Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature

Ancient Egyptian scribes and specific skeletal occupational risk markers (Abusir, Old Kingdom)

Men with writing proficiency enjoyed a privileged position in ancient Egyptian society in the third millennium BC. Research focusing on these officials of elevated social status ("scribes") usually concentrates on their titles, scribal statues, iconography, etc., but the individuals themselves, and their skeletal remains, have been neglected. The aim of this study is to reveal whether repetitive tasks and maintained postures related to scribal activity can manifest in skeletal changes and identify possible occupational risk factors. A total of 1767 items including entheseal changes, non-metric traits, and degenerative changes were recorded from the human remains of 69 adult males of well-defined social status categories from the necropolis at Abusir (2700-2180 BC). Statistically significant differences between the scribes and the reference group attested a higher incidence of changes in scribes and manifested themselves especially in the occurrence of osteoarthritis of the joints. Our research reveals that remaining in a cross-legged sitting or kneeling position for extended periods, and the repetitive tasks related to writing and the adjusting of the rush pens during scribal activity, caused the extreme overloading of the jaw, neck and shoulder regions.

Gym and Fitness Injuries amongst those Aged 16-64 in New Zealand: Analysis of Ten Years of Accident Compensation Corporation Injury Claim Data

BACKGROUND

To provide epidemiological data for minor and moderate-to-serious injury claims for gym and fitness related injuries amongst those aged 16-64 in New Zealand, to inform the development of an injury prevention program.

METHODS

Retrospective analytical review of gym and fitness related injury entitlement minor and moderate- to-serious Accident Compensation Corporation (ACC) claims from 1 July 2011 to 30 June 2020. Data were analysed by cause of injury, geographical region, sex, age, body site and injury type. Qualitative analysis of free text describing the activity causing the injury was conducted.

RESULTS

Over the ten-year period, 16-64 year olds made 345,254 injury claims, costing ACC NZ$241,298,275 in treatment charges. Soft tissue injuries were the most prevalent making up 96% (331,343) of all claims and 88% (NZ$213,049,197) of the total charges. Strenuous movement with lifting (n = 154,467, 47%), strenuous movement without lifting (n = 84,469, 25%), impact/contact with object (n = 39,610, 12%) and impact/contact with ground (n = 25,351, 8%) were the top four mechanisms resulting in injury, accounting for 92% of soft tissue injuries. Males and females aged 21 to 30 years old were most frequently injured. The four most injured body sites (lower back/spine, shoulder, knee, neck/back of head) accounted for 63% of injuries in females, and 65% in males.

CONCLUSIONS

The most common cause of injury from gym and fitness activity claims in 16-64 year olds in New Zealand was lifting/carrying/strain resulting in lower back/spine and shoulder (including clavicle/blade) soft tissue injuries. Soft tissue injuries accounted for 96% of the total claims. Males and females aged 21 to 30 years old were most frequently injured age group.

Differential effects of sex on upper body kinematics and kinetics during fatiguing, Asymmetric lifting

This study quantified sex-specific biomechanical adaptations to fatigue in asymmetric lifting. Twenty-one females and fifteen males performed a prolonged asymmetric lifting protocol while upper body, trunk and pelvis kinematics were collected. Features of movement identified with principal component analysis, and peak joint angular velocities and moments were calculated. Sex-specific kinematic adaptations to fatigue included females adopting a 'stoop-like' lifting strategy to a greater extent than males. Additionally, females exhibited higher vertical elbow positions during load rotation, moved their body toward the destination for load deposit, and did not reduce peak right shoulder flexion velocities, in contrast to male participants. Females also had greater low back and shoulder peak normalized joint moments. When fatigued, females adopted an asymmetric lifting strategy that minimized metabolic demand as supported by smaller decreases in maximum voluntary contractions. However, females' fatigue-related adaptations increased biomechanical exposures associated with injury risk.

Investigation of Musculoskeletal System Problems and Psychosocial Status of Teachers and Physiotherapists Working in Special Education Centers

Amaç: Bu çalışmanın amacı; özel eğitim ve rehabilitasyon merkezlerinde aktif olarak çalışan öğretmen ve fizyoterapistlerin kas-iskelet sistemi problemleri ile ağrı, iş doyum, mesleki tükenmişlik ve yaşam kalitesi durumlarının incelenmesidir.Yöntem: Çalışmamıza özel eğitim merkezlerinde çalışan 92 öğretmen ve 92 fizyoterapist katıldı. Çalışma yüz yüze görüşmeler şeklinde gerçekleştirildi. Katılımcıların demografik bilgileri kaydedilerek, Kas İskelet Sistemi Sağlık Sorgulaması (KİS-SS), McGill-Melzack Ağrı Anketi, Minnesota İş Doyum Anketi, Maslach Tükenmişlik Anketi ve EuroQol 5D Yaşam Kalitesi Ölçeği anket formları uygulandı.Bulgular: Katılımcıların yaş ortalamaları ve vücut kütle indeksi (VKİ) ortalamaları açısından grupların benzer olduğu belirlendi (p>0.05). Her iki grupta da kadın katılımcı sayısının erkeklerden daha fazla olduğu, cinsiyet dağılımlarının gruplarda farklı olduğu tespit edildi (p<0,05). Meslekte aktif çalışma sürelerinin her iki grupta da benzer olduğu görüldü (p>0,05). Haftalık çalışma sürelerinde ise öğretmenlerin fizyoterapistlerden daha uzun süre çalıştığı belirlendi (p<0,05). Aynı zamanda fizyoterapistlerin yaşam kalitelerinin daha yüksek (p<0,05), ağrı seviyesinin daha düşük olduğu saptanırken (p<0,05); iş doyum, mesleki tükenmişlik ve KİS-SS değerlerinin benzer olduğu bulundu (p>0,05).Sonuç: Çalışmanın sonunda özel eğitimde çalışan fizyoterapist ve öğretmenlerin iş doyumu, mesleki tükenmişlik ve kas-iskelet sistemi sorunlarının benzer olduğu belirlendi. Genel yaşam kalitesinin fizyoterapistlerde daha yüksek olduğu ve öğretmenlerin ağrı skorlarının daha fazla olduğu tespit edildi. Fizyoterapistlerin öğretmenlere göre haftalık çalışma süresinin daha az olması ağrı skorlarının daha az olmasının bir nedeni olabileceği gibi, öğretmenlere göre daha aktif bir çalışma modeline sahip olmaları ve bir sağlık profesyoneli olarak fizyoterapistlerin ağrı yönetimi konusunda bilgi sahibi olmaları da bu sonucun bir nedeni olabilir. Yaşam kalitesinde ortaya çıkan farkın ise ağrı skoruyla ilişkili olabileceğini düşünmekteyiz. İş doyum, mesleki tükenmişlik ve KİS-SS değerlerinin benzer olmasının sebebi olarak aynı merkezlerde çalışan fizyoterapist ve öğretmenlerin benzer sorunlar yaşaması, benzer yöneticilerle çalışması ve benzer tatmin duyguları tatmaları olduğunu düşünmekteyiz.

