Can exposure variation be promoted in the shoulder girdle muscles by modifying work pace and inserting pauses during simulated assembly work?

Physiological responses, trunk posture, and work pace in commercial building cleaning in Washington State: An observational field study

INTRODUCTION

This study aimed to investigate whether work pace is a critical indicator for predicting a janitor's risk of work-related musculoskeletal disorders (WMSDs).

METHOD

Field measurements were obtained from commercial building janitors as well as the determination of work pace. Physiological responses collected were heart rate, energy expenditure (calories), activity level (METs), steps, trunk posture. Data were obtained using direct measurements, along with a time study, which was performed by shadowing 13 janitors in Washington State. The measured values were summarized descriptively, and five of the most common janitorial tasks were compared. The relationships between work pace and the physiological response variables were determined by calculating the Pearson product-moment correlation coefficients.

RESULTS

The highest average percent heart rate reserve (47.4%) was reported during restroom cleaning, while the highest activity and energy expenditure levels (3.6 METs and 217.1 calories/h) were reported for mopping. The top 90% of trunk flexion angles and the highest percentage of time in trunk flexion from 20° to 60° were recorded during restroom cleaning. Restroom cleaning showed the highest correlation between all the physiological response variables and work pace. In most of the tasks, a high work pace may have increased the degree and duration of severe trunk flexion.

CONCLUSION

Overall, when several tasks were considered, the extent of physiological responses, trunk joint angles, and exposure time to awkward postures tended to increase with an increase in work pace.

PRACTICAL APPLICATIONS

This study showed the feasibility of using the work pace measured from time studies as a predictive indicator of WMSDs risks. Using this information, managers may compose a schedule that can minimize WMSDs risks while considering actual work pace deviations that may impact a janitor's ability to complete assigned tasks properly within a shift.

An exploratory study comparing three work/rest schedules during simulated repetitive precision work

The pattern of work and rest can influence both physical fatigue and task performance in manual operations. However, there is relatively limited evidence regarding the influences of specific work/rest schedules in tasks requiring high repetitiveness and precision demands, along with relatively low exertion levels. Eighteen participants completed an exploratory study that simulated such tasks, to compare the effects of three distinct work/rest schedules (i.e. short frequent [short] and long infrequent breaks [long], and a self-selected schedule) on muscle fatigue, task performance (in terms of accuracy and speed), and preference. Schedules with long or self-selected breaks generally induced less muscle fatigue, compared with the short break condition. Participants preferred the self-selected condition the most and the long-break condition the least. The different schedules tested did not influence task performance. A self-selected schedule may be beneficial for repetitive precision task, to achieve a balance across muscle fatigue, task performance, and individual preference. Practitioner summary: Influences of three work/rest schedules (i.e. short and long breaks, and a self-selected schedule) on fatigue, performance, and preference were explored during repetitive precision tasks. Schedules with long or self-selected breaks induced less muscle fatigue and none of the three schedules influenced performance. A self-selected schedule was the most preferred.

The effect of different work-rest schedules on ergonomic risk in poultry slaughterhouse workers

BACKGROUND:

Rest breaks are an organizational measure to reduce the high risk of upper limb work-related musculoskeletal disorders (UL-WMSDs) to which slaughterhouse workers are subject.

OBJECTIVE:

To analyze the effect of different work-rest schedules on ergonomic risk in poultry slaughterhouse workers.

METHODS:

A total of 36 repetitive tasks was selected in a Brazilian slaughterhouse. Using the Occupational Repetitive Action (OCRA) Checklist, the level of exposure of workers to risk factors of UL-WMSDs in two work-rest schedules was evaluated. In the real condition, 6 rest breaks of 10 minutes were performed, and in the simulated condition, 3 rest breaks of 20 minutes.

RESULTS:

The right side of the body presented a higher score on the OCRA Checklist (72%of the tasks) than the left side (p = 0.037) in the real condition. Additionally, the OCRA score (18.3±2.5) was significantly lower (p < 0.001) than the simulated condition (21.9±3.0). It was verified that the risk level in simulated condition remained the same in 13 (36%) tasks, while in 23 (64%) tasks there was an increase in the risk level.

CONCLUSIONS:

Work-rest schedule of 6 breaks of 10 minutes was better than 3 breaks of 20 minutes to reduce the risk of UL-WMSDs in poultry slaughterhouse workers.

