body sway while backward translation and downward rotation cause anterior body sway. Whether there are fundamental differences in postural responses between the two types of perturbation and the two body sway directions remains unclear. In contrast to a large number of studies that have focused on postural reactions to surface translation and rotation in the pitch and/or roll planes, few studies have examined postural control in response to surface rotation in the horizontal plane
Therefore the purposes of this thesis were to 1) examine the precision and accuracy of the three-DOF moveable platform's movements, 2) preliminarily investigate kinematic postural responses to the platform, 3) explore the postural responses to translational and upward/downward rotational perturbation to examine the effects of the type and direction of support surface perturbation on postural responses, and 4) explore the postural responses to right/left rotational perturbations to examine the effects of velocity and amplitude on postural responses, and to compare the responses between right and left rotation and between the eyes-open and eyes-closed conditions. Electromyography (EMG) and kinematics were applied to analyze postural responses. It was believed that a basic understanding of the EMG and kinematic factors required for balance will lead to better therapeutic methods for improving posture and balance, and to strategies that can be used to prevent falls.
The results showed that 1) the three-DOF moveable platform is a reliable and valid instrument for providing postural perturbations. 2) The preliminary investigation of the kinematic postural responses to translational and upward/downward rotational perturbation showed that this platform is a useful apparatus for balance research. 3) For translational and upward/downward rotational perturbations, the results showed that there was a direction-specific muscle response pattern for translational perturbation. The timing of the muscle and joint responses did not show an ascending pattern; instead, the major contributor for balance correction would initiate first. Perturbation type and body sway direction had significant effects on postural responses as translational and posterior body sway perturbation induced larger upper body instability and evoked faster muscle activation as well as faster and larger hip or knee joint movements. The perturbation type and body sway also affected onset latency and the magnitude of horizontal and vertical COM displacements. These findings provide insights into an appropriate support surface perturbation for evaluation and training of balance. 4) For right/left rotational perturbation, the results showed that median latency postural responses were induced for right/left rotation, and distal ankle and knee muscles were activated earlier than the trunk and head muscle. The joint kinematics also demonstrated an ascending pattern, and the angle changes in axial rotation were larger than that in flexion/extension. Velocity and amplitude of the perturbation had no effect on the onset latency or magnitude of muscle activation. However, velocity and amplitude significantly affected joint movements and COM displacements. No significant differences were noted between right and left or between the eyes-open and eyes-closed conditions on most of the variables. The results provide normative data for healthy subjects that could be a basis for comparison with pathological patients.

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