The assessment of material handling strategies in dealing with sudden loading: The effects of load handling position on trunk biomechanics (original) (raw)
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Sudden unexpected loading has been identified as a risk factor of work-related low back pain (LBP). This study investigated the effects of different foot placements and load-releasing locations on trunk biomechanics under an unexpected sudden loading event. Fifteen subjects experienced sudden release of a 6.8-kg external load from symmetric or asymmetric directions while maintaining four different foot placements. The results showed that subjects experienced on average 4.18 less trunk flexion, 6.6 Nm less L5/S1 joint moment and 32.0 N less shear force with staggered stance with the right foot forward (the most preferred placement) compared with wide stance (the least preferred placement). Asymmetric load-releasing positions consistently resulted in smaller impacts on trunk biomechanics than symmetric positions. The findings suggest that staggered stance and asymmetric load-holding position can be used as a protective load-handling posture against LBP caused by sudden loading. Practitioner Summary: In a work environment, unexpected sudden loading may cause low back pain (LBP). In this study, we used empirical data to demonstrate how different foot placements and load-releasing locations can be used to mitigate the impact of sudden loading on the spine and to reduce the risk of LBP.
As a major risk factor of low back injury, sudden loading often occurs when performing manual material-handling tasks on uneven ground surfaces. Therefore, the purpose of the current study was to investigate the effects of a laterally slanted ground on trunk biomechanical responses during sudden loading events. Thirteen male subjects were subjected to suddenly released loads of 3.4 and 6.8 kg, while standing on a laterally slanted ground of 0°, 15° and 30°. The results showed that 8.3% and 5.6% larger peak L5/S1 joint compression forces were generated in the 30° condition compared with the 0° and 15° conditions, respectively. The increase of L5/S1 joint moment in the 30° condition was 8.5% and 5.0% greater than the 0° and 15° conditions, respectively. Findings of this study suggest that standing on a laterally slanted ground could increase mechanical loading on the spine when experiencing sudden loading.
Sagittal trunk movements during load carrying activities: a pilot study
International Journal of Industrial Ergonomics, 2003
The objective of this study was to describe trunk movements in sedentary subjects, and in workers with and without musculoskeletal symptoms, when carrying loads in simulated tasks. The 38 subjects who participated in this study were divided into 4 groups, consisting of 9 male students, 10 female students, 10 female symptomatic industrial workers and 9 asymptomatic industrial workers. The trunk movements of all subjects were recorded by a biaxial back electrogoniometer when carrying loads between surfaces of different heights. An analysis of variance for repeated measures were performed, which was followed by the Duncan post hoc test for comparison of anthropometrical data between subjects, amplitude of movement, and time spent in each movement per group and per experimental condition. The height of the surfaces to which the loads were carried to or from, significantly influenced the trunk positions during handling (po0:01), as if subjects were anticipating the target position whilst handling. Also, more time was spent in flexion (po0:01) than in extension. These aspects increase the risks of possible injury in such activities.
Sudden and Unexpected Loading Generates High Forces on the Lumbar Spine
Spine, 2000
Study Design. A cross-sectional study of spinal loading in healthy volunteers. Objectives. To measure the bending and compressive forces acting on the lumbar spine, in a range of postures, when unknown loads are delivered unexpectedly to the hands. Summary of Background Data. Epidemiologic studies suggest that sudden and unexpected loading events often lead to back injuries. Such incidents have been shown to increase back muscle activity, but their effects on the compressive force and bending moment acting on the spine have not been fully quantified. Furthermore, previous investigations have focused on the upright posture only. Methods. In this study, 12 volunteers each stood on a force plate while weights of 0, 2, 4, and 6 kg (for men, 40% less for women) were delivered into their hands in one of three ways: 1) by the volunteer holding an empty box with handles, into which an unknown weight was dropped; 2) by the same way as in 1, but with volunteer wearing a blindfold and earphones to eliminate sensory cues; or 3) by the volunteer sliding a box of unknown weight off a smooth table. Experiments were carried out with participants standing in upright, partially flexed, and moderately flexed postures. Spinal compression resulting from muscular activity was quantified using electromyographic signals recorded from the back and abdominal muscles. The axial inertial force acting up the long axis of the spine was calculated from the vertical ground reaction force. The bending moment acting on the osteoligamentous spine was quantified by comparing measurements of lumbar curvature with the bending stiffness properties of cadaveric lumbar spines. Results. The contribution from abdominal muscle contraction to overall spinal compression was small (average, 8%), as was the axial inertial force (average, 2.5%), and both were highest in the upright posture. Peak bending moments were higher in flexed postures, but did not increase much at the moment of load delivery in any posture. Peak spinal compressive forces were increased by 30% to 70% when loads were suddenly and unexpectedly dropped into the box, and by 20% to 30% when they were slid off the table, as compared with loads simply held statically in the same posture (P Ͻ 0.001). The removal of audiovisual cues had little effect. Conclusions. Sudden and alarming events associated with manual handling cause a reflex overreaction of the back muscles, which substantially increases spine com-pressive loading. Manual handling regulations should aim to prevent such events and limit the weight of objects to be lifted.
