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Effects of Computer Monitor Viewing Angle and Related Factors on Strain, Performance, and Preference Outcomes
Abstract
A model of visual and musculoskeletal strain associated with computer monitor placement was developed. The main premise of which is that monitor placement decisions must take into consideration development of both visual and musculoskeletal strains. Certain factors in the model that were thought to affect one or both types of strain. or that were considered important to rule out for effect, were tested in a lab setting. These factors were viewing angle (eye level, midlevel, low level), monitor size (14 in., 19 in.), keyboard familiarity (touch typist, nontouch typist), and task (reading, mousing, typing). Outcomes included indicators of visual and musculoskeletal strain, preference, and performance. Muscle activity was generally greater for the low viewing angle, for the standard monitor (14 in.), and for non-touch typists. Participants preferred the midlevel placement. Task performance was slightly diminished with eye-level placement. Results are interpreted in relation to the model and to several hypotheses that were formed to focus the inquiry. Actual or potential applications of this research include monitor placement decisions in the design or modification of computer workstations.
... As for the mouse task time period, it is worth noting that holding the full arm supporting on the work surface may have further highlighted the difference between the two tasks. During the typing task compared with mouse work task, higher activity level of CES and UT muscles is consistent with the findings of Sommerich et al. (2001) and Szeto et al. (2009) studies. In the study conducted by Sommerich et al. (2001), neck flexion as well as left levator scapulae, left and right sternocleidomastoid, trapezius and neck extensor muscle activities were higher during typing compared with mouse work task (Sommerich et al., 2001). ...
... During the typing task compared with mouse work task, higher activity level of CES and UT muscles is consistent with the findings of Sommerich et al. (2001) and Szeto et al. (2009) studies. In the study conducted by Sommerich et al. (2001), neck flexion as well as left levator scapulae, left and right sternocleidomastoid, trapezius and neck extensor muscle activities were higher during typing compared with mouse work task (Sommerich et al., 2001). Yang and Cho (2012) have also reported higher neck and shoulder flexion and upper trapezius muscle activities during typing task compared with mouse work task (Yang & Cho, 2012). ...
... During the typing task compared with mouse work task, higher activity level of CES and UT muscles is consistent with the findings of Sommerich et al. (2001) and Szeto et al. (2009) studies. In the study conducted by Sommerich et al. (2001), neck flexion as well as left levator scapulae, left and right sternocleidomastoid, trapezius and neck extensor muscle activities were higher during typing compared with mouse work task (Sommerich et al., 2001). Yang and Cho (2012) have also reported higher neck and shoulder flexion and upper trapezius muscle activities during typing task compared with mouse work task (Yang & Cho, 2012). ...
Laptop work may increase risks of neck and back injuries in the long term due to awkward postures and increased mechanical loads on cervical and lumbar spine. This study was intended to compare the muscle activities and postural changes as well as discomfort of the neck and back resulted from the laptop work in a conventional and adjusted setup. 20 young healthy males performed two 8-min sessions of computer-mouse work and typing in a conventional setup and in an ergonomically adjusted setup during laptop work. In the adjusted setup, the screen height was individually adjusted by a riser and the keyboard was externally connected. The posture of the cervical, thoracic, lumbar spines, and shoulder, as well as electromyographic activity of cervical and lumbar erector spinae, multifidus, upper trapezius and anterior deltoid muscles, were recorded during the first and last 2 min of each computer work session. Having completed the computer work session, furthermore, the participants scored their neck, back, and general discomfort. The very research findings implied that adjusting the screen height and keyboard placement was effective during laptop work in reducing the cervical (−4.53 deg) and thoracic flexion angles (−3.14 deg) as well as the cervical erector spinae (−10.31%) and multifidus (−15.57%) muscle activities, and resulted in lower discomfort. The typing task was associated with higher muscle activity and awkward posture compared with the mouse work. As for workstation setup, simple modifications may reduce risk factors of musculoskeletal complaints.
Eprint link:
https://www.tandfonline.com/eprint/VWPYYWKXFTTM3MIYIZYW/full?target=10.1080/10447318.2020.1825204
... Placing notebook on a higher workstation to optimize head and neck posture can improve neck posture but in turn causing discomfort in other body part. The forward head posture (FHP) formed as a consequence of using notebook inflict lower cervical flexion and upper cervical extension is believed to contribute to the development of neck and shoulder pain [15]. ...
... Though the incline reduces neck flexion, the keyboard attached to the notebook causes hands follow the slope created by the incline. There might not be an ideal placement where both musculoskeletal strain and poor posture can be minimized by raising notebook, but there might be a configuration or location where both can be reasonably low [15]. ...
... It is not surprising that there is no significant difference between the upper trapezius as some previous studies have shown similar results [14]. However, reducing even low muscle activity levels can be beneficial [15] since some previous studies have shown that time spent in using notebook computer causes sedentary posture, which is also linked with musculoskeletal disorder. ...
This study evaluated the use of external peripheral to form inclines as a means to improve the posture and minimize the muscle activity of using notebook computer. These days, users often use notebook computers in public places or external environments where no adjustable workstation is provided because of the design of laptops which are portable, lightweight, and space-saving. Furthermore, the design of laptop where the display is connected with the input device causes poorer posture to the user. Electromyography (EMG) was used to investigate the upper trapezius, cervical erector spinae, sternocleidomastoid, extensor digitorum, and extensor carpi ulnaris muscle activities when using notebook with different inclines (0°, 12°, 25°, and 30°). Head-neck posture is measured with craniocervical angle to assess the improved posture formed through applying different inclines in notebook usage. The perceived discomfort, comfort, and ease of use by the computer users were also evaluated followed by calculating the efficiency of the typing task in each incline. Based on the EMG result, the 12° induced the less overall muscle activity of the muscles examined. This result was also supported by the respondents’ subjective valuation of the inclines. Even though bigger incline offers more improved head-neck posture, it doesn’t correspond with the muscle activity result as well as the subjective valuation. Therefore, this study suggests the utilization of 12° when using laptop to improve posture and reduce the risk of any musculoskeletal disorder.
... Many studies indicated that sustaining the static posture with tilted head and flexed neck for extended durations leads to muscle fatigue which might decreases productivity (Asundi, Odell, Luce, & Dennerlein, 2012;Dockrell, Bennett, & Culleton-Quinn, 2015;Ekşioğlu, 2017;Gold et al., 2012;Straker, Jones, & Miller, 1997;Werth & Babski-Reeves, 2014). Since working with a computer in non-neutral posture may lead to musculoskeletal strain (Sommerich, Joines, & Psihogios, 2001) and laptop users are working with their devices for extended periods of time, laptop users would benefit from neutral neck posture in order to mitigate resultant muscle pain. While there is a controversial opinion of the "right" posture during computer use, it is recommended using a computer for a short period of time when it is necessary for computer users to perform their work in non-neutral posture (Gold et al., 2012). ...
... Since head tilt and neck flexion are considered to be major risk factors of muscle discomfort during computer use (Dockrell et al., 2015;Gold et al., 2012;Asundi et al., 2012), head tilt and neck flexion were the posture measurements assessed in this study. Three reflective markers were placed on the left side of the participant's head and neck (canthus, tragus, and C7) with angle shown in Figure 3 (Sommerich et al., 2001). The participant's posture while performing the reading and typing task was videotaped by the Go-pro camera located at the left side of the participant. ...
... Figure 3. The angle measurement for neck angle and head tilt (Sommerich et al., 2001). ...
The paper aims to investigate the potential impact of a wearable glasses-type intervention regarding the posture and the productivity of laptop users in a standard working environment. Participants performed reading and typing tasks with a laptop with and without wearing the wearable device to compare the results. Posture markers were placed on the participant’s body to measure neck flexion and head tilt. Typing speed was measured in words per minute (WPM). The results of this study indicated that participants’ head tilt and neck flexion angles are significantly different during the reading and typing tasks with the intervention as compared to those without the intervention. While the average typing speed with the intervention was slower than without the intervention, some participant’s typing speeds and interviews support the notion that the participants’ typing speed would have improved if more time was given.
... A moderate level of evidence was found to support the statement that a lower screen, top edge of screen approximately 10 cm below horizontal eye level when viewing distance is approximately 57 cm (line of sight 15-30 0 below the horizontal line of sight), results in positive health effects (Aaras et al., 1997;Burgess-Limerick et al., 1998Fostervold et al., 2006;Izquierdo et al., 2004;Konig et al., 2015;Korhonen et al., 2003;Sommerich et al., 2001;Straker et al., 2009aStraker et al., , 2009bTurville et al., 1998). Two moderate quality studies (Straker et al., 2009b;Turville et al., 1998) found a screen lower than 40 0 resulted in increased strain on neck muscles. ...
... One high-quality study found a screen height corresponding to less than 20 0 below horizontal eye level was linked to a tendency to develop neck pain (Korhonen et al., 2003). Two studies concluded that a screen height corresponding to a line of sight 14 0 or 17 0 below horizontal resulted in lower neck pain and muscle activity (Izquierdo et al., 2004;Sommerich et al., 2001). One high-quality study found a lower monitor position of 30°below horizontal enabled decreased atlanto-occipital extension, which could be interpreted as lower tension in the muscles (Burgess-Limerick et al., 1998), and another study by the same authors (Burgess-Limerick et al., 1999) reported the user was able to adopt their preferred position at this angle. ...
... 14 (Aaras et al., 1997;Babski-Reeves et al., 2005;Burgess-Limerick et al., 1998Fostervold et al., 2006;Fries Svensson and Svensson, 2001;Izquierdo et al., 2004;Konig et al., 2015;Korhonen et al., 2003;Sommerich et al., 2001;Straker et al., 2009aStraker et al., , 2009bTurville et al., 1998) Positive overall, decreased neck muscle activity, allows preferred gaze angle ...
Purpose:
This paper outlines an approach to develop practical guidelines to support the design of submarine control console workstations.
Method:
Guideline development was undertaken for 13 physical design criteria, provided to the research team. Data was gathered from four sources: a systematic literature review, relevant standards, population specific anthropometric data, and user focus groups. The systematic review included risk of bias, quality assessment and evidence synthesis.
Results & conclusion:
The systematic review retrieved 43 relevant articles in relation to seven of the 13 design criteria. Very few high-quality studies were identified. The combined evidence available from each of the four data sources was collated and used to provide a set of guidelines for each of the 13 criteria, highlighting the importance of the use of multiple data sources. This approach has applicability beyond this study where the need exists to collate evidence sources beyond the scientific literature.