Sex-specific effects of localized muscle fatigue on upper body kinematics during a repetitive pointing task

BACKGROUND

Females are reported to have a higher risk of musculoskeletal disorders than males. Repetitive motions can lead to muscle fatigue, which may play a mediator role in the development of musculoskeletal disorders. However, sex differences in adaptations to localized fatigue at different joints are poorly understood. We examined the sex-specific effects of fatigue location on shoulder, elbow and spinal joint angles, and angular variabilities during a repetitive pointing task.

METHODS

Seven males and ten females performed a 30-s standing repetitive pointing task with their right upper limb when they were non-fatigued (NF), elbow-fatigued (EF), shoulder-fatigued (SF) and trunk-fatigued (TF), while trunk and upper body tridimensional kinematic data was recorded. Joint angles and angular variabilities of shoulder, elbow, upper thoracic spine, lower thoracic spine, and lumbar spine were calculated.

RESULTS

Results showed that shoulder angles changed the most after EF in males, but after SF in females. The similarities between sexes were that SF increased the variabilities at upper (lateral flexion: 0.15° greater than NF, rotation: 0.26° greater than all other conditions) and lower thoracic spine (lateral flexion: 0.13° greater than NF, rotation: averagely 0.1° greater than all other condition) in both sexes. TF altered upper thoracic spine variability (0.36° smaller than SF), lower thoracic spine angle (lateral flexion: 3.00° greater than NF, rotation: 1.68° greater than SF), and lumbar angle (averagely 1.8° smaller than all other conditions) in both sexes. However, females had greater lower thoracic spine angle (lateral flexion: 8.3° greater, p = 0.005) as well as greater upper (rotation: 0.53° greater, p = 0.006) and lower thoracic spine (rotation: 0.5° greater, p = 0.007; flexion: 0.6° greater, p = 0.014) angular variabilities than males.

CONCLUSIONS

Results suggest that females' fatigue responses focused on the trunk and spine. Results highlight a few sex differences in adapting to localized muscle fatigue, which may help explain how sex differences in repetitive motion-related injuries differ between joints.

Ergonomic considerations when slotting piece-pick operations in distribution centers

Many warehouse slotting algorithms have overlooked worker ergonomics. This research aimed to develop ergonomics slotting guidelines based upon the back and shoulder postures and electromyographic (EMG) responses of the deltoid and erector spinae muscles when individual items are picked from, or full cases replenished to, different shelf heights In the first study of two studies, participants lifted small items representative of piece-pick tasks from seven shelf heights. In the second study, participants performed a simulated full case replenishment task in which they lifted boxes weighing between 2.7 and 10.9 kg from a cart into a flow rack. Shelf height significantly affected all postural and EMG variables and there was a trade-off between back and shoulder muscle activity across the varying shelf heights. Together, these studies were used to develop some general ergonomic slotting guidelines that could be implemented to reduce biomechanical load exposures experienced by distribution center workers.

Work-related and personal factors in shoulder disorders among electronics workers: findings from an electronics enterprise in Taiwan

BACKGROUND

The electronics industry is one of the largest global industries, and significant numbers of workers are engaged in this industry. Evidence suggests two associations, including one between ergonomic risks and shoulder disorders and another between psychological stress and psychological problems among workers in this industry. Investigations on ergonomic risks, psychological stress, and sex effects for shoulder disorders in this industry are limited. This study aimed to explore personal and work-related factors associated with shoulder disorders and to investigate the combined effect of similar ergonomic risk factors.

METHODS

In this cross-sectional study, 931 workers aged 20 to 58 from an electronics factory in Taiwan were recruited. A Nordic musculoskeletal questionnaire was used to assess shoulder symptoms. Sociodemographic factors and work-related factors, including psychological stress, were assessed. One hundred random sample workers with shoulder symptoms underwent a standardized clinical test for the evaluation of subacromial impingement syndrome. The ergonomic risks were assessed by the risk filter of 'upper limb disorders in the workplace', including repetition, posture, force, vibration, and duration of exposure.

RESULTS

The prevalence of shoulder symptoms was 30.5, and 19% of those with shoulder symptoms had subacromial impingement syndrome. In multivariable analyses, older age (adjusted odds ratio (aOR) = 1.37, 95% CI 1.01-1.86), repetition (aOR = 1.73, 95% CI 1.15-2.60) and posture (aOR = 1.85, 95% CI 1.10-3.11) were associated with shoulder symptoms. Regarding the gender effect, older age (aOR = 1.46, 95% CI 1.01-2.11), repetition (aOR = 1.64, 95% CI 1.00-2.68), posture (aOR = 1.89, 95% CI 1.01-3.52), and force (aOR = 1.68, 95% CI 0.99-2.85) were associated with shoulder symptoms in men, whereas posture (aOR = 2.12, 95% CI 0.99-4.57) was associated with symptoms in women.

CONCLUSIONS

This study implies that repetition and posture are important risk factors for shoulder disorders in the electronics industry. The risk exhibited sex differences, and force was more important for shoulder disorders in men. Such information is useful to help occupational health practitioners and policy makers conduct preventive programmes on shoulder disorders in this working population. Future longitudinal studies on work-related shoulder disorders are warranted.

Dynamic Joint Motions in Occupational Environments as Indicators of Potential Musculoskeletal Injury Risk

The objective of this study was to test the feasibility of using a pair of wearable inertial measurement unit (IMU) sensors to accurately capture dynamic joint motion data during simulated occupational conditions. Eleven subjects (5 males and 6 females) performed repetitive neck, low-back, and shoulder motions simulating low- and high-difficulty occupational tasks in a laboratory setting. Kinematics for each of the 3 joints were measured via IMU sensors in addition to a "gold standard" passive marker optical motion capture system. The IMU accuracy was benchmarked relative to the optical motion capture system, and IMU sensitivity to low- and high-difficulty tasks was evaluated. The accuracy of the IMU sensors was found to be very good on average, but significant positional drift was observed in some trials. In addition, IMU measurements were shown to be sensitive to differences in task difficulty in all 3 joints (P < .05). These results demonstrate the feasibility for using wearable IMU sensors to capture kinematic exposures as potential indicators of occupational injury risk. Velocities and accelerations demonstrate the most potential for developing risk metrics since they are sensitive to task difficulty and less sensitive to drift than rotational position measurements.

