Annals of Rehabilitation Medicine

"Electromyogram"

Original Articles

Working Posture and Muscle Tension according to Screen Position during VDT Operation.: Yu, Ji Yeon , Ha, Tae Hyun , Son, Sook , Kim, Jeong Han , Park, Young Ok; J Korean Acad Rehabil Med 2000;24(4):765-775.

Abstract
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Objective: To evaluate working condition in way of measuring working posture and muscle tension using the desktop personal computer and notebook personal computer having different screen height.

Method: Seventeen healthy men performed wordprocessing task in three workstation: desktop PC on the conventional computer table (DPC (on)); desktop PC under the 'inside' type computer table (DPC (under)); notebook PC on the table (NPC). The viewing distance and angle, head and neck angle, thoracic bending and trunk inclination were measured. Muscle tension of right posterior neck muscle, upper trapezius, sternocleidomastoid (SCM), and upper back muscle was also measured by integrated electromyogram (IEMG).

Results: 1) The viewing distance was the longest in DPC (under). 2) The lower the screen height, the more downward viewing angle and more flexed position in upper neck. 3) The posterior neck muscle tension was the lowest in DPC (on). 4) Stooped position was most frequently seen in NPC and the highest tension of posterior neck muscle and upper back muscle was shown in NPC. 5) In relation between postural analysis and muscle tension, muscle tension decreased with increasing backward reclining position, and the neck and thorax became more erect with increasing in viewing distance.

Conclusion: These results suggest that the stooped posture was worst and most frequently seen in NPC. If neck flexion is avoided, DPC (under) position could lessen the visual and musculoskeletal problem. More Ergonomical study would be needed about working posture using computer.

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EMG Power Spectrum of Lumbar Back Muscle in Chronic Low Back Pain Patients.: Sohn, Min Kyun , Yoon, Yeo Sam , Jun, Kae Ho; J Korean Acad Rehabil Med 1998;22(1):68-76.

Abstract
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Surface electromyogram in the lumbar paraspinal muscles was studied to evaluate back muscle impairment in twenty chronic low back pain patients and twenty control subjects. Turns-amplitude and power spectrum analysis of electromyographic signals were performed at different force levels during fatigue from sustained isometric contraction and recovery from fatigue in trunk extensor muscles. Results indicated that with increasing force level mean amplitude and Root Mean Square (RMS) values were increased, but mean and median frequencies increased initially until 20% Maximal Voluntary Contraction (MVC) and decreased tendency after then. Turns, mean amplitude, RMS, mean and median frequencies were all higher in control subject than those of low back pain patients. During sustained isometric contraction at 70% MVC, mean and median frequencies were linearly decreased, and the slopes were steeper in the patients group. Mean amplitude and RMS value showed decreased tendency during fatigue. During recovery from fatigue turns, mean and median frequencies increased especially in the first 3 minutes and nearly completely recovered in the 7~8 minutes in both patients and control groups. Therefore the mean amplitude and RMS value could be used as indicators of the level of muscle contraction and the mean and median frequencies reflect well the muscle fatigue in paralumbar muscle. These results validate the use of surface EMG spectral parameters as an objective measure of back muscle impairment in chronic low back pain patients.