... To avoid this, the users may incline their head upwards to shift the zone of clear vision upwards. The consequence may be complaints in the neck (Horgen et al. 1995(Horgen et al. , 2002Horgen, Aarås, and Thoresen 2004;Aarås et al. 2001;Ariëns et al. 2001;Sommerich, Joines, and Psihogios 2001;Wahlström 2005;Helland et al. 2008;Straker et al. 2009). As a potentially better alternative, the present field intervention study introduces lower monitor positions. ...
... Studies differ in the mean favourable gaze inclination from 2 88 to 2 308. This large range may be a result of different test conditions ( Kroemer and Hill 1986;Heuer et al. 1991;Menozzi et al. 1994;Burgess-Limerick, Plooy, and Ankrum 1998;Burgess-Limerick et al. 1999;Mon-Williams et al. 1999;Sommerich, Joines, and Psihogios 2001;Delleman and Berndsen 2002;Delleman 2004;Allie, Purvis, and Kokot 2005;Straker et al. 2009;Masseida, Perske, and Jaschinski 2013a). ...
... Laboratory research of the comfortable gaze inclination at comfortable head inclination revealed somewhat different values from 2 88 to 2 308. This large range may result from different test conditions Kroemer and Hill 1986;Heuer et al. 1991;Menozzi et al. 1994;Burgess-Limerick, Plooy, and Ankrum 1998;Burgess-Limerick et al. 1999;Mon-Williams et al. 1999;Sommerich, Joines, and Psihogios 2001;Delleman and Berndsen 2002;Delleman 2004;Allie, Purvis, and Kokot 2005;Straker et al. 2009;Masseida, Perske, and Jaschinski 2013a). Masseida, Perske, and Jaschinski (2013a) and Masseida et al. 2013b) suggested that the visual tasks may play a role. ...
At office computer work, musculoskeletal complaints can occur when workplace conditions are not designed according to physiological dispositions of the office worker. Regarding neck pain, the vertical position of the monitor should be adjusted in a way that the head adopts a comfortable posture. For investigating this physiological condition, this research compares several measures of performance and strain as a function of the inclination angle of the head. Head movement performance was measured when the head moves horizontally in a tracking task, while the myoelectrical activity of two types of neck muscles was recorded, i.e. of the sternocleidomastoid muscle and splenius capitis muscle. Additionally, the subjective rating of perceived musculoskeletal strain was assessed by questionnaires in the tracking task and in an office field study. All these measures represent ergonomic stress-strain functions that can be useful in physiologically based ergonomic research. Lowering the head inclination by a few degrees was able to reduce the subjectively rated musculoskeletal strain in field studies. The inclination of the head and vertical gaze direction to the monitor should agree with individual physiological dispositions.
... Some of the researchers in the ergonomics literature studied the effects of different display screens on neck and shoulder pain when compared to a single display. These studies investigated the smartphone screen's height, viewing angle, and distance from the face [30][31][32][33][34]. Many studies have suggested that a smartphone screen with a lower height and a gaze angle of about 15 degrees is suitable for visual comfort [30,32,33]. ...
... These studies investigated the smartphone screen's height, viewing angle, and distance from the face [30][31][32][33][34]. Many studies have suggested that a smartphone screen with a lower height and a gaze angle of about 15 degrees is suitable for visual comfort [30,32,33]. However, the most accepted recommendation nowadays is to position the smartphone screen at eye level. ...
The prevalence of neck pain, a chronic musculoskeletal disease, has significantly increased due to the uncontrollable use of social media (SM) devices. The use of SM devices by younger generations increased enormously during the COVID-19 pandemic, being—in some cases—the only possibility for maintaining interpersonal, social, and friendship relationships. This study aimed to predict the occurrence of neck pain and its correlation with the intensive use of SM devices. It is based on nine quantitative parameters extracted from the retrospective X-ray images. The three parameters related to angle_1 (i.e., the angle between the global horizontal and the vector pointing from C7 vertebra to the occipito-cervical joint), angle_2 (i.e., the angle between the global horizontal and the vector pointing from C1 vertebra to the occipito-cervical joint), and the area between them were measured from the shape of the neck vertebrae, while the rest of the parameters were extracted from the images using the gray-level co-occurrence matrix (GLCM). In addition, the users’ ages and the duration of the SM usage (H.mean) were also considered. The decision tree (DT) machine-learning algorithm was employed to predict the abnormal cases (painful subjects) against the normal ones (no pain). The results showed that angle_1, area, and the image contrast significantly increased statistically with the time of SM-device usage, precisely in the range of 2 to 9 h. The DT showed a promising result demonstrated by classification accuracy and F1-scores of 94% and 0.95, respectively. Our findings confirmed that the objectively detected parameters, which elucidate the negative impacts of SM-device usage on neck pain, can be predicted by DT machine learning.
... It has been reported that muscle fatigue is linked to the use of a high-set VDU, particularly in both trapezius and cervical erector spinae (Seghers, Jochem, & Spaepen, 2003;Sommerich, Joines, & Psihogios, 2001). When the VDU is placed at eye level or just below 5˚, investigators have found a proportional relationship between muscle activity and neck angle (NA) and head tilt (HT; Seghers et al., 2003;Sommerich et al., 2001;Straker, Pollock, Burgess-Limerick, Skoss, & Coleman, 2008). ...
... It has been reported that muscle fatigue is linked to the use of a high-set VDU, particularly in both trapezius and cervical erector spinae (Seghers, Jochem, & Spaepen, 2003;Sommerich, Joines, & Psihogios, 2001). When the VDU is placed at eye level or just below 5˚, investigators have found a proportional relationship between muscle activity and neck angle (NA) and head tilt (HT; Seghers et al., 2003;Sommerich et al., 2001;Straker, Pollock, Burgess-Limerick, Skoss, & Coleman, 2008). Therefore, the cervical region (upper and lower) should be studied in posture research because it may influence head position. ...
OBJECTIVE. This study’s objective was to discover whether a difference exists in four postural angles while performing a typing task on a laptop and a desktop computer.
METHOD. Twenty healthy participants performed a 5-min typing task on each computer.
RESULTS. Statistically significant differences for all angles were found when comparing sitting at the desktop computer with sitting at the laptop. Neck angle (p < .0005), head tilt (p < .0005), and lumbar lordosis (p = .018) were significantly higher when using the laptop. The greatest posterior pelvic tilt was associated with the desktop (p = .018).
CONCLUSION. A desktop appears to be more appropriate for the cervical and lumbar regions; however, using a laptop may be more suitable for pelvic tilt.
... Different types of monitors include LCD, LED, and OLED, each with distinct characteristics, such as response time, color accuracy, and refresh rate. [32] There are many types of monitors in the current market, most of which have differences in response time, color accuracy, color gamma range, and so on. ...
... To maximize screen size whilst maintaining the surface perpendicular to the user, curved screens have been introduced [156]. Research has highlighted that display size and resolution influences a wide range of variables including viewing distance [105,157,158], text legibility [159,160], accommodation [161], asthenopia [162], pupil size [163], musculoskeletal strain [164,165] and visual performance [166], although many of these effects are likely to be device specific. These larger high-resolution displays have been shown to aid productivity [167][168][169][170][171] and improve the ability to share content [172], but such displays typically have increased power demands, device weight/bulk and a requirement for more graphical processing power. ...
Eye strain when performing tasks reliant on a digital environment can cause discomfort, affecting productivity and quality of life. Digital eye strain (the preferred terminology) was defined as "the development or exacerbation of recurrent ocular symptoms and/or signs related specifically to digital device screen viewing". Digital eye strain prevalence of up to 97% has, due to no previously agreed definition/diagnostic criteria and limitations of current questionnaires, failed to differentiate such symptoms from those arising from non-digital tasks. Objective signs such as blink rate or critical flicker frequency changes are not 'diagnostic' of digital eye strain nor validated as sensitive. The mechanisms attributed to ocular surface disease exacerbation are mainly reduced blink rate and completeness, partial/uncorrected refractive error and/or underlying binocular vision anomalies, together with the cognitive demand of the task and differences in position, size, brightness and glare compared to an equivalent non-digital task. In general, interventions are not well established; patients experiencing digital eye strain should be provided with a full refractive correction for the appropriate working distances. Improving blinking, optimizing the work environment and encouraging regular breaks may help. Based on current, best evidence, blue-light blocking interventions do not appear to be an effective management strategy. More and larger clinical trials are needed to assess artificial tear effectiveness for relieving digital eye strain, particularly comparing different constituents; a systematic review within the report identified use of secretagogues and warm compress/humidity goggles/ambient humidifiers as promising strategies, along with nutritional supplementation (such as omega-3 fatty acid supplementation and berry extracts).
... These awkward postures could increase biomechanical stress at the neck or shoulder. During neck flexion, there were increases of compressive and anteroposterior shear forces at the cervical spine [9] together with greater Cervical Erector Spinae (CES) activation [10,11] that could lead to discomfort [12]. Moreover, greater shoulder flexion was also associated with increased Upper Trapezius (UT) and Anterior Deltoid (AD) muscle activity [13]. ...
Background
Although young adults regularly perform tablet writing, biomechanics during the tablet writing with different tilt angles has not been studied. The objective of this study was to compare posture, muscle activity, and discomfort at the neck and shoulder between tablet writing with 0° (horizontal) and 30° tablet tilt angles over 40 minutes in healthy young adults.
Methods
Twenty participants wrote continuously for 40 minutes on a tablet with both tilt angles in a randomized order. Between conditions, there was a 5-minute activity break. Differences in neck and shoulder posture, muscle activity, and discomfort between both tablet tilt angles and changes in the outcomes every 10 minutes over 40 minutes were investigated.
Results
With the tilted tablet, there were lower neck flexion (Z = -4.637, P<0.001), lower shoulder extension (Z = -3.734, P<0.001), and lower neck Visual Analogue Scale (VAS) (left; Z = -4.699, P<0.001 and right; Z = -3.874, P<0.001) as compared to the no tilt condition. However, the right upper trapezius muscle activity was higher in the tilted condition as compared to the no tilt one.
Over 40 minutes, the neck VAS (left; χ²(4) = 30.235, P<0.001 and right; χ²(4) = 32.560, P<0.001) and heart rate variability (χ²(4) = 12.906, P = 0.012) showed notable increases after 20 minutes compared to baseline.
