Objectives This study assessed work postures, movements, psychosocial job demands, and shoulder and wrist extensor muscle activity and registered the prevalence of musculoskeletal symptoms of ...computer-aided design (CAD) operators. Methods A questionnaire survey was used to study the use of the computer mouse, psychosocial work factors, and musculoskeletal symptoms among 149 CAD operators. A workplace study was performed using observations, electrogoniometers on the wrists, and electromyography to measure exposures and physiological responses during CAD work among a subgroup of the CAD operators. Results Musculoskeletal symptoms were far more prevalent for the arm or hand operating the mouse than for the other arm or hand, and women were more affected than men. The symptoms may be related to such risk factors as repetitive movements, static postures (eg, ulnar-deviated and extended wrist on the mouse side), and static muscular activation patterns. The risk factors were present due to continuous mouse use and possibly also due to high demands for mental attentiveness, precision, and information processing. Conclusions Exposure during work with a computer mouse may present a risk for developing musculoskeletal symptoms. Improvements should focus on introducing more variation.
A typical occupational risk factor for developing neck symptoms is prolonged flexion of the cervical spine. The present aim was to determine joint moments and muscle activity of the neck during ...forward flexion of the cervical spine to evaluate the load in the neck region. Three dimensional video (3-D) and surface electromyography (EMG) from the splenius muscles were recorded in two common work postures. Using a 3-D static link segment model, moments at the atlanto-occipital (A-O) joint and the seventh cervical-first thoracal (C7-T1) joint were estimated. Maximal extension moments were estimated from maximal neck extension strength. Extension moments at the C7-T1 joint were significantly higher for a highly flexed position (45% of max) compared to a moderately flexed position (32% of max), but remained unchanged at the A-O joint (40% of max). The mean RMS amplitude was 9% of maximal EMG in both positions (no bilateral differences). This difference between mechanical load and muscle load indicates that EMG may seriously underestimate the total loads of the tissue. Lateral flexion influenced the lateral flexion moment while rotation did not influence the rotation moment. The study demonstrates the importance of quantification of joint loads in occupational risk assessment of the neck.
Relevance to industry
3-D biomechanical calculations provide information on the mechanical load during work. Because EMG may underestimate total tissue load, calculations of joint moments in combination with information on muscle activity and strength are necessary to estimate different tissue loading of significance for overall risk identification.
The primary aim was to study associations between duration of computer and mouse use and musculoskeletal symptoms among computer users. A questionnaire was delivered to 5033 employees in 11 Danish ...companies and institutions and 3475 subjects responded (69%). Logistic regression analyses on 2579 full-time working employees showed that working almost the whole working day with a computer was associated with neck symptoms (OR=1.92, CI: 1.21–3.02) and shoulder symptoms (OR=1.83, CI: 1.13–2.95) among women and hand symptoms (OR=2.76, CI: 1.51–5.06) among men. These odds ratios were adjusted for psychosocial factors. Among respondents working almost all of their work time with a computer the gender and age-adjusted odds ratio for mouse use more than half of the work time was 1.68 (CI: 1.22–2.31) for hand/wrist symptoms. Call center and data entry workers experienced the lowest possibilities for development at work. All work tasks involving computer use, except computer maintenance, were characterised by a higher frequency of movements than desk work without using a computer. Call center work was characterised by the highest level of repetitiveness as both work tasks and movements were perceived as repetitive.
Computer users with a long daily duration of computer use and mouse use experienced more musculoskeletal symptoms than those with a short duration of computer use. Computer work in general seemed characterised by repetitive movements, which may be a risk factor for musculoskeletal symptoms.
The purpose was to assess risk factors in dentistry which may contribute to musculoskeletal disorders. A questionnaire was used to identify common work tasks, and to estimate one year prevalence for ...troubles (65% for the neck/shoulder, 59% for the low back). In a field study working postures and electromyography (shoulder/neck) were registered during the three most common work tasks. Prolonged neck flexion and upper arm abduction were found, as well as high static muscle activity levels (splenius and trapezius muscles). No differences between work tasks were found regarding postures, frequencies of movements or muscle activity. Alterations between the three work tasks do not produce sufficient variation to reduce musculoskeletal load on the neck and shoulders.
