Mechanical load on the low back and shoulders during pushing and pulling of two-wheeled waste containers compared with lifting and carrying of bags and bins

Effect of occupational pushing and pulling combined with improper working posture on low back pain among workers

This study aimed to investigate the impact of occupational pushing and pulling combined with improper working posture on work-related low back pain (LBP) among workers. A web-based survey was conducted in 2022 to collect data from 15,623 workers, who were categorized into proper and improper working posture groups. Multiple logistic regression analysis was used to analyze the association between pushing and pulling loads and LBP in each group. In the proper working posture group, the odds ratios (ORs) of LBP for workers who pushed and pulled were not significantly different compared with those of no-handling workers. However, in the improper working posture group, the ORs of LBP were significantly greater among workers who pushed and pulled compared with those of no-handling workers, and this association became stronger with increasing weights. Therefore, improper working posture combined with pushing and pulling were strongly associated with LBP among workers, particularly with heavier weights.

Manual rolling load and low back pain among workers in Japan: a cross-sectional study

OBJECTIVES

Manual rolling of heavy objects remains in the workplace. The Health and Safety Executive (HSE) in the United Kingdom recommends load weights of <400 kg in the rolling task. However, the association of rolling weights <400 kg with work-related low back pain (LBP) has not been sufficiently investigated. This study examined the effect of rolling loads weighing <400 kg on LBP among Japanese workers.

METHODS

A web-based survey gathered information from 15 158 workers in 2022. Among them, 15 035 did not handle loads, whereas 123 handled rolling weights <400 kg. Load weight was categorized into 4 groups: no-handling (0 kg) and rolling weights of ≤20, 20-40, and >40 kg. Multiple logistic regression analysis examined the association between the subdivided rolling weight and LBP.

RESULTS

No significant differences in odds ratio (OR) of LBP were found for workers handling ≤40 kg rolling weights compared with that for no-handling workers. However, workers handling >40 kg rolling weights had a significantly greater OR of LBP than those not handling loads.

CONCLUSIONS

Rolling weights between 40 and 400 kg could place a high stress on the lower back. Implementation in Japan of the HSE recommendations regarding rolling load should be carefully considered.

Assessing the impact of job demands and hazardous workload activities on musculoskeletal symptoms in stone, sand, and gravel mining operations

BACKGROUND

Musculoskeletal disorders (MSDs) and associated musculoskeletal symptoms (MSS) are problematic in stone, sand, and gravel mining. Research is needed to explore relationships between job demands, work-related hazards and MSS.

OBJECTIVE

An exploratory study was conducted in Indiana during 2019-2020 to examine associations between job demands, work-related hazards and MSS.

METHODS

Through convenience sampling, cross-sectional survey data from 459 workers were collected and analyzed using logistic multiple and binary logistic regression methods. Outcome variables were MSS to the low back, neck/shoulder, and wrist/hand. Predictor variables and MSS measures are based on the Dutch Musculoskeletal Questionnaire.

RESULTS

Increased odds of low back MSS were related to dynamic loads (OR = 2.14), pushing/pulling heavy loads (OR = 1.56), torso bending or twisting (OR = 2.36), bent, stooped, or twisted posture (OR = 2.04), uncomfortable postures (OR = 2.07), repetition (OR = 1.67) and vibrating tools (OR = 1.81). Increased odds of neck/shoulder MSS were related to dynamic loads (OR = 1.83), static loads (OR = 1.24), heavy lifting (OR = 1.50), pushing/pulling heavy loads (OR = 1.68), bending or twisting of the neck (OR = 1.82), twisted neck posture (OR = 1.77) and uncomfortable postures (OR = 1.81). Increased odds of wrist/hand MSS were related to dynamic loads (OR = 2.06), static loads (OR = 1.45), bending or twisting of the wrists/hands (OR = 10.52), extended reaching (OR = 3.05), repetition (OR = 5.25), awkward postures (OR = 4.47), working above shoulder level (OR = 2.47), and vibrating tools (OR = 1.78).

CONCLUSION

Hazards that increased the likelihood of MSS were identified. These hazards should be abated or controlled to prevent MSDs in stone, sand, and gravel mining. More applied research, including ergonomic assessments to further identify hazards that can be controlled or abated, is warranted.

Job-related stress associated with work-related upper extremity musculoskeletal disorders (UEMDs) in municipal waste collectors: the moderation and mediation effect of job support

Background

Since the policy of “keeping trash off of the ground” in Taiwan, long-term exposure to repetitive motion in waste collection process results in high risk of upper extremity musculoskeletal disorders (UEMDs). Thus, we assessed the moderation and mediation effects of job-related stress and job support on work-related UEMDs among municipal waste collectors.

Methods

A cross-sectional study was conducted in two cities located at northern Taiwan during 2018–2019. 626 municipal waste collectors voluntarily participated and anonymously filled out a structured questionnaire. The moderation and mediation effects of effort-reward imbalance (ERI) and social support on UEMDs were analyzed by Haye’s Process Macro Model.

Results

Prevalence of UEMDs in municipal waste collectors were 43.4% for neck, 56.0% for shoulder, 24.1% for upper back, and 33.1% for hand/wrist. There was high prevalence of shoulder (72.2%), neck (48%), and upper back (30%) in female workers compared to male, most significantly in shoulders. In univariate and multivariate analysis, high ERI and low job support were significantly associated with ORs of 3.11 (95% CI:1.58–6.13) for elbow, 2.79 (95% CI:1.39–5.56) for shoulder, 3.39 (95% CI:1.64–7.00) for upper back and 3.83 (95% CI:1.98–7.41) for hand/wrist. Prevalent UEMDs were positively associated with high ERI in municipal waste collectors but negatively with job support. The moderation effects of ERI and job support on UEMDs, of which the measured synergy index exceeded one, were 18.24 for shoulder, 3.32 for elbow, and 2.45 for hand/wrist, but mediation effects were not significant.

Conclusions

This study found municipal waste collectors with work-related upper extremity disorders were significantly associated with work-related psychological risk factors. Therefore, waste collection cannot only to be improved by semi-automatic and automatic processes but immediate intervention programs for the reduction of psychological risk factors is needed promptly.

Optimizing Calibration Procedure to Train a Regression-Based Prediction Model of Actively Generated Lumbar Muscle Moments for Exoskeleton Control

The risk of low-back pain in manual material handling could potentially be reduced by back-support exoskeletons. Preferably, the level of exoskeleton support relates to the required muscular effort, and therefore should be proportional to the moment generated by trunk muscle activities. To this end, a regression-based prediction model of this moment could be implemented in exoskeleton control. Such a model must be calibrated to each user according to subject-specific musculoskeletal properties and lifting technique variability through several calibration tasks. Given that an extensive calibration limits the practical feasibility of implementing this approach in the workspace, we aimed to optimize the calibration for obtaining appropriate predictive accuracy during work-related tasks, i.e., symmetric lifting from the ground, box stacking, lifting from a shelf, and pulling/pushing. The root-mean-square error (RMSE) of prediction for the extensive calibration was 21.9 nm (9% of peak moment) and increased up to 35.0 nm for limited calibrations. The results suggest that a set of three optimally selected calibration trials suffice to approach the extensive calibration accuracy. An optimal calibration set should cover each extreme of the relevant lifting characteristics, i.e., mass lifted, lifting technique, and lifting velocity. The RMSEs for the optimal calibration sets were below 24.8 nm (10% of peak moment), and not substantially different than that of the extensive calibration.

