Effect of screen configuration on the neck angle, muscle activity, and simulator sickness symptoms in virtual reality.

BACKGROUND: There is a lack of information about the optimal setup of multiple screen configurations in virtual reality (VR) office work. OBJECTIVE: The objective of this study was to evaluate the effects of different screen configurations on neck flexion, rotation, neck muscle activity, and simulator sickness symptoms during Virtual Reality (VR) office work. METHODS: Twelve participants (7 males; 21 to 27 years old) performed copy-paste and drag-drop tasks in three different screen configurations (single screen, primary-secondary screen, and double screen) in a randomized order. Optical motion capture system, electromyography (EMG) device, and simulator sickness questionnaire (SSQ) were used to measure the users' responses. RESULTS: Neck rotation angles, muscle activities, and VR sickness were significantly affected by the screen configurations (p <  0.021). The primary-secondary screen showed the highest right rotation angle (median: -33.47°) and left sternocleidomastoid (SCM) muscle activities (median: 12.57% MVC). Both single (median: 22.42) and primary-secondary (median: 22.40) screen showed the highest value of SSQ. CONCLUSIONS: The screen configurations in VR could be an important design factor affecting the users' physical demands of the neck and VR sickness symptoms. Asymmetric neck rotations caused by the primary-secondary screen conditions should be avoided.

Evaluation of ergonomic risks for work-related musculoskeletal disorders of nursing tasks in Korea.

Among all industrial accident-induced diseases, musculoskeletal disorders (MSDs) are most prominently observed among nurses. The physical load of everyday tasks involved in nursing work was assessed in this study using a developed risk index, whereby the physical burden was evaluated using the exposure duration and work intensity levels. This survey targeted nine small, medium and large-sized hospitals in South Korea and categorized representative nursing tasks into six groups. The subtasks within these six categories (evaluated as high risk) included changing a patient's posture and assisting with walkers or wheelchairs, transporting/handling drug carts, bathing patients, replacing bedding, traction therapy, cardiopulmonary resuscitation and artificial manual breathing unit, and computer work. The risk index ratio was significantly different by task type for each task. We demonstrated that the risk index developed in this study can be used to evaluate MSDs in hospitals.

Research trends in ergonomics, industrial safety and health: semantic network and topic analyses.

We evaluated the research trends in ergonomics, industrial safety and health from the 1980s to the present. In the ergonomics area, keywords and abstracts from five journals were analyzed. For industrial safety and health, six journal databases were evaluated. A frequency analysis, a semantic network of keywords and a topic network of abstracts were conducted. The results of ergonomics showed that 'macro-ergonomics' and 'manual material handling' were the most popular topics, and 'ergonomic' and 'electromyography' were the most cited keywords. 'Posture' and 'biomechanics' were the most frequently used with high centrality. The results of industrial safety and health showed that 'job stress' and 'organizational safety' were the most popular topics, and 'occupational exposure' and 'occupational health' were the most cited keywords. 'Dust' and 'exposure' were frequently used with high centrality. The results would be helpful in understanding the trends of research efforts and foreseeing trends of future research.

Effects of error rates and target sizes on neck and shoulder biomechanical loads during augmented reality interactions.

Augmented reality (AR) interactions have been associated with increased biomechanical loads on the neck and shoulders. To provide a better understanding of the factors that may impact such biomechanical loads, this repeated-measures laboratory study evaluated the effects of error rates and target sizes on neck and shoulder biomechanical loads during two standardized AR tasks (omni-directional pointing and cube placing). Twenty participants performed the two AR tasks with different error rates and target sizes. During the tasks, angles, moments, and muscle activity in the neck and shoulders were measured. The results showed that the target sizes and error rates significantly affected angles, moments, and muscle activity in the neck and shoulder regions. Specifically, the presence of errors increased neck extension, shoulder flexion angles and associated moments. Muscle activity in the neck (splenius capitis) and shoulder (anterior and medial deltoids) also increased when the errors were introduced. Moreover, interacting with larger targets resulted in greater neck extension moments and shoulder abduction angles along with higher muscle activity in the splenius capitis and upper trapezius muscles. These findings indicate the importance of reducing errors and incorporating appropriate target sizes in the AR interfaces to minimize risks of musculoskeletal discomfort and injuries in the neck and shoulders.

