Workplace layout for seated manual handling tasks: an electromyography study

A study was conducted to determine the effect of varying magnitude of load and work rate on muscular strain in seated manual handling tasks performed with one hand. The study also investigated the effect of direction of movement on muscular strain. Ten subjects (males and females) participated in the study who performed the task of moving weights from a conveniently located outwards position to a point closer to the body midline. Subject used the dominant hand to perform the task and handled weights of magnitude 1 and 2 kg at the work rates of 10 and 20 movements/min. Starting positions were fixed at 45 degrees, 90 degrees and 150 degrees with respect to the body midline. The distance over which weights were moved was fixed at 38 cm. Using a metronome precisely controlled the pace of the work. Subjects worked at an adjustable work station and adjusted it until their elbow height and table height were at the same level. Electromyography (EMG) activity was recorded from 5 muscles of the dominant arm-shoulder region using a computerised data recording and analysis system. Root-mean-squared (RMS) values of EMG signals were computed to compare the influence of experimental conditions on muscle strain. Static, dynamic and mean components of EMG activities were obtained. Total muscle load was also determined. Results of the study show that muscular strain as measured by EMG activity was in general sensitive to Variations in magnitude of load and work rate. Work rate had relatively large influence on muscular strain as compared to magnitude of load. The results of the study indicate that the total muscle load was dependent on the direction of movement. Individual muscle strain also showed some direction of movement dependence though the results varied from muscle to muscle. The results of the present study have been compared with other published studies and suggestions for future work have been given.