注意力聚焦與站立形式對比目魚肌H反射的影響：年齡效應

Abstract

研究背景與目的: 注意力策略為動作控制的關鍵因素之一，動作注意力可分為內聚焦與外聚焦，內聚焦為在執行動作時將注意力聚焦於自身肢體動作，而外聚焦為在執行動作時將注意力聚焦於外在環境。研究證據顯示：當在執行動作過程中使用不同的注意力策略，可以影響動作精準度或姿勢平衡。目前多數研究支持使用外聚焦策略會有較佳的動作或平衡表現，其原因可能是外聚焦策略傾向以「反射控制模式」執行動作，使動作控制較自動化。然而，近期有學者提出，過去研究對於內聚焦的不當指令可能是造成動作表現差異的主要原因，且姿勢困難度與動作執行者的年齡都可能會影響聚焦策略的適用性。此外，關於聚焦策略對動作控制的影響目前尚無詳盡的神經機制探討，尤其對於「反射控制模式」，仍缺乏神經生理證據支持。因此，本研究目的為利用H反射與肌電圖工具，探討不同年齡族群(年輕組、年長組)於不同姿勢困難度下，以外聚焦、內聚焦策略執行動作時的動作表現與其相對應之神經肌肉活動。 研究方法: 本研究共徵求15位健康年輕受試者(23.87 ± 2.61歲)與15位健康年長受試者(66.73 ± 3.97歲)。於實驗進行前先將電子量角器黏貼於受試者右手肘關節、一塊壓克力板固定於受試者右前臂，再請受試者站立於不同平面(穩定平面、非穩定平面)，以內、外聚焦策略(注意手肘彎曲角度、注意板子傾斜角度)執行角度追蹤動作。行為表現參數為角度追縱誤差、角度追蹤速動方均根(jerk square mean)、左右向與前後向壓力中心晃動之方均根(root mean square)與近似熵(approximate entropy)；電生理參數為比目魚肌H反射、追蹤目標角度時之肱二頭肌之肌電訊號方均根數值、比目魚肌與脛前肌共同收縮係數(co-contraction index)。 結果與討論: 於角度追蹤動作表現結果，年輕與年長族群無論在穩定或不穩定姿勢下，使用內聚焦策略皆有較小的角度誤差值(p < .01)；而在年齡效應上，老年組於各情況下的角度誤差值皆大於年輕組(p < .01)，此外，老年組在使用外聚焦策略時，相較於穩定平面(18.22 ± 1.61度)，於不平穩平面時其角度誤差值會較低(15.65 ± 1.04度)(p < .05)。但角度追蹤速動方均根不論在注意力策略、姿勢困難度和年齡皆無顯著差異(p > .05)。於姿勢表現上，年輕組與年長組在使用外聚焦策略時，壓力中心晃動之方均根在前後與左右向皆較使用內聚焦策略時低，且有較高的壓力中心晃動近似熵數值，代表使用外聚焦策略時，有較自動化的姿勢控制。 於電生理量測參數上，年輕組於外聚焦策略下有較高的H反射數值，代表在外聚焦策略情況下，可偏向使用「反射控制模式」來維持姿勢穩定；此外，H反射也隨著姿勢困難度增加而減少。然而，注意力聚焦與姿勢難度對H反射調節在老年族群有降低的現象，H反射不受內外聚焦策略影響，且僅在內聚焦策略下，於不穩定平面時會降低H反射數值。而在外聚焦策略下，比目魚肌和脛前肌的共同收縮係數皆低於內聚焦策略下的數值，代表外聚焦策略較不會以加強主動肌-拮抗肌活動形式來穩定身體。在肱二頭肌肌電訊號上，老年組在使用內聚焦策略時，肱二頭肌的活動顯著高於外聚焦策略下的活動強度(p < .01)，代表內聚焦策略對於上姿勢角度追蹤策略仍是一個較耗能的方式。 結論與臨床應用: 在本次實驗中，姿勢控制與過往探討注意力聚焦的實驗結果一致，在外聚焦策略下有較好的姿勢穩定性和自動化控制，此外，本此研究利用H反射應證了外聚焦策略於年輕族群上，具有「反射控制模式」的神經生理特質。老年族群可能因需較高階的神經系統調控姿勢，因此注意力聚焦效應無法反應在H反射上。而在上姿勢動作表現上，發現使用內聚焦策略會有較高的動作精準度，與過往的研究結果並不一致，此差異可能是本研究使用的上姿勢作業為連續性追蹤動作，與以往研究使用的非連續性動作在動作控制上有不同特質導致。由於本次研究對象為健康年輕和老年族群，未來的研究可針對神經疾病患者進行相關神經電生理研究，為注意力策略提供更多有力的訓練價值。

Background and Purpose: Focus of attention has been reported as a critical factor for motor control. When performing a motor task, attention could be directed to the action itself (internal focus, IF) or to the effect of the action (external focus, EF). Most previous studies believed that EF strategy is superior to IF strategy with a “reflex-type control” mode. However, some researchers proposed worse performance of internal focus control may result from inappropriate instruction. Besides, both postural difficulty and aging effects are also the important factors for attentional focus control. And there is insufficient evidence for “reflex-type control” of EF strategy. The purpose of this study was to investigate the effects the attentional focus on motor and postural performance and its related neuromuscular activities under stable and unstable stance between young and old adults. Methods: Fifteen younger healthy (mean age: 23.87 ± 2.61) and fifteen elderly healthy (mean age: 66.73 ± 3.97) adults were recruited in this study. With an electrogoniometer and acrylic plate attached on right elbow joint and forearm respectively, participants were requested to perform a motor tracking task with directing their attention to elbow movement (IF) or to plate movement (EF) when standing on a stable or unstable surface. Tracking error and jerk, postural sway amplitude and approximate entropy (ApEn), soleus H-reflex, and EMG co-contraction activity of soleus and tibialis anterior were measured. Result: For the behavior performance, tracking error suggested that there were significant main effects of attentional focus (F1,28 = 83.04, p < .01), with less tracking error in the IF conditions. For the smoothness of tracking trajectory, jerk square mean did not vary with attentional focus, posture difficulty, or age difference. In regard to postural performance, decreased postural sway and increased ApEn with EF strategy were observed for both younger and older adults. For electrophysiological findings, H/Mmax ratio and co-activation index were modulated by attentional focus with larger H/Mmax in the younger group and smaller co-contraction index in the EF conditions for both groups. On the other hand, EMG activity of biceps brachii was smaller when adopting an EF strategy to perform the tracking task in the older adults (p < .05) but not in the young adults (p > .05). Conclusion: This study showed that both attentional focus and postural task difficulty influence the performance of a posture-suprapostural task between younger and older healthy adults. For a continuous tracking task, IF might be a better control strategy than EF. Based on H-reflex results, the hypothesis of “reflex-type control” for EF strategies was evidenced in younger adults. The results of the present study could be applied on older adults for providing adequate control strategy while performing a postural-suprapostural task. Further studies would be needed to be confident in these conclusions for patients with neurological disease.