Globalization and neoliberalism are having significant impacts upon the cleaning industry, as in the drive for greater work “efficiency”. One way in which cleaning companies have sought to increase ...efficiency is through the introduction of new equipment and forms of work organization. However, such moves appear to be having negative impacts upon cleaners’ bodies, and many report significant work‐related health problems. In light of this, here we explore the bodily consequences of two possible strategies for giving cleaners a healthier workday—increasing variation within cleaners’ current work tasks or allowing them to engage in a broader range of tasks through job enlargement. Drawing upon a literature review performed as part of a recent European Union project concerning the degree of physical strain to which cleaners are exposed during cleaning, a Danish laboratory study focusing on the loads to which cleaners’ shoulder muscles, backs, and hearts were exposed by different cleaning tasks, and a field study investigating the effects of job enlargement in Danish hospitals, we show that cleaning work is characterized by repetitive work for the muscles of the body's upper extremities and by high levels of dynamic and static force upon these muscles, regardless of which modes of cleaning (old or new style of cleaning tools) are used. Equally, monitoring of heart rates and assessment of the psychosocial environment suggest that simply interchanging current cleaning tasks does not provide sufficient variation in cleaners’ work to prevent work‐related musculoskeletal or cardiovascular damage, nor to create a less mentally stressful work environment. Although introducing greater work variation through job enlargement (such as combining cleaning with kitchen and portering tasks) is often presented as an effective way to minimize musculoskeletal and cardiovascular damage, our field study shows that even this does not provide sufficient variation in physical work conditions, although improvement in some cleaners’ mental health was noted. Therefore, we conclude, prevention of musculoskeletal and cardiovascular disorders demands a much more comprehensive strategy of work redesign than that proposed by some employers and government agencies. Whether this is likely, given competitive pressures towards increased outsourcing and privatization, is, of course, the question.
Objectives The electromyographic (EMG) activity of shoulder and forearm muscles was recorded during a standardized computer task with different combinations of time pressure, precision demands, and ...mental demands to study the interaction of these factors and their effect on muscular response during simulated computer work. Methods The computer task lasted 5 minutes, and it was performed by 14 female computer-aided design (CAD) operators during 8 exposure combinations that differed with respect to time pressure, precision demand, and mental demand. Performance (number of produced drawings, mouse clicks, and errors) were recorded. The EMG activity was recorded from the trapezius, infraspinatus, deltoid, and extensor digitorum muscles. An electrogoniometer was used to measure wrist postures and movements. Results High time pressure (combined with low precision and low mental demands) resulted in higher EMG activity for all the muscles and in a small increase in the number of produced drawings. High precision demands caused a large reduction in the number of produced drawings, but not always a change in EMG activity. High precision demands and high mental demands led to no change or a reduction in muscle activity because the number of drawings was greatly reduced. Conclusions The interaction between work pace and other exposure factors must be taken into account when the effects of changes in exposure demands on muscular response are predicted. Only then can it be predicted whether changing demands will constitute a risk of developing musculoskeletal disorders.
Biomechanical models which require information on, e.g., joint torque and muscle force are useful in the estimation of when and how mechanical overload of the musculoskeletal system may lead to ...disorders. The aim was to study the reliability and validity of magnetic resonance imaging (MRI) to quantify muscle sizes and moment arms by MRI and to test selected anthropometric measures as predictors of muscle sizes and moment arms. A total of 20 healthy Scandinavian women (age 22-58 years) participated in an MRI scanning of their dominant shoulder. With a PC-based program the reliability and the validity of the MRI measurements was estimated to be high, and mean anatomical cross-sectional areas (ACSA) and muscle lengths were measured to be 4.0, 9.8 and 12.1 cm(2) and 12.0, 12.6 and 12.8 cm for m. supraspinatus, m. infraspinatus and m. subscapularis, respectively. Volumes were calculated to be 48.8, 125.1 and 153.6 cm(3). Moment arms were measured with the upper arm in a neutral position and in a functional position of 34 degrees abduction for m. supraspinatus only, and were 2.4 and 2.6 cm. Physiological cross-sectional area (PCSA) and its fiber force component were estimated from dissected fiber length and pennation angle. MRI volume and PCSA were 1.4-1.7 times higher than dissection data, primarily because of age differences. No external anthropometric measures were found to be predictors of volumes or moment arms.
