The impact of computer display height and desk design on muscle activity during information technology work by young adults

The effects of target sizes on biomechanical and cognitive load and task performance of virtual reality interactions

This study evaluated the effects of target sizes on biomechanical and cognitive load and the performance of virtual reality (VR) interactions. In a repeated-measures laboratory study, each of the twenty participants performed standardised VR tasks with three different target sizes: small, medium, and large. During the VR tasks, biomechanical load in the neck and shoulders (joint angles, joint moments, and muscle activity), cognitive load (perceived workload and cognitive stress), and task performance (completion time) were collected. The neck and shoulder joint angles, joint moments, and muscle activities were greater with the large targets compared to the medium and small targets. Moreover, the larger VR targets caused greater temporal demand and longer task completion time compared to the other target sizes. These findings indicate that target sizes in VR interfaces play important roles in biomechanical and cognitive load as well as task performance.

The effect of deep neck flexor endurance on craniovertebral angle changes and neck and shoulder muscle activities during a computer task

The deep neck flexors are important for maintaining neck posture by stabilizing and supporting it through low-intensity contraction, ensuring static endurance. The subjects performed computer tasks after having their deep neck flexor endurance measured using a pressure biofeedback unit. The craniovertebral angle (CVA) and the muscle activities were measured while participants were completing computer tasks for 10 min. The deep neck flexor endurance was significantly negatively correlated with CVA changes at 0-2 min. The deep neck flexor endurance was significantly negatively correlated with sternocleidomastoid muscle and upper trapezius activity at 0-2 min. The deep neck flexor endurance negatively predicted CVA changes at 0-2 min and explained 28.8% of the variance in the CVA changes. The lower the deep neck flexor endurance, the earlier the simultaneous changes occurred in the CVA and the neck and shoulder muscle activities during computer tasks.

Between Two Rocks and in a Hard Place: Reflecting on the Biomechanical Basis of Shoulder Occupational Musculoskeletal Disorders

OBJECTIVE

The aim was to review the biomechanical origins of occupational shoulder damage, while considering the complexity of shoulder mechanics and musculoskeletal consequences of diverse task demands.

BACKGROUND

Accessible measures of physical exposures are the primary focus of occupational shoulder assessments and analyses. This approach has led to guidelines and intervention strategies that are often inadequate for mitigating shoulder disorders amongst the complexity of modern workplace demands. Integration of complex shoulder mechanics into occupational assessments, analyses, and interventions is critical for reducing occupational shoulder injury risk.

METHOD

This narrative review describes shoulder biomechanics in the context of common injury mechanisms and consequent injuries, with a particular focus on subacromial impingement syndrome. Several modulators of shoulder injury risk are reviewed, including fatigue, overhead work, office ergonomics considerations, and pushing and pulling task configurations.

RESULTS

Relationships between work requirements, muscular demands, fatigue, and biomechanical tissue loads exist. This review highlights that consideration of specific workplace factors should be integrated with our knowledge of the intricate arrangement and interpersonal variability of the shoulder complex to proactively evaluate occupational shoulder demands and exposures.

CONCLUSION

A standard method for evaluating shoulder muscle exposures during workplace tasks does not exist. An integrated approach is critical for improved work design and prevention of shoulder tissue damage and accompanying disability.

APPLICATION

This review is particularly relevant for researchers and practitioners, providing guidance for work design and evaluation for shoulder injury prevention by understanding the importance of the unique and complex mechanics of the shoulder.

Variations in Concurrent Validity of Two Independent Inertial Measurement Units Compared to Gold Standard for Upper Body Posture during Computerised Device Use

Inertial measurement units (IMUs) may provide an objective method for measuring posture during computer use, but research is needed to validate IMUs' accuracy. We examine the concurrent validity of two different IMU systems in measuring three-dimensional (3D) upper body posture relative to a motion capture system (Mocap) as a potential device to assess postures outside a laboratory environment. We used 3D Mocap and two IMU systems (Wi-Fi and Bluetooth) to capture the upper body posture of twenty-six individuals during three physical computer working conditions (monitor correct, monitor raised, and laptop). Coefficient of determination (R2) and root-mean-square error (RMSE) compared IMUs to Mocap. Head/neck segment [HN], upper trunk segment [UTS], and joint angle [HN-UTS] were the primary variables. Wi-Fi IMUs demonstrated high validity for HN and UTS (sagittal plane) and HN-UTS (frontal plane) for all conditions, and for HN rotation movements (both for the monitor correct and monitor raised conditions), others moderate to poor. Bluetooth IMUs for HN, and UTS (sagittal plane) for the monitor correct, laptop, and monitor raised conditions were moderate. Frontal plane movements except UTS (monitor correct and laptop) and all rotation had poor validity. Both IMU systems were affected by gyroscopic drift with sporadic data loss in Bluetooth IMUs. Wi-Fi IMUs had more acceptable accuracy when measuring upper body posture during computer use compared to Mocap, except for trunk rotations. Variation in IMU systems' performance suggests validation in the task-specific movement(s) is essential.