Conclusion
In conclusion, adjusting the tablet tilt to 30° and limiting time spent to 20 minutes are recommended for young adults during the tablet writing to prevent neck problems.
... The works dealing with positioning a computer monitor are either related to ergonomics or body healthiness. In [21], Sommerich et al. investigated the effects of the viewing angle of a computer monitor on muscle activity. They concluded that low viewing angle conditions require much muscle activity. ...
This paper introduces an approach aiming to determine head pose healthiness of computer users. The main contributions of this paper are: 1) Image Quality Assessment (IQA) based Stacked Autoencoder (referred to as IQASAE) which adjusts the value of learning rate based on the quality of images; 2) Head Pose Healthiness Prediction (HPHP) framework which leverages the proposed IQASAE algorithm in combination with image processing operations; 3) A set of features suitable for face analysis applications; 4) Ontology-driven semantic framework which enables further exploiting pose estimation results within applications in synergy with healthcare expert domain knowledge about pose healthiness. Our framework was evaluated on both offline (BIWI and AFLW) and online (our own, collected using Arduino) datasets. Furthermore, it was compared to several state-of-art methods, including Multi-Layer Perceptron (MLP), CART, Random Forest, Convolutional Neural Networks (CNN), Temporal Deep Learning Model (TDLM), hybrid CNN with Support Vector Machine (SVM), Quatnet and Trinet. According to the achieved experimental results, it reaches accuracy up to 79.63% outperforming all of them, except Quatnet and Trinet. However, the main advantages of IQASAE compared to state-of-art methods are: 1) it does not require selection of features, so the processing time is reduced, 2) utilizing angle between chin and mouth reduces training time for SAE, 3) leveraging vector-based feature set to create training data resulted in a significant improvement, especially in offline facial images.
... A significant amount of research and system design consideration has been given to reducing operator visual fatigue (asthenopia) to improve operator comfort and performance (Arvanitis et al., 2007;Blehm et al., 2005;Dillon and Emurian, 1996;Emoto et al., 2005;Rajabi-Vardanijani et al., 2014;Rempel et al., 2007;Sommerich et al., 2001;Wang and Huang, 2004). However, significantly less is known about how the visual system influences the cognitive states of operators. ...
Deficits in the accommodative and/or vergence responses have been linked with inattentive behavioral symptoms. While using automated systems (e.g., self-driving cars, autopilot), operators (e.g., drivers, pilots, soldiers) visually monitor displays for critical changes, making deficits in the accommodative and/or vergence responses potentially hazardous for individuals remaining actively engaged in the task at hand. The purpose of this study was to determine if symptoms of accommodative-vergence deficits predict an individual's level of task engagement and cognitive fatigue while performing a flight simulation task with or without automation. Eighty-four participants performed a flight simulation task with or without automation. Prior to task completion, self-report accommodative-convergence deficit symptoms were assessed with the Convergence Insufficiency Symptom Survey (CISS). Before and after the flight simulation task participants rated their task engagement and cognitive fatigue. Electroencephalographic activity (EEG) was recorded concurrently during task performance. Results showed that higher scores on the CISS were related to increased feelings of fatigue and decreased ratings of task engagement. The CISS was also positively related to parietal-occipital fast alpha power during the last 10 min of the task for participants using automation, suggesting increased cortical idling. CISS scores did not predict performance. Results have implications for optimizing operator cognitive states over extended task performance.
... This is in line with the recommended flexion threshold for eye-to-monitor angles of under 20° (Chaffin, 1973;Kilbom & Persson, 1987) or preferred workstation angle ranges between +10° and -25° in relation to the horizontal line (Menozzi et al, 1994). Whilst the additional 17° required to perform the 29° tilt may seem small it is worth mentioning that for every degree increase in tilt, further strain is put upon various muscles in the head and neck region (Sommerich et al, 2001). The angle increase in the elevation at Sergels Torg, compared to Kungsträdgården, is in itself a more physically straining environment, but more importantly is the connotations that our brains develop due to the strain our naturally limited April 23 rd ,12:23 anatomy inflicts in interactions with forms that enforces movements than cause such discomfort. ...
Some public squares experience large amounts of human activity and some experience very little, even though external conditions between them create comparable opportunities for public life. The field of public life studies observes the human activity of public spaces and presents principles that predicts human public behaviour to gain a better understanding for what elements of space people are attracted to. The human staying activity at two central public square in Stockholm – Kungsträdgården and Sergels Torg – was studied with the methodology of public life studies as outlined in Gehl & Svarre (2013) How to Study Public Life. A stationary activity mapping was performed for the two squares where female, male, sitting and standing activity was registered. The result show that Kungsträdgården attracts more than twice the staying activity as Sergels Torg, and that the two squares are mirror images of each other in terms of gender and activity proportions, with Kungsträdgården being predominately female and sitting and Sergels Torg male and standing. The principles,theories, previous observations and hypotheses from a selection of the most seminal works within the public life studies field frame the seven themes used to analyse the human stationary activity at the two squares; Sitting, Standing, Thermal Comfort, Psychological Comfort, Sensory Comfort, Aesthetics and Human Interaction.
... The performance drops severely after 30 degrees due to the LED sensitivity view limited by the current LED manufacture technology. However, the primary screen viewing angle is from 3 • to 20 • [54], within our sensing range. The performance of SpecEye remains unaffected. ...
Digital devices have become a necessity in our daily life, with digital screens acting as a gateway to access a plethora of information present in the underlying device. However, these devices emit visible light through screens where long-term use can lead to significant screen exposure, further influencing users' health. Conventional methods on screen exposure detection (\textite.g., photo logger) are usually privacy-invasive and expensive, further, require ideal light conditions, which are unattainable in real practice. Considering the light intensity and spectrum vary among different light sources, an effective screen spectrum estimation can provide vital information about screen exposure. To this end, we first investigate the characteristics of the junction between p-type and n-type semiconductor (i.e., PN junction) to sense the spectrum under various conditions. Empirically, we design and implement, \textsfSpecEye, an end-to-end, low cost, wearable, and privacy-preserving screen exposure detection system with a mobile application. For validating the performance of our system, we conduct comprehensive experiments with 54 commodity digital screens, at 43 distinct locations, with results showing a base accuracy of 99%, and an equal error rate (EER) approaching 0.80% under the controlled lab setup. Moreover, we assess the reliability, robustness, and performance variation of \textsfSpecEye under various real-world circumstances to observe a stable accuracy of 95%. Our real-world study indicates \textsfSpecEye is a promising system for screen exposure detection in everyday life.
... Various VDT tasks have been considered in visual display evaluations, including proofreading (Buchner et al., 2009;Piepenbrock et al., 2013;Schotter et al., 2014), reading (Hwang et al., 1988;Sommerich et al., 2001), searching (Wang et al., 2012), and watching (Kong et al., 2011). More recent display curvature studies have also used a variety of tasks including proofreading (Park et al., 2016a;Choi et al., 2018), reading (Häkkinen et al., 2008;Mustonen et al., 2015;Na et al., 2015), visual searching (Lin et al., 2009;Park et al., 2017;Wang et al., 2012), visual discrimination (Wang et al., 2007), computer tasks (Czerwinski et al., 2003;Ling et al., 2016;Robertson et al., 2005), and video or image watching (Mun et al., 2015;Ohtsuka et al., 2016;Park et al., 2016b;Yi et al., 2015). ...
This study examined the effects of display curvature and task duration on proofreading performance, visual discomfort, visual fatigue, mental workload, and user satisfaction. Five 27″ rear-screen mock-ups with distinct curvature radii (600R, 1140R, 2000R, 4000R, and flat) were used. Ten individuals per display curvature completed a series of four 15 min comparison-proofreading trials at a 600 mm viewing distance. Only proofreading speed benefited from display curvature, with 600R providing the highest mean proofreading speed. Proofreading speed increased and accuracy decreased for all display curvatures over the 1 h proofreading period. Visual discomfort, visual fatigue, and mental workload increased during the first 15 min of proofreading. A decrease in critical fusion frequency during that period indicated increases in visual fatigue and mental workload. A short break between 15 min proofreading tasks could be considered to prevent further degradation of task performance and ocular health.
... While they were distracted by an everyday work tasks to capture images, the camera was mounted on a tripod stand, fixed at a standardized distance of 200cm from the subject's lateral foot, using electronic angle finder to insure that camera at vertical level. The tripod height was adjustable so that the camera would be at the same level of C7 spinous process (Silva et al., 2009). Repeated captures were taken to overcome the subject's tension during image capturing as well as to overcome the difference between measurements because of postural swaying. ...
Sustained sitting posture is attributed to the high prevalence of neck pain in office workers with computer-based tasks. Purpose: To investigate the effect of cranio-cervical flexion training (CCFT) and supplemental rest breaks on the ability of Visual Display Unit (VDU) users on the accuracy of work. 24 computer users randomly assigned into 2 groups (“A” control & “B” study). Both groups received a lecture on proper posture during work, assessment and modification of workstation set up but only group “B” received CCFT and supplementary rest breaks daily for of six weeks. Pain intensity, functional neck disability, and work habitual posture were measured and compare between before and after intervention using Visual Analogue Scale, Neck Disability Index, and Digital Imaging for Postural Assessment method (DIPA), respectively. Both groups showed intergroup difference in all the measured parameters, except for Gaze angle in group A showed non-significant difference. Between group comparisons showed significant difference in VAS and CCFT in favor of group B. For neck angles there was significant difference in favor of group B except for neck flexion and Gaze angles and same was noted in Neck Disability Index. The study revealed that 6 weeks of repeated micro rest breaks and deep cervical training improves cervical angles and deep flexors strength thus enhance neck postural control. This exercise could be used as preventive measure against the development of neck dysfunctions in risk population.
... Touchscreen use required an approximately 3° greater gaze angle than did mouse use, which was consistent with a previous study that found that gaze angle in the touch condition was significantly higher than in the no touch condition [10]. This greater gaze angle could be associated with increased muscle demand in the neck and shoulder regions [10,19]. However, the gaze angle (16°) in the touchscreen task here was only slightly higher than the 15° ANSI/HFES 2007 recommends [17], so the gaze angle itself would not cause substantial physical demands on the neck in the touchscreen condition. ...
