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Abstract
Previous studies have indicated that the knee joint is subject to impact forces greater than 3000 newtons when workers use a knee-kicker to install carpet. Such forces may be modified, however, by the action of large muscle groups in the legs and upper body. To evaluate the role of these key muscle groups, electromyographic (EMG) data were collected from the rectus femoris, long head of the biceps femoris, anterior deltoid, and extensor carpi radialis muscles of eight male subjects. Each subject simulated the four static body postures most commonly used during carpet installation. These were (a) on hands and knees, (b) beginning kick cycle, (c) mid-kick cycle and (d) impact kick cycle. To assess the dynamic component of the task, each subject performed the act of carpet stretching using a knee-kicker. For both static and dynamic activities, the anterior deltoid showed the highest normalized EMG values. It was also found that immediately before the impact phase the knee flexor muscles contracted, and it appears that such muscle activity in conjunction with activities (not measured in this study) of other hamstring muscles, facilitates development of an optimal blow to the kicking tool. Finally, the results seemed to support the recommendation that forward body movement post-impact phase be minimized in order to reduce excessive activity of the shoulder flexors.