EMG Characterization and Processing in Production Engineering

Electromyography (EMG) signals are biomedical signals that measure electrical currents generated during muscle contraction. These signals are strongly influenced by physiological and anatomical characteristics of the muscles and represent the neuromuscular activities of the human body. The evolution of EMG analysis and acquisition techniques makes this technology more reliable for production engineering applications, overcoming some of its inherent issues. Taking as an example, the fatigue monitoring of workers as well as enriched human–machine interaction (HMI) systems used in collaborative tasks are now possible with this technology. The main objective of this research is to evaluate the current implementation of EMG technology within production engineering, its weaknesses, opportunities, and synergies with other technologies, with the aim of developing more natural and efficient HMI systems that could improve the safety and productivity within production environments.

Working time and upper limb musculoskeletal symptoms: a longitudinal study among assembly line workers

This study followed assembly line workers during 7 months, comprising a 4-wk season holidays. The main purposes were to determine the potential effect of working time on the presence and intensity of upper limb musculoskeletal symptoms, as to verify the effect of 4 wk of job interruption in the upper limb musculoskeletal symptoms presence and intensity. Data was collected during 6 moments. Generalized estimating equations analyses were used. For the effect estimates, odds ratio with corresponding 95% confidence intervals were reported for each outcome/model. The upper limb musculoskeletal symptoms showed a significant increase (p=0.001), especially after the 4 wk off. In all data collection points there was a significant positive association between the upper limb musculoskeletal symptoms and general health status (p<0.001). Considering symptoms’ intensity, significant relations were found (p<0.001). Work time had a negative effect on the work-related upper limb musculoskeletal symptoms over 7 months (OR 0.909, 95% CI 0.861–0.960, p=0.001). For the intensity of upper limb symptoms, the effect of time was also statistical significant (OR 0.115, 95% CI 1.031–1.220, p=0.008). A 4-wk job interruption did not show an immediately positive effect on upper limb musculoskeletal symptoms presence.

Sex differences in postures of the upper body during a simulated work task performed above shoulder level

The aim of this study was to evaluate if there are sex differences in postures of upper arm, upper back, head and neck after muscle fatigue induced by a simulated work task, requiring upper arm movements performed above shoulder level. Nineteen females and 18 males were evaluated. Upper arm elevation, upper back, head and neck forward flexion postures were recorded using digital inclinometers. The first and the last cycles of the task were considered as pre- and post-fatigue periods, respectively. For both periods, Amplitude Probability Distribution Function (APDF) was calculated for 10th, 50th and 90th percentiles, as well as the angular ranges between the 5th and 95th percentiles (APDF_5-95 range). The APDF_5-95 range for upper arm elevation was higher with fatigue, but with a higher increase for males. After fatigue, there was also a decrease in the upper arm elevation, with a larger decrease in males for the 10th and 50th percentiles. For head and neck, females showed higher APDF_5-95 ranges than males, regardless of the task period evaluated. After muscle fatigue, males adopted more neutral postures of the upper arm than females. Furthermore, females showed more non-neutral postures for head and neck. These findings suggest that the kinematic strategies adopted by females and males during a simulated work task are different and may predispose females to a higher risk of developing work-related musculoskeletal disorders of the neck.

Does sEMG normalization change results on sex differences in the activation of the shoulder girdle muscles during a simulated work task?

The aim was to investigate if the method of normalizing surface electromyography (sEMG) can change results on sex differences in the muscular activation of the shoulder girdle muscles during a simulated work task. sEMG was recorded in 36 asymptomatic participants (17 females, 19 males) from four parts of trapezius and from serratus anterior muscles during a simulated work task. Four normalization methods, one involving maximal voluntary contractions (MVCs) and three involving submaximal voluntary contractions were applied. Sex differences in absolute and normalized amplitude of sEMG were analyzed. The normalization method had a significant influence on the observed sex differences. Females only showed higher sEMG amplitude than males when the sEMGs were normalized to MVC and to a submaximal contraction based on 20% of MVC for the upper trapezius (acromial fibers). Researchers and practitioners should be aware of the impact of the sEMG normalization method in sex differences investigation.