... While an adjustable monitor arm and monitor can be positioned in nearly unlimited positions, in general, the distance between the eyes and monitor should range between 28-36 inches (71-91 centimeters) [161]. The viewing angle should range between -10 degrees and -30 degrees from the horizontal line of sight [162]. However, monitor viewing depends on numerous factors, such as age, illumination, flicker, and glare. ...
... While an adjustable monitor arm and monitor can be positioned in nearly unlimited positions, in general, the distance between the eyes and monitor should range between 28-36 inches (71-91 centimeters) [161]. The viewing angle should range between -10 degrees and -30 degrees from the horizontal line of sight [162]. However, monitor viewing depends on numerous factors, such as age, illumination, flicker, and glare. ...
... While an adjustable monitor arm and monitor can be positioned in nearly unlimited positions, in general, the distance between the eyes and monitor should range between 28-36 inches (71-91 centimeters) [161]. The viewing angle should range between -10 degrees and -30 degrees from the horizontal line of sight [162]. However, monitor viewing depends on numerous factors, such as age, illumination, flicker, and glare. ...
... The monitor is either too low or too high, it can lead to an increase in either flexion or extension or bending of the head relative to the neck [34,35,36] and an increase in muscle activity [37,38,39]. Sommerich, et al. [40] states that, muscle activity is generally greater for the low viewing angle for the standard 14 inch monitor and proposed a conceptual Ushaped model to depict the conflict, and suggested the viewing angle at a range of 0° to approximately 45° below eye level. However, most of the researchers suggest a mid position ranging from 15° to 25° below gaze inclination [41]. ...
In order to facilitate the advancement of computer based technology and prevent health risk associated with computer workstations (non-ergonomics), a modification of the computer workstations is essential. The ergonomics for design of computer workstations leads to motivate the work, higher performance, efficiency and quality of work. Current scenario, our society spends lot of time with computers, thus the computer workstation needs to provide comfort to users. Discomfort position can harmfully affect the overall health and performance of work. In this past, present and future trends of computer workstation designs are discussed. Furthermore this paper offers the suggestions for design of computer workstations and simple exercises to reduce musculoskeletal disorders of prolong time users.
... Although it may be argued that because of ocular movements, horizontal gaze is possible even with the head angled downward [43,44], or that the more commonly assumed headneck posture angles downward instead of truly horizontal [45,46], the ability to keep one's face upright remains favorable [40,47,48]. Conditions that tend to favor a slightly downward head-neck posture, such as severe ankylosing spondylitis [49,50] or fusion of the entire spine [51], are uncommon and should be evaluated on a case-by-case basis. ...
Background Context
As sagittal alignment of the cervical spine is important for maintaining horizontal gaze, it is important to determine the former for surgical correction. However, horizontal gaze remains poorly-defined from a radiological point-of-view.
Purpose
To establish radiographic criteria to define horizontal gaze.
Study design/Setting
This study was conducted at a tertiary healthcare institution over a 1-month period.
Patient Sample
A prospective cohort of healthy patients was used to determine the best radiological criteria for defining horizontal gaze. A retrospective cohort of patients without rigid spinal deformities was used to audit the incidence of horizontal gaze.
Outcome measures
Two categories of radiographic parameters for determining horizontal gaze were tested: (1) the vertical offset distances of key identifiable structures from the horizontal gaze axis; and (2) imaginary lines convergent with the horizontal gaze axis.
Methods
Sixty-seven healthy subjects underwent whole body EOS® radiographs taken in a directed standing posture. Horizontal gaze was radiographically defined using each parameter, as represented by their means, 95% confidence intervals (CI) and associated two standard deviations (SD). Subsequently, applying the radiographic criteria, a retrospective audit of such radiographs (prior to the implementation of strict radioimaging standardization) was conducted. There were no sources of funding, and no conflicts of interest related to this study.
Results
The mean age of our prospective cohort was 46.8 years while that of our retrospective cohort was 37.2. Gender was evenly distributed across both cohorts. The 4 parameters with the lowest 95% CI and 2SD were the distance offsets of the midpoint of the hard palate (A), and the base of the sella turcica (B), as well as the horizontal convergents formed by the tangential line to the hard palate (C), and the line joining the centre of the orbital orifice with the internal occipital protuberance (D). In the prospective cohort, good sensitivity (>98%) was attained when two or more parameters were used. Audit using criteria B+D yielded compliance rates of 76.7% – a figure much closer to that of A+B+C+D (74.8%). From a practical viewpoint, criteria B+D is most suitable for clinical use, and can be simplified to the “3-6-12 rule” as a form of cursory assessment. Verbal instructions in the absence of stringent postural checks only ensured that ~75% of subjects achieved horizontal gaze.
Conclusions
Fulfilment of criteria B+D is sufficient to evaluate for horizontal gaze. Further criteria can be added to increase sensitivity. Verbal instructions alone yield high rates of inaccuracy when attempting to image patients in horizontal gaze. Apart from improving methods for obtaining radiographs, a radiological definition of horizontal gaze should be routinely applied for better evaluation of sagittal spinal alignment.
... Since console operators receive visual information from displays for a long time, it is liable to get musculoskeletal disorders and psychological discomfort, if the displays are not in the right position (Sommerich et al., 2001). To achieve physical comfort, visual angle should be taken into account. ...
A console of a submarine is a collection of user interfaces composed of control devices and two vertically installed displays. Since console operators receive most visual information from these displays for a long time, it may cause musculoskeletal disorders and psychological discomfort if the screen is not in the right position. Therefore, the aim of this study is to derive optimal design values for the position and tilting angle of displays. We identified the environmental constraints of control room and the visual angle of the operators. In addition, we considered the physical characteristics of target user population. Thus, we used anthropometric data of Korean males aged from 20s to 30s, who are representative user segments that operates the console. Tasks were divided into ‘direction’ tasks that operators usually perform, and ‘detection’ tasks, which should be performed in case of emergencies. The variables of monitor height, maximum vertical height, work surface height, eye height, and distance between eye and monitor were selected, and conditional equations were established with consideration of design factors and environmental constraints. With these equations, the optimal value was derived through a GRG (Generalized Reduced Gradient) method. After, we evaluated the appropriateness of the proposed optimal values with a full-scale mockup of a console. 10 ergonomics experts conducted usability test, and reaction time (RT) as well as electromyography (EMG) activity of the cervical vertebral were measured during the experiment. As a result, participants reacted within a fairly short time with little fatigue on the cervical vertebral. Overall, we successfully suggested the optimal ranges of tilting angles for two vertically arranged monitors while considering context-of-use, anthropometric characteristics of South Koreans, and human visual characteristics.
... The TFT-LCD was positioned on a table 70 cm in height [22][23][24]. The inclination angle of the TFT-LCD screen was 105° [24,25] with respect to the vertical axis. A chinrest restrained each participant's head at 25 cm above the table and maintained their viewing distance at 60 cm during the experiment. ...
This study empirically investigated the effects of noise type, noise intensity, and illumination intensity on reading performance. Three levels of noise types: factory noise, classical music, and pop with lyrics; three levels of noise intensity: 45 dBA, 65 dBA, and 85 dBA; and three levels of illumination intensity: 200 lx, 600 lx, and 1000 lx were tested. Results indicated that all three independent variables had significant effects on reading performance. Reading performance for classical music was significantly greater than that for pop with lyrics and factory noise. For noise intensity, 45 dBA resulted in the best reading performance, followed by 65 dBA, and 85 dBA. For illumination intensity, 600 lx resulted in the best reading performance, followed by 1000 lx and 200 lx. The interaction effects of noise type × illumination intensity were statistically significant. In conclusion, reading performance was best with classical music, low noise intensity, and normal illumination intensity conditions.
... Various VDT tasks have been considered in visual display evaluations, including proofreading (Buchner et al., 2009;Piepenbrock et al., 2013;Schotter et al., 2014), reading (Hwang et al., 1988;Sommerich et al., 2001), searching (Wang et al., 2012), and watching (Kong et al., 2011). More recent display curvature studies have also used a variety of tasks including proofreading (Park et al., 2016a;Choi et al., 2018), reading (Häkkinen et al., 2008;Mustonen et al., 2015;Na et al., 2015), visual searching (Lin et al., 2009;Park et al., 2017;Wang et al., 2012), visual discrimination (Wang et al., 2007), computer tasks (Czerwinski et al., 2003;Ling et al., 2016;Robertson et al., 2005), and video or image watching (Mun et al., 2015;Ohtsuka et al., 2016;Park et al., 2016b;Yi et al., 2015). ...
This study examined the effects of display curvature (400, 600, 1200 mm, and flat), display zone (5 zones), and task duration (15 and 30 min) on legibility and visual fatigue. Each participant completed two 15-min visual search task sets at each curvature setting. The 600-mm and 1200-mm settings yielded better results than the flat setting in terms of legibility and perceived visual fatigue. Relative to the corresponding centre zone, the outermost zones of the 1200-mm and flat settings showed a decrease of 8%e37% in legibility, whereas those of the flat setting showed an increase of 26%e45% in perceived visual fatigue. Across curvatures, legibility decreased by 2%e8%, whereas perceived visual fatigue increased by 22% during the second task set. The two task sets induced an increase of 102% in the eye complaint score and a decrease of 0.3 Hz in the critical fusion frequency, both of which indicated an increase in visual fatigue. In summary, a curvature of around 600 mm, central display zones, and frequent breaks are recommended to improve legibility and reduce visual fatigue.
... Concerning the dimension of the reduction of exposure level, most studies focusing on workstation design address desk and display design [25,26]. The workstation design can influence short-term variation in posture and muscular variability [25]. ...
There is limited research on the effects of different types of rest-break interventions for VDU (Visual display Units) operators on neck and shoulder postures. This study examined the effect of rest-break interventions on the neck and shoulder postures of symptomatic VDU operators during prolonged computer work. Thirty subjects were randomly and equally assigned to breaks with stretching, breaks with dynamic movement, and passive breaks. Subjects performed the typing task for 60 min and received 3-min breaks after 20-min of work. The craniovertebral and forward shoulder angles were obtained from a 3D motion analysis system. Results showed that there were no significant differences in the craniovertebral and forward shoulder angles among any types of rest–breaks. It can be concluded that the three types of rest-break interventions had positive effects on neck and shoulder posture during prolonged computer terminal work.