Effects of typing positions on the upper trapezius and neck extensor muscles electromyography in office employees: A single-blind cross-sectional study

BACKGROUND

Holding incorrect postures over a long period could lead to chronic nonspecific neck pain (CNNP) in office employees.

OBJECTIVE

The present study aimed to evaluate the effects of different typing positions on the activity of the neck extensor and upper trapezius (UT) muscles of office employees diagnosed with CNNP.

METHODS

This assessor-blinded cross-sectional study was performed on 22 female subjects with the mean age of 39.95±5.30 years. The neck extensors and UT muscle activities of the participants were assessed in the upright, forward, and slouching postures by electromyography (EMG). In addition, neck proprioception and the performance of the cervical stabilizer muscles were evaluated using an inclinometer and biofeedback pressure unit, respectively.

RESULTS

A significant difference was observed between the cervical erector spine (CES) and UT muscle activities in the upright, forward, and slouching typing positions (P < 0.05). In addition, a difference was observed between the upright and slouching postures in these muscles. A positive correlation was denoted between CES muscle activity in the slouching and forward postures and the activation index of neck muscles (P < 0.05). Furthermore, a significant, negative correlation was observed between the UT muscle activity in the slouching posture and neck proprioception (P < 0.05). A positive correlation was also noted between the pain index and repositioning error rates (P < 0.05).

CONCLUSION

CES muscle activity increased in a forward head posture, which could damage neck proprioception through causing early fatigue and stimulating a cumulative damage cycle.

Investigation of the multi-component ergonomics intervention effects on improving musculoskeletal outcomes and speech communication: A case study in open-plan offices

BACKGROUND

Office workers are at high risk of developing musculoskeletal symptoms (MSS) due to improper workstations. Open-plan bank office employees must communicate with bank clerks properly and perform financial activity precisely, but noise is a factor that disrupts their communication. Therefore, MSS and annoying noise are two of the main problems in open-plan offices.

OBJECTIVE

This study evaluated the effects of a multi-component intervention involving individual (employee ergonomics training) and physical (improvements in workstation design and work environment) ergonomic factors on musculoskeletal outcomes and speech communication in open-plan environments.

METHODS

A preliminary survey was carried out to investigate the overall ergonomics problems, the tasks and time analysis, workstations setup, the prevalence of MSS (Nordic Musculoskeletal Questionnaire), physical discomfort (Visual Analogue Scale [VAS]), and posture (assessed by Rapid Upper Limb Assessment [RULA] method), environmental status (measurement of noise), and speech intelligibility (assessed by Speech Interference Level [SIL] method based on ISO 9921). The multi-component interventions were performed afterward based on the data collected. A baseline assessment and a 9-month follow-up assessment were conducted.

RESULTS

The results showed a significant decrease in the prevalence of musculoskeletal complaints (shoulders, elbows, and low back), physical discomfort, and awkward working postures after the intervention. A considerable improvement was also found in speech intelligibility post-intervention. The post-intervention questionnaire survey also indicated that employees generally favored the redesigned workstations.

CONCLUSION

The results support the effectiveness of implementing multi-component interventions in open-plan bank offices to improve musculoskeletal complaints and speech communication.

Effects of aircraft tray table height and neck posture on passenger comfort: A study of the economy class cabin

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.