Trapezius muscle activity variation during computer work performed by individuals with and without neck-shoulder pain

This study aimed at determining the extent to which individuals with neck-shoulder pain and non-symptomatic individuals differ in muscle activation patterns, when performing computer work, as quantified by exposure variation analysis (EVA). As a secondary aim, we also aimed to quantify the day-to-day reliability of EVA variables describing trapezius muscle activation in a non-symptomatic control group. Thirteen touch-typing computer users (pain: n = 5, non-symptomatic: n = 8) completed three pre-selected computer tasks in the laboratory. Upper trapezius muscle activity was recorded using electromyography and analyzed using EVA with five amplitude and five duration categories. Individuals with neck-shoulder pain spent less time at low amplitudes and exhibited longer uninterrupted periods of muscle activation compared to their non-symptomatic counterparts. Thus, non-symptomatic workers tended to switch between exposure levels more often than individuals with pain. For a majority of EVA variables, ICCs ranged from 0.6 to 0.9, and between-days coefficients of variation were between 0.4 and 2.2.

Methods in Experimental Work Break Research: A Scoping Review

The number of studies on work breaks and the importance of this subject is growing rapidly, with research showing that work breaks increase employees’ wellbeing and performance and workplace safety. However, comparing the results of work break research is difficult since the study designs and methods are heterogeneous and there is no standard theoretical model for work breaks. Based on a systematic literature search, this scoping review included a total of 93 studies on experimental work break research conducted over the last 30 years. This scoping review provides a first structured evaluation regarding the underlying theoretical framework, the variables investigated, and the measurement methods applied. Studies using a combination of measurement methods from the categories “self-report measures,” “performance measures,” and “physiological measures” are most common and to be preferred in work break research. This overview supplies important information for ergonomics researchers allowing them to design work break studies with a more structured and stronger theory-based approach. A standard theoretical model for work breaks is needed in order to further increase the comparability of studies in the field of experimental work break research in the future.

Association between Psychosocial Working Conditions and Perceived Physical Exertion among Eldercare Workers: A Cross-Sectional Multilevel Analysis of Nursing Homes, Wards and Workers

This cross-sectional multilevel study aims at investigating the associations between psychosocial working conditions of different workplace levels and perceived physical exertion among eldercare workers. Data were obtained from the 'Danish Observational Study of Eldercare work and musculoskeletal disorderS' (DOSES) study, including 536 eldercare workers, nested in 126 wards and 20 nursing homes. Psychosocial working conditions were measured by the Copenhagen Psychosocial Questionnaire (COPSOQ). The physical workload was measured with a self-administered scale (0-10) rating perceived physical exertion. Multilevel linear mixed models were used to determine associations of psychosocial conditions between nursing homes, wards, and workers with physical exertion. Most of the variance in the perceived physical exertion was explained by differences between workers (83%), but some variance was explained by wards (11%) and nursing homes (6%). Workers employed in nursing homes with low influence (p = 0.01) and poor leadership (p = 0.02), and in wards with high quantitative demands (p = 0.03), high work pace (p < 0.001), and low justice (p = 0.01) were at increased risk of reporting higher physical exertion. The strongest associations were found for low influence, low quality of leadership, and high work pace at nursing homes and ward levels. In conclusion, improving specific psychosocial working conditions at nursing home and ward levels may be of particular importance to reduce excessive physical workload in eldercare workers.

Are there sex differences in muscle coordination of the upper girdle during a sustained motor task?

PURPOSE

The higher prevalence of work-related musculoskeletal disorders among women compared with men could be explained by sex-gender differences related to biological and physiological processes. The aim of this study was to evaluate sex differences in motor coordination during a sustained and repetitive motor task.

METHODS

Seventeen healthy females and 21 healthy males participated. The surface electromyography (sEMG) of the trapezius portions and serratus anterior were recorded. Root mean square (RMS) values were computed to assess the level of muscle activity. The standard deviation (SD) and coefficient of variation (CV) were computed as metrics of size of variability. The normalized mutual information (NMI) values were calculated as index of functional connectivity between muscles pairs.

RESULTS

Females had higher normalized RMS values for the upper trapezius (acromial fibers) and serratus anterior muscles compared with males. RMS decreased, SD and CV increased while NMI decreased for almost all muscle pairs over time.

CONCLUSION

The present work showed some signs of sex differences in muscle coordination of the shoulder girdle during a sustained motor task, performed with the upper limb positioned below of the shoulder level.