Effect of Object Shape and Work Height on Upper Limb Load(Theory and Methodology)

本研究では,立位姿勢での品物や部品を並べる作業を想定した実験を行い,把持対象物の形状と作業面の高さが異なる場合の上肢負担を明らかにすることを目的とした.被験者は上肢に疼痛のない健常な男子学生10名,実験条件は品物に見たてた把持対象物の形状が3条件,品物を並べる棚に見たてた作業面の高さが2条件とし,これらを組み合わせた計6条件で実験を行った.測定項目は,把持力分布測定システムを用いた把持力および筋電図とし,それと同時に主観的な負担感および作業のしにくさ,把持対象物の握りにくさも調査した.実験の結果,対象物を並べる作業において上肢負担に与える要因が明らかとなった.Laying out objects via manual handling requires upper limb work with repeated carrying and grasping of objects. It is important to clarify the factors influencing work load because repetitive upper limb work causes damage to hands, arms and shoulders. There are many studies related to repetitive upper limb work, but most of them relate to production line work in industry. In addition, there are few studies on the effect of the object shape. The shape of an object may affect how it is grasped. In this study, we therefore intended to clarify the effect of the object shape and work height on upper limb load. In this experiment, ten healthy male subjects were asked to carry objects placed on a shelf using combinations of three object shape conditions and two work height conditions. We used a can, book and fruit to simulate the object shape condition, and eye height and waist height for the work height condition. The widths of the can, book and fruit were 64, 32 and 100mm, respectively. The grasp force and muscle activity were used as evaluation indices. We also investigated subjective indices for burden, difficulty of the task and difficulty of grasping the object. Electromyography was performed at the flexor digitorum superficialis muscle, the extensor digitorum muscle, the biceps brachii muscle, the middle part of the deltoideus muscle, and the upper part of the trapezius muscle. The results showed that grasp force and its distribution were different depending on object shape, and muscular load on the shoulder joint varied depending on work height