Principle component analysis of exposure variation analysis during computer work at presence of delayed onset muscle soreness

Eleven healthy volunteers took part in three sessions where computer work was performed for 10 min in each session. The recordings were made on two consecutive days. After the first session, the subjects underwent a series of high intensity eccentric exercises of shoulder elevation to induce muscle soreness. The second session was performed immediately after the exercises and third session 24 hours after the exercise. Surface electromyography (EMG) of descending and ascending trapezius, deltoideus anterior and serratus anterior was recorded. Exposure variation analysis (EVA) centroid and marginal distribution was computed. Principle component analysis (PCA) was performed on both cases. Describing more than 80% of variance, first eight components for EVA marginal distributions and first four ones for EVA centroid were picked to be investigated. The sole EVA amplitude levels played a practically significant role to describe the variation in EVA marginal distribution. However, a significant pattern of load redistribution to superficial muscles was not found. This may suggest investigating the role of deep muscles in redistribution of load during computer work in response to high level eccentric contractions.     

The effect of Video Display Terminal (VDT) mouse use on muscle contractions in the neck and forearm

This study used surface electromyography (EMG) to examine the percent of maximum voluntary contraction (%MVC) of the upper trapezius, the flexors of the wrist/fingers and extensors of the wrist/fingers during Video Display Terminal (VDT) mouse use with the mouse positioned either next to the computer or on a lapdesk. Thirty participants, between the ages of 18 and 40, used a VDT mouse to follow a prescribed pattern for three trials at each location. Although there was a trend towards the lapdesk location producing lower %MVC than the computer location for the trapezius and wrist/finger flexors (lapdesk: trapezius M 4.71%, wrist/finger flexors M 3.53%; computer: trapezius M 5.74%, wrist/finger flexors M 3.94%) a two way ANOVA controlling for sequence and order found no significant difference between the means. There was no trend for the effects of location for the wrist/finger extensors. These results suggest that changing the position of the mouse may not significantly reduce muscle contractions.     

The influence of an abdominal support for a dental stool in the distributions and electrical activity of the longissimus and the superior trapezius muscle in dentists

This study evaluated the influence an abdominal support attached to a traditional stool, of those used by dentists, has on the body's distribution of the electrical activity of the superior trapezius and the longissimus thoracic muscles of dental students during the execution of a clinical procedure. The results showed no significant difference in the body's distribution in the seat and backrest, but did reveal there was a weight discharge of 3.1 ± 1.9% of dentist's body weight in the abdominal support. The 9 o'clock position proved to be the best position to perform clinical procedures. It was also observed that the position was closer to the body's axis.     

Level of self-reported neck/shoulder pain and biomechanical workload in cleaners

The aim of the present study was to investigate the relation between self-reported pain, muscular activity and postural load during cleaning tasks. Eighteen cleaners performed usual cleaning tasks in both a laboratory and a lecture room. The level of perceived pain in the neck-shoulder region during the last 7 days was recorded. Bipolar surface electromyography (SEMG) was recorded bilaterally from upper trapezius and erector spinae muscles during cleaning. Root mean square (RMS) and permutation entropy (PE) values representing amplitude and complexity of SEMG time-series were estimated. A tri-axial accelerometer package was mounted on the low back (L5-S1) to measure postural changes during cleaning tasks. The 10th, 50th and 90th percentiles of the angular distributions were computed to characterize postures and movements. Pain tended to play a significant role on RMS of left/right trapezius and left erector spinae muscles (P≤0.08). Cleaners with low pain level exhibited higher muscular activity during cleaning. Pain played or tended to play a significant role on PE of left and right erector spinae muscles (P≤0.08). Pain played a significant role on the 10th, 50th and 90th percentile (P<0.05) of lateral flexion angle (side bending). The present study emphasizes biomechanical adaptations occurring in presence of neck-shoulder pain during cleaning tasks.     

