目的：過去的研究顯示正常人頭部過度屈曲或伸展，會改變前庭交感神經的活性，進而影響心血管之交感神經活性。常人於執行日常活動時，常會合併頭後仰，但其對血壓及心臟自律神經的影響，目前較少相關的研究。本研究的目的在評估上肢阻力運動中合併頭部後仰對心跳、平均動脈壓及心臟自律神經調控的影響。方法：以十三位健康男性為受試者，接受二次運動測試，以心電圖儀及非侵入性血壓計持續收集心跳及平均動脈壓的變化。將心電圖以快速傅利葉數學公式轉換成頻譜強度，做心跳變異性分析。二種測試姿為分別為（一）遮眼頭擺正中（二）遮眼頭後仰30°；兩種測試順序採平衡隨機且間隔1天以上。上肢運動是以電腦滑輪系統做右肩關節斜角屈曲運動，運動強度為30%單次最大肌力，以每分鐘30下的速度重複120下。以無母數相依樣本Wilcoxon signed ranks test檢測二種頭部擺位對各種參數的影響。結果：頭部擺位對平均動脈壓與平均心跳變化，兩參數未達顯著差異(p>0.05)。心跳變異性分析顯示，只有常化後低頻功率以遮眼頭後仰30°大於遮眼頭擺正中達顯著差異(p<0.05)。恢復期之心跳變異性分析則顯示三參數皆達顯著差異(p<0.05)，其中常化後高頻及低頻功率以遮眼頭後仰30°大於遮眼頭擺正中，而高低頻功率比值亦同。結論：頭部後仰對運動期之心跳變異性未有顯著影響，乃因運動刺激增加心臟交感神經的興奮性，與頭後仰增強副交感神經的作用相拮抗；但在運動停止後心跳變異性分析則顯示頭後仰有較高的副交感神經的興奮性，較低的交感神經的興奮性。因本研究設定之運動強度及頭部位置改變的程度，使骨骼肌與前庭交感神經的訊息強弱的消長是平衡的，所以心跳、平均動脈壓的改變未達顯著差異。

Purpose: Shoulder resistance exercise (SRE) is commonly used to improve the function of upper extremity. To provide more sensory inputs, SRE is usually combined with head movement. However, previous studies reported that passive head extension and flexion position caused specific changes of both otoliths and neck muscle afferents. These changes affect in heart rate, blood pressure, heart rate variability and muscle sympathetic nerve activity. The purpose of this study was to evaluate the effects of head position on the cardiac autonomic activities during SRE. Methods: Heart rate(HR)and mean artery pressure(MAP)were continually measured using electrocardiography and blood pressure monitor. Power spectrum was used to analyze the fluctuations of heart rate variability(HRV)in 13healthy male subjects (mean age 21.3±1.5yr).SRE protocols were 30% of 1 RM and 30repetitions per minute for four minutes. Subjects were assessed for HRV during the following two experimental conditions in randomized order. The two trails were(1) head in midline with eyes closed(HM),(2)head in hyperextension 30°with eyes closed(HE) to activate otoliths and neck muscle afferents. All the variables were tested with Wilcoxon signed ranks test. Results: There is no significant influence of head position on the HR and MAP in two trails. All the HRV variables showed significant difference between HM and HE in recovery stage (p<0.05) but not in exercise stage. The values of normalized low-frequency power were 21.25±4.98, 46.50±2.37% respectively during HM and HE. The values of normalized high-frequency were 46.91±1.98, 52.82±2.15% respectively and the ratio of low-frequency to high-frequency were 1.17±0.078, 0.923±0.089 respectively during HM and HE(p<0.05). Conclusion: Our data indicate that the HE results in an increased vagal activity during recovery stage, including increases in HFnu and decreases in LF/HF. The results suggest that the vestibular apparatus during head hyperextension mediates the reduction in sympathetic activities which contrast to in skeletal muscles sympathetic afferents increase and consquently, neither MAP nor HR was affected significantly by head hyperextension during exercise stage.