Examination of muscular pain when using an innovative smartphone app for adults

BACKGROUND: Smartphones are very convenient and accessible communication devices. Smartphone usage over long durations with poor posture can lead to musculoskeletal pain in adult users. OBJECTIVE: To compare pain in the neck, shoulder, upper back, lower back, arm, hand, and eye regions. METHODS: Thirty-five asymptomatic adults aged 18-25 years were divided into two groups: 1. use of an innovative smartphone app for the promotion of ergonomic behaviour (app use) and 2. no use of the innovative smartphone app (no app use). Participants sat upright, holding a smartphone with two hands, eyes 30-40 cm away from the screen, with frequent breaks consisting of stretching the neck and hand muscles while resting the eyes. The task involved taking part in online social networking for a duration of 45 minutes. A body pain chart and the visual analog scale (VAS) were used to evaluate the location and severity of pain. RESULTS: Pain in the neck, shoulder, upper back, arm, and hand regions in the “app use” condition were significantly lower than in the “no app use” condition at 15, 30, and 45 min (p-value<0.05). However, there were negligible differences between the two groups for eye pain, and lower back pain. CONCLUSION: Pain in the neck, shoulder, upper back, and arm regions in adult users in the “app use” condition was less than in the “no app use” condition. We would recommend that adults use the innovative smartphone app to prevent the risk of musculoskeletal pain potentially caused by smartphone usage.

Differences in upper body posture between individuals with and without chronic idiopathic neck pain during computerised device use: A 3D motion analysis study

BACKGROUND

Computer use is associated with poor postures and increased risk of developing neck pain. Evaluating differences in working posture of individuals with and without chronic neck pain may assist the development of strategies to lessen or prevent pain.

OBJECTIVE

To identify if upper body kinematics differs between individuals with and without chronic idiopathic neck pain during four conditions (tablet, laptop, and desktop computer sitting and standing).

METHODS

Three-dimensional (3D) motion capture measured upper body kinematics in 44 individuals with chronic idiopathic neck pain > 90 days (Cases n = 22) and without pain (Control n = 22), during a typing task under four conditions: tablet, laptop, desktop computer (sitting and standing). Differences between groups were evaluated using generalised linear mixed models.

RESULTS

Across all conditions and compared to controls, cases had significantly less flexion between their head-neck and upper trunk segments (between group mean difference 7.15°, 2.1, 12.2, p = .006), greater upper trunk flexion relative to the laboratory (-6.15°, -10.9, -1.3, p = .012), greater shoulder flexion bilaterally (left 12.35°, 6.7, 17.9, p < .001; right 13.49°, 7.9, 19.1, p < .001) and less right elbow flexion (-6.87°, -12.1, -1.7, p = .010). Approaching significance, the case group had less left elbow flexion (between group mean difference -5.36°, -10.9, 0.1, p = .056) and a smaller mean craniocervical angle for the seated desktop condition (group x condition interaction -6.37°; 95% CI -12.7, -0.1, p = .052).

SIGNIFICANCE

Individuals with neck pain consistently used different upper body postures compared to individuals without pain when working on computerised devices under varying workstation conditions. This finding suggests that people with neck pain work in potentially aggravating postures that may be associated with their pain.

Posture during the use of electronic devices in people with chronic neck pain: A 3D motion analysis project

BACKGROUND

Non-neutral postures during computerised device use coupled with increased usage may increase the risk of neck pain. Greater knowledge of postures that individuals with neck pain adopt during computerised device use is warranted.

OBJECTIVE

To evaluate neck and upper limb posture while using a tablet, laptop and desktop computer (sitting and standing) in individuals with chronic neck pain.

METHODS

Differences in three-dimensional kinematic variables were assessed during four conditions: tablet, laptop, desktop computer (sitting and standing) in 22 individuals with chronic neck pain >3 months. Differences between kinematic variables were determined using one-way repeated measures ANOVA with Bonferroni post-hoc tests.

RESULTS

Compared to the desktop (sitting), tablet and laptop use resulted in increased neck flexion (mean difference tablet - 14.42°, 95% CI - 19.88, -8.96, P < 0.001; laptop -7.19°, -12.08, -2.31, P = .020); upper trunk flexion (tablet -14.89°, -20.22, -9.56, P < 0.001; laptop -5.56°, -10.02, -1.09, P = .009) and tablet bilateral shoulder elevation (left 11.01 mm, 2.01, 20.04, P < .016; right 13.08 mm, 3.09, 23.11, P < .006).

CONCLUSIONS

Tablet and laptop use resulted in greater neck flexion, bilateral shoulder elevation and upper trunk flexion compared to a standard desktop computer, suggesting individuals with chronic neck pain should be mindful of their posture when using these smaller devices. Future research should explore how differences in posture may influence neck pain.

