Determining preferred work posture in repetitive task for various work load and height

Abstract

Manual material handling involving lifting, bending and twisting motions of torso is one of the major causes of lower back pain. The lower back is perhaps the most vulnerable link of the musculoskeletal system in material handling because it is most distant from the load handled by the hands. The postures that are most often used during material handlings (MMH) are stooped and squatted. The stooped posture substantially increases the moment (thus the force) of the intervertebral discs of the spine. The squatted posture, on the other hand, often causes twisting motion of the trunk to accomplish a lift. Awkward postures may lead to high demands of energy expenditure and develop high work stress on workers which may lead to musculoskeletal disorders. The objective of the study is to determine the preferred work posture , either squatting or stooping in manual handling for various workload and working heights. The methodology involved experimental work in the laboratory. The task was designed for workloads at 5kg, 10kg, 15kg and 20kg. For each load carried, the participants were required to lift at 0.5m, 1m and 2.0m. Ten physically healthy male with similar physical conditions (height, weight and age) were selected to participate in the experiment. They were briefed on the task ahead, and practised on the methods of lifting to avoid inter-variability between subjects. Throughout the experiment, the maximum heart rate was measured. After the experiment was completed, a short questionnaire was administered to identify other factors which may influence the subjects and to obtain feedback on the preferred postureposture. In all the experiments, the stooped posture showed lower heart rate, indicating that the stooped posture consumes less energy than the squat posture. Based on the questionnaire, most of the subjects preferred the stooped posture at all workload and work heights. The subjects indicated they had problems with the lower back and mostly neck with the stooped posture, whereas in the squat posture, they had mainly thigh muscle and knee problems. From the experiment, it can be concluded that the stoop posture require less energy expenditure, and that more energy is consumed at higher lift heights. It is recommended that more physiological measurements have to be taken to increase the reliability of the study.