Co-variation in time between near-far accommodation of the lens and trapezius muscle activity

Visual strain and discomfort may contribute to the generation of work-related musculoskeletal disorders among e.g. computer workers. A positive correlation on a group level between eye-lens accommodation and trapezius muscle activity has been reported. In this study we investigated the possibility of a direct, fast, connection between lens accommodation and trapezius muscles activity. The subjects focused alternately on Near and Far targets, with a mean switch time of 5 s, through four different lenses. The cross-correlation, R(tau) was computed, between the time signals of accommodation and electromyography (EMG) from 23 subjects. In the overall mean R(tau) of 736 curves, a small but significant correlation peak (0.019) with a delay (of the EMG signal) of about 0.3 s, revealed a small common component in the two signals. Among the lenses, the positive lens (3.5 D), showed the highest correlation peak (0.040). The correlation may be caused by a direct "hard-wired" connection between the ciliary and trapezius muscles. But it could also be caused indirectly by the subject's need for a more stable head in a more demanding visual task. The latter is supported by the result that the correlation was the highest in the positive lens condition. The present correlation is however weak and it has probably a low practical importance.     

The effects of a continuous passive motion device on myoelectric activity of the erector spinae during prolonged sitting at a computer workstation

Continuous passive motion (CPM) has been proposed as a method to help individuals with low back pain cope with prolonged sitting. The purpose of this study was to investigate the effects that a commercially available CPM device had on lumbar and thoracic erector spinae (ES) muscle activation (using surface electromyography, "EMG"), and on subjective discomfort during prolonged seated computer work with and without the use of the CPM device. There were no significant differences in average ES muscle activation levels, amplitude probability distribution functions, and EMG gaps number and length when sitting with the CPM device was compared to sitting normally. Subjective ratings of discomfort were also not significantly different between the two sitting conditions. The results indicated that there were no clear mechanisms by which the CPM device may reduce ES muscle pain and fatigue for the tasks and pain-free individuals studied.     

Ergonomics evaluation of a government office building

An ergonomics team from the US Army Center for Health Promotion and Preventive medicine evaluated 465 video display terminal (VDT) workstations in a Government office building over an 18-day period. Each workstation evaluation involved an assessment of the worker, the chair, the desk, the keyboard, the pointing device, the monitor, and the office environmental conditions. The team also collected worker pain and injury information. The problems seen during the evaluation were characteristic of most office environments where VDT workstation furniture was purchased before the advent of mouse-driven software. The majority of furniture evaluated was not designed to meet the demands of intensive mouse use for prolonged periods of time. Much of the workstation furniture was not adjustable, chairs lacked adequate back support, and workers assumed non-neutral postures. As a result, more than 35% of the workers evaluated complained of on-the-job pain. New office furniture that is adjustable, adequate desk space and storage space were among the solutions recommended by the ergonomics team.     

Spatially Specific Changes in Infants' Muscle Coactivity as They Learn to Reach

Infants first reach out and touch objects between the ages of 3 and 5 months. This article reports changes in muscle coactivity associated with this transition. A group of 4 infants were observed weekly from 3 to 30 weeks and every 2 weeks from 30 to 52 weeks. Hand kinematics of both prereaching and reaching movements were collected, as was electromyographic activity from the trapezius, deltoid, biceps, and triceps. Before infants first reached for toys presented at midline, they used biceps and triceps to move their hands near the toy in front of them and 45° to the side of midline. After the transition, they used trapezius and deltoid to move the hand toward the toy and combinations of multiple muscles when their arms were high and extended near the toy. Thus, infants showed a dramatic change in which muscles worked together across the transition to reaching, even though their hands moved in similar spatial regions.     