Physical and psychosocial demand at work: inequities related to race/skin color

This cross-sectional study investigated the association between self-reported race/skin color and two outcomes - psychosocial demand and physical demand at work - in 1,032 workers in an urban cleaning services company and two footwear manufacturers, located in the State of Bahia, Brazil. Psychosocial demand was measured through the Job Content Questionnaire and physical demand was measured through questions about postures and cargo handling. A Cox regression analysis provided prevalence ratios (PR) adjusted by age, gender, and educational level. Among blacks, there is a higher proportion of garbage collectors and a lower proportion of supervisory positions. Black workers are more subject to high psychological demand and low job control and, consequently, to high strain (PR=1.65). Also, they are more exposed to work with arms above shoulder level (PR=1.93), and material handling (PR=1.62), compared to white workers. Brown workers are more exposed to low job control (PR=1.36), work with arms above shoulder level (PR=1.48), and material handling (PR=1.25), also compared with whites. Social support is lower among blacks and brown. The study demonstrated inequities in psychosocial and physical exposures at work that are in line with the structural conception of racism. This evidence can contribute to the adoption of practices that increase equity in the world of work.

Exploring the prospective efficacy of waste bag-body contact allowance to reduce biomechanical exposure in municipal waste collection

Municipal waste collectors must avoid bag-body contact, requiring waste bags to be held further from the body. Donning sharps-proof clothing would permit bag-body contact, allowing the bag to be closer to the body, reducing biomechanical exposures. To test this hypothesis, 25 participants loaded waste bags into a simulated garbage truck hopper under two lifting (contact allowed, no contact) and bag mass (7 kg and 20 kg) conditions. Bottom-up rigid-link biomechanical modelling results including peak low back compression force, antero-posterior shear force and peak low back flexion angle were not different between the lifting conditions, but cumulative compression was decreased with bag-body contact, although only at the 20 kg mass. Bag mass had significant effects on outcome measures, causing compression to increase to 4663 (±697) N, exceeding recommended thresholds. Sharps-proof clothing and municipally mandated 23 kg maximum allowable bag mass restrictions may not sufficiently reduce biomechanical exposures to prevent MSD.

The effects of hospital bed features on physical stresses on caregivers when repositioning patients in bed

Repositioning patients in bed is the most common patient handling activity and is associated with musculoskeletal disorders in caregivers. Hospital bed features may mitigate the risk of injury. The current study investigated the effect of bed features on the physical stress on caregivers. Ten nurses were recruited to perform three repositioning activities. Hand forces were recorded, and spine loading was estimated using a dynamic biomechanical model. Results demonstrated that except for the peak L5/S1 compressive load in the turning task, the use of assistive features significantly reduced the physical stresses for all repositioning activities. However, recommended thresholds for injury were still exceeded in many conditions. Compared with spinal load, hand force was much higher relative to the injury thresholds, suggesting a greater risk of shoulder and upper extremity injuries than low back injury. Mechanical lift equipment remains the safest and most robust way to reposition a patient.

Comparison of push/pull force estimates using a single-axis gauge versus a three-dimensional hand transducer

This study investigated the effects of using a single-axis force gauge for push/pull force measurement on kinetic/kinematic measures associated with the exertion and assessed agreement between forces recorded from two technologies (single-axis gauge, three-dimensional hand transducer) and various test conditions via intraclass correlations. Independent measures included exertion type (push, pull, turn), test condition (natural/cart alone, using force gauge at fast/slow/self-selected paces), and cart weight (light, heavy). Dependent measures included mean angles of force application, peak forces recorded from both technologies, and cart velocity. Excellent agreement was observed between technologies (ICC = 0.998). Likewise, peak forces using the single-axis gauge at the fast pace agreed best with the natural test condition (ICC = 0.631). Forces should be measured using a faster initial acceleration and sustained velocity than is prescribed by the current standard if they are to accurately approximate forces relative to existing push/pull guidelines. Future work should also develop recommendations for measuring turning forces.

Biomechanical analysis of common solid waste collection throwing techniques using OpenSim and an EMG-assisted solver

The solid waste collection industry is one of the most common occupations resulting in low back pain (LBP). Lumbar peak joint reaction forces and peak and integrated moments are strong correlates of LBP. To investigate these risks, this study compared three common waste collection throwing techniques of varying lumbar symmetry: the symmetric (SYM) technique, the asymmetric fixed stance (AFS) technique, and the asymmetric with pivot (AWP) technique. Lumbar moments and joint reaction loads were computed for throwing garbage bags of 3, 7, and 11 kg to quantify the effects that technique and object weight have on LBP risk. LBP risk factors were computed using a full-body musculoskeletal model in OpenSim. Muscle activations were estimated using two methods: the EMG-assisted method, which included electromyography data in the solution, and the conventional static optimization method, which did not. The EMG-assisted method more accurately reproduced measured muscle activation, resulting in significantly larger peak compressive and shear forces (p < 0.05) of magnitudes indicative of LBP risk. Risk factors associated with the SYM technique were either larger or not statistically different compared to the asymmetric techniques for the 3 kg condition; however, the opposite result occurred for the 7 and 11 kg conditions (p < 0.05). These results suggest using rapid, asymmetric techniques when handling lightweight objects and slower, symmetric techniques for heavier objects to reduce LBP risk during waste collection throwing techniques. Results indicating increased risk between asymmetric techniques were mostly inconclusive. As expected, increasing bag mass generally increased LBP risk factors, regardless of technique (p < 0.05).

Work-related stress levels and musculoskeletal disorders among municipal solid waste collectors in Ankara

BACKGROUND

Industrialization and rising standards of living have contributed to a growing amount of solid waste and consequent disposal problems. Solid waste collection is among the occupations with the highest risk for musculoskeletal disorders.

OBJECTIVE

We have conducted this study to assess musculoskeletal complaints and work-related stress levels among municipal solid waste (MSW) collectors.

METHODS

The subjects were all currently employed at the MSW Department of the City of Ankara, Turkey. Validated questionnaires were completed by 267 MSW collectors. Data analysis was performed using SPSS software (22.0 version).

RESULTS

Upper back pain rate was 89.1% among the collectors. 47.9% of collectors reported having had upper back pain during the last 12 months and 38.7% had experienced it during the last month. 80.9% of the sample complained of shoulder pain. Wrists/hands and neck pain rates were found at rates of 78.7% and 67.8% respectively. Psychological demands, were significantly higher among MSW collectors living with moderate-severe pain.

CONCLUSIONS

Ergonomics education, healthy work habits, occupational safety training and improvements in the psychosocial work environment should be considered.

