POSTURAL AND MUSCULAR ADAPTATIONS TO REPETITIVE SIMULATED ASSEMBLY LINE WORK

Abstract

<p>Few studies have shown the process of adaptation in muscle activity and joint angle during prolonged repetitive work. Fifteen healthy men performed 1 minute cycles of automotive-related tasks, which included a finger pull, knob turn, drill press and hose connector push. The experiment occurred on two days, separated by 24 hours. Day 1 required 61 cycles, with 5 cycles on day 2. Electromyography and kinematics of the upper extremity were analyzed at 12-minute intervals. Time to complete work cycle decreased by 6.3 s at the end of day 1 and 5.3 s on day 2. Peak EMG decreased for triceps brachii (TB), anterior deltoid (AD) and infraspinatus (IN) during work cycle, TB (finger pull), biceps brachii (BB), TB, AD, middle deltoid (MD) and IN during the hose insertion task. Peak EMG increased for MD and IN during the drill task. Mean EMG decreased for MD (work cycle), BB (hose insertion) and AD (finger pull), while MD and IN increased (drill task) and upper trapezius increased during the work cycle. EMG COV decreased for TB, AD, posterior deltoid and IN during the work cycle, TB during the finger pull task and AD during the hose insertion task. COV increased for BB during the work cycle, AD during the finger pull and for BB and lower trapezius during the drill press. Peak shoulder flexion decreased by 7.0° during the work cycle. Perceived discomfort increased by 1.2 units. This thesis found adaptations to highly repetitive but light work in only one hour, some of these changes persisted through the next day suggesting an adaptive process. This thesis is one of the first to examine adaptations to a highly repetitive simulated assembly work and has provided new insights into the evaluation of repetitive jobs as a whole and as isolated subtasks.</p>