Stationarity test of electromyographic signals during isokinetic trunk exertions

The aim of this study is to investigate the stationarity of the electromyographic (EMG) signals during isokinetic exertions of the trunk muscle. Six healthy subjects participated in this study. The erector spinae muscles were used to collect the signals. In order to simulate the isokinetic exercises of the trunk, a Cybex system with a trunk modular component was used. All subjects performed sustained exertions with a combination of load (25%, 50% MVC) and angular velocity (0, 15, 30 degree/s). The stationarity of the signals was tested by the reverse arrangements test and modified reverse arrangements test. In the results, the signal stationarity was high in all conditions in the reverse arrangements test. However, in the modified reverse arrangements test it was relatively low at about the 30 degree/s angular velocity. In the analysis of variance, the effect of angular velocity was statistically significant at the 0.05 significance level in the modified reverse arrangements test and Tukey's HSD grouping showed that the stationarity of 30 degree/s angular velocity was significantly different from 0, 15 degree/s condition. These results indicate that the stationarity of the EMG signals showed no difference between isometric and isokinetic conditions when the angular velocity was equal to 15 degree/s.     

White Racism,Social Class,and the Backlash Against Affirmative Action

Among scholars in sociology and history, the backlash against affirmative action has been blamed on White working‐class Americans. What has received far less attention is the individual and collective institutional role(s) played by the White middle and upper middle‐class in backlash politics. Given that individuals in these social classes have far greater institutional power than White working‐class Americans, their beliefs and practices deserve sustained critical attention, and, as the few existing research studies demonstrate, White middle‐class and upper middle‐class Americans have played an influential role in backlash politics. Part of the reason for this gap in the literature is that these groups are more difficult to access as research subjects. Gaining access to this population may require working through many levels of a bureaucratic organization designed to protect their time and privacy. Moreover, when interviewed, these Americans are more likely than their working‐class counterparts to mask racist sentiments through the polite language of “color blindness.” Research methods that complement surveys and in‐depth interviews are recommended as strategies for probing White middle and upper middle‐class Americans' deeply hidden beliefs.     

Cervico‐motor reflex: Description of the reflex and role in sexual acts

A recently identified reflex, termed the “cervico‐motor reflex,” was studied in 15 healthy women (mean age 36.6 years). The response of levator ani (LA) and puborectalis (PR) muscles to electrical and mechanical stimulation of the cervix uteri (CU) was determined. One concentric needle electrode was inserted into the CU (stimulating), a second into the LA (recording), and a third into the PR (recording). The vaginal pressure was measured at rest and on cervical stimulation by balloon‐tipped catheters. Electrical stimulation of the CU led to a reduction in pressure in the upper portion of the vagina (p < .05) and an increase in pressure in the middle and lower portions (p < .001). Stimulation also caused an increase in the electromyographic (EMG) activity of the LA and PR muscles (p < .01). Mechanical stimulation induced the same effects but to a lesser degree. Stimulation of the anesthetized CU, LA, or PR did not evoke the response. The data suggested the presence of a reproducible reflex relationship between the CU and both the LA and PR. During the sexual act and penile buffeting of the CU, levator contraction “balloons” the upper vagina, which acts as a “receptacle” for the semen. Meanwhile, PR contraction narrows the lower vagina, which may effect an increase of penile erection and rigidity. The cervico‐motor reflex may be incorporated as an investigative tool in sexual act disorders.     

The effect of individually adjusted workstations on upper quadrant posture and muscle activity in school children

Evidence suggests there is increasing use of computers by children and poor workstation designs for children. This laboratory study investigated the effect of adjusting computer display height and desk height on upper quadrant posture and muscle activity. Thirty three children aged 4-17 years worked on a desktop computer at a standard school workstation and at a workstation adjusted to the individual, typically consisting of a lower display and desk height. The adjustments resulted in increased head tilt, neck flexion, gaze angle, cervical erector spinae activity and a trend for lower right upper trapezius activity. The recent evidence that suggests more head and neck flexion is not necessarily worse is discussed and normative values for children's head tilt and neck flexion presented. The role of forearm support in decreasing trapezius activity is also discussed.     