Individual, physical, and organizational risk factors for musculoskeletal disorders among municipality solid waste collectors in Shiraz, Iran

In Iran-Shiraz, municipal solid waste is collected manually requiring strenuous physical activities. This study was conducted to determine the prevalence rate of musculoskeletal disorders (MSDs) and its associated risk factors. Two hundred male waste collectors participated in this cross-sectional study, in which task analysis followed by motion and timeline analysis were performed. The data were collected using demographic, occupation-specific physical and organizational demands, and Nordic musculoskeletal questionnaires. Logistic regression analysis was used for identifying independent risk factors for MSDs. Ten motions observed during waste collection, and the most physical and organizational demands were related to the running along with bag carriage, and the time pressure, respectively. About 39% and 36.5% of the workers reported very high physical and psychological workloads, respectively. Totally, 92.5% of waste collectors reported MSDs symptom at least in one body region during the last 12 months. Lower back and knee injuries were more prevalent and more severe. Some individual factors (age, body weight, and waste collecting duration), physical demands (lifting bag/bucket, pulling/pushing waste container, walking along with bag/bucket carriage, and jumping up/down on the garbage truck), and organizational demands (low vacation and high decision authority) were the most important risk factors for developing MSDs.

Biomechanically determined hand force limits protecting the low back during occupational pushing and pulling tasks

Though biomechanically determined guidelines exist for lifting, existing recommendations for pushing and pulling were developed using a psychophysical approach. The current study aimed to establish objective hand force limits based on the results of a biomechanical assessment of the forces on the lumbar spine during occupational pushing and pulling activities. Sixty-two subjects performed pushing and pulling tasks in a laboratory setting. An electromyography-assisted biomechanical model estimated spinal loads, while hand force and turning torque were measured via hand transducers. Mixed modelling techniques correlated spinal load with hand force or torque throughout a wide range of exposures in order to develop biomechanically determined hand force and torque limits. Exertion type, exertion direction, handle height and their interactions significantly influenced dependent measures of spinal load, hand force and turning torque. The biomechanically determined guidelines presented herein are up to 30% lower than comparable psychophysically derived limits and particularly more protective for straight pushing. Practitioner Summary: This study utilises a biomechanical model to develop objective biomechanically determined push/pull risk limits assessed via hand forces and turning torque. These limits can be up to 30% lower than existing psychophysically determined pushing and pulling recommendations. Practitioners should consider implementing these guidelines in both risk assessment and workplace design moving forward.

Trunk response and stability in standing under sagittal-symmetric pull-push forces at different orientations, elevations and magnitudes

To reduce lifting and associated low back injuries, manual material handling operations often involve pulling-pushing of carts at different weights, orientations, and heights. The loads on spine and risk of injury however need to be investigated. The aim of this study was to evaluate muscle forces, spinal loads and trunk stability in pull-push tasks in sagittal-symmetric, static upright standing posture. Three hand-held load magnitudes (80, 120 and 160 N) at four elevations (0, 20, 40 and 60 cm to the L5-S1) and 24 force directions covering all pull/push orientations were considered. For this purpose, a musculoskeletal finite element model with kinematics measured earlier were used. Results demonstrated that peak spinal forces occur under inclined pull (lift) at upper elevations but inclined push at the lowermost one. Minimal spinal loads, on the other hand, occurred at and around vertical pull directions. Overall, spinal forces closely followed variations in the net external moment of pull-push forces at the L5-S1. Local lumbar muscles were most active in pulls while global extensor muscles in lifts. The trunk stability margin decreased with load elevation except at and around horizontal push; it peaked under pulls and reached minimum at vertical lifts. It also increased with antagonist activity in muscles and intra-abdominal pressure. Results provide insight into the marked effects of variation in the load orientation and elevation on muscle forces, spinal loads and trunk stability and hence offer help in rehabilitation, performance enhancement training and design of safer workplaces.

Comparative assessment of respiratory and other occupational health effects among elementary workers

Objective. This study was conducted to assess hazards faced by elementary workers. Methods. A questionnaire survey and a respiratory function test (spirometry) were carried out on 150 respondents. Results. Major hazards identified related to sharp objects, heavy weight lifting, thermally harsh conditions, working at height, whole body vibration, chemicals, pathogens, increased noise levels and confined space entry. Workers suffered from upper and lower respiratory disorder symptoms, digestive problems, optical and musculoskeletal issues, etc. Spirometric measurement showed obstructive lung disorders to be highest among construction workers (CW) (48%) followed by sanitation workers (SW) (32%) and solid waste pickers (SWP) (28%). Restrictive lung pattern was dominant among SW (56%) followed by SWP (46%) and CW (42%). The observed FEV₁/FVC in diseased SWP, SW and CW ranged from 51 to 96%, from 52 to 98% and from 31 to 99% respectively while observed mean FEV₁ was 2.15, 1.79 and 1.70 L, respectively. Conclusion. The study findings show that occupational exposure can significantly influence respiratory system impairment and contribute to other ailments among elementary workers. The study recommends use of appropriate protective equipment and regular medical examination for early recognition of any health risk so that timely interventions for effective management may be undertaken.

Pushing, pulling and manoeuvring an industrial cart: a psychophysiological study

One of the most frequent manual occupational tasks involves the pushing and pulling of a cart. Although several studies have associated health risks with pushing and pulling, the effects are not clear since occupational tasks have social, cognitive and physical components. The present work investigates a real case of a pushing and pulling occupational task from a manufacturing company. The study initially characterizes the case in accordance with Standard No. ISO 11228-2:2007 as low risk. An experiment with 14 individuals during three modalities of pushing and pulling was performed in order to further investigate the task with the application of electrophysiology. At the end, a simple questionnaire was given. The results show electrophysiological differences among the three modalities of pushing and pulling, with a major difference between action with no load and fully loaded with a full range of motions on the cart to handle.

Bioaerosols, Noise, and Ultraviolet Radiation Exposures for Municipal Solid Waste Handlers

Few studies have investigated the occupational hazards of municipal solid waste workers, particularly in developing countries. Resultantly these workers are currently exposed to unknown and unabated occupational hazards that may endanger their health. We determined municipal solid waste workers' work related hazards and associated adverse health endpoints. A multifaceted approach was utilised comprising bioaerosols sampling, occupational noise, thermal conditions measurement, and field based waste compositional analysis. Results from our current study showed highest exposure concentrations for Gram-negative bacteria (6.8 × 103 cfu/m3) and fungi (12.8 × 103 cfu/m3), in the truck cabins. Significant proportions of toxic, infectious, and surgical waste were observed. Conclusively, municipal solid waste workers are exposed to diverse work related risks requiring urgent sound interventions. A framework for assessing occupational risks of these workers must prioritize performance of exposure assessment with regard to the physical, biological, and chemical hazards of the job.

A biologically-assisted curved muscle model of the lumbar spine: Model structure

BACKGROUND

Biomechanical models have been developed to assess the spine tissue loads of individuals. However, most models have assumed trunk muscle lines of action as straight-lines, which might be less reliable during occupational tasks that require complex lumbar motions. The objective of this study was to describe the model structure and underlying logic of a biologically-assisted curved muscle model of the lumbar spine.