... The muscles tested were upper trapezius (UT) and sternocleidomastiod (SCM) where these two muscles involved in the rotation and as the indicator of the increased load on shoulder and neck areas. High level of muscle activities also is an indicative of higher muscle effort in performing a task, and if this is sustained for a long period, there may be greater muscle loading which may lead to fatigue and overstrain in the muscle (11,12). The neck and shoulder region of the subjects were cleaned using 70% alcohol swap and the hair was shaved if necessary. ...
Background: Workstation design has shift from using single monitor screen to dual monitor screens, which may impose some impacts towards the muscles activity. This study aimed to determine the effect of using dual monitor screen computer to the neck-shoulder muscle activity among computer user. Method: This experimental study was conducted in 2015 among 28 healthy students in University Malaysia Perlis. The muscle activity of sternocleidomastoid and trapezius were recorded using surface electromyography (sEMG) as the participants perform two types of computer task: (1) proofreading task for 10 minutes (2) typing task for 20 minutes in setting; single and dual monitor screens. Results: There was a significant reduction in the median frequency of the left trapezius muscle (t=-2.515, P=0.018). Sternocleidomastoid muscle activity for both sides also showed a significant reduction in the median frequency where right SCM (t=-2.579, P=0.016) and left SCM (t=-2.345, P=0.027). When compared between both setup of screen display, it is showed that dual screen gave a lower trend of muscle activity compared to single screen. Conclusions: Using dual screen may results in increasing the movement frequency and reducing the static strain in the neck-shoulder muscle area.
Background:
The tray table in economy class air travel may cause excessive neck flexion and discomfort in passengers.
Objective:
The purpose of this study is to examine the influence of different tray table heights on the neck posture and discomfort perception of passengers.
Methods:
A passenger experience survey was used to determine the passengers' view that the tray table was not high enough, and that most passengers were dissatisfied with the overall comfort evaluation of the tray table, especially passengers with obesity. Three head-neck angles and discomfort perceptions of six body parts in 58 participants were recorded by neck posture 3D scanning and perceived level of discomfort assessment, respectively.
Results:
Tray tables at the original height (68 cm) caused unnatural neck posture and discomfort in participants. Raising the tray table can improve the neck posture of participants and reduce discomfort. However, raising the tray table too high will cause more shoulder discomfort in participants. Based on the results, 78 (±2) cm is suggested as the suitable thresholds range of tray tables for economy class air travel.
Conclusion:
The results and findings of this study could provide a theoretical base for the optimization of tray table design.
This study aims to compare the changes in neck angles, muscle activities, ergonomic risk, and body discomfort caused by the use of two different computer screen sizes. The 36 female users participated and used displays with 46.99 and 58.42-centimeter screen sizes who were assessed for craniocervical angle (CCA), craniovertebral angle (CVA), upper trapezius (UT), and sternocleidomastoid (SCM) muscle activity, ergonomic risk, and body discomfort for a duration of 1 hour. The results showed there were no significant differences when comparing between both computer screen sizes usage (p > 0.05). However, there were significant differences in the CCA, UT muscle activity, and body discomfort when comparing between before and after usage for both computer screen sizes (p < 0.05). The results indicate that computer users can select different screen sizes for working but should be concerned with neck angle, muscle activity, and body discomfort when using for long periods of time.
Spending considerable amount of time watching videos on the digital screens can lead to visual fatigue. A consistent source of light, when directed at the eye, can also lead to the deterioration of one’s cornea and lens. This study was aimed at investigating the effect of screen brightness on visual fatigue whilst watching videos. Visual fatigue at three different brightness levels of the monitor- low, medium and high, was studied with the help of the Asthenopia questionnaire form. It was found that setting the screen brightness at a medium level caused minimum visual fatigue in a room well lit by LED luminaries.
Prior research has found that office workers may not be fully utilizing their chair's back support. This may be due in part to cognitive demands or other psychological stressors. Not using the back support may increase the muscle tension and contribute to muscle fatigue and discomfort. Historically, footrests have been advocated to address anthropometric disparities in office settings. In this laboratory study, it was hypothesized that a footrest may facilitate the use of the backrest and mediate the biomechanical demands on the back and neck muscles, especially when cognitive workload is elevated. Twenty participants performed computer tasks, which varied in their complexity levels, both with and without an angled footrest. Using a footrest increased workers' use of a chair's backrest, increased pelvic rotation towards the backrest, and had a corresponding change in spine flexion. However, no changes were found in the sampled electromyographic activities due to the footrest.
Human Factors and Ergonomics (HFE) academic and professional communities emphasize an interdisciplinary approach to help solve complex problems, particularly for New Product Development (NPD). Data visualization is an effective way of understanding complex data and information. The HFE research community has traditionally used static explanatory graphics to communicate with other disciplines and to support publications and conference presentations. These graphics are typically designed for collaborators and audiences that are familiar with the underlying data or graphical form. While there have been multiple attempts at visually communicating HFE concepts and data to other disciplines, not many attempts have been made to utilize spatio-temporal visualizations to understand the dynamic HFE data. The utilization of the visualized HFE data that are easily consumable in an interdisciplinary team will stimulate the effective application of HFE in NPD. This can also help interdisciplinary teams as well as university students studying tangential subjects like Industrial Design understand this data in order to facilitate NPD. The purpose of this study is to explore data visualization approaches that will help HFE professionals to effectively communicate HFE data to collaborators outside their disciplinary expertise. We conducted a literature review of existing static and dynamic anthropometric data visualizations that have been used by HFE professionals to communicate the results of ergonomic studies. Additionally, we used datasets from a previous intervention design study to develop spatio-temporal visualization examples. Our examples use three-dimensional space as well as the temporal nature of the digital medium in order to communicate a complete picture of the data in a cohesive manner. We developed these examples using the Processing programming language. The developed examples will be utilized to examine the effectiveness of data consumption from non HFE professionals, such as industrial designers, in future studies.
Background:
Neck discomfort and pronounced neck flexion have been associated with smartphone use.
Objective:
Eye glasses with a 90 deg prism in each lens were investigated as a potential intervention to reduce awkward head and neck postures during activities involving viewing the device.
Methods:
Sixteen smartphone users with neck pain and 9 asymptomatic users performed a texting task on a smartphone with and without the prism glasses, in sitting and standing postures in a laboratory setting.
Results:
Cervical erector spinae and upper trapezius muscle activity, head posture and motion, performance, discomfort and other subjective perceptions were assessed. Prism glasses reduced neck extensor muscle activity, neck flexion, and head tilt compared to the direct view. In the symptomatic group, the intervention produced less neck and shoulder discomfort compared to the direct view.
Conclusions:
This intervention could offer an alternative way of interacting with a smartphone while texting in stationary postures, by reducing exposure to pronounced flexed neck and head posture commonly seen in users, and thereby could reduce neck discomfort associated with smartphone use.
Background:
The use of tablet during the office work is on the rise, but the biomechanical response of tablet use under various sitting postures is not well understood.
Objective:
This study quantitatively measured changes in trunk kinematics under three sitting conditions (raised leg, neutral leg, and lowered leg) while using a tablet.
Methods:
Fifteen participants were asked to sit on a chair with three different postures while staring at a handheld tablet or gazing straight ahead with a bare hand, and the head flexion, lumbar flexion and trunk inclination were captured with electrical goniometers.
Results:
The results revealed significantly less lumbar flexion (12.8%) and trunk inclination (28.0%) while using the tablet compared to the empty hand condition (p < 0.001), but at a significant cost of increased head flexion (90.8%; p < 0.001). Further, while using the tablet, participants showed less head flexion in the raised leg condition (p < 0.001) than in the others (9.7% and 7.5%, respectively), but larger trunk inclination and lumbar flexion were required (p < 0.001 in both).
Conclusions:
Collectively, the lower extremity sitting posture significantly changed the way to observe the tablet by adopting more head flexion in neutral and lowered leg conditions or more trunk flexion in raised leg condition.
Purpose: Cervical spine flexion is a common posture for those using computers, tablets, and smartphones; the latter being dubbed ‘text-neck’ in recent years. Coincidentally, flexion has been flagged as a significant mechanical risk factor for the development of chronic neck pain. Unfortunately, few modelling endeavors have attempted to quantify the intervertebral joint loads throughout the cervical spine in flexion, while still accounting for muscular activation.
Methods: Eight healthy male subjects undertook five trials beginning in a neutral posture, flexed to 45 degrees, and returned to a neutral posture. 3D head-trunk angles and surface electromyography from 10 neck muscles (5 bilaterally) were used as inputs into an inverse dynamic cervical spine model based on a 50th percentile male to compute the compression and anteroposterior (AP) shear forces for this flexion task.
Discussion & Conclusion: In general, compression increases cranially to caudally throughout the cervical spine, but levels off at the C5-C6 level. Conversely, in a neutral posture, there is a constant 18 N of anterior shear at each joint level. Compression increased twofold throughout the cervical spine with flexion, whereas anterior shear increased fourfold in the upper cervical spine and dramatically decreased caudally. The dramatic change in joint kinetics provides some mechanical evidence for the role of posture and interplay with muscle activity in the development of chronic neck pain. Results from this study can reinforce the need for appropriate workstation and monitor configurations and support the increased loading hypothesized to occur in ‘text neck’ postures.
Practitioner’s Summary: The purpose of this investigation was to quantify the compression and shear forces in the neck in 45 degrees of flexion compared to neutral. Flexion increased compression throughout the cervical spine 1.6-fold compared to a neutral posture. In the upper cervical spine, AP-shear increased four-fold compared to neutral.
Background:
Laptop computers are used in various places and situations. The number of laptop users experiencing musculoskeletal disorders (MSDs) has increased drastically due to, in part, inappropriate workstations.
Objective:
To investigate the neck and shoulder postures, and muscle activity relative to perceived pain when using the laptop at a low-height table, sofa, and bed.
Methods:
Twenty male participants aged 18- 25years were randomly assigned to perform laptop computer operation at 3 workstations for 10 minutes during which neck and shoulder angles, muscle activity, and pain were recorded by using an Electro-goniometer, Electromyography (EMG), and visual analog scale (VAS), respectively.
Results:
Neck flexions when working at the sofa (18.6°±12.2°) and bed (17.2°±10.5°) were significantly (p < 0.05) greater than that at the low-height table (7.8°±6.5°). However, shoulder flexion when working at the low-height table (28.2°±13.0°) was significantly (p < 0.05) greater than that at the sofa (13.8°±8.6°) and bed (10.91°±7.8°). Working at the low-height table caused the shoulder flexor muscle activity to be significantly (p < 0.05) higher than working at the sofa and bed. Neck pain was reported during laptop computer use at the sofa and bed, and upper back pain when working at the low-height table.