Spine loading during trunk lateral bending motions
Journal of Biomechanics, 1997
Increases in lateral trunk velocities have been identified as a mechanism for increasing the risk of low-back disorder. Previous studies have identified an increase in coactivation of the trunk musculature during lateral bends, but no studies have evaluated how spine loading changes as lateral trunk velocity increases. Twelve subjects were asked to lift loads laterally at one static and three dynamic velocities. Ten trunk muscle activities and trunk kinematics were documented and used as input parameters to an EMG-assisted model to evaluate spine loading. Muscle coactivation was observed in all lateral bends. Coactivation significantly increased during dynamic trials compared to the static trials. Coactivity increased spinal loads by as much as 25% compared to values predicted by models that did not consider coactivity. Movements to the right significantly increased spine loadings (252 N increase in compression) compared to movements to the left. Spine compression, A-P shear, and lateral shear all increased in the dynamic trials compared to the static conditions. Peak compression increased by an average of 525 N at 45" s-l compared to static loading. Compression and lateral shear increased monotonically as trunk velocity increased. It is expected that this combined (compression and lateral shear) loading is the mechanism for increased risk observed in industry.
Clinical Biomechanics, 2002
To compare two groups of worker with and without upper limb musculoskeletal symptoms when simulating handling tasks, regarding trunk movements and load support. Simultaneous lumbar movements and load support were quantified by a flexible electrogoniometer and load cell, respectively. Workers can adopt different motor strategies to perform similar tasks, possibly resulting in different physical demands. No previous studies on different movement patterns as a possible strategy for coping with physical demands by injured workers are available. 9 asymptomatic and 10 symptomatic industrial workers, carried a device for measuring contact between load and trunk during simulated tasks. An ANOVA was performed to compare results between symptomatic and asymptomatic workers. Most of the symptomatic workers supported the load on their trunk, whilst most of the asymptomatic workers did not. Higher values of lumbar flexion occurred for the symptomatic workers (P<0.05). Apparently, differences in movement and load support were adopted by injured workers as a possible strategy to share upper limb overload with other body regions. Workers suffering from work-related musculoskeletal disorders may adopt different motor strategies to cope with their job physical demands. An effort should be made to reallocate injured workers if major cost is to be avoided.
The Influence of Load Handling Height on Shoulder Biomechanics during Sudden Loading
Proceedings of the Human Factors and Ergonomics Society Annual Meeting
Shoulder disorders have been reported as the most severe musculoskeletal disorders among all body parts. Multiple occupational risk factors such as manual material handling, repetitive motion, overexertion, fatigue, and overhead tasks have been reported to be associated with the development of shoulder disorders. The objective of this study was to investigate the effect of height (low, middle, high) on shoulder muscles during sudden loading. Kinematics and Electromyography (EMG) was recorded from 14 male participants. Effect of height found to be significant on normalized EMG and load travel distance. Bilateral shoulder muscles indicated higher NEMG with the increase of the load's altitude. This increase of muscle activity could have resulted from the greater potential energy of the load at higher altitudes which required extra muscle activity to maintain the biomechanical stability of the shoulder. Reduced stability of shoulder at higher altitudes caused proprioceptive deficit which resulted in higher load travel distance.
International journal of occupational hygiene, 2021
Due to the negative influence of manual load handling on the lower back, it leads to low back disorders and high mechanical loads. The present study was aimed to investigate forces exerted on the lower back during manual handling in young workers in selected block-making workshops. This descriptive, cross-sectional study was carried out on 40 young workers with an average age of 31 years old in several block-making industries in 2020. 3DSSPP Software was used for biomechanical analysis of the forces exerted on the lower back. The prevalence of musculoskeletal disorders was assessed using the Standard Cornell Questionnaires. Spearman, Friedman, and ANOVA correlation tests via SPSS software version19 were used to determine the relationship between demographic variables, the prevalence of musculoskeletal disorders, the relationship between the prevalence of musculoskeletal disorders, the amount of compressive, and shear forces on workers' backs. The results showed that the mean compressive and shear forces exerted to the lumbosacral joint (L5/S1) were 3194.85 ± 1064.326 and 473.17 ± 89.451 N, the intervertebral disc (L4/L5) were 3924.78 ±4344.87 and 383.18 ± 154.554. The findings also indicated that the highest prevalence of pain was related to the lower back 45% and right knee 30%. There was a significant relationship between the mean score of musculoskeletal disorders obtained from the Cornell questionnaire with age, work experience, and weight and body mass (0.001> P). The shear forces exerted to the lower back were higher than the permissible levels by 30% to 37% of respondents, and on average 42.5% of them experienced compressive forces. Thus, it can cause a lot of injuries to the back if lasts for a long time. The results showed that manual load handling was dangerous for this group's ages. Consequently, people may suffer serious injuries and disorders particularly lower back disorders.
Are the anticipatory trunk movements occurring during load-carrying activities protective or risky?
International Journal of Industrial Ergonomics, 2008
This study evaluated anteroposterior trunk movements and the time spent on activities of load-carrying to surfaces at different heights, among experienced and inexperienced individuals. Thirty-six healthy males (16 experienced and 20 inexperienced in load-carrying) had their trunk movements recorded by an electrogoniometer while transporting boxes (7 and 15 kg) to surfaces of variable heights (low, low intermediate, high intermediate and high). Longer time was spent on trunk flexion when carrying loads to low surfaces and on trunk extension when carrying to high surfaces (po0.05). Differences in time spent on trunk flexion/extension were identified between loads, and between groups for the heavier load. There were no differences in flexion/extension amplitudes between groups or loads. Although unnecessary flexion/extension occurring prior to a task may increase the exposure of the trunk to risky movements, the amplitudes reported here were relatively small and seemed to have occurred to facilitate the final tasks.