Support of the upper limbs of office workers during a daily work journey

Generally, the studies assess the upper limbs postures during the work with Visual Display Terminal - VDT through the measurement of the angles formed by the segments or through the relation with the pre-defined anatomical postures (e.g., flexion, extension, abduction). However, few studies were found in the literature which had focused in the measurement of the upper limbs support during a real situation of work with VDT and in the definition of analysis categories for this kind of behavior. The main objective of this study was to measure, in a real situation and using a systematic observation method through video analysis, the main kinds of support for the upper limbs. The analysis was done considering 480 work hours of 30 office workers. Data were collected using a methodology proposed by Rebelo, Filgueiras & Soares [1] and related with the work organization and workspace conditions, the participants had: a) minimum of eight hours daily of work; b) similar activities, characterized as office work; c) same furniture and equipment; and, d) computers with the same hardware, software and peripherals. Results were analyzed 46554 dynamic events, considering only the fourteen Interaction Categories - ICs, for upper limps support. In this way, percentage was computed, considering the total number of occurrence, for the Right arm is: arm support (0.06%); forearm support (31,8%); elbow support (31,92%); hand support (7,41%); multiple supports (12,32%) and without support 16,41%- For the Left arm the results is: forearm support (0,11%); arm support (53,69%); elbow support (8,70%); hand support (7,97%); multiple supports (8,43%) e without support (21,11%). This systemic and ecological approach was obtained through a method which enables experimental Biomechanics and Physiology methods to develop more efficient functional requirements and recommendations for the work with VDTs.     

The impact of school furniture on fourth grade children's on-task and sitting behavior in the classroom: a pilot study

Schoolchildren spend much of their day sitting in classroom furniture that is often too large or too small. To assess the impact of the size and fit of school furniture on the sitting and task behaviors of schoolchildren, 63 fourth-graders were observed while seated in 2 different sizes, types, and arrangements of furniture in their classroom. A correlated group design was used to compare the sitting and task behaviors of the students while seated in their traditional classroom furniture consisting of tables and chairs, and while sitting in smaller, appropriately sized desks and chairs, arranged in clusters and then in rows. The results indicate that the children sat better and were on task more when seated in the smaller furniture, as indicated by a significant main effect for condition, F = 51.478 (4, 330), p<0.05. There was no difference in sitting and task behaviors with the new furniture arranged in clusters compared to rows. Girls showed a slightly greater improvement compared to boys, and there was a significant correlation between better sitting positions and being on-task (r = 0.549, p<0.01). These findings indicate that students would likely benefit from sitting in smaller furniture that fits their size better.     

The utilization of infrared imaging for occupational disease study in industrial work

Infrared imaging has been used to visualize superficial temperatures in industrial employers standing and working in an indoor environment at 22°C. Temperature distributions and changes have been recorded digitally and analyzed. Mean skin temperatures determined by this method have been compared with superficial temperatures obtained with a probe thermocouple. During working hours, surface temperatures were higher over extensor muscles than over other structures and their spatial distributions differed dramatically from those observed before working hours. The authors also analyzed the cold water immersion of the hands during work. This paper showed that working generates different thermal effects on human skin that reflect physiological and pathological occupational conditions and can be monitored by infrared imaging.     

Modified track shoes and their effect on the EMG activity of calf muscles

Although track and field spike shoes are crafted for runners, these shoes are not designed for regular walking. With such shoes, runners may eventually encounter serious chronic injuries such as plantar fasciitis, shin splints, achilles tendinitis, chondromalacia, and iliotibial band syndrome. To address this problem, a modified spike shoe was tested and compared to a regular spike shoe. The modification consists of adding a removable heel to the shoe sole in order to reduce the flexion of the foot and properly level the foot for walking. Nine healthy participants performed walking drills at 2 and 3 mph, using the original and the modified shoes. Electromyography (EMG) measurements were used to evaluate muscle activities. Participants also rated their discomfort on a 0-10 scale. Results show that the use of modified shoes resulted in a reduction of 22% and 24.25% EMG activity for the tibialis and gastrocnemius muscles, respectively. Comfort ratings increased by an average of 2.7, 2.6, 3.9, and 4.2 points at the knees, calves, ankles, and feet, respectively.     