Work above shoulder level and shoulder complaints: a systematic review

OBJECTIVE

To investigate the association and the exposure-response relationship between work above shoulder height and shoulder pain or disorders.

METHODS

A systematic search was performed in Medline, Embase, and Health and Safety Science Abstracts. Included were articles with prospective cohort, case-control, cross-sectional, or intervention study designs. Quality assessment was based on an evaluation scheme adjusted to study design and normalized to 100%. The cut-off for sufficient quality to include articles was above 40% and cut-off for high-quality articles was above 50% of maximal score. The level of strength of evidence for an association between exposure and effect was assessed according to the GRADE guidelines.

RESULTS

Thirty-four articles were included. Articles that document large effects (higher risk estimates; OR ≥ 2) have higher quality score, include analyses of severe arm elevation, more often use clinical outcome, and report an exposure-response relationship compared to studies reporting lower risk estimates. The studies that reported large effects were all significant. An exposure-response relationship was found in many high-quality studies when relating exposure intensity of arm elevation (level of arm elevation, amplitude) as well as duration of arm elevation, especially > 90°.

CONCLUSION

We conclude on a limited evidence for an association between arm elevation at work and shoulder disorders. Severe arm elevation with elbows above shoulder level (i.e., > 90°) shows a moderate evidence for an association with shoulder disorders.

Effect of Mechanically Passive, Wearable Shoulder Exoskeletons on Muscle Output During Dynamic Upper Extremity Movements: A Computational Simulation Study

Wearable passive (ie, spring powered) shoulder exoskeletons could reduce muscle output during motor tasks to help prevent or treat shoulder musculoskeletal disorders. However, most wearable passive shoulder exoskeletons have been designed and evaluated for static tasks, so it is unclear how they affect muscle output during dynamic tasks. The authors used a musculoskeletal model and Computed Muscle Control optimization to estimate muscle output with and without a wearable passive shoulder exoskeleton during 2 simulated dynamic tasks: abduction and upward reach. To an existing upper extremity musculoskeletal model, the authors added an exoskeleton model with 3-dimensional representations of the exoskeleton components, including a spring, cam wheel, force-transmitting shoulder cable, and wrapping surfaces that permitted the shoulder cable to wrap over the shoulder. The exoskeleton reduced net muscle-generated moments in positive shoulder elevation by 28% and 62% during the abduction and upward reach, respectively. However, muscle outputs (joint moments and muscle effort) were higher with the exoskeleton than without at some points of the movement. Muscle output was higher with the exoskeleton because the exoskeleton moment opposed the muscle-generated moment in some postures. The results of this study highlight the importance of evaluating muscle output for passive exoskeletons designed to support dynamic movements to ensure that the exoskeletons assist, rather than impede, movement.

Effects of different fatigue locations on upper body kinematics and inter-joint coordination in a repetitive pointing task

Studies have shown that muscle fatigue can lead to posture, joint angle, inter-joint coordination and variability alterations. However, the three-dimensional kinematic effects of localized muscular fatigue on a multijoint movement remain unclear. Healthy young adults (N = 17, 10 females) performed a standing repetitive pointing task when they were non-fatigued, and after localized muscle fatigue was induced at the elbow, the shoulder, and the trunk using isometric protocols performed until exhaustion. Joint angles and angular standard deviation (SD) of trunk, shoulder and elbow, and continuous relative phase (CRP) and CRP SD between trunk and shoulder, and shoulder and elbow were computed and compared between fatigue conditions. Results showed that trunk lateral flexion SD increased after fatigue of the elbow (0.1°, p = 0.04), shoulder (0.1°, p = 0.04) and trunk (0.1°, p<0.01). However, fatigue at different muscles brought different kinematic changes. Shoulder fatigue induced the greatest overall changes, with angular changes at all three joints. Trunk fatigue increased the shoulder horizontal abduction SD, elbow flexion SD and trunk-shoulder CRP. Elbow fatigue induced angular changes at trunk, shoulder and elbow, but did not affect CRP or CRP SD. This study highlights the crucial role of trunk variability in compensating for localized muscle fatigue during a repetitive upper limb task performed while standing.

Wrist pain: a systematic review of prevalence and risk factors- what is the role of occupation and activity?

OBJECTIVE

To evaluate the prevalence and risk factors of wrist pain.

METHODS

Systematic review.

DATA SOURCES

The MEDLINE and EMBASE via OVID, CINAHL and SPORTDiscus via EBSCO databases were searched from database inception to 9th March 2018. Specific criteria were used to define inclusion and exclusion. Data was extracted independently by a pair of reviewers.

RESULTS

In total 32 cross sectional studies were identified for inclusion (1 with a longitudinal component). The median prevalence of wrist pain in the general population and non-manual workers within the short term (within last week) was 6 and 4.2% within the medium term (> 1 week and within a year). The median prevalence of wrist pain in physically demanding occupations and sports people was 10% within the short term and 24% within the medium term. Non-modifiable factors associated with wrist pain included increased age (1 study in adults and 3 studies in children/adolescents) and female sex (2 studies). Modifiable risk factors included high job physical strain (2 studies), high job psychological strain (1 study), abnormal physeal morphology in children/adolescents (2 studies), high frequency impact tool use (1 study) and effort reward imbalance (1 study).

CONCLUSIONS

Wrist pain is highly prevalent in groups who partake in physically demanding activities from day to day such as manual labourers and sportspeople. It is less prevalent in the general population and non-manual workers, although there is a relative lack of research in the general population.

TRIAL REGISTRATION

The review protocol was registered with PROSPERO under the registration number CRD42018090834.

LEVEL OF EVIDENCE

1 (Prognostic study).

Biomaterials to Mimic and Heal Connective Tissues

Connective tissue is one of the four major types of animal tissue and plays essential roles throughout the human body. Genetic factors, aging, and trauma all contribute to connective tissue dysfunction and motivate the need for strategies to promote healing and regeneration. The goal here is to link a fundamental understanding of connective tissues and their multiscale properties to better inform the design and translation of novel biomaterials to promote their regeneration. Major clinical problems in adipose tissue, cartilage, dermis, and tendon are discussed that inspire the need to replace native connective tissue with biomaterials. Then, multiscale structure-function relationships in native soft connective tissues that may be used to guide material design are detailed. Several biomaterials strategies to improve healing of these tissues that incorporate biologics and are biologic-free are reviewed. Finally, important guidance documents and standards (ASTM, FDA, and EMA) that are important to consider for translating new biomaterials into clinical practice are highligted.