E-worker postural comfort in the third-workplace: An ergonomic design assessment

BACKGROUND

Biomechanical simulation is an important tool in human-centred design, allowing for the assessment of comfort interactions between user, product and space, to optimize design features from an ergonomics perspective.

OBJECTIVE

The aim of this study was to develop a biomechanical model for the evaluation of postural comfort levels.

METHODS

The study used the scenario-based method to focus on the electronic-worker (e-worker) sedentary tablet tasks at public workplace (third-workplace) configurations. An empirical method determined work-related musculoskeletal disorders (WMSDs) risk levels. The experimental method was based on a motion-capture marker-based laboratory protocol and biomechanical model. Body postures were analysed to determine the WMSDs risk to the joints, and were compared to subjective questionnaires.

RESULTS

Posture was affected by the tablet target location and workplace setting. The findings confirmed our hypothesis, that neutral-position cost functions govern human motion. Almost half of the time, the e-workers' joints tended to remain in the neutral position range; of the three third-workplaces, high-risk variability was less significant between the 'restaurant' and 'lounge' settings, compared to the 'anywhere' configuration.

CONCLUSIONS

This evaluation model can contribute to optimizing comfort level in design for third-workplace settings and other sedentary work activities; it can be used to develop guidelines for minimizing work-related strain and health hazards.

Pain and muscle activity of neck, shoulder, upper back, and forearm during touch screen tablet use by children

BACKGROUND

Children regularly use tablets in a variety of postures. Previous studies have shown that prolonged use of such an IT device increases the risk of musculoskeletal pain.

OBJECTIVE

To investigate pain and muscle activity during tablet use by children in three different workstation positions-on the table with a case set, on a table, and on the lap.

METHODS

Twenty five healthy and right-handed participants aged 10-12 years were recruited and assigned to play computer games for 15 minutes in each workstation. Pain(VAS) was measured at the neck, shoulder, upper back, and forearm regions immediately after tablet use. Electromyography (EMG) was measured at the cervical erector spinae (CES), upper trapezius (UT), middle trapezius (MT), and wrist extensors (WE) muscles during the final two minutes.

RESULTS

Results showed that using a tablet on the table with a case set caused the least pain in the neck region (p < 0.05), compared with the use on the table and on the lap(which had pain scales of 0.37±0.86, 1.74±1.77, 1.72±1.90, respectively; mean±SD). EMG of cervical erector spinae during tablet use on the table with a case set was significantly lower (p < 0.05) than those on the table and on the lap (muscle activity of 22.38±9.54,35.37±16.82, 35.29±13.30 respectively).

CONCLUSIONS

Tablet use on the table with a case set demonstrated a significantly lower severity of pain at the neck region than tablet use on the table and on the lap. To prevent musculoskeletal disorders, tablet use on the table with a case set is recommended as the optimal workstation for children.

Effects of cycle and treadmill desks on energy expenditure and cardiometabolic parameters in sedentary workers: review and meta-analysis

Purpose. The aim of this article was to evaluate the effects of cycle and treadmill desks on energy expenditure and cardiovascular and biochemical indicators in sedentary workers. Materials and methods. In February 2018, six databases were searched. Both parallel and crossover design studies evaluating workplace cycle and treadmill desks compared to a conventional seated condition were included. Results. Twenty-two studies met the inclusion criteria. Cycle and treadmill desks significantly increased energy expenditure (standard mean difference [SMD] = 3.84, p < 0.001, I² = 95%) and the heart rate (SMD = 1.68, p < 0.001, I² = 91%), and lowered blood glucose and insulin levels (SMD = -0.54, p < 0.001, I² = 0% and SMD = -3.13, p < 0.001, I² = 76%, respectively). The interventions had no effect on blood pressure and other biochemical indicators. Conclusion. Cycle and treadmill desks may positively influence energy expenditure in sedentary workers and could be effective for reducing negative effects of workplace-related sedentary behaviour. However, considerable heterogeneity is present in the measuring protocols for energy expenditure.

Differences in posture kinematics between using a tablet, a laptop, and a desktop computer in sitting and in standing

BACKGROUND

Alternative methods of accessing the internet and performing computing-related work tasks are becoming common, e.g., using tablets or standing workstations. Few studies examine postural differences while using these alternative methods.

OBJECTIVE

To assess neck and upper limb kinematics while using a tablet, laptop and desktop computer (sitting and standing).

