出版社：National Institute of Occupational Safety and Health
摘要：Through a fled survey of about 300 female checkers of cash-registers at some supermarket, it was found that notwithstanding improvement of a key pushing force of electronic cash-register (ECR) which was quite lighter than that of me-chanical cash-register (MCR), the checkers had complained of stiff-shoulder, although complaints associated with the arms had decreased. Through preliminary experi-ments in our laboratory, it was revealed that at the end of continuous key pushing experiment an increase of muscular tension and an increase of the low frequency components in the electromyogram (EMG) on the arms and shoulders could not be recognised clearly, on the contrary, both of them were observed in the experiment of writing performance mentioned in Part 1. The muscular tension in key pushing was kept constant or decreased plainly. Using the observed values of the EMG on trapezius, forearm flexor, forearm extensor and triceps and the key pushing force, the following five factors with two levels were assigned with an orthogonal array table L16(215) to make variance analysis: types of cash-registers (MCR and ECR), heights of key-board, registering items (a numerical table for training of the checkers or practical merchandise as a matter to be registered), physical posture (sitting or standing) and experience of subjects. It was concluded that muscular burden for operating of ECR was lighter than that for the MCR except that both the cash-registers had the same effect on the shoulder. The effect of the height of the key-board appeared on the shoulder and the lower position was better from the view-point of the muscular burden. The sitting posture also increased muscular burden on the shoulder. On the correlation matrix calculated, the values to explain the relation between the muscles and the key pushing force, called contribution rate, indicated to be larger on the muscles except the trapezius and those corresponding to correlation between mutual muscles, called cooperation rate, indicated to be larger on the ant-agonistic muscles (flexor and extensor) and the cooperative muscles (flexor and triceps).
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