背景與目的：現代社會隨著科技進步，許多場合都會使用螢幕顯示器，譬如電腦或是投影機。現代化教學也多採用將教材投影至螢幕上播放。然而，教室內座椅設計多為固定不變的，無法符合教室各方位坐著的聽眾之人體工學。對於需要長時間維持固定姿勢的學生來說，在教室中找到一個最適宜觀看螢幕的位置，讓眼睛、頭頸肩以及軀幹，維持在一個舒適的狀態是很重要的。因此本研究的目的乃在比較不同高度的遠距離投影螢幕，是否會影響身體姿勢、頸肩部肌力以及疼痛狀況。方法：研究者收取30位受試者，分別比較在實驗前後，不同高度投影螢幕的情況下，其肌力、頸肩部姿勢、頸肩部壓痛閾值，以及疼痛指數的差異。統計方法採用t檢定以及多變數分析重複型評量。結果：在不同螢幕高度下，頸部壓痛閾值（p<0.001、p<0.001）、肩部壓痛閾值（p=0.003、p=0.020），都有明顯差異。在不同螢幕高度下，頸部角度有明顯差異（p=0.047）。而在實驗後，上斜方肌肌力則明顯比實驗前低（左：p=0.030、右：p=0.004）。在高螢幕情況下，有66.7%的受試者主訴頸部疼痛，占最高比例。結論：隨著螢幕高度升高，頸、肩部的壓痛閾值下降，頸部角度增加，頸部疼痛的比例也增加。長時間維持固定姿勢看螢幕，尤其是高螢幕，比較容易造成頸部過度抬高的姿勢，甚至造成頸肩肌力降低。因此，日常生活儘量避免長時間維持同一姿勢，並減少頸部過度抬高的姿勢去觀看螢幕，如此可以減少肩頸疼痛的產生。

Background and Purposes: Visual display terminals are prevalent in modern society such as computer screen or projector. Projecting the teaching material on the screen is common in the modern classroom. However, a lot of the tables and chairs in the classroom are fixed and not ergonomically designed. Therefore, it is crucial to find a proper seat location which can make a person feel comfortable to sit in classroom for a long period of time. The purpose of this study was to investigate the effect of different projector screen height on posture, muscle strength, and pressure pain threshold for related body regions. Methods: Thirty subjects were recruited on campus. Each of them would watch movies for ten minutes at three different projector screen heights. Repeated measures ANOVA and t-test were used for statistical analysis. Results: There were significant differences of the pain pressure threshold for neck and shoulder regions among three screen heights (p < 0.01). Neck angle was also significantly different among three screen heights (p = 0.047). Muscle strength of the upper trapezius was lower after watching movies than before (p < 0.05). Besides, a higher percentage of the subjects complained about neck soreness under the high screen condition. Conclusion: As the projector screen increases, pain pressure threshold of the neck and shoulder decreases, neck angle increases, and incidence of neck pain increases. Maintaining a fixed posture to watch high screen for a long period of time may result in increasing neck angle and decreasing muscle strength of the shoulder region. In order to decrease the musculoskeletal symptoms for the neck and shoulder regions, people have to use a lower screen height and reduce the long period time of screen use.