METHODS

Differences in neck flexion/extension, lateral flexion, rotation; elbow flexion/extension; wrist flexion/extension, radial/ulnar deviation; and shoulder elevation in 30 participants were assessed in four conditions, three in sitting (tablet, laptop and desktop computer) and one in standing (desktop computer). Three-dimensional motion capture recorded posture variables during an editing task. Differences between variables were determined using one-way ANOVA with Bonferroni post-hoc tests.

RESULTS

Compared to the desktop (sitting), tablet and laptop use resulted in increased neck flexion (mean difference tablet 16.92°, 95% CI 12.79-21.04; laptop 10.92, 7.86-13.97, P < 0.001) and shoulder elevation (right; tablet 10.29, 5.27-15.11; laptop 7.36, 3.72-11.01, P < 0.001). There were no meaningful posture differences between the sitting and standing desktop.

CONCLUSIONS

These findings suggest that using a tablet or laptop may increase neck flexion, potentially increasing posture strain. Regular users of tablets/laptops should consider adjustments in their posture, however, further research is required to determine whether posture adjustments prevent or reduce musculoskeletal symptoms.

Texting with touchscreen and keypad phones - A comparison of thumb kinematics, upper limb muscle activity, exertion, discomfort, and performance

This study aimed to compare thumb kinematics and upper limb muscle activity, and the influence of hand size, when texting on a keypad smartphone and a touchscreen smartphone. Furthermore, the study compared exertion, discomfort, and performance when texting on the two phones. The thumb kinematics were tracked using a 3D motion analysis system and muscle activity was registered in six upper limb muscles using surface electromyography in 19 participants. When texting on the touchscreen phone compared to the keypad phone thumb flexion (p = 0.008) and flexion/extension range of motion were smaller (p = 0.02), the thumb was on average less internally rotated (p = 0.02), and activity (50th and 90th percentile) of the thumb and forearm muscles was lower (p ≤ 0.05). The differences in thumb flexion were found only in the group with shorter hands and the differences in muscle activity was found only in the group with longer hands. These findings suggest there are differences in risks for developing musculoskeletal disorders during smartphone use with different key activation mechanisms and different hand sizes.

Keyboards types of selected electronic devices and the occurrence of pain in the shoulder girdle and upper limb - a review of literature

Introduction: Nowadays, computers, personal telephones (smartphones) and other electronic devices are widely used in many areas of everyday life, making them indispensable tools in the workplace, as well as other environments, e.g. at home. Studies from recent years have shown that the mere use of a computer keyboard for many hours carries the risk of pain in the hand, forearm, arm, shoulder girdle, neck and other parts of the motor organs. Aim: The aim of the literature review carried out in this work was to determine what potential threats are posed by standard keyboards and smartphone touch keypads, as well as the comparison of standard and ergonomic keyboards. Material and methods: The following databases were searched: PubMed, ResearchGate and Cochrane Library, in which 13 articles meeting the inclusion and exclusion criteria were found (6 regarding standard keyboards, 3 concerning ergonomic keyboards and 4 related to smartphone keypads). Results: The results of these studies indicate exposure to dysfunctions of the musculoskeletal system associated with typing on keyboards, especially when writing fast, with high pressure, in unnatural positions of the wrists and forearms and during long-term writing. Ergonomic keyboards can be a good alternative to standard keyboards, especially for those who use one for more than four hours a day. This literature review indicates the need for more research, especially randomized clinical trials among a large population. Conclusions: 1. The use of keyboards of selected electronic devices with different ergonomic characteristics has an adverse effect on the functionality of the shoulder girdle and upper limb, mainly generating painful symptoms with different clinical characteristics. 2. The most important influence on the occurrence of functional disorders and pain complaints concerning the shoulder girdle and upper limb when using a keyboard with different ergonomic characteristics regards the strength of pressure on the keys, speed of typing as well as long-lasting and forced positioning of the wrists and forearms. Keyboards, ergonomics, pain

Electromyographic Activity of the Upper Limb in Three Hand Function Tests

Objective/Background

Occupational therapists usually assess hand function through standardised tests, however, there is no consensus on how the scores assigned to hand dexterity can accurately measure hand function required for daily activities and few studies evaluate the movement patterns of the upper limbs during hand function tests. This study aimed to evaluate the differences in muscle activation patterns during the performance of three hand dexterity tests.

