Manual handling
- 1. 1 How does the biomechanical exposure of the upper body in manual box handling differ from exposure in other tasks in the real industrial context?
- 2. 2 Abstract
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- 4. 44 Twelve workers had biomechanical exposure assessed through trapezius muscle activity and posture recordings (upper back and upper arms) during 4 h of a regular working day. Handling tasks demonstrated the highest biomechanical demand to the upper body, particularly for peak loads of the upper trapezius activation and upper back forward flexion postures. However, handling tasks were also associated with a high exposure variation. Interventions aiming to decrease loads in handling tasks can be relevant to decreasing peak loads and avoiding musculoskeletal disorders on the upper limbs.
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- 6. 6 Relevance to industry Manual box handling is an occupational task commonly associated with musculoskeletal injury risk. Knowing the representativeness of manual box handling tasks in real work contexts can help practitioners to better understand the actual need for task-centered interventions.
- 7. 77 Introduction Some researchers have focused on the investigation of the effect of box weight or handling height in biomechanical exposure of workers (Habes et al., 1985; Vrije et al., 2016; Oliveira et al., 2011). Others have investigated preventive strategies, such as the use of handles on boxes to decrease musculoskeletal load (Drury, 1980; Garg and Saxena, 1980; Jung and Jung, 2010; Silva et al., 2013). In any approach, experience seems to play an important role (Plamondon et al., 2013; Gagnon, 2005). A previous study of our group identified that experienced workers did not have the same biomechanical advantages as inexperienced subjects when handling boxes designed to decrease biomechanical demand (Nogueira et al., 2016). Both experienced and inexperienced subjects had a lower biomechanical load when handling the non-commercial boxes compared to the commercial ones. However, experienced workers did not have the same advantage as inexperienced subjects when handling those new boxes. This shows the complexity of controlling the musculoskeletal workload of handlers. On the other hand, studies addressing biomechanical loads during manual box handling have been developed using laboratory setups (Gagnon et al., 2016; Plamondon et al., 2010, 2013).
- 8. 88 Methods Subjects All the subjects were working in a supply and assembly company, and agreed to participate. They had no history of musculoskeletal disorders in the past six months and were all right-handed. The sample was composed by thirteen male workers (28.14 ± 6.73 years, 81.26 ± 13.92 kg, 1.64 ± 0.49 m), who signed the informed consent form. Only one volunteer was excluded due to failure to capture biomechanical exposure recordings. The study was approved by the Ethics Committee of the Federal University of São Carlos (Process #28891014.2.0000.5504). 8
- 9. 99 Protocol Biomechanical exposure recordings, based on muscle electrical activity and posture, were performed for each worker during 4 h of their regular paid work. Data collection was performed in the three different work shifts. However, for workers in the same shift, data collection was performed in the same time of the day. No disturbances to production were observed during data collection. The 4-h data collection duration was chosen based on a previous investigation (Trask et al., 2008), which showed that this recording period is representative of a regular working day. Direct observation was used to categorize work in three different task categories. The total period recorded was considered as the job exposure. A trained researcher had a 4-year experience, and was trained on this work setting in order to become familiar with the working tasks performed within the industry. The researcher followed each participant during the data recording and entered the task and time information into a hand-held computer.
- 10. 10 Handling tasks: Non-handling tasks: Vigorous tasks: tasks with high force demand, associated with manual box handling tasks not requiring high force, associated with warehouses without load handling– checking notes of materials, component counting, and loading or transferring through automatic guided vehicles tasks with high force demand, not associated with manual box handling, involving pushing and pulling materials through manual guided vehicles. Tasks were classified into the following categories:
- 11. All tasks were performed in standing position. Upper arm elevation as well as forward postures were limited by shelves heights. Safe limits had been determined by ergonomic warning signs to control awkward postures. Movie recordings were not allowed by the company. Therefore, the researcher recorded the frequency of box handlings during data collection. Some boxes were weighted before and after the recordings to provide a general idea on the loads handled. Boxes had between 7 and 20 kg, with similar dimensions– most of the boxes had 42.5 cm length x 20.0 cm width x 39.5 cm height. 11
- 13. ALPINE SKI HOUSE The EMG of the upper trapezius muscle was taken bilaterally. The activation of the trapezius muscle has been addressed as an indicator of shoulder workload Besides the low back, manual handlers also report high prevalence of musculoskeletal complaints on upper limbs. Therefore, there is a need to achieve a better understanding on the interaction between this segment and physical risk factors in the workplace. The growing health problem affecting neck/shoulder region also in the general working population (Côté et al., 2009) justifies the evaluation of the upper trapezius. 13 EMG
- 14. CMRR>92 dB; input impedance>1015Ω in parallel, with 0.2 pF; a preamplifier gain of 10 V/V; and noise at 1.2 μV (RMS). The sensor was placed 2 cm lateral from the middle point between the seventh cervical vertebrae (C7) and the acromion. An adhesive reference electrode (5 × 5 cm) was placed on the manubrium sternal. The signals were conditioned by the main amplifier (Myomonitor IV, Delsys, Boston, USA), with gain of 1000 V/V, a frequency band of 20– 450 Hz, 16 bits of resolution, and 1.2 μV (RMS) of noise. 14 The characteristics of the electrodes
- 16. 16 Posture recording-inclinometer (INC) Inclinometer sensors (Logger Teknologi HB, Åkarp, Sweden) were used to record upper back forward and lateral flexion, as well as upper arm elevation, with a sampling rate of 20 Hz. Before coupling to the subject, each inclinometer was calibrated according to the procedures described by Hansson et al. (2001). The inclinometers were fixed to the body with double-sided tape: on the right side, between the spinous processes of C7 and T1, and below the distal insertion of the deltoid muscle, bilaterally. Reference postures were recorded in order to calibrate the system to a neutral position and to specify the direction of movement.
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