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.

Primary and Secondary Consequences of Rotator Cuff Injury on Joint Stabilizing Tissues in the Shoulder

Rotator cuff tears (RCTs) are one of the primary causes of shoulder pain and dysfunction in the upper extremity accounting over 4.5 million physician visits per year with 250,000 rotator cuff repairs being performed annually in the U.S. While the tear is often considered an injury to a specific tendon/tendons and consequently treated as such, there are secondary effects of RCTs that may have significant consequences for shoulder function. Specifically, RCTs have been shown to affect the joint cartilage, bone, the ligaments, as well as the remaining intact tendons of the shoulder joint. Injuries associated with the upper extremities account for the largest percent of workplace injuries. Unfortunately, the variable success rate related to RCTs motivates the need for a better understanding of the biomechanical consequences associated with the shoulder injuries. Understanding the timing of the injury and the secondary anatomic consequences that are likely to have occurred are also of great importance in treatment planning because the approach to the treatment algorithm is influenced by the functional and anatomic state of the rotator cuff and the shoulder complex in general. In this review, we summarized the contribution of RCTs to joint stability in terms of both primary (injured tendon) and secondary (remaining tissues) consequences including anatomic changes in the tissues surrounding the affected tendon/tendons. The mechanical basis of normal shoulder joint function depends on the balance between active muscle forces and passive stabilization from the joint surfaces, capsular ligaments, and labrum. Evaluating the role of all tissues working together as a system for maintaining joint stability during function is important to understand the effects of RCT, specifically in the working population, and may provide insight into root causes of shoulder injury.

Part I: Participatory Ergonomics Approach to Waste Container Handling Utilizing a Multidisciplinary Team

This multidisciplinary team approach to waste container handling, developed within the Grassroots Ergonomics process, presents participatory ergonomic interpretations of quantitative and qualitative aspects of this process resulting in a peer developed training. The lower back, shoulders, and wrists were identified as frequently injured areas, so these working postures were a primary focus for the creation of the workers' training. Handling procedures were analyzed by the team to identify common cycles involving one 5 gallon (60 pounds), two 5 gallons (60 and 54 pounds), 30 gallon (216 pounds), and 55 gallon (482 pounds) containers: lowering from pallet, transporting to/from transport vehicles, loading/unloading on transport vehicles, and loading onto pallet. Eleven experienced waste container handlers participated in this field analysis. Ergonomic exposure assessment tools measuring these field activities included posture analysis, posture targeting, Lumbar Motion Monitor™(LMM), and surface electromyography (sEMG) for the erector spinae, infraspinatus, and upper trapezius muscles. Posture analysis indicates that waste container handlers maintained non-neutral lower back postures (flexion, lateral bending, and rotation) for a mean of 51.7% of the time across all activities. The right wrist was in non-neutral postures (radial, ulnar, extension, and flexion) a mean of 30.5% of the time and the left wrist 31.4%. Non-neutral shoulder postures (elevation) were the least common, occurring 17.6% and 14.0% of the time in the right and left shoulders respectively. For training applications, each cycle had its own synchronized posture analysis and posture target diagram. Visual interpretations relating to the peak force modifications of the posture target diagrams proved to be invaluable for the workers' understanding of LMM and sEMG results (refer to Part II). Results were reviewed by the team's field technicians and their interpretations were developed into ergonomic training that address the issues originally raised. This training includes intervention methods, ergonomic tools used, data acquired, and effects of waste container handling techniques on lower back, shoulder, and wrists and methods to help proactively reduce injuries associated with this profession.

Occupational exposure to the municipal solid waste workers in Chandigarh, India

Manual handling of municipal solid waste is of serious concern owing to emerging occupational risks. Considering this, health risks of municipal solid waste workers involved in street sweeping, waste collection, waste processing and rag picking were assessed in Chandigarh, India, using an interview schedule as a study tool. Result shows that the waste worker profession is mainly dominated by males, except in rag pickers, and with a lower literacy rate. Age distribution shows that 16% of waste collectors and 11% of rag pickers were below 18 years of age. Daily income of the waste workers ranges from ₹100 to ₹200. It was observed that 22.2% of waste collectors, 43.2% of street sweepers and 25.5% of rag pickers do not use any type of protective gears owing to their casual attitude, which results in various types of injuries. The major occupational health issues reported by various categories of waste workers were respiratory disorders, injuries and allergies having prevalence of 12.3%-17.6%, 4.9%-44.4% and 35.3%-48.9%, respectively. Waste workers are vulnerable to occupational health hazards and hence there is a need to safeguard them through formulation of new laws and policies.

Strength Training Improves Fatigue Resistance and Self-Rated Health in Workers with Chronic Pain: A Randomized Controlled Trial

Chronic musculoskeletal pain is widespread in the working population and leads to muscular fatigue, reduced work capacity, and fear of movement. While ergonomic intervention is the traditional approach to the problem, physical exercise may be an alternative strategy. This secondary analysis of a randomized controlled trial investigates the effect of strength training on muscular fatigue resistance and self-rated health among workers with chronic pain. Sixty-six slaughterhouse workers with chronic upper limb pain and work disability were randomly allocated to 10 weeks of strength training or usual care ergonomic training (control). At baseline and follow-up, participants performed a handgrip muscular fatigue test (time above 50% of maximal voluntary contraction force) with simultaneous recording of electromyography. Additionally, participants replied to a questionnaire regarding self-rated health and pain. Time to fatigue, muscle strength, hand/wrist pain, and self-rated health improved significantly more following strength training than usual care (all P < 0.05). Time to fatigue increased by 97% following strength training and this change was correlated to the reduction in fear avoidance (Spearman's rho = −0.40; P = 0.01). In conclusion, specific strength training improves muscular fatigue resistance and self-rated health and reduces pain of the hand/wrist in manual workers with chronic upper limb pain. This trial is registered with ClinicalTrials.gov NCT01671267.

General Health status of workers among different workplaces in Qom Province, Iran

INTRODUCTION

In a healthy organization, psychological health and physical health are as important as production and productivity; and healthy workers have higher productivity. Regarding lack of information about workers' general health profile in Qom Province, this study aimed to assess and compare the staffs' general health and its components among different workplaces in 2014.

