Experimental pain leads to reorganisation of trapezius electromyography during computer work with active and passive pauses (original) (raw)
Related papers
Applied Ergonomics, 2011
We investigated the interactive effects of shoulder pain and wrist extensor muscle soreness on surface electromyography (EMG) during computer mouse work. On day one, subjects (N ¼ 12) performed computer work with/without acute muscle pain induced in the trapezius muscle. Subsequently, eccentric exercise was performed to induce delayed onset muscle soreness (DOMS) in wrist extensor muscles. In presence of DOMS on day two, computer work recordings with/without pain were repeated. EMG signals were recorded from the descending part of trapezius bilaterally, flexor carpi ulnaris and extensor carpi radialis brevis. Experimental muscle pain in trapezius led to a decrease in the muscular activity of the wrist extensor (P < 0.02) and decreased the relative rest time in the wrist flexor even in presence of DOMS (P < 0.01). The present result suggests that shoulder pain plays a role in the coordination of wrist flexors and extensors during computer work.
2007
Work related musculoskeletal disorders (WMSDs) in the shoulder/neck area are a common and increasing problem among European computer workers, especially women. Long-term low-level workloads with low degree of muscle rest are a potential risk factor for developing WMSDs. The purpose of the present study of female computer users (age 45-65 years) in Denmark and Sweden was to investigate if subjects with self-reported neck/shoulder complaints (cases, N = 35) show less trapezius muscle relative rest time (RRT) than controls (N = 44) when performing standardised short-term computer work tasks in controlled laboratory conditions. Surface electromyography (EMG) signals were recorded bilaterally from the upper trapezius muscles during a type, edit, precision and colour word stress task. Besides RRT, 10th percentile RMS values were calculated. On the average, 15 of the cases and 18 of the controls showed analysable EMG files per task. For the colour word stress task, the results showed lower RRT values and higher 10th percentile RMS amplitude levels among cases compared to controls. No such signs could be found for the other tasks performed. The present results indicate an increased motor response to a psychological stressor among subjects with self-reported neck/shoulder complaints.
Journal of Electromyography and Kinesiology, 2007
Work related musculoskeletal disorders (WMSDs) in the shoulder/neck area are a common and increasing problem among European computer workers, especially women. Long-term low-level workloads with low degree of muscle rest are a potential risk factor for developing WMSDs. The purpose of the present study of female computer users (age 45-65 years) in Denmark and Sweden was to investigate if subjects with self-reported neck/shoulder complaints (cases, N = 35) show less trapezius muscle relative rest time (RRT) than controls (N = 44) when performing standardised short-term computer work tasks in controlled laboratory conditions. Surface electromyography (EMG) signals were recorded bilaterally from the upper trapezius muscles during a type, edit, precision and colour word stress task. Besides RRT, 10th percentile RMS values were calculated. On the average, 15 of the cases and 18 of the controls showed analysable EMG files per task. For the colour word stress task, the results showed lower RRT values and higher 10th percentile RMS amplitude levels among cases compared to controls. No such signs could be found for the other tasks performed. The present results indicate an increased motor response to a psychological stressor among subjects with self-reported neck/shoulder complaints.
Journal of Electromyography and Kinesiology, 2003
The Cinderella hypothesis postulates the continuous activity of specific motor units (MUs) during low-level muscle contraction. The MUs may become metabolically overloaded, with the subject developing muscle pain and strain. The hypothesis requires MUs that are active for a time long enough to actually damage muscle fibers. The aim of this study was to determine if there are continuously active MUs in the right trapezius muscle during normal computer work using a computer mouse. Fourteen healthy subjects executed an interactive computer-learning program (ErgoLight) for 30 min. Six-channel intramuscular EMG and twochannel surface EMG signals were recorded from two positions of the trapezius muscle. Decomposition was achieved with automated, multi-channel, long-term decomposition software (EMG-LODEC). In two out of the 14 subjects, three MUs were continuously active throughout the 30 min. Although the majority of the MUs were active during only part of the experimental session, an ordered on-off behavior (e.g. substitution) pattern was not observed. As long-lasting activity was verified in some subjects, the results support the Cinderella hypothesis. However, it cannot be concluded here how long the MUs could stay active. If continuous activity overloads low threshold MUs, the potential exists for selective fibre injuries in low threshold MUs of the trapezius muscle in subjects exposed to long-term computer work.
International journal of occupational safety and ergonomics : JOSE, 1995
Ten female participants performed work at a video display terminal (VDT) station over a whole working day. Subjective local muscular fatigue was evaluated by means of the Category Ratio 10 scale. Electromyographic activity of the upper right and left trapezius was measured. A comparison was made between five participants who had previous complaints and 5 participants who reported no musculoskeletal problems in the shoulder-neck region. The subjective scores for the shoulder differed significantly between the two groups, being higher for the group with complaints. Both groups showed a decrease in discomfort after the lunch break. The activity of the trapezius increased significantly for both groups, in a more pronounced way for the group with disorders. Although it is found in literature that VDT work is a task with very low static loads, it seems from this study that the EMG activity increase can be an indication of muscle fatigue: more effort was required to accomplish the same VDT...