Methods

Twenty university students underwent a surface electromyographic (sEMG) assessment of eight upper limb muscles during the performance of the box and blocks test (BEST), nine-hole peg test (9HPT), and functional dexterity test (FDT). The description and comparison of each muscle activity during the test performance, gender differences, and the correlation between individual muscles’ sEMG activity were analysed through appropriate statistics.

Results

Increased activity of proximal muscles was found during the performance of BEST (p < .001). While a higher activation of the distal muscles occurred during the FDT and 9HPT performance, no differences were found between them. Comparisons of the sEMG activity revealed a significant increase in the muscle activation among women (p = .05). Strong and positive correlations (r > .5; p < .05) were observed between proximal and distal sEMG activities, suggesting a coordinate pattern of muscle activation during hand function tests.

Conclusion

The results suggested the existence of differences in the muscle activation pattern during the performance of hand function evaluations. Occupational therapists should be aware of unique muscle requirements and its impact on the results of dexterity tests during hand function evaluation.

Exploration of the associations of touch-screen tablet computer usage and musculoskeletal discomfort

BACKGROUND

Tablet users may be at high risk of developing physical discomfort because of their usage behaviors and tablet design.

OBJECTIVE

Investigate the usage of tablets, variations in head and neck posture associated with different tablet tilt angles, and the association of tablet use with users' musculoskeletal discomfort.

METHODS

A survey of users' subjective perceptions conducted by questionnaire and measurements of users' postures by a 3D Motion analysis system was used to explore the effects of tablet use.

RESULTS

The questionnaire results indicated that over half of the participants reported physical discomfort after using tablets, with the most prevalent discomfort in the neck and shoulders, and more intensity of discomfort for the back although only few participants experienced it. Chi-squared tests indicated that significantly more participants who tended to use tablet computers to play games reported having musculoskeletal discomfort after using a tablet. In addition, preferences for tablet tilt angles varied across tasks (reading and game playing). The results from the 3D motion analysis revealed that head and neck flexion angles were significantly reduced when the tablets were positioned at relatively steep tilt angles. Neck flexion angle was significantly higher in game playing.

CONCLUSIONS

These data add information regarding to the usage of tablet and its associations with physical discomfort (significantly more participants who tended to use tablet computers to play games reported having musculoskeletal discomfort after using a tablet). Steep tilt angles (such as 60°) may cause tablet users to decrease their head and neck flexion angles, which could lead to a more neutral, effortless, and ergonomically correct posture. Maintaining proper neck posture during active activities such as game playing is recommended to avoid neck discomfort.

The influence of a semi-reclined seated posture on head and neck kinematics and muscle activity while reading a tablet computer

Increased tablet computer usage calls for a proper understanding of potential injury risks from these devices. The purpose of this study was to assess the influence of tablet computer reading postures on head and neck flexion and muscle activity. Nineteen participants completed read a tablet computer in four different postures (standard computer monitor, tablet on a desk, tablet in the lap, semi-reclined with tablet in the lap). Reading the tablet in a semi-reclined trunk posture with the tablet in one's lap increased (p < 0.001) neck flexion angle (71.6%ROM) relative to reading from the standard computer monitor (6.39%ROM). Head flexion in the semi-reclined posture (19.7%ROM) and muscle activity (8.88%MVC) were similar to when reading from a standard computer monitor. Despite potentially reducing the gravitational moment produced by the head, the semi-reclined position could still compromise the force capabilities of the neck extensor musculature and result in increased strain on the passive tissues of the spine. Future work should assess how the semi-reclined position influences cervical intervertebral angles and passive tissue properties of the cervical spine. Overall, more research needs to be conducted on thoracic spine kinematics while reading a tablet computer.

The influence of school furniture on students' performance and physical responses: results of a systematic review

The purpose of this study was to determine, using a systematic review, whether the design and/or dimensions of school furniture affect the students' physical responses and/or their performance. Of the review studies, 64% presented positive results, i.e. proven effects; 24% presented negative effects or no change/effect; and the remaining 12% showed an unclear effect. The compatibility between school furniture dimensions and students' anthropometric characteristics was identified as a key factor for improving some students' physical responses. Design characteristics such as high furniture, sit-stand furniture, and tilt tables and seats also present positive effects. Finally, we concluded that further research should be conducted exploring various aspects of those variables, particularly focusing on more objective measures complemented by controlled and prospective design. Practitioner Summary: A systematic review of the literature presents a clearly positive effect of school furniture dimensions on students' performance and physical responses. Similar results appeared when school furniture design was tested. However, studying the effects of design and dimensions together produced an unclear positive effect.

