脊柱穩定是藉由關節韌帶及肌肉組織來共同維持，因此對於下背痛病患而言，脊柱穩定訓練成為很盛行的運動治療方式之一。脊柱穩定的動作可藉由訓練核心肌群來增加脊柱的穩定性，這些肌群包括腹部肌群、背部肌群及其它深層肌群。治療球(Swiss ball)介入的脊柱穩定運動，對於下背痛患者而言，亦是一種治療方式運用。根據近年來的研究發現，在運動過程中，人體的質量中心（Center of Mass, COM）可以做為穩定性評估的參考指標之一，並且穩定性是在人體運動過程中為不可或缺的因素之一，與質量中心在支持面(base of support , BOS) 的投影有關，在現今的研究中對於探討核心穩定運動的相關研究甚多，但是極少有研究利用質量中心與壓力中心( Center of Pressure, COP)的參數來探討姿勢控制方面的相關議題。對於利用治療球來維持在俯撐雙腳置於治療球球上的動作，球的大小可能會對訓練結果有所影響的，故在此實驗中的主要目的在於探討在不同大小的支撐面和球上執行運動時，其腹部與背部的肌肉活化狀態與身體姿勢穩定控制能力是否有所差異。
本實驗徵召18位健康受試者(11男性與7位女性)，採用俯撐雙腳置於治療球上的動作，並使受試者雙腳至於自行設計的可調式模擬球上，並利用動作分析系統、力板以及表面肌電訊號來觀測運動過程中質量中心與壓力中心的位移，質量中心和壓力中心間的偏移距離(separation distances)和偏移角度(inclination angles)，同時並探討肌肉活化的狀態。在全身上的特定解剖位置貼上反光球，評估受試者在自行設計的可調式模擬球上，兩種不同的支撐面與三種不同的高度上其質量中心的位移量。表面肌電訊號則是用來偵測腹直肌、腹外斜肌、豎棘肌及多裂肌在運動過程中的活化狀態。
研究結果發現當在運動過程中球越大時，其質量中心的前後向與左右偏移量亦會有增大的趨勢，同樣的現象也可以在壓力中心參數中發現，換句話說當質量中心的高度越高時，對於維持身體穩定的難度亦會隨之增加。倘若就兩種不同接觸面積來做探討可發現，當在不穩定的接觸面積上運動時，其質量中心的前後與左右偏移量和壓力中心的左右偏移量皆有顯著性的增加，故可得知當在一個不可預測的接觸面積上運動時對於維持身體的穩定會有一定的難度存在。對於質量中心和壓力中心的參數來做深入探討，當球的大小越大時，其質量中心和壓力中心間偏移角度會有明顯增加的趨勢，但是就兩種不同的接觸面積而言，在前後向的質量中心和壓力中心偏移角度就無顯著性的差異存在，也就是說當身體處於一個較低的姿勢下，其較容易保持身體的平衡。
在較不穩定及較小的接觸面積下，腹部肌群與背部肌群會有較強的收縮產生，根據之前的研究發現當在治療球上執行核心運動時其肌肉的活化會增加，也就是說運用治療球的介入可用來提供腹部肌群及背部肌群的訓練。然而在小球上執行俯撐雙腳置於治療球上的動作時，其軀幹肌群的活化程度皆會比在大球上來的高，猜測可能是由於在小球上執行動作時，手部所產生的力量較沒大球上來的大， 所以需要較多的軀幹肌群活化來維持身體的穩定。
研究結果可提供臨床醫師進行脊椎穩定運動時做為一個參考指標，同時可進行有效性和安全問題的評估。

Spinal stabilization training is one of the most popular therapeutic exercises for patients with low back pain. Spinal stabilization movements can increase proximal spinal stability by training the core muscles including abdominals, back extensors and deep muscles. The contact area, for example, used ball (Swiss Ball), could be the other method to modify the training intensity for spinal stabilization exercise. In recent years, studies had suggested that motion of the whole body’s center of mass (COM) had could be identified as the stabilization. Stabilization is an essential component of human movement, and associated with projection of the COM within the base of support (BOS). For stability ball exercise kept at a roll out position with both feet on top of a ball, the ball size is hypothesized to have effects on the training outcomes. Therefore, the purpose of this study was to investigate the effects of ball size and its ground contact area and on muscle activation intensity of abdominal muscles and back extensors and the control of whole body balance.
Eighteen healthy volunteers (11 male and 7 female) were participated in this study. The selected stabilization movement was roll out exercise. This study used motion analysis system, force plate and surface electromyography (EMG) to measure COM, center of pressure (COP) displacements, COM-COP inclination angles and muscle activation during movements.
For this study, the results showed that when the ball size was bigger, the anterior-posterior (AP) (p=0.000) and medial-lateral (ML) (p=0.000) sway of COM were larger. The AP (p=0.004) and ML (p=0.000) sway of COP was greater during exercise in big ball size. The higher COM increased difficulty in maintaining stable posture. For two different ground contact areas, when exercise in unstable support base, there were significantly increased in AP (p=0.000) and ML (p=0.000) sway of COM, ML (p=0.000) sway of COP. In an unpredictable surface, it is more difficult to maintain body in balance. When ball size was small, AP (p=0.002) and ML (p=0.006) COM-COP inclination angles were smallest. However, there were no significant differences in AP COM-COP inclination between (p=0.302) two ground contact areas. It indicates that it is easier to maintain body balance when the whole body is kept at a lower posture.
Abdominal and back muscles had stronger contraction in unstable ground contact with small size of base of support than in big (stable) base of support. The legs supported on the ball caused the increased muscle activation in agreement with previous studies. It indicated that the ball can provide training abdominal and back muscles. And when kept roll out position on smaller ball size, the muscle activation of abdominal and back extensor muscles were higher than in bigger one. May be during exercise in small ball, the hands provide less force than exercise in bigger ball, so there is more muscle activation of trunk needed to keep body in balance.
The findings may provide a reference for the clinicians to conduct spinal stabilization exercise while considering the effectiveness and safety of this intervention.

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