Conclusions:
High neck flexion and pain were found while working at sofa and bed, whereas high muscle activity at shoulder and upper back pain were found while working at the low-height table.
Increasing concerns about musculoskeletal disorders in the upper back arising from excessive daily use of the smartwatch have been widely validated by the rising prevalence of discomfort. This study explored the smartwatch as a potential ergonomic intervention over the smartphone. Fourteen healthy participants completed five tasks (application setting, calling, message typing, message checking and vocal message entry) with smartphone and smartwatch in both sitting and standing postures. The neck-shoulder kinematics and muscle activation levels were monitored to assess the effects of the tasks, devices, and postures. The results indicated greater head flexion, head rotation and shoulder abduction and greater muscle activities for smartwatch use compared to smartphone use, but the performance measure (i.e., elapsed time) was superior for smartwatch use in all tasks except message typing. Collectively, only short and simple tasks such as message checking and application setting should be conducted with the smartwatch.
Introduction
Evaluer les contraintes biomécaniques associées aux cervicalgies parmi les opérateurs sur écran.
Méthodes
Etude ergonomique réalisée au prés de 325 opérateurs sur écran dans 25 établissements de l’université du centre tunisien, basée sur une étude anthropométrique du poste du travail sur écran et une analyse semi-quantitative sur des enregistrements vidéo des activités des travailleurs conduits sur une période représentative de 30 minutes.
Résultats
La prévalence des cervicalgies évaluée à 72,3%, a concerné une population de travailleurs qui exerçait avec un siège et un plan de travail inadaptés (84,6%) et un écran bas situé par rapport au regard horizontal (81,2%). L’analyse semi-quantitative par enregistrement vidéo du poste de travail a conclu que la nuque était maintenue en flexion franche de plus de 40 degrés sur 69% du temps global du travail. La flexion latérale a été visible sur 50,3% du temps de travail et la rotation droite ou gauche sur 57,4% du temps de travail. Ainsi, Les opérations de prise d’information de l’écran, de regard du clavier et de consultation des documents se sont dégagées comme les plus de contraignantes pour la nuque sur le plan gestuel et postural.
Conclusion
Nos résultats mettent en évidence l’importance des contraintes biomécaniques associées à la conception du poste de travail sur écran non conforme aux dimensions anthropométriques ergonomiquement recommandées. Ces contraintes sont associées à une prévalence élevée des cervicalgies traduisant la nécessité d’aménagement ergonomique de ces postes de travail pour prévenir ce fléau.
Musculoskeletal discomfort is common among surgeons. Surveys show that 77–100% of laparoscopic surgeons experience physical symptoms or discomfort attributed to operating, but few seek treatment. Surgeons are exposed to many risk factors for musculoskeletal discomfort and occupational injury, and surgical residents may be at additional risk given their inexperience. Surgeon discomfort has potential negative consequences on surgeon performance and patient outcomes, resulting in lost revenue and surgeon burnout. Improving surgical ergonomics can reduce discomfort and mitigate negative downstream consequences. In the operating room, this includes awareness of body posture and proper operating room setup. Other strategies include a warm-up prior to the first case and taking scheduled breaks during surgery. Outside of the operating room, surgeons can reduce discomfort by improving the ergonomics of their office environment and maintaining good health through routine exercise and stretching. Surgeon educators should teach residents ergonomic principles as well as model their implementation in the operating room.
The angle at which a computer display is viewed may have an impact on the musculoskeletal and visual comfort of the user. Although scientific literature regarding viewing angles has grown in the past decade, a research gap still remains. As a result, one is challenged to design workstation solutions that satisfy the performance requirements of both the musculoskeletal and visual systems, and at the same time, adapt to individual preferences. The following recommendations are offered based on a “middle ground” approach where research findings regarding eye comfort, neck comfort and user preferences are all taken into account: (1) the top of the display screen should be placed at or lower than 5° below the horizontal line of sight; and (2) the center of the display should be positioned no more than 25° below the user's horizontal line of sight. These recommendations create a viewing angle range that is less than current recommendations stated in ergonomic standards for VDT workstations.
Touchscreen interfaces for computers are known to cause greater physical stress compared to traditional computer interfaces. The objective of this study was to evaluate how physical demands and task performance of a tap gesture on a computer touchscreen vary between target locations and display positions. Twenty-three healthy participants conducted reach-tap-return trials with touch targets at fifteen locations in three display positions. Mean completion time, touch accuracy and electromyography of the shoulder and neck extensor muscles were compared between the target locations and display positions. The results demonstrated that participants completed the trial 12%–27% faster with 13%–39% less muscle activity when interacting with targets in the lower area of the display compared to when tapping upper targets (p < 0.05). The findings suggest that proper target placement and display positioning can improve task performance and lessen physical demands of computer touchscreen interface use.
Background:
With the increase of tablet usage in both office and industrial workplaces, it is critical to investigate the influence of tablet usage on spine posture and movement.
Objective:
To quantify spine kinematics while participants interacted with a tablet or desktop computer.
Methods:
Fourteen participants volunteered for this study. Marker clusters were fixed onto body regions to analyze cervical and lumbar spine posture and sampled at 32 Hz (Optotrak Certus, NDI, Waterloo, Canada). Participants sat for one hour in total. Cervical and lumbar median angles and range of motion (10th to 90th % ile angles) were extracted from amplitude probability distribution functions performed on the angle data.
Results:
Using a sloped desk surface at 15°, compared to a flat desk, influenced cervical flexion (p = 0.0228). Completing the form fill task resulted in the highest degree of cervical flexion (p = 0.0008) compared to the other tasks completed with cervical angles between 6.1°-8.5° higher than emailing and reading respectively. An interaction between device and task (p = 0.0061) was found for relative lumbar median spine angles.
Conclusions:
Increased lumbar flexion was recorded when using a computer versus a tablet to complete various tasks. Task influenced both cervical and lumbar spine posture with the highest cervical flexion occurring while completing a simulated data entry task. A work surface slope of 15° decreased cervical spine flexion compared to a horizontal work surface slope.
Zusammenfassung
Das Sehen am Bildschirm erfordert die abgestimmte Bewegungskoordination der Augen und des Kopfes. Dabei kann die eingenommene Kopfneigung von Bedeutung sein. Diese Studie untersucht horizontale Kopfb ewegungen mithilfe des Trackingverhaltens und weiterer Indikatoren für eine physiologisch günstige Kopfneigung. Die komfortable Kopfneigung, die Probanden spontan in einem Schnelltest selbst einstellen, war korreliert mit zwei weiteren Indikatoren: erstens mit der Kopfneigung, bei der die subjektiv beurteilte Nackenanstrengung minimal war, und zweitens mit der Ruhe-Kopfneigung, auf die sich der Kopf vertikal hinbewegt, wenn der Proband horizontale Kopfb ewegungen mit geschlossenen Augen ausführt. Einige Indikatoren, darunter das Elektromyogramm des Musculus Sternocleidomastoideus und die subjektive Beurteilung von Nackenbeschwerden, zeigten einen ähnlichen Beanspruchungsverlauf als Funktion der vorgegebenen Kopfneigung. Die Bestimmung der komfortablen Kopfneigung und der dazugehörigen komfortablen Blickneigung erscheint als ein einfaches und praxisgerechtes Verfahren, das als Anhaltspunkt für die individuelle Optimierung der vertikalen Bildschirmposition nützlich sein kann.
Zusammenfassung
Experiment 1 vergleicht verschiedene Indikatoren der physiologisch günstigen Blickneigung bei individuell komfortabler Kopfneigung: beim Blick auf Sehzeichen wird die Blickneigung minimaler Anstrengung (a) und die bevorzugte Blickneigung (b) bestimmt; weiterhin wird die Ruheblickneigung in Dunkelheit mit einem Eye-tracker gemessen (c) und die komfortable Blickneigung mit einem Schnelltest (d) erfasst: dabei bringt man die Augen in eine bequeme vertikale Position und gibt beim öffnen der Augen ein spontan fixiertes Zeichen auf einer vertikalen Skala an. Alle Indikatoren waren korreliert und ergaben individuelle Unterschiede. Eine Anpassung des Schnelltest-Ergebnisses um 5° nach unten kommt den Befunden mit Sehreizen nahe.
Experiment 2 zeigt, dass die komfortable Blickneigung bei Variation der Kopfneigung nahezu konstant relativ zum Kopf bleibt, während eine Literaturübersicht von Verfahren mit visuellen Reizen eine zunehmende Absenkung der günstigen kopfb ezogenen Blickneigung ergibt, je weiter der Kopf nach unten geneigt ist.
Performing NOTES procedures in the endoscopy suite is a new concept and may help expand the scope of NOTES and its widespread use. The dedicated NOTES room design is an essential requirement for efficient, safe, and state-of-the-art performance of NOTES procedures. The proposed “high-tech” design decreases clutter, eases personnel movement, maintains sterile field, improves ergonomics, and allows the use of fluoroscopy and laparoscopic equipment when needed.
The authors provide a consideration of the vergence system and suggest an extension of the original model proposed by H. Heuer, M. Bruwer, T. Romer, H. Kroger, and H. Knapp (1991) to explain why preferred vertical gaze angle is downward when fixating proximal targets. The practical implication of the revised model is that heterophoria (open-loop vergence bias) provides an indication of potential vergence effort. The extended model has several advantages: It allows for modification of workstations, is consistent with models of the accommodation and vergence system, is compatible with clinical data, and provides a more complete explanation of extant research data. The extended model was able to predict oculomotor responses, explain postural adjustments, and provide ergonomically useful data. (PsycINFO Database Record (c) 2012 APA, all rights reserved)
With horizontal gaze, the resting posture of binocular vergence typically corresponds to a distance of about 1 m. The effect of vertical direction of gaze on this basic resting posture was investigated. The dark vergence of twenty-four subjects was measured while they fixated a dim monocular light-point at vertical directions ranging from -45 degree (lowered) to +30 degrees (elevated). In one condition, gaze was varied by changes in eye position with the head held upright; in a second condition, gaze was varied by changes in head inclination with the eyes held in constant (horizontal) position with respect to the head. In both conditions, dark vergence shifted in the convergent (nearer) direction with lowered gaze and in the divergent (farther) direction with elevated gaze. The effect of varied eye inclination was larger, more variable across subjects, and more stable over time than that of varied head inclination. These findings indicate that multiple mechanisms contribute to gaze-related variations of the resting posture of the eyes. They may help to explain the variations of space perception and visual fatigue that are observed with different gaze inclinations.
