ABSTRACT
It is known that lifting tasks are one of the risk factors of musculoskeletal disorders in the automotive industry. Extensive research has been carried out over the years to develop guidelines and determine safe limits in which an individual can lift. For this reason, the objective of this study is to determine the significant risk factors of musculoskeletal discomfort among manual lifting task workers in the automotive industry, and propose a methodological framework for future research on manual lifting tasks. The subjects of this study comprise 211 manual material handling workers from the automotive industry. The subjects completed a set of questionnaires which are used to elicit information on their demographic characteristics, as well as physical factors and the prevalence of musculoskeletal discomfort. The Chi-Square test was used to determine the relationship between the risk factors and musculoskeletal discomfort. The findings of the study show that the following postures (trunk bent slightly forwards, hands above the knee level (p < 0.05), trunk twisted (over 45o) and bent sideways (p < 0.05) are the significant risk factors of musculoskeletal discomfort among manual lifting task workers in the automotive industry. A methodological framework on manual lifting task in the automotive industry is proposed based on the findings of this study. The framework is developed based on the need to model human lifting capabilities so that task demands can be designed to fit the workers’ capacity when performing lifting tasks.
ABSTRACT
Extensive research has been carried out over the years to determine the maximum acceptable weight that a worker is capable of lifting in a given situation among the Occidental populations in the Europe and US. At present, there is a scarcity of studies in which lifting frequency is used as the measuring variable, especially in developing countries such as Malaysia. Therefore, the objective of this study is to determine the effects of lifting loads on the maximum acceptable frequency limit (MAFL), physiological response (muscle activity) and rating of perceived exertion (RPE) for asymmetric lifting and lowering tasks of Malaysian males.Ten male subjects are recruited in this study and they perform asymmetric lifting and lowering tasks repetitively for 30 minutes. Two lifting loads are considered (1) 1 kg and (2) 5 kg. Each of the subjects adjusts his frequency of lifting using a psychophysical approach. The subjects are instructed to perform the lifting and lowering task as fast as they could over duration of 30 minutes without exhausting themselves or becoming overheated. Electromyography (EMG) signals are recorded from four muscles (Right Erector Spinae (RES), Left Erector Spinae (LES), Right Trapezius p Descendenz (RTD) and Left Trapezius p Descendenz (LTD) and analysed in terms of the normalized MVC during asymmetric lifting and lowering tasks. The ratings of perceived exertion (RPE) for four body parts (arms, lower back, shoulders and entire body) are also collected after the subjects have completed the lifting and lowering task. The mean frequency of the lifting and lowering task obtained from the experiment is 13.41 and 9.66 times/minute for a lifting load of 1 and 5 kg, respectively. The results of the independent sample t-test show that load has a statistically significant effect on the maximum acceptable frequency limit (p 0.05). The percentage decrease in the maximum acceptable frequency for Malaysian males is higher than the Occidental populations for both of the loads investigated in this study.
ABSTRACT
Most studies have examined the association of ergonomic risk factors and musculoskeletal discomfort in developed countries. Meanwhile the data are still lacking in developing countries such as Malaysia. The aim of this study was to determine the relation between risk factors and musculoskeletal discomfort among manual material handling workers in Malaysian automotive industries. A total of211 manual material handling workers from automotive industries completed a set of questionnaire on the individual, physical and environmental factors and the prevalence of musculoskeletal discomfort. The Chi-Square test and logistics regression analysis were used to determine the relationship of the risk factors and musculoskeletal. The findings highlighted that job tenure was significantly correlated with musculoskeletal discomfort among the workers (OR=2.33-5.56). The most significant physical risk factor that was associated with musculoskeletal discomfort was bending the trunk forward slightly, hands above knee level, which was significantly related to lower back discomfort (OR=5.13, 95%CI=1.56-16.8), thigh discomfort (OR=5.1, 95%CI=1.01-25.53) and wrist discomfort (OR=3.65, 95%CI=1.06-12.53). Twisting of the trunk (over 45o) and bending sideways were significantly associated to lower back discomfort (OR=4.04, 95%CI=1.44-14.44), and thigh discomfort (OR=4.3, 95%CI=1.29-8.50). The findings also highlighted that environmental factors was associated with musculoskeletal discomfort (p < 0.05. Musculoskeletal discomfort can be reduced by lowering work-related risk factors among automotive manual material handling workers, particularly by focusing on significant factors, including job tenure, bending or twisting postures and environmental factors.