METHODS

In a cross-sectional study, 2,276 employees working at 46 industries and organizations completed a standardized General Health Questionnaire (GHQ 28) and a demographic questionnaire. Data were analyzed using t-test, ANOVA, and Pearson product-moment correlation coefficient by IBM SPSS version 20.

RESULTS

The mean age of the participants was 32.22 (±7.55) years. Seventy-nine point four percent of participants were married and the rest were single. Highest and lowest scores belonged to social dysfunction and depression, respectively. Also, total score of staffs' general health was 17.87 ± 10.93. The results showed that, in spite of the non-relationship between general health score difference among married and single personnel (p > 0.05), there was a significant difference between men and women and among organizations and industries with regards to general health score (p < 0.05), and drivers had the most difference with others. The relationship between workers' ages and GH was significant (p < 0.05, Pearson's bivariate correlation coefficient = -0.05).

CONCLUSION

The findings of this study collectively indicated that participants had an acceptable condition for mental factors, such as depression, but not in viewpoints of social dysfunction. In other words, staffs' interfaces with circumstances and personal innovation/creativity in the workplaces are at risk. Altogether, the general health score in the studied population was suitable in its entirety.

Developing and validating a self-report assessment tool for software biomechanics

BACKGROUND

There are many effective methods for decreasing the likelihood of repetitive strain injury (RSI) for those who work at a computer in an office environment. This study is focused on the highly repetitive task of interpreting seismic data. The skilled geoscientists who perform this work are very well compensated, and their work is vital to the success of the oil company. However, RSIs are still occurring in situations where effective methods of mitigating injuries have been successfully implemented and this has been occurring very frequently for geoscientists. This suggests that there are other elements contributing to the development of these injuries and one element could be the software interaction design. However, it is difficult for software designers to determine this because most measures associated with muscle activity require expensive data collection methods.

OBJECTIVE

This paper describes research conducted to determine if survey-based subjective measures might be used to assess the potential for RSI for software programs.

METHODS

In laboratory and field settings, data were collected using three different survey instruments (NASA-Task Load Index, Latko's Busiest Hand Activity Level Scale, and the Borg CR10 Rating of Perceived Exertion Scale) and conventional measures of muscle activity (sEMG). Correlations between the surveys and muscle activity were then calculated.

RESULTS

For both the laboratory and the field, people were able to provide reliable self-report information related to their muscle activity. However, the effect sizes were not large.

CONCLUSIONS

These results suggest that self-report tools could be utilized to identify software interaction designs related associated with risks of RSI.

Neck muscle function in violinists/violists with and without neck pain

Neck pain is associated with changes in neuromuscular control of cervical muscles. Violin and viola playing requires good function of the flexor muscles to stabilize the instrument. This study investigated the flexor muscle behaviour in violin/viola players with and without neck pain using the craniocervical flexion test (CCFT). In total, 12 violin/viola players with neck pain, 21 violin/viola players without neck pain in the preceding 12 weeks and 21 pain-free non-musicians were included. Activity of the sternocleidomastoid muscles (SCM) was measured with surface electromyography (EMG) during the CCFT. Violin/viola players with neck pain displayed greater normalised SCM EMG amplitudes during CCFT than the pain-free musicians and non-musicians (P < 0.05). Playing-related neck pain in violinists/violists is associated with altered behaviour of the superficial neck flexor muscles consistent with neck pain, despite the specific use of the deep and superficial neck flexors during violin playing.

The (dys)functional extracellular matrix

The extracellular matrix (ECM) is a major component of the biomechanical environment with which cells interact, and it plays important roles in both normal development and disease progression. Mechanical and biochemical factors alter the biomechanical properties of tissues by driving cellular remodeling of the ECM. This review provides an overview of the structural, compositional, and mechanical properties of the ECM that instruct cell behaviors. Case studies are reviewed that highlight mechanotransduction in the context of two distinct tissues: tendons and the heart. Although these two tissues demonstrate differences in relative cell-ECM composition and mechanical environment, they share similar mechanisms underlying ECM dysfunction and cell mechanotransduction. Together, these topics provide a framework for a fundamental understanding of the ECM and how it may vary across normal and diseased tissues in response to mechanical and biochemical cues. This article is part of a Special Issue entitled: Mechanobiology.

Effect of horizontal pick and place locations on shoulder kinematics

In this study the effects of horizontal bin locations in an order picking workstation on upper arm elevation, trunk inclination and hand use were investigated. Eight subjects moved (self-paced) light or heavy products (0.2 and 3.0 kg) from a central product bin to an inner or outer order bin (at 60 or 150 cm) on the left or right side of the workstation, while movements were recorded. The outer compared to inner bin location resulted in more upper arm elevation and trunk inclination per work cycle, both in terms of number of peak values and in terms of time integrals of angles (which is a dose measure over time). Considering the peak values and time integrals per minute (instead of per work cycle), these effects are reduced, due to the higher cycle times for outer bins. Hand use (left, right or both) was not affected by order bin locations.

The effect of police cruiser restraint cage configuration on shoulder discomfort, muscular demands, upper limb postures, and task performance during simulated police patrol

Advances in police-specific technology have led to changes in work layout and physical occupational demands of mobile police officers. This study investigated the influence of police cruiser compartment configuration on perceived discomfort, muscle activation, shoulder kinematics, and typing performance during simulated police patrol. Participants completed a one-hour session including simulated driving and 2-min typing trials in a standard compartment configuration with a fixed mobile data terminal (MDT) location (ST), and in a modified compartment configuration with an MDT in front of the user and a rearward translated seat (MOD). The MOD configuration resulted in reductions of 55-65% in perceived shoulder discomfort, up to 3.4% MVC in shoulder muscle demands, and more neutral humeral orientations (shoulder elevation reduced by 13-25°). These improvements associated with the MOD configuration may have ergonomic implications for future police car designs, particularly as new technology is introduced in the mobile environment and advanced solutions are sought.

Ergonomic evaluation of a wearable assistive device for overhead work

Overhead work is an important risk factor for upper extremity (UE) musculoskeletal disorders. We examined the potential of a mechanical arm and an exoskeletal vest as a wearable assistive device (WADE) for overhead work. Twelve participants completed 10 minutes of simulated, intermittent overhead work, using each of three payloads (1.1, 3.4 and 8.1 kg) and with/without the WADE. Ratings of perceived discomfort (RPDs) and electromyography (EMG) were obtained for the upper arms, shoulders and low back. Using the WADE, UE RPDs decreased by ∼50% with the heavier payloads, whereas smaller (∼25%) and non-significant increases in low-back RPDs were found and were relatively independent of payload. Changes in RPDs with WADE use were consistent with physical demands indicated by EMG, though EMG-based differences in fatigue were less apparent. Participants generally preferred using the WADE, particularly with heavier payloads. These results supported the potential utility of a WADE as an intervention for overhead work.

