改變鍵盤位置與坐姿對上肢肌肉活性之影響

Abstract

自電腦發明以來，隨著電腦相關科技的發展，利用電腦做為工作，或平日休閒用途的人口逐年增加。同時，因為使用電腦而伴隨的肌肉骨骼問題也慢慢受到重視。隨著電腦的普遍使用，一些研究結果也指出，電腦使用者容易出現肩頸，和上肢部位的肌肉骨骼不適現象。此問題不只對個人的日常生活造成影響，同時也會影響工作者的生產能力。因此，如何預防及減少在使用電腦時，對肌肉骨骼系統產生的不良影響，便是值得關注的議題。而本研究的目的，主要在探討於不同坐姿及鍵盤位置下，肌肉活性的變化情形、罹患上肢肌肉骨骼問題的風險，以及電腦使用者在不同姿勢下，從事打字活動的主觀感受。 本研究總計徵求到20名健康受試者，包含10名男性及10名女性。進行實驗時，主要控制的變項為坐姿，包含軀幹分別維持在90°及110°的坐姿，以及鍵盤位置，包含鍵盤底部距離桌邊，分別為前臂長度的25%、60%及100%的位置，共計有6種實驗情境。每位受試者，都會在6個實驗情境下，各接受2分鐘的打字測試，而實驗情境出現的順序是隨機的。同時，會利用表面肌電圖，偵測伸指肌、橈側伸腕肌、尺側伸腕肌、前三角肌，以及上斜方肌等五條肌肉的肌肉活性。並使用快速上肢評量表，評估在各實驗情境下，罹患上肢肌肉骨骼疾病風險的程度。在每個實驗情境的測試結束後，亦會讓受試者填寫主觀舒適度問卷，以了解受試者對於不同打字姿勢的主觀感受。 除此之外，在統計上，也包含「性別」這項因子，以了解性別的不同，是否會造成打字時，在肌肉活性、罹患上肢肌肉骨骼疾病風險，以及主觀舒適度上的差異。另外，也會了解表面肌電圖的結果，是否與快速上肢評量表的結果，具有相關性。亦會比較藉由表面肌電圖所測量出，肌肉活性較低的打字姿勢，是否即為快速上肢評量表，所評定的風險程度較低，以及受試者主觀舒適度較高的姿勢。 研究結果發現，坐姿、鍵盤位置，以及性別等三個因素，對於上肢肌肉的肌肉活性，都可能會產生影響。而採用軀幹維持在90°的坐姿，鍵盤底部距離桌邊，為前臂的100%位置，對肩頸部的肌肉而言，肌肉活性較低，或許是較為理想的打字姿勢。但在此姿勢下，橈側伸腕肌的肌肉活性較高，是否會因此增加手腕肌肉骨骼問題的風險，則可能需要進一步的研究探討。在性別的部份，也發現女性的肌肉活性，普遍高於男性，這可能與男女受試者，在力氣及手長上的差異有關。而這也暗示著，一般鍵盤的設計，可能並不符合女性的需求。因此，使用相同的鍵盤打字時，對女性而言，比較容易造成上肢的肌肉骨骼問題。 而藉由表面肌電圖，偵測上肢肌肉所得到的肌肉活性值、肌肉休息時間，與經由快速上肢評量表，所計算的上肢姿勢風險分數，經統計分析之後發現，有呈現低度相關的情形。不過，若比較表面肌電圖、快速上肢評量表，以及主觀舒適度的結果時，則發現結果不太一致。受試者的主觀舒適度，與表面肌電圖的結果較為一致，但與快速上肢評量表的結果，較不一致。這可能與快速上肢評量表，對於姿勢變化的敏感度較為不足有關。 若綜合表面肌電圖、快速上肢評量表，以及主觀舒適度感受的結果，可以發現，在從事電腦打字時，以人因工程建議的標準姿勢為基準，接著再將鍵盤放置在，鍵盤底部距離桌邊，為前臂長度的100%位置，可能會是主觀感受較舒適，且上肢肌肉活性較低的位置。不過，使用此姿勢打字，是否會因此增加前臂以及手腕，罹患肌肉骨骼問題的風險，則仍需進一步的研究了解。

Since computers invented, with the development of computer relevant science and technology, the population of utilizing computers to work, or participating leisure activities were increasing. Meanwhile, the musculoskeletal symptom accompanied with using computers was paid attention. With widespread using computers, some studies indicated that computer users were likely to have shoulder、neck and upper extrimeties musculoskeletal symptom. This problem not only influenced daily life, but also influenced workers' working capacity. So how to prevent and reduce the harmful effects while using computers was an important issue. Therefore, the purpose of this study was to investigate muscle activity、the risk suffering from musculoskeletal symptom and subjective feelings during different sitting posture and keyboard position. There were twenty healthy subjects, including 10 men and 10 women participating in the experiment. The independent variables of the experiment were sitting posture and keyboard position. Sitting posture was divided into two conditions that were maintaining trunk at 90 degrees and 110 degrees. Keyboard position was divided into three conditions that the distance from keyboard bottom to the desk, were 25%, 60% and 100% of forearm length. Totally, there were six experimental conditions. Every subject was accepting two minutes typing test under these conditions. The sequence of these conditions was random. The muscle activity of extensor digitorum communis、extensor carpi radialis、extensor carpi ulnaris、upper trapezius and anterior deltoid were detected by surface electromyography. The risk of suffering from upper extremities musculoskeletal symptom was evaluating by Rapid Upper Limb Assessment. Subjective feeling of every subject was obtained by a subjective comfort questionnaire. In addition, gender difference was included in statistics process, in order to find out whether different gender caused different muscle activity、different risk of suffering from musculoskeletal disorder、different subjective feelings or not. Besides, the correlation coefficient between muscle activity and the risk of suffering from musculoskeletal disorder was calculated. Whether the typing posture of lower muscle activity was the same with lower risk of suffering from musculoskeletal disorder、higher subjective comfort or not would be compared. The result found that sitting posture、keyboard position, and gender were influencing muscle activity. Adopted the sitting posture of maintaining trunck at 90 degree and the distance from keyboard bottom to the desk was 100% of forearm length, maybe a good typing posture because the muscle activity of upper trapezius was lowest. But under this posture, the muscle activity of extensor carpi radialis was relative higher, whether this posture would increase the risk of wrist symptom or not, might need further research. The result also found women's muscle activity was generally higher than men. This was probably related with difference in strength and hand length between men and women. This finding was implied that the design of the keyboard might not fit in with women's demand. So, while using the same keyboard, women would be easier suffering musculoskeletal symptom than men. Muscle activity detected by surface electromyography and the risk suffering from musculoskeletal disorder evaluated by RULA had a lower correlation coefficient. But, when comparing the results from surface electromyography、RULA, and subjective feelings, it was found that these results were inconsistent. This might because RULA was not sensitive to posture changes. If considered the results of surface electromyography、RULA, and subjective feelings at the same time, a better typing posture might be that according ergonomic principle to set up computer workstation at first, and then put keyboard at the distance from keyboard bottom to the desk was 100% of forearm length. This posture might be a comfort position and had lower muscle activity. But whether this posture would increase the risk of suffering from forearm and wrist musculoskeletal disease or not, might need further study.