At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and -16 degrees downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.
The study has a parallel group design with two intervention groups (T and S) and one control group (C) of VDU operators. Three serial interventions were carried out in the T and S groups, first a new lighting system, then new workplaces and last an optometric examination and corrections if needed. The new lighting gave significantly increased illuminance levels, increased luminances of the room surfaces and better luminance distribution. The two intervention groups reported significant improvement of the lighting conditions, as well as of the visual conditions and significantly reduced visual discomfort and glare. Significant reduction of headache was found in one of the intervention groups. Optometric corrections reduced the visual discomfort in both the intervention groups. When looking at those given new corrections, a significant reduction was found in the T group and a clear tendency was also found in the S group. The C group reported no improvements for any of these health outcomes. The workplace intervention gave the operator the possibility to support the whole forearm and hand on the table top. Before the intervention there were no significant differences between the three groups regarding shoulder pain and static trapezius electromyographic (EMG) load. Two years after the intervention, a significant reduction of shoulder pain was reported in the T and S groups in parallel with a significant reduction in static trapezius load, while no such reduction was found in the C group. At the same time, both static trapezius load and shoulder pain were significantly lower in the T and S groups compared with the C group. Pain in the forearm and hand showed no significant changes in any of the groups during the study period. However, there seem to be a relationship between pain in the forearm and hand and the time the operator used the mouse. The C group reported significantly higher intensity of pain and used the mouse significantly more than the S group.
A study was carried out on ten subjects working with computer–aided design/computer–aided manufacture (CAD/CAM) systems to examine the effect of a new position of the VDU monitor on sitting posture. According to a biomechanical study of the neck, the position of the head in which the neck muscle forces are minimal differs from the position of the head when some commonly accepted recommendations regarding sitting posture of VDUs are carried out, and on this basis a direction of view of 15° above the horizontal would be preferable to one of 15° below. By means of continuous recording of the positions of the head and trunk, the effect of this new position of the monitor on sitting posture was examined. Analysis of the results showed that working at a monitor placed in such a position that the direction of view was 15° above the horizontal resulted in a considerably better posture than the former position of the monitor: one is sitting more erect and the head is less bent forward. The active direction of view was 3° above the horizontal. The test subjects did not seem to prefer a greater angle. The results of this test indicate that placing the middle of the monitor at eye level results in a better sitting posture for CAD/CAM workers.
A computer desk was designed and built which allowed sinking and tilting the monitor axis to coincide with the vision axis of when looking through the reading portion of a bifocal glass. Ten subjects (four males and six females) wore a glass frame appropriately fitted whose distance vision portion was blocked with cardboard leaving reading portion cut out for clear vision. Such subjects worked with computer with its monitor placed in one of the three positions: (a) monitor sunken and backward inclined by 35°; (b) monitor placed on desk top level and horizontal; and (c) monitor placed horizontal but raised by CPU beneath it. Postural details of head-neck inclination, torque due to it, angle of gaze, angular span of vision, and upper extremity was recorded by photography. EMG of trapezius and sternomastoid was recorded bilaterally. Subjective discomfort rating was obtained using visual analog scale and Borg's scale. The head-neck inclination and torque were highest with sunken monitor, but it recorded 30% to 40% less EMG compared to raised monitor. Upper extremity postures were not significantly different between the monitor positions. The discomfort rating was in ratio of 1:2:4 for sunken, level, and raised monitors respectively.
By recording electrical impulses from muscles during movements, it is possible to find the number of muscles taking part in the movement and when they are in activity and to estimate the force of contraction. The different factors which influence typewriting can therefore be studied by electromyography.From these experiments it would appear that the most important factor is thorough practice on the typewriter. The person tested must also use favourable equipment (e.g. chair and table) and a satisfactory working position. The environment must be well lighted, not too cold, nor too noisy. The typist must use the highest preferred working speed, and take a short rest when tired.
Photographic and video analyses show that the primary position of the eyes is a natural constant position in alert normal humans, and the eyes are automatically saccadically reset to this position from any displacement of the visual line. The primary position is not dependent on fixation, the fusion reflex, gravity, or the head position. The primary position is defined anatomically by head and eye planes and lines that are localized by photography, magnetic resonance imaging, and x-rays of the head and neck. The eyes are in the primary position when the principal (horizontal) retinal plane is coplanar with the transverse visual head (brain) plane (TVHP), and the equatorial plane of the eye is coplanar with a fixed orbital plane (Listing's plane). Evidence is presented to indicate an active neurologic basis for the primary position instead of passive mechanical forces. A different understanding of the primary position and the conception of the TVHP may be valuable in analyzing oculomotor defects.
Without fixation stimuli--for instance, in darkness--accommodation and convergence of the eyes reach an intermediate state that is relatively stable within a subject but which ranges from about 30 cm to infinity across subjects. This study investigated whether these oculomotor positions in darkness are related to visual strain. During work at a visual display unit (VDU), visual strain at a viewing distance of 50 cm was stronger than at 100 cm (with characters twice as large). The more distant the individual's dark convergence, the greater was the visual strain at the 50-cm viewing distance. When subjects were free to adjust the viewing distance to their comfort level, they chose distances between 51 and 99 cm (mean 74 cm) with characters 5 mm tall.
Two experiments examined the link between vergence effort and subjective reports of visual fatigue following prolonged near work. In Experiment 1, dark vergence and reports of visual fatigue symptoms associated with computer use were measured in 104 persons. Dark vergence was significantly correlated with four of six symptoms of visual fatigue. In Experiment 2, 16 subjects who exhibited clear "Heuer effects" (systematic gaze-related changes in dark vergence) read from a video display terminal (VDT) at a distance of 20 cm for 60 min under two gaze elevation conditions: 20 deg above and 20 deg below a baseline gaze elevation. This manipulation was designed to vary the amount of vergence effort required to fixate the VDT. Results indicate a positive relation between vergence effort and visual fatigue both within and between subjects, and that prolonged near work leads to decreased vergence accuracy at far distances. Implications for VDT workstation design are discussed.
Work in the manufacturing industry is associated with a high prevalence of cervicobrachial disorders.
This research concerned the angle at which people prefer to look down at visual targets and tasks. Thirty-two subjects participated in a study with four different head positions, two visual tasks, and two target distances. The overall preferred mean angle in the midsagittal plane below the Frankfurt Plane was -34 deg. Head position had significant effects on angle: subjects sitting with their heads upright preferred an average declination of -29 deg, but -40 deg when supine. Target distance also significantly affected the line-of-sight angle, with subjects preferring targets at 0.50 m to be at -38 deg, but targets at twice that distance at -30 deg. The task did not influence the preferred angle.
In order to analyse the effect of changing the sitting posture on the level of neck and shoulder muscular activity, an electromyographic (EMG) study of ten healthy experienced female workers from an electronics plant was undertaken. A standardized, simulated task was performed in eight different sitting work postures. Using surface electrodes, the level of muscular activity was recorded as normalized, full-wave rectified low-pass filtered EMG. The results showed that the whole spine flexed sitting posture gave higher levels of static activity in several neck and shoulder muscles than the posture with a straight and vertical spine, which in turn gave higher levels than the posture with slightly backward-inclined thoraco-lumbar spine.
Postural responses of seven male and seven female subjects were compared during sitting, lifting, preparing to stand, standing, standing on tip-toes, and deep breathing. The responses were measured in terms of the linear and angular displacement of the head and the differential activity of two groups of neck muscles. The data were given statistical treatment. Significant differences were found in the behaviour of the two groups of muscles and in the responses of male and female subjects. It is suggested that the postural aspect of responses should be taken into consideration if neck-muscle tension is used as an index of activation level or anxiety.
A field study was conducted to assess the preferences of VDT operators with regard to their body posture and the settings of an adjustable VDT workstation. Subjects came from four different companies, and the study took place during subjects' customary working activities. Means and ranges of the preferred settings are given. The operators preferred body postures that are distinctly different from those recommended in textbooks and other publications. Some of the workstation settings they preferred also strongly deviate from such recommendations.
There is a great demand for perceptual effort ratings in order to better understand man at work. Such ratings are important complements to behavioral and physiological measurements of physical performance and work capacity. This is true for both theoretical analysis and application in medicine, human factors, and sports. Perceptual estimates, obtained by psychophysical ratio-scaling methods, are valid when describing general perceptual variation, but category methods are more useful in several applied situations when differences between individuals are described. A presentation is made of ratio-scaling methods, category methods, especially the Borg Scale for ratings of perceived exertion, and a new method that combines the category method with ratio properties. Some of the advantages and disadvantages of the different methods are discussed in both theoretical-psychophysical and psychophysiological frames of reference.
In a field study of 162 VDT and 133 control workplaces it was found that constrained postures of VDT workplaces and in full-time typists were sometimes associated with physical impairments in the hands, arms, shoulders and neck. The reported complaints were confirmed by medical findings on muscles, tendons and joints. The incidence of impairments was increased when the distance from the surface of the keyboards to the desk surface was large; the height of the keyboard from the floor was low; there was insufficient space to rest the forearms and hands; the lateral deviation of the hands operating keyboards was great; and there Was a pronounced inclination or turning of the head. Several recommendations for the proper design of VDT workstations are deduced from the present study
A number of individual, ergonomic, and organizational factors of presumed importance for the occurrence of musculoskeletal disorders were investigated in a group of 260 visual display terminal (VDT) workers. The cross-sectional study utilized medical and workplace investigations as well as questionnaires. The results were subjected to a multivariate analysis in order to find the major factors associated with various upper-body muscular problems. Several such factors were identified for each investigated type of musculoskeletal problem. Some were related to the individual: age, gender, woman with children at home, use of spectacles, smoking, stomach-related stress reactions, and negative affectivity. Organizational variables of importance were opportunities for flexible rest breaks, extreme peer contacts, task flexibility, and overtime. Identified ergonomic variables were static work posture, hand position, use of lower arm support, repeated work movements, and keyboard or VDT vertical position.
Perceived exertion caused by the extraocular muscles was assessed as a function of the direction of gaze and recorded in 114 subjects using a psychometric method. The results confirm statements in the literature that maximum comfort is achieved when gaze is aimed downwards. We found no correlations between perceived exertion and age or viewing distance. The relationship is relevant to ergonomics, for example in lens fitting and workplace layout.