Shoulder muscle fatigue development in young and older female adults during a repetitive manual task

Age may modify the association between occupational physical demand and muscle loading, and ultimately increase the risk of musculoskeletal disorders. The goal of this study was to investigate age-related differences in shoulder muscle fatigue development during a repetitive manual task. Twenty participants in two age groups completed an 80-minute simulated low-intensity assembly task. Electromyographic (EMG) manifestation of muscle fatigue was observed in the upper trapezius, deltoid and infraspinatus muscles in both age groups, and coincided with an increase in the subjective ratings of perceived exertions. Compared with the younger group, older group showed a more monotonic decrease in EMG power frequency in the upper trapezius and deltoid muscles. However, the age-related difference in EMG amplitude was less consistent. Relative rest time of the upper trapezius muscle in the older group was less than the young group throughout the task. The observed patterns of EMG measures suggest that older participants may have disadvantages in fatigue resistance in the upper trapezius and posterior deltoid muscles during the simulated repetitive manual task.

Strengths and limitations of a musculoskeletal model for an analysis of simulated meat cutting tasks

This study assessed the capacity of a musculoskeletal model to predict the relative muscle activation changes as a function of the workbench height and the movement direction during a simulated meat cutting task. Seven subjects performed a cutting task alternating two cutting directions for 20 s at four different workbench heights. Kinematics, electromyography (EMG), and cutting force data were collected and used to drive a musculoskeletal model of the shoulder girdle. The model predicted the muscle forces exerted during the task. Both the recorded and computed activation of the muscles was then compared by means of cross-correlation and by comparison of muscle activation trends with respect to the workstation parameters, i.e. cutting direction and workbench height. The results indicated that cutting movements involving arm flexion are preferable to movement requiring internal arm rotation and abduction. The optimal bench height for meat cutting tasks should be between 20 and 30 cm below the worker's elbow height. The present study underlines a beneficial use of musculoskeletal models for adjusting workstation parameters.

High intensity physical exercise and pain in the neck and upper limb among slaughterhouse workers: cross-sectional study

Slaughterhouse work involves a high degree of repetitive and forceful upper limb movements and thus implies an elevated risk of work-related musculoskeletal disorders. High intensity strength training effectively rehabilitates musculoskeletal disorders among sedentary employees, but less is known about the effect among workers with repetitive and forceful work demands. Before performing randomized controlled trials it may be beneficial to assess the cross-sectional connection between exercise and musculoskeletal pain. We investigated the association between high intensity physical exercise and pain among 595 slaughterhouse workers in Denmark, Europe. Using logistic regression analyses, odds ratios for pain and work disability as a function of physical exercise, gender, age, BMI, smoking, and job position were estimated. The prevalence of pain in the neck, shoulder, elbow, and hand/wrist was 48%, 60%, 40%, and 52%, respectively. The odds for experiencing neck pain were significantly lower among slaughterhouse workers performing physical exercise (OR = 0.70, CI: 0.49-0.997), whereas the odds for pain in the shoulders, elbow, or hand/wrist were not associated with exercise. The present study can be used as general reference of pain in the neck and upper extremity among slaughterhouse workers. Future studies should investigate the effect of high intensity physical exercise on neck and upper limb pain in slaughterhouse workers.

High intensity physical exercise and pain in the neck and upper limb among slaughterhouse workers: cross-sectional study

Slaughterhouse work involves a high degree of repetitive and forceful upper limb movements and thus implies an elevated risk of work-related musculoskeletal disorders. High intensity strength training effectively rehabilitates musculoskeletal disorders among sedentary employees, but less is known about the effect among workers with repetitive and forceful work demands. Before performing randomized controlled trials it may be beneficial to assess the cross-sectional connection between exercise and musculoskeletal pain. We investigated the association between high intensity physical exercise and pain among 595 slaughterhouse workers in Denmark, Europe. Using logistic regression analyses, odds ratios for pain and work disability as a function of physical exercise, gender, age, BMI, smoking, and job position were estimated. The prevalence of pain in the neck, shoulder, elbow, and hand/wrist was 48%, 60%, 40%, and 52%, respectively. The odds for experiencing neck pain were significantly lower among slaughterhouse workers performing physical exercise (OR = 0.70, CI: 0.49-0.997), whereas the odds for pain in the shoulders, elbow, or hand/wrist were not associated with exercise. The present study can be used as general reference of pain in the neck and upper extremity among slaughterhouse workers. Future studies should investigate the effect of high intensity physical exercise on neck and upper limb pain in slaughterhouse workers.

Cluster-based exposure variation analysis

Background

Static posture, repetitive movements and lack of physical variation are known risk factors for work-related musculoskeletal disorders, and thus needs to be properly assessed in occupational studies. The aims of this study were (i) to investigate the effectiveness of a conventional exposure variation analysis (EVA) in discriminating exposure time lines and (ii) to compare it with a new cluster-based method for analysis of exposure variation.

Methods

For this purpose, we simulated a repeated cyclic exposure varying within each cycle between “low” and “high” exposure levels in a “near” or “far” range, and with “low” or “high” velocities (exposure change rates). The duration of each cycle was also manipulated by selecting a “small” or “large” standard deviation of the cycle time. Theses parameters reflected three dimensions of exposure variation, i.e. range, frequency and temporal similarity.

Each simulation trace included two realizations of 100 concatenated cycles with either low (ρ = 0.1), medium (ρ = 0.5) or high (ρ = 0.9) correlation between the realizations. These traces were analyzed by conventional EVA, and a novel cluster-based EVA (C-EVA). Principal component analysis (PCA) was applied on the marginal distributions of 1) the EVA of each of the realizations (univariate approach), 2) a combination of the EVA of both realizations (multivariate approach) and 3) C-EVA. The least number of principal components describing more than 90% of variability in each case was selected and the projection of marginal distributions along the selected principal component was calculated. A linear classifier was then applied to these projections to discriminate between the simulated exposure patterns, and the accuracy of classified realizations was determined.

Results

C-EVA classified exposures more correctly than univariate and multivariate EVA approaches; classification accuracy was 49%, 47% and 52% for EVA (univariate and multivariate), and C-EVA, respectively (p < 0.001). All three methods performed poorly in discriminating exposure patterns differing with respect to the variability in cycle time duration.