METHODS

The developed model structure including curved muscle geometry, separation of active and passive muscle forces, and personalization of muscle properties was described. An example of the model procedure including data collection, personalization, and data evaluation was also illustrated.

FINDINGS

Three-dimensional curved muscle geometry was developed based on a predictive model using magnetic resonance imaging and anthropometric measures to personalize the model for each individual. Calibration algorithms were able to reverse-engineer personalized muscle properties to calculate active and passive muscle forces of each individual.

INTERPRETATION

This biologically-assisted curved muscle model will significantly increase the accuracy of spinal tissue load predictions for the entire lumbar spine during complex dynamic occupational tasks. Personalized active and passive muscle force algorithms will help to more robustly investigate person-specific muscle forces and spinal tissue loads.

Human Body Mechanics of Pushing and Pulling: Analyzing the Factors of Task-related Strain on the Musculoskeletal System

The purpose of this review is to name and describe the important factors of musculoskeletal strain originating from pushing and pulling tasks such as cart handling that are commonly found in industrial contexts. A literature database search was performed using the research platform Web of Science. For a study to be included in this review differences in measured or calculated strain had to be investigated with regard to: (1) cart weight/ load; (2) handle position and design; (3) exerted forces; (4) handling task (push and pull); or (5) task experience. Thirteen studies met the inclusion criteria and proved to be of adequate methodological quality by the standards of the Alberta Heritage Foundation for Medical Research. External load or cart weight proved to be the most influential factor of strain. The ideal handle positions ranged from hip to shoulder height and were dependent on the strain factor that was focused on as well as the handling task. Furthermore, task experience and subsequently handling technique were also key to reducing strain. Workplace settings that regularly involve pushing and pulling should be checked for potential improvements with regards to lower weight of the loaded handling device, handle design, and good practice guidelines to further reduce musculoskeletal disease prevalence.

A systematic critical review of epidemiological studies on public health concerns of municipal solid waste handling

AIMS

The ultimate aim of this review was to summarise the epidemiological evidence on the association between municipal solid waste management operations and health risks to populations residing near landfills and incinerators, waste workers and recyclers. To accomplish this, the sub-aims of this review article were to (1) examine the health risks posed by municipal solid waste management activities, (2) determine the strengths and gaps of available literature on health risks from municipal waste management operations and (3) suggest possible research needs for future studies.

METHODS

The article reviewed epidemiological literature on public health concerns of municipal solid waste handling published in the period 1995-2014. The PubMed and MEDLINE computerised literature searches were employed to identify the relevant papers using the keywords solid waste, waste management, health risks, recycling, landfills and incinerators. Additionally, all references of potential papers were examined to determine more articles that met the inclusion criteria.

RESULTS

A total of 379 papers were identified, but after intensive screening only 72 met the inclusion criteria and were reviewed. Of these studies, 33 were on adverse health effects in communities living near waste dumpsites or incinerators, 24 on municipal solid waste workers and 15 on informal waste recyclers. Reviewed studies were unable to demonstrate a causal or non-causal relationship due to various limitations.

CONCLUSION

In light of the above findings, our review concludes that overall epidemiological evidence in reviewed articles is inadequate mainly due to methodological limitations and future research needs to develop tools capable of demonstrating causal or non-causal relationships between specific waste management operations and adverse health endpoints.

Musculoskeletal disorders among municipal solid waste workers in India: A cross-sectional risk assessment

Background:

Waste management is a necessary activity around the world, but involves a variety of health hazards. In a developing country like India, municipal solid waste is collected manually requiring heavy physical activity. Among all occupational health issues, musculoskeletal problems are common among waste collectors in the form of nonfatal injuries because of the presence of such risk factors (lifting, carrying, pulling, and pushing). We have thus conducted this study to evaluate musculoskeletal disorders (MSDs) among municipal solid waste (MSW) workers.

Methodology:

A cross-sectional study using probability proportionate to size sampling, recruited 220 MSW workers from the Chennai Municipal Corporation, India for this study. A pretested validated questionnaire has been used to collect data on demographic and occupational history and information on musculoskeletal pain. Data analysis was performed using R software (3.0.1 version).

Results:

70% of the participants reported that they had been troubled with musculoskeletal pain in one or more of the 9 defined body regions during the last 12 months, whereas 91.8% had pain during the last 7 days. Higher prevalence of symptoms in knees, shoulders, and lower back was found to be 84.5%, 74.5%, and 50.9% respectively. Female illiterate workers with lower socioeconomic status were found to have higher odds for MSDs. Similarly, higher body mass index having no physical activity increases the chance of odds having MSDs.

Conclusion:

The higher percentage of musculoskeletal symptoms among MSW workers could be attributed to the long duration of employment, the low job control, and the nature of their job, which is physically demanding. A workplace of health promotion model integration can minimize the reported high prevalence, and a prospective cohort study could be recommended further.

Assessing the impact of waste picking on musculoskeletal disorders among waste pickers in Mumbai, India: a cross-sectional study

OBJECTIVE

To assess the prevalence of musculoskeletal disorders (MSDs) as well as the impact of the occupation of waste picking on complaints of MSDs among waste pickers. The study attempts to understand the risk factors for MSDs in various areas of the body.

DESIGN

A cross-sectional household survey was conducted using a case-control design. The survey instrument for measuring musculoskeletal symptoms was adopted from a standardised Nordic questionnaire. The impact of the occupation of waste picking on MSDs was analysed using the propensity score matching (PSM) method.

PARTICIPANTS

The study population consisted of waste pickers (n=200) who had been working for at least a year and a control group (n=213) selected from among or living close to the same communities.

RESULTS

The 12-month prevalence of MSDs was higher among waste pickers (79%) compared to controls (55%) particularly in the lower back (54-36%), knee (48-35%), upper back (40-21%) and shoulder (32-12%). Similar patterns were observed in the 12-month prevalence of MSDs which prevented normal activity inside and outside the home, particularly for the lower back (36-21%), shoulder (21-7%) and upper back (25-12%) for waste pickers and controls. Analysis of the impact of waste picking on complaints of MSDs suggests that the occupation of waste picking raises the risk of MSDs particularly in the shoulder, lower and upper back. Older age and longer duration of work are significant risk factors for MSDs.

CONCLUSIONS

The findings suggest a relatively higher prevalence of MSDs among waste pickers, particularly in the lower and upper back and shoulder, compared to controls. Preventive measures and treatment to minimise the burden of MSDs among waste pickers are strongly recommended.