Comparison of Spinal Angles in a Typing Task on a Laptop and a Desktop Computer: A Preliminary Study

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.

Reproducibility of the low back clinical postural grouping in adolescents

OBJECTIVE

The purpose of this study was to analyze the intra- and inter-rater reliability of the Low Back Clinical Postural Grouping (LBCPG).

METHODS

Fifty-eight school adolescents were evaluated by lateral photography. The examiners classified the posture of the participants as: hyperlordotic, sway back, flat back or neutral. The intra- and inter-rater reliability were quantified by the percentage agreement between clinicians and the kappa coefficient with 95% confidence intervals (95% CI).

RESULTS

The intra-rater percentage agreement was 91.4%, k = 0.87 (95% IC 0.77-0.98, p < 0.001) for the more experienced rater, and 86.2% k = 0.79 (IC 95% 0.62-0.96, p < 0.001) for the less experienced rater. The percentage agreement between clinicians was 55.17% k = 0.39 (95% CI: 0.23-0.55, p < 0.001). The agreement rose to 70.69%, k = 0.58 (95% CI 0.41-0.74, p < 0.001) when an optional second opinion of the raters was also considered.

CONCLUSION

The LBCPG was reliable when used by the same clinician. The strategy of a second opinion could be used to improve the inter-rater reliability in epidemiological studies with large samples.

Taping across the upper trapezius muscle reduces activity during a standardized typing task - an assessor-blinded randomized cross-over study

Clinically, taping is believed to alter muscle activity. The purpose of this study was to investigate: (1) whether taping across the upper trapezius (UT) muscle influenced the level of UT and lower trapezius (LT) muscle activity and the ratio of these activities (UT/LT ratio) during a static typing task; and (2) if the activity of these muscles varied with the application of tensioned taping. Forty-two healthy participants performed a 15-min typing task on three separate occasions under one of three conditions: taping applied perpendicular to the UT fibers with tension; taping without tension; and no taping. Activity of the UT and LT muscles was assessed using surface electromyography. Between conditions, significant differences were found in the change of the normalized amplitude in the UT activity (p=.027) and UT/LT ratio (p=.024) but not in the LT activity (p=.93). Compared with the no taping condition, the UT activity was less in both the tensioned taping (p=.009) and the non-tensioned taping (p=.004). There was no difference between the two taping conditions in the change of the UT (p=.91) activity and the UT/LT ratio (p=.92). In conclusion, both tensioned and non-tensioned taping across the UT muscle reduces its activity during a typing task.

Evaluation of document location during computer use in terms of neck muscle activity and neck movement

This study evaluated the impact on neck movement and muscle activity of placing documents in three commonly used locations: in-line, flat desktop left of the keyboard and laterally placed level with the computer screen. Neck excursion during three standard head movements between the computer monitor and each document location and neck extensor and upper trapezius muscle activity during a 5 min typing task for each of the document locations was measured in 20 healthy participants. Results indicated that muscle activity and neck flexion were least when documents were placed laterally suggesting it may be the optimal location. The desktop option produced both the greatest neck movement and muscle activity in all muscle groups. The in-line document location required significantly more neck flexion but less lateral flexion and rotation than the laterally placed document. Evaluation of other holders is needed to guide decision making for this commonly used office equipment.

[Ergonomically designed radiology workplace]

An ergonomically designed radiology workplace is a key factor for concentrated work during the whole day and is essential in preventing negative long-term effects due to inappropriate physical strain. To avoid such negative effects it is of paramount importance to know the factors that might cause strain on the radiologist, the appropriate application for workplace design to address these factors and how work-related disorders emerge. To minimize physical strain due to long-lasting and repetitive movements, the workspace must be adapted to the physical needs of the radiologist. Adjustable settings for the work desk and seat, together with correct screen positioning and distance from the screen, are examples of such important factors in an ergonomic workplace design. In addition, adjustable ambient light, an adjustable conditioned climate, an appropriate color design for the environment and a reduction of unnecessary noise are also crucial factors for an ergonomic workplace. This review gives an overview about the factors that influence the radiology workspace and summarizes the current literature on this topic.