Conclusion

While C-EVA had a higher accuracy than conventional EVA, both failed to detect differences in temporal similarity. The data-driven optimality of data reduction and the capability of handling multiple exposure time lines in a single analysis are the advantages of the C-EVA.

Comparison of Upper Arm Kinematics During a Volleyball Spike Between Players With and Without a History of Shoulder Injury

Volleyball players are at high risk of overuse shoulder injuries, with spike biomechanics a perceived risk factor. This study compared spike kinematics between elite male volleyball players with and without a history of shoulder injuries. Height, mass, maximum jump height, passive shoulder rotation range of motion (ROM), and active trunk ROM were collected on elite players with (13) and without (11) shoulder injury history and were compared using independent samplesttests (P< .05). The average of spike kinematics at impact and range 0.1 s before and after impact during down-the-line and cross-court spike types were compared using linear mixed models in SPSS (P< .01). No differences were detected between the injured and uninjured groups. Thoracic rotation and shoulder abduction at impact and range of shoulder rotation velocity differed between spike types. The ability to tolerate the differing demands of the spike types could be used as return-to-play criteria for injured athletes.

Participatory ergonomic intervention versus strength training on chronic pain and work disability in slaughterhouse workers: study protocol for a single-blind, randomized controlled trial

Background

The prevalence of musculoskeletal pain in the shoulder, arm and hand is high among slaughterhouse workers, allegedly due to the highly repetitive and forceful exposure of these body regions during work. Work disability is a common consequence of these pains. Lowering the physical exposure through ergonomics intervention is the traditional strategy to reduce the workload. An alternative strategy could be to increase physical capacity of the worker through strength training. This study investigates the effect of two contrasting interventions, participatory ergonomics versus strength training on pain and work disability in slaughterhouse workers with chronic pain.

Methods/design

66 slaughterhouse workers were allocated to 10 weeks of (1) strength training of the shoulder, arm and hand muscles for 3 x 10 minutes per week, or (2) participatory ergonomics involving counseling on workstation adjustment and optimal use of work tools (~usual care control group). Inclusion criteria were (1) working at a slaughterhouse for at least 30 hours per week, (2) pain intensity in the shoulder, elbow/forearm, or hand/wrist of at least 3 on a 0–10 VAS scale during the last three months, (3) pain lasting for more than 3 months, (4) frequent pain (at least 3 days per week) (5) at least moderate work disability, (6) no strength training during the last year, (7) no ergonomics instruction during the last year.

Perceived pain intensity (VAS scale 0–10) of the shoulder, elbow/forearm and hand/wrist (primary outcome) and Disability of the Arm, Shoulder and Hand (Work module, DASH questionnaire) were measured at baseline and 10-week follow-up. Further, total muscle tenderness score and muscle function were assessed during clinical examination at baseline and follow-up.

Discussion

This RCT study will provide experimental evidence of the effectiveness of contrasting work-site interventions aiming at reducing chronic pain and work disability among employees engaged in repetitive and forceful work.

Trial registration

ClinicalTrials.gov:NCT01671267

Wrist activity monitor counts are correlated with dynamic but not static assessments of arm elevation exposure made with a triaxial accelerometer

There is evidence in the literature of a link between workplace arm elevation exposure and atraumatic shoulder injuries. However, there are several methods that can be used to assess this exposure. The goal of the present study was to compare the outcomes of an activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus. Twenty-one workers wore both sensors over the course of a full workday. While the activity monitor data was not significantly correlated with any static humeral parameters, it was strongly correlated with all dynamic parameters. The use of a simple, commercially available activity monitor might offer an inexpensive alternative for the assessment of a large number of subjects over multiple workdays to determine the relationship between dynamic motion and occupation shoulder injuries in the future.

PRACTITIONER SUMMARY

Arm overuse has been linked to occupation-related shoulder injuries. An activity monitor attached to the wrist and a triaxial accelerometer mounted on the humerus were compared in a field trial. The results demonstrate that, under certain conditions, a commercially available activity monitor might be a useful tool for exposure assessment.

Sensory manifestations in experimental and work-related chronic neck-shoulder pain

Little is known about the mechanisms leading to chronic neck-shoulder musculo-skeletal disorders. The aim of the present study was to investigate and compare the sensory manifestations of experimental or chronic neck-shoulder pain under controlled, low load, repetitive work. Experimental and clinical experiments were carried out. In Experiment 1, experimental muscle pain was induced in healthy subjects by intramuscular injection of hypertonic saline in the trapezius (n = 10) and infraspinatus (n = 10) muscles. Experiment 2 was performed on 18 workers with (n = 12) and without (n = 6) chronic neck-shoulder pain. Sensory assessments were performed before and/or after a session of controlled, low load, repetitive work. The pain intensity was assessed by a visual analogue scale. The pain quality and location(s) were monitored together with pressure-pain thresholds. Moderate-to-strong deep pain intensity was experienced in the experimental and clinical part of the working session (six patients out of 12). The verbal descriptors used to describe the experimental or chronic pain qualities were partially similar, i.e. first of all verbal descriptors from the sensory class. The patterns of local and referred pain characteristics were similar (around the shoulder girdle), but it is difficult to evoke pain in extensive areas with hypertonic saline. Patients exhibited hypersensitivity or tenderness to pressure stimuli in both sides of the upper body, i.e. in the trapezius, supraspinatus, infraspinatus and pectoralis major muscles (p < 0.05). This hypersensitivity was only seen at the referred pain site in the healthy volunteers exposed to infraspinatus experimental muscle pain. In conclusion, the present study demonstrated similar sensory manifestations in the experimental and clinical neck-shoulder pain experiments. The presented experimental model can most likely be used to investigate the underlying pain mechanisms involved in work-related chronic musculoskeletal pain.

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.

Workstyle risk factors for work related musculoskeletal symptoms among computer professionals in India

INTRODUCTION

Work-related musculoskeletal disorders are common in computer professionals. Workstyle may be one of the risk factors in the development of musculoskeletal discomfort. The objective of this retrospective study was to examine the prevalence of adverse workstyle in computer professionals from India and to evaluate if workstyle factors were predictors of pain and loss of productivity.

METHODS

Office workers from various information technology (IT) companies in India responded to the short-form workstyle questionnaire and pain questionnaire. Correlation analyses were conducted to examine the associations between different variables followed by a multivariate logistic regression to understand the unique predictors of pain and loss of productivity.