Manual handling: differences in perceived effort, success rate and kinematics between three different pushing techniques

This study examined the perceived effort, success rates and kinematics for three push strategies in a simulated lateral patient transfer (horizontal slide). Thirteen healthy subjects (four males) completed three repetition pushing loads of 6, 10 and 14 kg in random order; with a spontaneous push strategy, then with a straight-back bent-knees (squat) strategy and the preparatory pelvic movement ('rockback') strategy in random order. Perceived effort and kinematic parameters measured at the onset of movement and at maximum push excursion were compared between strategies and between loads with repeated measures ANOVA. The spontaneous and 'rockback' strategies achieved the pushing task with less perceived effort across all loads than the squat push (P < 0.001). Only 3/13 participants were successful on all attempts at pushing the 14 kg load using a squat strategy, which contrasted with 12/13 participants when the spontaneous strategy or the 'rockback' strategy was used. Forward movement of the pelvis and forward trunk inclination may be positively associated with lower perceived effort in the push task. Practitioner Summary: In a manual-handling task that simulated a lateral patient transfer (horizontal slide), perceived effort and success rates of three push strategies were compared. A straight-back bent-knees push (squat) strategy demonstrated greater perceived effort and lower success rates than a spontaneous push strategy, or a push strategy with preparatory 'rockback' pelvic movement.

Are pushing and pulling work-related risk factors for upper extremity symptoms? A systematic review of observational studies

Systematically review observational studies concerning the question whether workers that perform pushing/pulling activities have an increased risk for upper extremity symptoms as compared to workers that perform no pushing/pulling activities. A search in MEDLINE via PubMed and EMBASE was performed with work-related search terms combined with push/pushing/pull/pulling. Studies had to examine exposure to pushing/pulling in relation to upper extremity symptoms. Two authors performed the literature selection and assessment of the risk of bias in the studies independently. A best evidence synthesis was used to draw conclusions in terms of strong, moderate or conflicting/insufficient evidence. The search resulted in 4764 studies. Seven studies were included, with three of them of low risk of bias, in total including 8279 participants. A positive significant relationship with upper extremity symptoms was observed in all four prospective cohort studies with effect sizes varying between 1.5 and 4.9. Two out of the three remaining studies also reported a positive association with upper extremity symptoms. In addition, significant positive associations with neck/shoulder symptoms were found in two prospective cohort studies with effect sizes of 1.5 and 1.6, and with shoulder symptoms in one of two cross-sectional studies with an effect size of 2.1. There is strong evidence that pushing/pulling is related to upper extremity symptoms, specifically for shoulder symptoms. There is insufficient or conflicting evidence that pushing/pulling is related to (combinations of) upper arm, elbow, forearm, wrist or hand symptoms.

L4-L5 compression and anterior/posterior joint shear forces in cabin attendants during the initial push/pull actions of airplane meal carts

The aim of the present study was to assess the acute low back load of cabin attendants during cart handling and to identify working situations which present the highest strain on the worker. In a setup, 17 cabin attendants (ten females and seven males) pushed, pulled and turned a 20 kg standard meal cart (L: 0.5m × W: 0.3 m × H: 0.92 m) loaded with extra 20 kg and 40 kg, respectively on two different surfaces (carpet and linoleum) and at three floor inclinations (-2°, 0° and +2°). Two force transducers were mounted as handles. Two-dimensional movement analysis was performed and a 4D WATBAK modelling tool was used to calculate the acute L4-L5 load. No working situations created loads greater than the accepted values for single exertions, however compression and anterior/posterior shear forces during pulling and turning were much higher when compared with pushing. There were significant effects of handling the cart on different floor types, at the varying inclinations and with different cart weights. Additionally, when external forces were reduced, the cabin attendants did not decrease push/pull force proportionally and thus the L4-L5 load did not decrease as much as expected.

Psychophysical basis for maximum pushing and pulling forces: A review and recommendations

The objective of this paper was to perform a comprehensive review of psychophysically determined maximum acceptable pushing and pulling forces. Factors affecting pushing and pulling forces are identified and discussed. Recent studies show a significant decrease (compared to previous studies) in maximum acceptable forces for males but not for females when pushing and pulling on a treadmill. A comparison of pushing and pulling forces measured using a high inertia cart with those measured on a treadmill shows that the pushing and pulling forces using high inertia cart are higher for males but are about the same for females. It is concluded that the recommendations of Snook and Ciriello (1991) for pushing and pulling forces are still valid and provide reasonable recommendations for ergonomics practitioners. Regression equations as a function of handle height, frequency of exertion and pushing/pulling distance are provided to estimate maximum initial and sustained forces for pushing and pulling acceptable to 75% male and female workers. At present it is not clear whether pushing or pulling should be favored. Similarly, it is not clear what handle heights would be optimal for pushing and pulling. Epidemiological studies are needed to determine relationships between psychophysically determined maximum acceptable pushing and pulling forces and risk of musculoskeletal injuries, in particular to low back and shoulders.

The influence of precision requirements and cognitive challenges on upper extremity joint reaction forces, moments and muscle force estimates during prolonged repetitive lifting

Prolonged repetitive lifting is a whole-body exertion. Despite this, the roles and physical exposures of the upper extremities are frequently neglected. The influence of precision requirements and cognitive distractions on upper extremity responses when lifting was evaluated by quantifying several biomechanical upper extremity quantities. Nine participants completed four 30-min lifting tasks with and without simultaneous cognitive distractions and/or precision placement constraints. Specific metrics evaluated were joint reaction forces and moments (wrist, elbow and shoulder) and modelled shoulder muscle forces (38 defined shoulder muscle mechanical elements). The addition of a precision requirement increased several metrics by up to 43%, while the addition of the cognitive distraction task had minimal influence. Furthermore, several metrics decreased by up to 14% after the first 10 min of lifting, suggesting a temporal change of lifting strategy.

PRACTITIONER SUMMARY

Lifting tasks often include precision placements and cognitive demands. This study shows that precision placement during prolonged repetitive lifting increases upper extremity forces and moments, while the addition of a cognitive task is benign. Furthermore, field assessments of repetitive lifting should include observations longer than 10 min, as adaptive strategies appear to be adopted.

Biomechanical loading of the shoulder complex and lumbosacral joints during dynamic cart pushing task

The primary objective of this study was to quantify the effect of dynamic cart pushing exertions on the biomechanical loading of shoulder and low back. Ten participants performed cart pushing tasks on flat (0°), 5°, and 10° ramped walkways at 20 kg, 30 kg, and 40 kg weight conditions. An optoelectronic motion capturing system configured with two force plates was used for the kinematic and ground reaction force data collection. The experimental data was modeled using AnyBody modeling system to compute three-dimensional peak reaction forces at the shoulder complex (sternoclavicular, acromioclavicular, and glenohumeral) and low back (lumbosacral) joints. The main effect of walkway gradient and cart weight, and gradient by weight interaction on the biomechanical loading of shoulder complex and low back joints was statistically significant (all p < 0.001). At the lumbosacral joint, negligible loading in the mediolateral direction was observed compared to the anterioposterior and compression directions. Among the shoulder complex joints, the peak reaction forces at the acromioclavicular and glenohumeral joints were comparable and much higher than the sternoclavicular joint. Increased shear loading of the lumbosacral joint, distraction loading of glenohumeral joint and inferosuperior loading of the acromioclavicular joint may contribute to the risk of work-related low back and shoulder musculoskeletal disorder with prolonged and repetitive use of carts.

