Workers’ biomechanical loads and kinematics during multiple-task manual material handling
Introduction
Manual material handling (MMH) tasks, such as lifting, carrying and lowering objects, are still common in various industries, and contribute substantially to both the number of claims for musculoskeletal disorders (MSDs) and their resulting costs (Murphy et al., 1996; National Academy of Sciences, 2001; Bureau of Labor Statistics, 2015). In order to reduce the number and severity of MMH injuries, many studies have investigated worker motion and biomechanical loads during MMH tasks (e.g., Lavender et al., 2003; Hoozemans et al., 2008; Qu and Nussbaum, 2009; Gallagher et al., 1988; Karwowski and Yates, 1986; Rose et al., 2013). However, these studies investigated cases in which workers conducted only a single MMH task (e.g., only lifting, only carrying), while in industry, workers often carry out multiple-task MMH jobs, which combine several sequential tasks (e.g., lifting a box from a shelf and turning simultaneously, or carrying a box and lowering it toward a platform).
For this reason, Plamondon and colleagues investigated workers’ biomechanics during a multiple-task palletizing job (Plamondon et al., 2010, 2012, 2014, 2017). The mass of the box being handled was either 15 or 23 kg, and the origin and destination heights were less than 96 cm. The body of work produced by these authors constitutes an important step in understanding the biomechanics of workers during multiple-task MMH; however, in many industrial cases the workers handle lighter objects and the platform heights are greater than 96 cm (Harari et al., 2018). Furthermore, these studies focused on the spinal load, while other joints that are positively correlated with MSDs during MMH tasks (Bureau of Labor Statistics, 2015), such as the shoulder, were not investigated.
Other studies focused on differences in biomechanics and physiological parameters between single-task and multiple-task MMH, and found differences in the subjects’ kinematics (Harari et al., 2019, Harari et al., 2019b), lower back moments, compression and shear forces (Harari et al., 2019, Harari et al., 2019b; Straker et al., 1997b), perceived rate of exertion (Straker et al., 1997a), and maximum acceptable weight limit (Straker et al., 1996). These studies and others (e.g., Garg and Kapellusch, 2009; Dempsey, 1999) suggested that worker physiology and biomechanics during multiple-task MMH jobs should be investigated separately, and that the analysis of multiple-task jobs in industry should be conducted using tools developed specifically for them.
When designing a new work process, it is important to be able to predict ergonomic measures as a function of the workplace parameters (e.g., origin height, box mass). Worker physiology during multiple-task MMH has been investigated, and prediction models for workers' oxygen consumption have been developed (Dempsey et al., 2008). A recent study investigated workers' pace during multiple-task MMH, and developed models predicting the time required to complete multiple-task MMH jobs (Harari et al., 2018). Yet, to the best of our knowledge, no models have been developed for predicting worker kinetics and kinematics during multiple-task MMH that occurs in 3D space. Thus, the objective of this study is to investigate worker biomechanics during multiple-task MMH, and to develop a prediction model for both the moments acting on the worker's spine and shoulders, and the worker's kinematics, during multiple-task MMH jobs.
Section snippets
Methods
An experiment in which subjects performed a continuous box-conveying work process was conducted. Each subject's motion was recorded using a motion-capture system, and biomechanical parameters were calculated (see Section 2.1). In order to analyze each of the tasks individually during the box-conveying work process, we developed a program that automatically identified and classified each of the tasks using the motion data (Section 2.2). Statistical analyses were conducted and prediction models
Significant main effects and interactions
The box mass, origin height (for the removing task) and destination height (for the depositing task) affected the peak and cumulative moments acting on the L5/S1 vertebrae and on the shoulder joints. These three variables also affected the kinematics (i.e., the peak trunk, shoulder and knee angles). For all of these main effects, p < 0.05. Subject height, interacting with the origin/destination height, affected both the moments acting on the L5/S1 and shoulder joints and the peak joint angles
Discussion
This study investigated worker biomechanics during multiple-task MMH with 3D motion components. We developed prediction models for the workers’ peak joint angles, and for the moments acting on the spine and shoulder.
Limitations
The subjects in this experiment were young and healthy university students. While this is a good representation of workers in some industries, other fields may include less fit or older populations, which will affect the weight distribution and the workers’ movements.
The design of the shelf stations (i.e., three shelves, one above the other) might have affected the subject's kinematics during the removing and depositing tasks. Specifically, the shelves could have obstructed the inclination of
Conclusion
During multiple-task removing and depositing of boxes weighing 2–12 kg, the platform's height was found to be the most important predictor of both the spinal and shoulder moments and the subject's kinematics (explaining between 36% and 81% of the variation). The relationship between the platform height and the spinal moment was nonlinear, with the moment being highest at 0.2 m, decreasing to a minimum at 1.1 m, and then slowly increasing as the origin height increased to 1.7 m. For the shoulder
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors would like to thank Alan De Asha from C-Motion for his support in the development of the automated program, and Mor Topaz and Yarden Avrahami for their assistance in the data collection. This research was supported by the Israel Science Foundation (grant no. 8/998).
References (35)
Utilizing criteria for assessing multiple-task manual materials handling jobs
Int. J. Ind. Ergon.
(1999)- et al.
Quantitative comparison of five current protocols in gait analysis
Gait Posture
(2008) - et al.
Lifting in stooped and kneeling postures: effects on lifting capacity, metabolic costs, and electromyography of eight trunk muscles
Int. J. Ind. Ergon.
(1988) - et al.
Factors determining workers' pace while conducting continuous sequential lifting, carrying, and lowering tasks
Appl. Ergon.
(2018) - et al.
The effects of initial lifting height, load magnitude, and lifting speed on the peak dynamic L5/S1 moments
Int. J. Ind. Ergon.
(2003) - et al.
Quantitative comparison of current models for trunk motion in human movement analysis
Clin. Biomech.
(2009) - et al.
Lifting strategies of expert and novice workers during a repetitive palletizing task
Appl. Ergon.
(2014) - et al.
Difference between male and female workers lifting the same relative load when palletizing boxes
Appl. Ergon.
(2017) - et al.
Determination of patient-specific multi-joint kinematic models through two-level optimization
J. Biomech.
(2005) - et al.
The ergonomic design of workstations using virtual manufacturing and response surface methodology
IIE Trans.
(2002)
Nonfatal Occupational Injuries and Illnesses Requiring Days Away from Work
A general framework for the manufacturing workstation design optimization: a combined ergonomic and operational approach
Simulation
Oxygen consumption prediction models for individual and combination materials handling tasks
Ergonomics
Working height, block mass and one-vs. two-handed block handling: the contribution to low back and shoulder loading during masonry work
Ergonomics
Applications of biomechanics for prevention of work-related musculoskeletal disorders
Ergonomics
The Revised Strain Index: an improved upper extremity exposure assessment model
Ergonomics
Relative importance for linear regression in R: the package relaimpo
J. Stat. Softw.
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