Technique, muscle activity and kinematic differences in young adults texting on mobile phones

The aim of this study was to investigate whether there are differences in technique between young adults with and without musculoskeletal symptoms when using a mobile phone for texting and whether there are differences in muscle activity and kinematics between different texting techniques. A total of 56 young adults performed a standardised texting task on a mobile phone. Their texting techniques were registered using an observation protocol. The muscular activity in six muscles in the right forearm/hand and both shoulders were registered by surface electromyography and the thumb abduction/adduction and flexion/extension were registered using a biaxial electrogoniometer. Differences in texting techniques were found between the symptomatic and the asymptomatic group, with a higher proportion of sitting with back support and forearm support and with a neutral head position in the asymptomatic group. Differences in muscle activity and kinematics were also found between different texting techniques. The differences in texting technique between symptomatic and asymptomatic subjects cannot be explained by them having symptoms but may be a possible contribution to their symptoms. STATEMENT OF RELEVANCE: There has been a dramatically increased use of mobile phones for texting especially among young people during the last years. A better understanding of the physical exposure associated with the intensive use is important in order to prevent the development of musculoskeletal disorders and decreased work ability related to this use.

User-preferred position of computer displays: effects of display size

OBJECTIVE

Effects of display size and dual display setting on preferred display and keyboard positions were evaluated.

BACKGROUND

User-preferred display position may vary as its size changes or when multiple displays are used. It is also not known whether the use of larger displays or multiple displays would influence positioning of the keyboard.

METHOD

Participants (N=19) who had normal visual acuity (20/30 or better) determined preferred positions of the display and the keyboard during a data entry task in four display setups (19, 24, 27.5, and dual 19 in.). The size of capital characters (3.2 mm high) was kept consistent between setups.

RESULTS

Preferred viewing distance ranged from 0.68 m (19-in. display) to 0.76 m (27.5-in. display). No significant differences in viewing distance and display height were found between the single 19-in. display and dual 19-in. displays setups. The preferred position of the keyboard was consistent between display setups.

CONCLUSION

Participants placed larger displays farther and lower while maintaining the display top at or near eye height. Preferred position of the dual displays in landscape setting did not differ from that of a single display. It appears that the preferred display position varies with the vertical dimension of the overall viewable area of the display.

APPLICATION

The results of this study can be used to determine the dimensions or adjustability of computer workstations for larger displays or multiple displays settings.

Effect of visual display height on modelled upper and lower cervical gravitational moment, muscle capacity and relative strain

Head and neck posture is an important factor in neck pain related to computer use; however, the evidence for an optimal posture is unconvincing. This study measured the 3-D postures of 36 young adults during use of three different display heights. Cervical extensor muscle strain was estimated using modelled gravitational load moments and muscle capacities. The influence of more or less upper vs. lower cervical movement was also explored across a broad range of potential postures. Overall cervical extensor muscle capacity diminished away from a neutral posture whilst gravity moment increased with flexion. Overall cervical extensor muscle strain increased with head flexion but remained stable into head extension. Individual differences in the amount of upper and lower cervical movement had an important effect on strain, particularly for some muscles. Computer display height guidelines are an important component of ergonomics practice, yet the relative strain on neck extensor muscles as a function of display height has not been examined. The current findings provide more detailed biomechanical evidence that ergonomists can incorporate with usability and other evidence to determine appropriate display height recommendations.

Children have less variable postures and muscle activities when using new electronic information technology compared with old paper-based information technology

Children now have considerable exposure to new information technologies (IT) such as desktop computers. A reported association between computer use and discomfort in children has prompted concerns about the musculoskeletal stresses associated with computer use. There were no detailed data on children reading and writing, nor any evidence on the variability of postures and muscle activity whilst children use IT. Twenty-four children (10-12 years old; 12 male) performed a reading and writing task using new IT (computer/keyboard/mouse with high display and mid height display) and old IT (book/paper/pen). Spinal and upper limb 3D posture and muscle activity were recorded and estimates of mean and variation calculated. The mean postures for children reading and writing with computers were more neutral than when they read and wrote with old IT. Similarly, mean muscle activity levels were lower during computer use than old IT use. However, new IT use also resulted in less variable, more monotonous postures and muscle activities. Moderate differences in computer display height had little effect on posture and muscle activity variation. Variation in musculoskeletal stresses is considered an important component of the risk of musculoskeletal disorders. Children should therefore be encouraged to ensure task variety when using new IT to offset the greater posture and muscle activity monotony.