Scapular kinematics and muscle activities during pushing tasks

OBJECTIVES

Pushing tasks are functional activities of daily living. However, shoulder complaints exist among workers exposed to regular pushing conditions. It is crucial to investigate the control of shoulder girdles during pushing tasks. The objective of the study was to demonstrate scapular muscle activities and motions on the dominant side during pushing tasks and the relationship between scapular kinematics and muscle activities in different pushing conditions.

METHODS

Thirty healthy adults were recruited to push a four-wheel cart in six pushing conditions. The electromyographic signals of the upper trapezius (UT) and serratus anterior (SA) muscles were recorded. A video-based system was used for measuring the movement of the shoulder girdle and scapular kinematics. Differences in scapular kinematics and muscle activities due to the effects of handle heights and weights of the cart were analyzed using two-way ANOVA with repeated measures. The relationships between scapular kinematics and muscle activities were examined by Pearson's correlation coefficients.

RESULTS

The changes in upper trapezius and serratus anterior muscle activities increased significantly with increased pushing weights in the one-step pushing phase. The UT/SA ratio on the dominant side decreases significantly with increased handle heights in the one-step pushing phase. The changes in upward rotation, lateral slide and elevation of the scapula decreased with increased pushing loads in the trunk-forward pushing phase.

CONCLUSIONS

This study indicated that increased pushing loads result in decreased motions of upward rotation, lateral slide and elevation of the scapula; decreased handle heights result in relatively increased activities of the serratus anterior muscles during pushing tasks.

Shoulder joint loading and posture during medicine cart pushing task

Excessive physical loads and awkward shoulder postures during pushing and pulling are risk factors for shoulder pain. Pushing a medicine cart is a major component of a work shift for nurses and medical assistants in hospitals and other health care facilities. A laboratory experiment was conducted to examine the effects of common factors (e.g., lane congestion, cart load stability, floor surface friction) on shoulder joint moment and shoulder elevation angle of participants during cart pushing. Participants pushed a medicine cart on straight tracks and turning around right-angle corners. Peak shoulder joint moments reached 25.1 Nm, 20.3 Nm, and 26.8 Nm for initial, transition, and turning phases of the pushing tasks, indicating that shoulder joint loading while pushing a medical cart is comparable to levels previously reported from heavy manual activities encountered in industry (e.g., garbage collection). Also, except for user experience, all other main study factors, including congestion level, cart load stability, location of transition strip, shoulder tendency, surface friction, and handedness, significantly influenced shoulder joint moment and shoulder elevation angle. The findings provide a better understanding of shoulder exposures associated with medicine cart operations and may be helpful in designing and optimizing the physical environment where medicine carts are used.

The complex spine: the multidimensional system of causal pathways for low-back disorders

OBJECTIVE

The aim of this study was to examine the logic behind the knowledge of low-back problem causal pathways.

BACKGROUND

Low-back pain and low-back disorders (LBDs) continue to represent the major musculoskeletal risk problem in the workplace,with the prevalence and costs of such disorders increasing over time. In recent years, there has been much criticism of the ability of ergonomics methods to control the risk of LBDs.

METHOD

Logical assessment of the systems logic associated with our understanding and prevention of LBDs.

RESULTS

Current spine loading as well as spine tolerance research efforts are bringing the field to the point where there is a better systems understanding of the inextricable link between the musculoskeletal system and the cognitive system. Loading is influenced by both the physical environment factors as well as mental demands, whereas tolerances are defined by both physical tissue tolerance and biochemically based tissue sensitivities to pain. However, the logic used in many low-back risk assessment tools may be overly simplistic, given what is understood about causal pathways. Current tools typically assess only load or position in a very cursory manner.

CONCLUSION

Efforts must work toward satisfying both the physical environment and the cognitive environment for the worker if one is to reliably lower the risk of low-back problems.

APPLICATION

This systems representation of LBD development may serve as a guide to identify gaps in our understanding of LBDs.

Association between spinal loads and the psychophysical determination of maximum acceptable force during pushing tasks

The objective of this study was to investigate potential associations between an individual's psychophysical maximum acceptable force (MAF) during pushing tasks and biomechanical tissue loads within the lumbar spine. Ten subjects (eight males, two females) pushed a cart with an unknown weight at one push every two minute for a distance of 3.9 m. Two independent variables were investigated, cart control and handle orientation while evaluating their association with the MAF. Dependent variables of hand force and tissue loads for each MAF determination and preceding push trial were assessed using a validated, electromyography-assisted biomechanical model that calculated spinal load distribution throughout the lumbar spine. Results showed no association between spinal loads and the MAF. Only hand forces were associated with the MAF. Therefore, MAFs may be dependent upon tactile sensations from the hands, not the loads on the spine and thus may be unrelated to risk of low back injury. Practitioner Summary: Pushing tasks have become common in manual materials handling (MMH) and these tasks impose different tissue loads compared to lifting tasks. Industry has commonly used the psychophysical tables for job assent and decision of MMH tasks. However, due to the biomechanical complexity of pushing tasks, psychophysics may be misinterpreting risk.

Musculoskeletal disorders among municipal solid waste collectors in Mansoura, Egypt: a cross-sectional study

OBJECTIVE

To assess the percentage of musculoskeletal complaints and their possible risk factors among municipal solid waste (MSW) collectors.

DESIGN

A descriptive cross-sectional study with a comparison group.

SETTING

Primary level of care, at the Western Municipality of Mansoura City, Egypt.

PARTICIPANTS

A total of 160 male MSW collectors fulfilled the eligibility criteria and 120 of them participated in the study (response rate of 75%). The inclusion criteria were permanent or temporary solid waste collectors employed for 1 year or more. A comparison group of 110 male service workers at the Faculty of Medicine, Mansoura University, comparable to MSW collectors in most of the variables.

OUTCOME

The percentage of musculoskeletal disorders (MSDs) among collectors, their risk factors (socio-demographic, psychosocial, physical), and the independent risk factors for having the disorders.

RESULTS

The percentage of musculoskeletal complaints during the past 12 months was higher among MSW collectors (60.8%) than the comparison group (43.6%). Low back was the most frequently affected body region among MSW collectors. The differences in the distribution of musculoskeletal complaints between the two groups were statistically significant for the neck and hip/thigh regions. Logistic regression analysis revealed that the independent risk factors for musculoskeletal symptoms among MSW collectors were the longer duration of employment (OR=0.4, 95% CI=0.1 to 0.9); low decision latitude (OR=0.3, 95% CI=0.1 to 0.7); lifting, pulling; pushing/carrying loads >20 kg (OR=5.5, 95% CI=1.8 to 17.0) and walking for long periods of time (OR=2.6, 95% CI=1.1 to 6.6).

CONCLUSIONS

Musculoskeletal complaints are highly prevalent among MSW collectors which require engineering, medical and legislative measures. We suggest further research in the interventions that could reduce the high percentage among collectors.

Health and safety in waste collection: Towards evidence-based worker health surveillance

BACKGROUND

Waste collectors around the world are at risk for work-related disorders and injuries. The aim of this study was to assess work demands, acute physiologic responses, illnesses, and injuries as a starting point for worker health surveillance (WHS).