A total of 272 normal persons (109 men, 163 women) between the age of 14 and 84 years was studied for age, body weight, height, neck circumference and neck length. For evaluation of performance, a lifting test and an isometric extension force test showed sex- and age-specific differences in this group. A reliability test with two independent observers showed a good correlation of two consecutive measurements. The lifting test (PILE) and the isometric neck extension force test (IMPET) have been shown to be easy to administer, inexpensive and reliable. The data presented can be used as a data base for European persons for clinical research.
In this study, 60 female subjects, aged between 25 and 40 years, were divided into two equal groups on the basis of absence or presence of headache. A passive accessory intervertebral mobility (PAIVM) examination was performed to confirm an upper cervical articular cause of the subjects' headache and a questionnaire was used to establish a profile of the headache population. Measurements of cranio-cervical posture and isometric strength and endurance of the upper cervical flexor muscles were compared between the two groups of subjects. The headache group was found to be significantly different from the non-headache group in respect to forward head posture (FHP) (t = -5.98, p < 0.00005), less isometric strength (t = 3.43, p < 0.001) and less endurance (t = 8.71, p < 0.0005) of the upper cervical flexors. A statistically significant relationship was also established between natural head posture and isometric endurance of the upper cervical flexor musculature which demonstrated that FHP corresponded with a low endurance capacity (chi 2 = 13.2; p < 0.01). The outcome of this study highlights the need to screen for cervical etiology in patients who are suspected of suffering from common migraine.
This paper proposes a comfortable visual display terminal (VDT) workstation layout based on an analysis of ocular surface area (OSA). A large OSA induces eye irritation and eye fatigue because the eye surface is highly sensitive to various stimuli. The authors considered that OSA must be one of the useful indices of visual ergonomics and applied it to evaluate VDT workstation layout. Each subject was asked to perform a word processing task using four different VDT workstation layouts. It was found that the main factor affecting OSA was not cathode ray tube (CRT) height itself but the distance between the CRT and keyboard. Thus the following workstation layout is recommended to realize comfortable VDT operation: (1) the desk height should be adjusted to the user's height; and (2) the CRT display should be set closer to the keyboard to provide a smaller OSA.
To understand the motions caused by the interaction among the different body parts, adjustments of both eye position and body posture to screen height settings of 80, 90, 100, 110 and 120 cm were determined in 10 subjects. The subjects engaged in a non-keyboard, interactive computer game requiring constant visual monitoring. Changes in body positions were determined by video image analysis for the posture parameters and by video frame analysis for the eye parameters. Analysis of variance and correlation analysis showed that neck angle, thoracic bending and vertical eye position were significantly affected by changes in the screen height of the VDT. The study of the interrelationship of eye position and body posture suggested that changes in body positions served to complement the eye position in attaining a better view of the visual target. Viewing angle was observed to be decided mainly by inclination of the neck and the eye. Thoracic bending was also noted to contribute in setting the viewing angle, although to a lesser extent. On the other hand, viewing distance and trunk inclination showed significant correlation.
Measurements of head position, mechanical load at C7, and level of muscle EMG activity in the muscles of the neck were compared across six document positions in both a reading task and a typing (word processing) task. Source documents, identified as a primary visual task, were placed in two positions in front of the subject, flat on the table to each side of the keyboard, and on a document stand at each side of the keyboard. Each of the 20 subjects performed both a reading task and a typing task in each of these document positions while measurements were taken. It was found that the greatest variations in head position occurred in head rotation with documents flat on the table. This document position on each side also produced the greatest level of muscle tension in both the neck extensors and, to a lesser degree, the sternocleidomastoid muscles. In addition, greater variability between document position measures was found in the typing condition.
The effects of the VDT screen height on working posture and electromyographic (EMG) activities of the neck and shoulder muscles were determined in 10 healthy subjects. The subjects performed a mouse-driven interactive task at the screen height settings of 80, 100 and 120 cm. Changes in body positions were measured by video image and frame analysis. Surface EMG recordings were done on the neck extensor muscle and the descending part of the trapezius muscle, both on the right side. The results of the postural analysis showed that at higher screen height settings, the neck became significantly more erect. The subjects also assumed a more backward-leaning trunk position at higher screen heights. The EMG activities of the neck and shoulder muscles were related to the neck angle and trunk inclination, respectively. A more flexed neck produced significantly higher neck extensor muscle activities. A backward-leaning trunk was also noted to decrease trapezius muscle activity in some subjects.
To quantitatively describe the postural alignment of the head and shoulders and the surface curvature of the thoracic spine in comfortable erect standing and to examine the effect of age and gender on head and shoulder alignment.
Descriptive survey.
Gait research laboratory.
One hundred sixty asymptomatic volunteers aged between 17 and 83 years.
Five photographic measurements of head and shoulder posture in the coronal and sagittal planes and a photographic measurement of the surface curvature of the thoracic spine in the sagittal plane.
Mean values of coronal head tilt, coronal shoulder angle, sagittal head tilt, sagittal C7-tragus angle, and sagittal shoulder-C7 angle were 180.1 degrees, 181 degrees, 172.1 degrees, 131.1 degrees, and 53.7 degrees, respectively. The 95% confidence intervals for the means ranged between 1 degree and 3.8 degrees. For each of the head and shoulder measurements there was no significant gender difference (p = .33 to .99). Of the five measurements, only sagittal C7-tragus angle was significantly correlated with age (r = .44), and none was correlated with surface curvature of the thoracic spine.
Head and shoulder posture was similar between genders. Only one postural description that has been described anecdotally was identified, i.e., that age was related to the position of the head with respect to the trunk in the sagittal plane, although the strength of the association was of questionable clinical significance. In contrast, other longstanding assumptions were not supported, and accordingly, a forward head was not associated with increased thoracic curvature or upper cervical spine extension.
A study was conducted on eight subjects, in order to investigate the influence of head posture with regards to the screen and copy holder position, the activity of cervical muscles and the subjective judgement given by the subjects. A total of eleven different positions (exercises) of screen and copy holder were investigated. Four different screen positions were examined in the upright (middle) sitting posture and three different screen positions were investigated in the backward sitting posture. In addition, four different positions of the copy holder were examined in the upright sitting posture. Head posture and muscle activity were continuously measured in each exercise for a duration of 5 min. At the end of each exercise, the subjects were asked how they judged the position of the screen and/or the copy holder in comparison with other positions. The results show that preference is to be given to a screen position in which the vision axis is horizontal or inclined slightly downwards. The copy holder should be arranged at one side of the screen.
The advent of compact and lightweight portable personal computers has offered its users mobility. Various sizes of PC-FPDs can now be seen in the occupational setting as an alternative to the desktop computers. However, the increasing popularity of this relatively new technology may not be without any accompanying problems. The present study was designed to evaluate the use of PC-FPDs in terms of postural changes, muscle load, subjective complaints and performance of the subjects. Ten subjects, 5 males and 5 females, were asked to perform a text-entry task for 5 minutes using each of the 5 types of personal computers--1 desktop and 4 PC-FPDs of various sizes. Results showed that the posture assumed by the subjects while using the PC-FPDs was significantly more constrained than that assumed during work with the desktop computer. Viewing and neck angles progressively lowered and the trunk became more forward inclined. The EMG results also revealed that the activities of the neck extensor in PC-FPDs were significantly higher than in the desktop computers. Trends of increasing discomfort and difficulty of keying with the use of smaller PC-FPDs were noted. Performance was significantly lower for smaller PC-FPDs. This study shows that PC-FPDs have ergonomic attributes different from the desktop computer. An ergonomic guideline specific for PC-FPDs users is needed to prevent the surge in health disorders previously seen among desktop computer users.
Prolonged use of video display terminals (VDTs) has been shown to be a risk factor for musculoskeletal and visual discomfort. A standard workplace design recommendation is to position the centre of the VDT 15 degrees below horizontal eye level. Recently a viewing angle of 40 degrees below horizontal has been suggested based on studies that have indicated that this is the preferred viewing angle for visually intensive tasks. The goal of this study was to investigate the effects of these two VDT positions on muscular activity, muscular fatigue, head/neck posture, visual acuity, operator performance (productivity and quality), heart rate and operator subjective assessment. The experimental task consisted of reading text from a computer screen and answering reading comprehension questions using a mouse and a keyboard. Each experimental session lasted 2 h. The 40 degree VDT position showed significantly greater head tilt angles and higher muscle activity levels for six of the 10 neck, shoulder and back muscles sampled. No significant differences in visual acuity, operator performance or heart rate were detected as a result of monitor location. Seven of the 12 subjects preferred the 15 degree monitor position.
OBJECTIVE:: The objectives were to determine the postural consequences of varying computer monitor height and to describe self-selected monitor heights and postures. DESIGN:: The design involved experimental manipulation of computer monitor height, description of self-selected heights, and measurement of posture and gaze angles. BACKGROUND: Disagreement exists with regard to the appropriate height of computer monitors. It is known that users alter both head orientation and gaze angle in response to changes in monitor height; however the relative contribution of atlanto-occipital and cervical flexion to the change in head rotation is unknown. No information is available with regard to self-selected monitor heights. METHODS: Twelve students performed a tracking task with the monitor placed at three different heights. The subjects then completed eight trials in which monitor height was first self-selected. Sagittal postural and gaze angle data were determined by digitizing markers defining a two-dimensional three-link model of the trunk, cervical spine and head. RESULTS: The 27 degrees change in monitor height imposed was, on average, accommodated by 18 degrees of head inclination and a 9 degrees change in gaze angle relative to the head. The change in head inclination was achieved by a 6 degrees change in trunk inclination, a 4 degrees change in cervical flexion, and a 7 degrees change in atlanto-occipital flexion. The self-selected height varied depending on the initial monitor height and inclination. CONCLUSIONS: Self-selected monitor heights were lower than current 'eye-level' recommendations. Lower monitor heights are likely to reduce both visual and musculoskeletal discomfort. RELEVANCE: Musculoskeletal and visual discomfort may be reduced by placing computer monitors lower than currently recommended.
Joines is an ergonomist at the North Carolina Ergonomics Resource Center and a Ph.D. student at North Carolina State University
- M B Sharon
Sommerich is an assistant professor of industrial engineering at North Carolina State University
- M Carolyn