Risk factors for incident carpal tunnel syndrome: results of a prospective cohort study of newly-hired workers

Carpal tunnel syndrome is one of the most costly upper extremity disorders in the working population. Past literature has shown an association between personal and work factors to a case definition of carpal tunnel syndrome but little is known about the combined effects of these factors with the development of this disorder. Few studies have examined these associations in longitudinal studies. The purpose of this paper is to identify risk factors for incident carpal tunnel syndrome in a longitudinal study of workers across a wide range of occupations.     

Temporal aspects of increases in eye-neck activation levels during visually deficient near work

In an experimental study two levels of oculomotor load were induced via optical trial lenses. Trapezius muscle activity was measured with bipolar surface electromyography and normalized to a submaximal contraction. Sixty-six subjects with a median age of 36 (range 19-47, std 8) viewed a black and white Gabor grating (5 c/deg) for two 7-min periods monocularly through a 0 D lens or binocularly through -3.5 D lenses. The effect of time was separately regressed to EMG in two different subgroups of responders: a High-Oculomotor-Load (HOL) and a Low-Oculomotor-Load (LOL) group. A linear regression model was fitted on group level with exposure time on the x-axis and normalized trapezius muscle EMG (%RVE) on the y-axis. The slope coefficient was significantly positive in the -D blur condition for only the HOL subgroup of responders: 0.926 + Time(min 1-7) × 0.088 (p = 0.002, r(2)=0.865). There was no obvious sign of this activity to level off or to stabilize. These results suggest that professional information technology users that are exposed to a high level of oculomotor load, during extended times, are at an increased risk of exhibiting an increased trap.m. activity.     

Reliability of normalisation methods for EMG analysis of neck muscles

Acceptable reliability of normalisation contractions in electromyography (EMG) is paramount for testing conducted over a number of days or if normal laboratory strength testing equipment is unavailable. This study examined the reliability of maximal voluntary isometric contractions (MVIC) and sub-maximal (60%) isometric contractions for use in neck muscle EMG studies. Surface EMG was recorded bilaterally from eight sites around the neck at C4/5 level from five healthy male subjects. Subjects performed MVIC and sub-maximal normalisation contractions using an isokinetic dynamometer (ID) and a portable cable dynamometer with attached strain gauge (PCD) in addition to a MVIC against a manual resistance (MR). Subjects were tested in flexion, extension, left and right lateral bending and were retested by the same tester within a two-week period. Intra class correlation co-efficients (ICC) were calculated for each testing method and contraction direction and a mean ICC was calculated across all contraction directions. All normalisation methods produced excellent within-day reliability (mean ICC >0.80) but only the MVICs using the ID and PCD had acceptable reliability when assessed between-days. This study confirmed the validity of using MVICs elicited using the ID and PCD as reliable reference contractions for the normalisation of neck EMG.     

Force steadiness in the lower extremities as an independent predictor of functional performance in older women

The relationship between isometric force control and functional performance is unknown. Submaximal steadiness and accuracy were measured during a constant force-matching task at 50% of maximal isometric voluntary contraction (MVC) of the knee extensors in 19 older women (70-89 years). Other variables included MVC, rate of torque development, and EMG activity. Functional performance was assessed during maximal performance of walking endurance, chair rising, and stair climbing. Isometric steadiness (but not accuracy) was found to independently predict chair-rise time and stair-climbing power and explained more variance in these tasks than any other variable. Walking endurance was related to muscle strength but not steadiness. These results suggest that steadiness is an independent predictor of brief, stressful functional-performance tasks in older women with mild functional impairment. Thus, improving steadiness might help reduce functional limitations or disability in older adults.