METHODS

A systematic search was performed in PubMed and Embase on work demands, acute bodily responses, health, and injuries. A quality assessment and evidence synthesis was performed.

RESULTS

From a total of 379 retrieved studies, 50 studies fulfilled the inclusion criteria. Waste collecting varied from informal manual gathering to semi-automated systems. Most studies ("number of studies") on work demands and/or acute bodily responses addressed bioaerosols (14). Studies of health effects addressed respiratory complaints (8), and those on injuries addressed acute musculoskeletal disorders (3). Strong evidence is available that exposure to bioaerosols exceeds recommendations. Moderate evidence is available for an increased risk of respiratory complaints and musculoskeletal injuries, with significant odds ratios reported varying between 1.9-4.1 and 1.5-3.3, respectively. Limited evidence exists for gastrointestinal disorders and hearing loss.

CONCLUSIONS

WHS in waste collection is warranted for early detection of respiratory, gastrointestinal, and musculoskeletal disorders, and hearing loss.

Loading along the lumbar spine as influence by speed, control, load magnitude, and handle height during pushing

BACKGROUND

Low back loading and risk associated with pushing activities have been poorly understood. Previous studies have demonstrated that increases in anterior/posterior shear forces are primarily initiated by antagonistic coactivity within the torso. Yet, few studies have considered the range of activities that might contribute to the antagonistic coactivation and subsequent spine loading.

METHODS

Twenty subjects were tested to examine how various physical factors might influence spine loads during pushing tasks that workers might experience in industrial settings. Load magnitude, speed of push, required control, and handle height were varied while pushing both carts and overhead suspended loads. A biologically-assisted biomechanical model was used to assess compression, anterior/posterior shear, and lateral shear over the various levels of the lumbar spine.

FINDINGS

Anterior/posterior shear loads were greatest at the upper levels of the lumbar spine and of a magnitude that would be of concern. Anterior/posterior shear was influenced by all experimental factors to varying degrees except for the nature of the load (cart vs. suspended).

INTERPRETATION

This study confirms the notion that pushing and pulling is not as simple a task as once believed since it entails a complex biomechanical activity. Spine shear forces result from a complex coactivation of trunk muscle activities and spine orientations that are influenced by several occupational factors. This study may help explain why low back pain rates in some work environments associated with lifting may not be reduced even when lifting interventions (that change the task from lifting to pushing) are employed.

Spine loading at different lumbar levels during pushing and pulling

As the nature of many materials handling tasks have begun to change from lifting to pushing and pulling, it is important that one understands the biomechanical nature of the risk to which the lumbar spine is exposed. Most previous assessments of push-pull tasks have employed models that may not be sensitive enough to consider the effects of the antagonistic cocontraction occurring during complex pushing and pulling motions in understanding the risk to the spine and the few that have considered the impact of cocontraction only consider spine load at one lumbar level. This study used an electromyography-assisted biomechanical model sensitive to complex motions to assess spine loadings throughout the lumbar spine as 10 males and 10 females pushed and pulled loads at three different handle heights and of three different load magnitudes. Pulling induced greater spine compressive loads than pushing, whereas the reverse was true for shear loads at the different lumbar levels. The results indicate that, under these conditions, anterior-posterior (A/P) shear loads were of sufficient magnitude to be of concern especially at the upper lumbar levels. Pushing and pulling loads equivalent to 20% of body weight appeared to be the limit of acceptable exertions, while pulling at low and medium handle heights (50% and 65% of stature) minimised A/P shear. These findings provide insight to the nature of spine loads and their potential risk to the low back during modern exertions.

Effects of trunk exertion force and direction on postural control of the trunk during unstable sitting

BACKGROUND

Pushing and pulling exertions have been implicated as risk factors of low-back disorders. In an attempt to investigate the mechanisms by which pushing and pulling influence risk for low-back disorders, the goal of this study was to investigate the effects of trunk exertion force and exertion direction on postural control of the trunk during unstable sitting.

METHODS

Seat movements were recorded while subjects maintained a seated posture on a wobbly chair against different exertion forces (0N, 40N, and 80N) and exertion directions (trunk flexion and extension). Postural control of the trunk was assessed from kinematic variability (root-mean-squared amplitude and 95% ellipse area) and non-linear stability analyses (stability diffusion exponent and maximum finite-time Lyapunov exponent).

FINDINGS

Kinematic variability and non-linear stability estimates increased as exertion force increased including root-mean-squared amplitude (P<0.001), 95% ellipse area (P<0.001), stability diffusion exponent (P=0.042), and maximum finite-time Lyapunov exponent (P<0.001). A subset of measures indicated postural control of the trunk was poorer during flexion exertions compared to extension exertions including root-mean-squared amplitude (P<0.001), 95% ellipse area (P=0.046), and maximum finite-time Lyapunov exponent (P=0.002).

INTERPRETATION

Trunk exertion force and exertion direction affect postural control of the trunk. This study may aid in understanding how pushing and pulling exertions can potentially contribute to low-back disorders.

Effect of block weight on work demands and physical workload during masonry work

The effect of block weight on work demands and physical workload was determined for masons who laid sandstone building blocks over the course of a full work day. Three groups of five sandstone block masons participated. Each group worked with a different block weight: 11 kg, 14 kg or 16 kg. Productivity and durations of tasks and activities were assessed through real time observations at the work site. Energetic workload was also assessed through monitoring the heart rate and oxygen consumption at the work site. Spinal load of the low back was estimated by calculating the cumulated elastic energy stored in the lumbar spine using durations of activities and previous data on corresponding compression forces. Block weight had no effect on productivity, duration or frequency of tasks and activities, energetic workload or cumulative spinal load. Working with any of the block weights exceeded exposure guidelines for work demands and physical workload. This implies that, regardless of block weight in the range of 11 to 16 kg, mechanical lifting equipment or devices to adjust work height should be implemented to substantially lower the risk of low back injuries.

The role of whole body vibration, posture and manual materials handling as risk factors for low back pain in occupational drivers

It seems evident that occupational drivers have an increased risk of developing back pain. Not only are they exposed to whole body vibration (vibration), their work often includes exposure to several other risk factors for low back pain (LBP), particularly the seated posture (posture) and manual materials handling (MMH). Excessive demands on posture are likely to be aggravated by vibration and vice versa, and the risks may be further compounded when MMH is performed. This study investigated the relative role of vibration, posture and MMH as risk factors for LBP and the stated hypothesis was that the risks for LBP in drivers are the combined effect of vibration, posture and/or MMH. The findings showed that interaction effects due to posture and one or both of vibration and MMH, rather than the individual exposure effects, are the main contributors for precipitation of LBP.

Active trunk stiffness during voluntary isometric flexion and extension exertions

OBJECTIVE

Compare muscle activity and trunk stiffness during isometric trunk flexion and extension exertions.

BACKGROUND

Elastic stiffness of the torso musculature is considered the primary stabilizing mechanism of the spine. Therefore, stiffness of the trunk during voluntary exertions provides insight into the stabilizing control of pushing and pulling tasks.

