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Upper Extremity Muscle Activity during Cyclic Push and Pull Task

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Title
Upper Extremity Muscle Activity during Cyclic Push and Pull Task
Other Titles
반복적인 동적 푸시-풀 동작에 따른 상지 근육의 사용량 분석 연구
Author
Bak, Haerim
Advisor
Shin, Gwanseob
Issue Date
2019-02
Publisher
Graduate School of UNIST
Abstract
Pushing and pulling task is one of the manual materials handling tasks of consumer products and rehabilitation of upper extremity muscles as well as industries. Pushing and pulling task conducted in the sub-maximum level with consumer products or rehabilitation equipment have received little attention compared to that of industry because it does not cause work-related musculoskeletal disorders or injuries. However, dynamic pushing and pulling motions at submaximal levels are enough to cause the muscle fatigue and physical discomforts even though it does not require maximum force or strength level efforts. The primary goal of this laboratory study was to quantitatively evaluate the level of upper extremity muscle activation during cyclic pushing and pulling tasks. The specific aim of this study was to evaluate and compare the relative impact of horizontal and vertical loads on the median and peak activation levels of major upper extremity muscles. Hand grip force and subjective ratings for perceived fatigue and weight felt in hand were also evaluated to explore relationships between the muscle activation level and other measures of physical efforts. Twenty young healthy females participated in this laboratory experiment. Each task was performing seven cycles of pushing/pulling motions. A total of twelve combinations of three horizontal loads (1kg, 2kg, 3kg), two vertical loads (0.6kg, 1.3kg) and two directions of exertion (push and pull) were performed in randomized order. During each task, muscle activity of seven upper extremity muscles, motions of pushing and pulling, and grip force were observed. After conducting each task, perceived fatigue and weight felt in hand were also measured. Results showed that muscle activities, hand grip force, and subjective ratings were significantly affected by the horizontal and vertical loads (p < 0.05). Most upper extremity and shoulder muscles tested in the current study generated greater activation levels with increased external loads (both horizontal and vertical load) during dynamic pushing and pulling movements, in general. It might be due to their roles in resisting the increased loads and maintaining the stability of motion. Relative effects of each external load on individual muscle varied depending on the role of the muscle and moment induced by each load. Change in the horizontal load more apparently affected the muscles near the shoulder joint, which are known as the primary muscles for pushing/pulling movements. On the other hand, the effect of the vertical load was more apparent for elbow and shoulder flexors to maintain the vertical location of the hand in the changes of the moment at the elbow and shoulder joints. To maintain joint stability, antagonist muscles that do not have major roles for pushing/pulling were more likely to be affected as their agonist muscles being affected by the two kinds of load. Grip forces and subjective ratings also increased with an increase in external load, complying with the results of muscle activation. Results of this study provided insights into designing consumer products or rehabilitation programs that include submaximal load level of cyclic pushing and pulling. Also, some considerations for expanding understanding of this study were proposed for future research in dynamic pushing and pulling tasks at submaximal exertion level.
Description
Department of Human Factors Engineering
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