During sustained static contractions an increase in the root mean square (rms) amplitude and a decrease in mean power frequency (MPF), or median power frequency (MF) of the electromyographic (EMG) ...signal are indicators for the development of muscle fatigue. However, when studying dynamic contractions the interpretation of these variables has been questioned. Therefore, the purpose was to compare the EMG variables recorded from a non-fatigued muscle during a slow low level dynamic contraction to those during a static contraction of similar force level. Surface and intramuscular EMG registrations were obtained from the brachial biceps muscle during: (a) a static isotonic contraction, (b) a dynamic contraction and (c) a static anisotonic contraction. During contractions (a) and (b) the recruitment pattern was analysed using the precision decomposition method. No differences in rms, MPF or MF between the dynamic and static contractions or between the concentric and eccentric phase of the dynamic contraction were found. Furthermore 60% of the identified motor units were active both in the concentric and the eccentric phase. This indicates that motor control during a slow dynamic contraction at low force level does not influence the power spectrum. We suggest that in occupational studies a possible muscle fatigue development with time can be estimated using EMG recordings from the work tasks.
Microglia respond to focal cerebral ischemia by increasing their production of the neuromodulatory cytokine tumor necrosis factor, which exists both as membrane-anchored tumor necrosis factor and as ...cleaved soluble tumor necrosis factor forms. We previously demonstrated that tumor necrosis factor knockout mice display increased lesion volume after focal cerebral ischemia, suggesting that tumor necrosis factor is neuroprotective in experimental stroke. Here, we extend our studies to show that mice with intact membrane-anchored tumor necrosis factor, but no soluble tumor necrosis factor, display reduced infarct volumes at one and five days after stroke. This was associated with improved functional outcome after experimental stroke. No changes were found in the mRNA levels of tumor necrosis factor and tumor necrosis factor-related genes (TNFR1, TNFR2, TACE), pro-inflammatory cytokines (IL-1β, IL-6) or chemokines (CXCL1, CXCL10, CCL2); however, protein expression of TNF, IL-1β, IL-6 and CXCL1 was reduced in membrane-anchored tumor necrosis factorΔ/Δ compared to membrane-anchored tumor necrosis factorwt/wt mice one day after experimental stroke. This was paralleled by reduced MHCII expression and a reduction in macrophage infiltration in the ipsilateral cortex of membrane-anchored tumor necrosis factorΔ/Δ mice. Collectively, these findings indicate that membrane-anchored tumor necrosis factor mediates the protective effects of tumor necrosis factor signaling in experimental stroke, and therapeutic strategies specifically targeting soluble tumor necrosis factor could be beneficial in clinical stroke therapy.
•TNF deficiency alters the spatial organization of neurogenic zones.•TNF deficiency decreases WNT signaling-related proteins.•TNF deficiency alters neuronal and microglial numbers.•Long-term use of ...non-selective TNF inhibitors impairs learning and memory.•Long-term use of the soluble TNF selective inhibitor XPro1595 does not affect neurogenesis, learning and memory.
Although tumor necrosis factor (TNF) inhibitors are used to treat chronic inflammatory diseases, there is little information about how long-term inhibition of TNF affects the homeostatic functions that TNF maintains in the intact CNS.
To assess whether developmental TNF deficiency causes alterations in the naïve CNS, we estimated the number of proliferating cells, microglia, and neurons in the developing neocortex of E13.5, P7 and adult TNF knock out (TNF−/−) mice and wildtype (WT) littermates. We also measured changes in gene and protein expression and monoamine levels in adult WT and TNF−/− mice. To evaluate long-term effects of TNF inhibitors, we treated healthy adult C57BL/6 mice with either saline, the selective soluble TNF inhibitor XPro1595, or the nonselective TNF inhibitor etanercept. We estimated changes in cell number and protein expression after two months of treatment. We assessed the effects of TNF deficiency on cognition by testing adult WT and TNF−/− mice and mice treated with saline, XPro1595, or etanercept with specific behavioral tasks.
TNF deficiency decreased the number of proliferating cells and microglia and increased the number of neurons. At the same time, TNF deficiency decreased the expression of WNT signaling-related proteins, specifically Collagen Triple Helix Repeat Containing 1 (CTHRC1) and Frizzled receptor 6 (FZD6). In contrast to XPro1595, long-term inhibition of TNF with etanercept in adult C57BL/6 mice decreased the number of BrdU+ cells in the granule cell layer of the dentate gyrus. Etanercept, but not XPro1595, also impaired spatial learning and memory in the Barnes maze memory test.
TNF deficiency impacts the organization of neurogenic zones and alters the cell composition in brain. Long-term inhibition of TNF with the nonselective TNF inhibitor etanercept, but not the soluble TNF inhibitor XPro1595, decreases neurogenesis in the adult mouse hippocampus and impairs learning and memory after two months of treatment.
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