METHODS

Twelve participants maintained an upright posture against external flexion and extension loads applied to the trunk. Trunk stiffness, damping, and mass were determined from the dynamic relation between pseudorandom force disturbances and subsequent small-amplitude trunk movements recorded during the voluntary exertions. Muscle activity was recorded from rectus abdominus, external oblique, lumbar paraspinal, and internal oblique muscle groups.

RESULTS

Normalized electromyographic activity indicated greater antagonistic muscle recruitment during flexion exertions than during extension. Trunk stiffness was significantly greater during flexion exertions than during extension exertions despite similar levels of applied force. Trunk stiffness increased with exertion effort.

CONCLUSION

Theoretical and empirical analyses reveal that greater antagonistic cocontraction is required to maintain spinal stability during trunk flexion exertions than during extension exertions. Measured differences in active trunk stiffness were attributed to antagonistic activity during flexion exertions with possible contributions from spinal kinematics and muscle lines of action.

APPLICATION

When compared with trunk extension exertions, trunk flexion exertions such as pushing tasks require unique neuromuscular control that is not simply explained by differences in exertion direction. Biomechanical analyses of flexion tasks must consider the stabilizing muscle recruitment patterns when evaluating spinal compression and shear loads.

Pushing and pulling: personal mechanics influence spine loads

This study assessed several mechanical issues related to low back loading during pushing and/or pulling tasks. Nine male participants performed two-handed pushing and pulling tasks at two handle heights with three loads, using a cable pulley system. Four of these men were professional firefighters trained in performing pushing and pulling tasks while the other five were graduate students who lacked manual work experience. The more experienced firefighters produced less spinal compression and shearing forces when compared to the less experienced students under the same conditions. The firefighters were able to create less muscle activation as compared to the students, which indicated a more efficient technique. The main contributing factors to the forces produced on the low back were the quantity of the load being pushed or pulled, handle height, experience level and the technique of the participant. Thus, attempts to set load limits for pushing and pulling tasks are difficult, since technique has such a large influence on back loading. In order to create safer working environments, education on proper pushing and pulling techniques is very important--more important than the physical variables in many cases.

Interface stability influences torso muscle recruitment and spinal load during pushing tasks

Handle or interface design can influence torso muscle recruitment and spinal load during pushing tasks. The objective of the study was to provide insight into the role of interface stability with regard to torso muscle recruitment and biomechanical loads on the spine. Fourteen subjects generated voluntary isometric trunk flexion force against a rigid interface and similar flexion exertions against an unstable interface, which simulated handle design in a cart pushing task. Normalized electromyographic (EMG) activity in the rectus abdominus, external oblique and internal oblique muscles increased with exertion effort. When using the unstable interface, EMG activity in the internal and external oblique muscle groups was greater than when using the rigid interface. Results agreed with trends from a biomechanical model implemented to predict the muscle activation necessary to generate isometric pushing forces and maintain spinal stability when using the two different interface designs. The co-contraction contributed to increased spinal load when using the unstable interface. It was concluded that handle or interface design and stability may influence spinal load and associated risk of musculoskeletal injury during manual materials tasks that involve pushing exertions.

Co-contraction recruitment and spinal load during isometric trunk flexion and extension

BACKGROUND

Pushing and pulling tasks account for 20% of occupational low-back injury claims. Primary torso muscle groups recruited during pushing tasks include rectus abdominis and the external obliques. However, analyses suggest that antagonistic co-contraction of the paraspinal muscles is necessary to stabilize the spine during flexion exertions. The study quantified co-contraction and spinal load differences during isometric flexion and extension exertions. The goal was to provide insight into the mechanisms requiring greater co-contraction during trunk flexion exertions compared to extension exertions.

METHODS

Electromyographic (EMG) signals were recorded from the trunk muscles of healthy volunteers during isometric trunk flexion and extension exertions. A biomechanical model was implemented to estimate total muscle force from the measured EMG and trunk moment data. A similar model estimated the muscle forces necessary to achieve equilibrium while minimizing the sum of squared muscle forces. The difference in these forces represented co-contraction. Spinal load attributed to co-contraction was computed.

RESULTS

Average co-contraction during flexion exertions was approximately twice the value of co-contraction during extension, i.e. 28% and 13% of total muscle forces respectively. Co-contraction accounted for up to 47% of the total spinal load during flexion exertions. Consequently, spinal compression during the flexion tasks was nearly 50% greater than during extension exertions despite similar levels of trunk moment.

INTERPRETATION

Co-contraction must be considered when evaluating spinal load during pushing exertions. Results underscore the need to consider neuromuscular control of spinal stability when evaluating the biomechanical risks.

Effect of job rotation on need for recovery, musculoskeletal complaints, and sick leave due to musculoskeletal complaints: a prospective study among refuse collectors

BACKGROUND

Job rotation might be an effective preventive measure to reduce the prevalence of musculoskeletal complaints, although its effect has not been yet established. The aim of the present study is to evaluate the effect of job rotation in refuse collecting on need for recovery, prevalence of musculoskeletal complaints, and sick leave due to musculoskeletal complaints.

METHODS

A 1-year prospective study among refuse collectors was performed, using standardized questionnaires. Job rotation was performed between collecting two-wheeled containers and driving a refuse truck. The experimental groups of rotating refuse collectors at t(0) and t(1) (group R-R) and non-rotating refuse collectors at t(0) and rotating refuse collectors at t(1) (group NR-R) were compared with a reference group of non-rotating refuse collectors at t(0) and t(1) (group NR-NR).

RESULTS

The adjusted need for recovery of group R-R was marginally significantly lower than need for recovery of the reference group. Groups R-R and NR-R had a more than two times higher risk for complaints of the low back than the reference group. No other significant results were found.

CONCLUSIONS

Job rotation seemed to coincide with a reduced need for recovery and was associated with an increased risk of low back complaints. No effects were found on sick leave due to musculoskeletal complaints. The results might be influenced by the healthy worker selection effect in the reference group and its inverse in the rotating groups.

Low-back biomechanics and static stability during isometric pushing

Pushing and pulling tasks are increasingly prevalent in industrial workplaces. Few studies have investigated low-back biomechanical risk factors associated with pushing, and we are aware of none that has quantified spinal stability during pushing exertions. Data recorded from 11 healthy participants performing isometric pushing exertions demonstrated that trunk posture, vector force direction of the applied load, and trunk moment were influenced (p < .01) by exertion level, elevation of the handle for the pushing task, and foot position. A biomechanical model was used to analyze the posture and hand force data gathered from the pushing exertions. Model results indicate that pushing exertions provide significantly (p < .01) less stability than lifting when antagonistic cocontraction is ignored. However, stability can be augmented by recruitment of muscle cocontraction. Results suggest that cocontraction may be recruited to compensate for the fact that equilibrium mechanics provide little intrinsic trunk stiffness and stability during pushing exertions. If one maintains stability by means of cocontraction, additional spinal load is thereby created, increasing the risk of overload injury. Thus it is important to consider muscle cocontraction when evaluating the biomechanics of pushing exertions. Potential applications of this research include improved assessment of biomechanical risk factors for the design of industrial pushing tasks.