RESULTS

4,500 participants responded to the workstyle and pain questionnaire. 22% of participants were reported to have a high risk of an adverse workstyle. 63% of participants reported pain symptoms. Social reactivity, lack of breaks, and deadlines/pressure subscales of workstyle questionnaire were significantly correlated with pain and loss of productivity. Regression analyses revealed that workstyle factors and duration of computer use per day were significant predictors of pain.

CONCLUSION

Workstyle seems to be a mediating factor for musculoskeletal pain, discomfort, and loss of productivity. Based on the study findings, it is recommended that intervention efforts directed towards prevention of musculoskeletal disorders should focus on psychosocial work factors such adverse workstyle in addition to biomechanical risk factors.

SHOULDER MUSCULOSKELETAL DISORDERS IN INDUSTRIAL AND OFFICE WORK

Although several studies addressed the work-related shoulder pathology, there is still a lack of knowledge regarding the causal relationship between different factors in industrial/office activities and shoulder musculoskeletal disorders. The goal of this review is to evaluate in a realistic manner the role of the factors implicated in the shoulder disorders development in high-risk activities. This article reviews the actual state of information regarding the etiological relationship between physical and psychosocial stress and occupational musculoskeletal problems in shoulder area, emphasizing the relationship between ergonomic interventions on musculoskeletal system. Secondly, a comprehensive presentation of the pathophysiology and etiology of shoulder muscle problems is provided. Critical factors such as arm elevation, lack of rest, overloading of several muscles and mental stress during performed tasks are discussed in relation to shoulder musculoskeletal disorders development. Finally, using the available data, the authors present a thorough recommendation of mandatory redesign interventions with suggestions for future research in this area.

Relationships between maximum holding time and ratings of pain and exertion differ for static and dynamic tasks

Ratings of perceived discomfort (0 to 10 scale) have been used to estimate relative maximum holding times (%MHT), particularly for static tasks. A linear 1:10% ratio has been described, where a rating of 5 corresponds to 50%MHT. It is unknown whether this linear ratio is valid for dynamic tasks. Additionally, whether pain or exertion are the primary predictors of discomfort is not clear. Thus, the goal of this study was to investigate both pain and exertion ratings during static (50% maximum; N=42) and dynamic (75% maximum; N=34) elbow flexion tasks until failure. Gender, self-reported physical activity, and peak torque were also assessed. Pain and exertion ratings reasonably matched the 1:10% ratio during the static task but not during the dynamic task. Exertion related more strongly to MHT than pain in both tasks. Neither gender nor activity level appeared to influence perceptual ratings, but peak torque explained approximately 20% of the variance in MHT.

In vivo measurement of humeral elevation angles and exposure using a triaxial accelerometer

OBJECTIVE

The aim of this study was to measure the capability of a triaxial accelerometer (Virtual Corset) to collect humeral elevation angles and exposure parameters in a simulated occupational environment.

BACKGROUND

There is a need for an economical ambulatory device to estimate elevation angles and exposure parameters in occupational groups.

METHOD

A magnetic tracking device was used to assess the ability of the Virtual Corset to evaluate humeral elevation angles and identify exposure parameters with in vivo dynamic conditions for 16 female dental hygienists.

RESULTS

Significant differences were found for the reaching task with the Virtual Corset, underestimating the means of the average humeral elevation angle by 10 degrees and the means for the range of the humeral elevation by 4 degrees. Furthermore, significant differences were found for the exposure parameters with the Virtual Corset, overestimating the jerk by 4% and underestimating the percentage time above 40 degrees and 60 degrees by 9% and 4%, respectively. However, the Virtual Corset was able to identify similar kinematics patterns and exposure data when compared with a magnetic tracking device.

CONCLUSION

The outcomes of the study suggest that the Virtual Corset may be useful for data collection during a dental hygienist workday. Professions that have similar patterns of angular velocity and acceleration and humeral range of elevation as the dental hygienist flossing technique may benefit from the use of the Virtual Corset.

APPLICATION

This study provides evidence that the Virtual Corset can be used to reconstruct humeral elevation angles and identify exposure parameters in some tasks of dental hygienists.

On functional motor adaptations: from the quantification of motor strategies to the prevention of musculoskeletal disorders in the neck-shoulder region

BACKGROUND

Occupations characterized by a static low load and by repetitive actions show a high prevalence of work-related musculoskeletal disorders (WMSD) in the neck-shoulder region. Moreover, muscle fatigue and discomfort are reported to play a relevant initiating role in WMSD.

AIMS

To investigate relationships between altered sensory information, i.e. localized muscle fatigue, discomfort and pain and their associations to changes in motor control patterns.

MATERIALS & METHODS

In total 101 subjects participated. Questionnaires, subjective assessments of perceived exertion and pain intensity as well as surface electromyography (SEMG), mechanomyography (MMG), force and kinematics recordings were performed.

RESULTS

Multi-channel SEMG and MMG revealed that the degree of heterogeneity of the trapezius muscle activation increased with fatigue. Further, the spatial organization of trapezius muscle activity changed in a dynamic manner during sustained contraction with acute experimental pain. A graduation of the motor changes in relation to the pain stage (acute, subchronic and chronic) and work experience were also found. The duration of the work task was shorter in presence of acute and chronic pain. Acute pain resulted in decreased activity of the painful muscle while in subchronic and chronic pain, a more static muscle activation was found. Posture and movement changed in the presence of neck-shoulder pain. Larger and smaller sizes of arm and trunk movement variability were respectively found in acute pain and subchronic/chronic pain. The size and structure of kinematics variability decreased also in the region of discomfort. Motor variability was higher in workers with high experience. Moreover, the pattern of activation of the upper trapezius muscle changed when receiving SEMG/MMG biofeedback during computer work.

DISCUSSION

SEMG and MMG changes underlie functional mechanisms for the maintenance of force during fatiguing contraction and acute pain that may lead to the widespread pain seen in WMSD. A lack of harmonious muscle recruitment/derecruitment may play a role in pain transition. Motor behavior changed in shoulder pain conditions underlining that motor variability may play a role in the WMSD development as corroborated by the changes in kinematics variability seen with discomfort. This prognostic hypothesis was further, supported by the increased motor variability among workers with high experience.

CONCLUSION

Quantitative assessments of the functional motor adaptations can be a way to benchmark the pain status and help to indentify signs indicating WMSD development. Motor variability is an important characteristic in ergonomic situations. Future studies will investigate the potential benefit of inducing motor variability in occupational settings.