Journal of Electromyography and Kinesiology, 1999
Firstly, upper trapezius EMG activity patterns were recorded on the dominant side of 6 industrial production workers and on the side operating a computer mouse of 14 computer-aided design (CAD) operators to study differences in acute muscular response related to the repetitiveness of the exposure. The work tasks were performed with median arm movement frequencies ranging from 5 min −1 to 13 min −1 and were characterized by work cycle times ranging from less than 30 sec to several days. However, the static and median EMG levels and EMG gap frequencies were similar for all work tasks indicating that shoulder muscle loads may be unaffected by large variations in arm movement frequencies and work cycle times. An exposure variation analyses (EVA) showed that the EMG activity patterns recorded during production work were more repetitive than during CAD work, whereas CAD work was associated with more static muscle activity patterns, both may be associated with a risk of developing musculoskeletal symptoms. Secondly, upper trapezius EMG activity patterns recorded on the mouse side of the CAD operators were compared with those recorded on the non-mouse side to study differences in muscular responses potentially related to the risk of developing shoulder symptoms which were more prevalent on the mouse side. The number of EMG gaps on the mouse side were significantly lower than the values for the upper trapezius on the non-mouse side indicating that more continous activity was present in the upper trapezius muscle on the mouse side and EVA analyses showed a more repetitive muscle activity pattern on the mouse side. These findings may be of importance to explain differences in the prevalence of shoulder symptoms.
International Journal of Industrial Ergonomics, 2002
Work-related musculoskeletal disorders are frequent in workers with light to moderate load repetitive work, e.g. computer operators. The Cinderella hypothesis proposes that the development of chronic muscular pain is due to an overuse of fibers belonging to low-threshold motor units. The hypothesis requires that there exist motor units that are active (1) for a time long enough to actually damage the fibers, and (2) in different postures and throughout movements. In this study, the firing behavior of motor units in the extensor digitorum communis (EDC) muscle was registered in eight subjects during a 25-min static low-level contraction and during full range of motion wrist movements.
Journal of Electromyography and Kinesiology, 1995
Surface electromyographic (EMG) amplitude from the upper trapezius muscle is widely used as a measure of shoulder-neck load in ergonomic studies. A variety of methods for normalizing EMG ampiitude from the upper trapezius (EMGamp,,) have been presented in the literature. This impedes meta-analyses of, for instance, upper trapezius load in relation to development of shoulder-neck disorders. The review offers a thorough discussion of different normalization procedures for EMGamp,,. The following main issues are focused: output variable, location of electrodes, posture and attempted movement during normalization, load and duration of reference contractions, signal processing and test-retest repeatability. It is concluded that translations of EMGamp,, into biomechanical variables, for example relative force development in the shoulder or in the upper trapezius itself, suffer from low validity, especially if used in work tasks involving large and/ or fast arm movements. The review proposes a standard terminology relating to normalization of EMGamp,, and concludes in a concrete suggestion for a normalization procedure generating bioelectrical variables which reflect upper trapezius activation. Pavia, pp 73-75, 1976. Jonsson B: Kinesiology. With special reference to eiectromyographic kinesiology. Cont Clin Neurophysiol EEG SUPPI 34: [417][418][419][420][421][422][423][424][425][426][427][428] 1978. Jonsson B: Measurement and evaluation of local muscular strain in the shoulder during constrained work.
Journal of Electromyography and Kinesiology, 2000
Surface electromyography (EMG) has been used extensively to estimate muscular load in studies of work related musculoskeletal disorders, especially for the trapezius muscle. The occurrences of periods of EMG silence (gaps), the time below a predetermined threshold level (muscular rest) and various percentiles of the amplitude distribution (APDF) are commonly used summary measures. However, the effects of the criteria used to calculate these measures (e.g., gap duration, threshold level, normalisation method) on the sensitivity of these measures to accurately differentiate work loads is not well known. Bilateral trapezius EMG was recorded, for a full workday, for 58 subjects following both maximal (MVE) and submaximal (RVE) reference contractions. Gap frequency, muscular rest, and percentiles were derived for eight fundamental work tasks. The calculations were performed using different gap duration criteria, threshold levels and normalisation methods. A gap duration of less than 1/2 s, and threshold level Ϸ0.3% MVE for gap frequency, and Ϸ0.5% MVE for muscular rest, were the criteria that optimised sensitivity to task differences. Minimal sensitivity to tasks and a high sensitivity to individuals was obtained using gap frequency with a threshold level of Ϸ1% MVE. Normalisation to RVE, rather than MVE, improved sensitivity to differences between tasks, and reduced undesirable variability. Muscular rest was more sensitive to task differences than APDF percentiles.