The Influence of Keyboard Position and Sitting Postureo Upper Extremity Muscle Activity
Date Issued
2009
Date
2009
Author(s)
Yi-Hsien Chiang
Abstract
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.
Subjects
computer workstation
surface EMG
rapid upper limb assessment
upper extremity musculoskeletal disorder
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