Direct Probing of Lattice-Strain-Induced Oxygen Release in LiCoO2 and Li2 MnO3 without Electrochemical Cycling.

Since the recognition of a significant oxygen-redox contribution to enhancing the capacity of Li transition-metal oxide cathodes, the oxygen release and subsequent structural variations together with capacity fading are critical issues to achieve better electrochemical performance. As most previous reports dealt with the structural degradation of cathodes after electrochemical cycling, it is fairly difficult to clarify how substantial the effect of lattice strain on the oxygen release will be while exclusively ruling out any electrochemical influences. By utilizing nanoindentation and mechanical surface polishing of single-crystal LiCoO2 and Li2 MnO3 , the local variations of both the atomic structure and oxygen content are scrutinized. Atomic-column-resolved imaging reveals that local LiM (M = Co and Mn) disordering and further amorphization are induced by mechanical strain. Moreover, substantial oxygen deficiency in the regions with these structural changes is directly identified by spectroscopic analyses. Ab initio density functional theory calculations also demonstrate energetically favorable formation of oxygen vacancies under shear strain. Providing direct evidence of oxygen release as a consequence of lattice strain, the findings in this work suggest that efficient strain relaxation will be of great significance for longevity of the anion framework in layered oxide cathodes.

Heterogeneous Integration of Freestanding Bilayer Oxide Membrane for Multiferroicity.

Transition metal oxides exhibit a plethora of electrical and magnetic properties described by their order parameters. In particular, ferroic orderings offer access to a rich spectrum of fundamental physics phenomena, in addition to a range of technological applications. The heterogeneous integration of ferroelectric and ferromagnetic materials is a fruitful way to design multiferroic oxides. The realization of freestanding heterogeneous membranes of multiferroic oxides is highly desirable. In this study, epitaxial BaTiO3 /La0.7 Sr0.3 MnO3 freestanding bilayer membranes are fabricated using pulsed laser epitaxy. The membrane displays ferroelectricity and ferromagnetism above room temperature accompanying the finite magnetoelectric coupling constant. This study reveals that a freestanding heterostructure can be used to manipulate the structural and emergent properties of the membrane. In the absence of the strain caused by the substrate, the change in orbital occupancy of the magnetic layer leads to the reorientation of the magnetic easy-axis, that is, perpendicular magnetic anisotropy. These results of designing multiferroic oxide membranes open new avenues to integrate such flexible membranes for electronic applications.

Reduced Muscle Activity of the Upper Extremity in Individuals with Spinal Cord Injuries.

Compromised physical ability due to musculoskeletal impairment among spinal cord injury (SCI) patients is known to negatively affect their quality of life. It is essential to comprehensively understand the muscle strength of the upper extremity among patients with SCI to enhance muscle function and capacity to engage in an active lifestyle. The objective of this study was to evaluate the muscle strength of 15 upper extremity muscles among patients with SCI and compare the relative weakness of individual muscles to the control group. Seven male patients with SCI with ASIA impairment scale D and E and 33 males in the control group participated in this study. Each participant performed maximal voluntary contraction of individual muscles, and the electromyography data were recorded. The results showed that the majority of the upper extremity muscles (12 out of 15) showed considerable weakness (24 to 53%) relative to the control group. Furthermore, the relative strength (ranking) of individual muscles among 15 upper extremity muscles was different between patients with SCI and the control group. This information would be useful to the selective strengthening of specific muscles as an intensive rehabilitation effort and prevent overuse and adverse injuries due to excessive muscle training.

Prediction and comparison of postural discomfort based on MLP and quadratic regression.

OBJECTIVE: The objective of this study was to predict postural discomfort based on the deep learning-based regression (multilayer perceptron [MLP] model). METHODS: A total of 95 participants performed 45 different static postures as a combination of 3 neck angles, 5 trunk angles, and 3 knee angles and rated the whole-body discomfort. Two different combinations of variables including model 1 (all variables: gender, height, weight, exercise, body segment angles) and model 2 (gender, body segment angles) were tested. The MLP regression and a conventional regression (quadratic regression) were both conducted, and the performance was compared. RESULTS: In the overall regression analysis, the quadratic regression showed better performance than the MLP regression. For the postural discomfort group-specific analysis, MLP regression showed greater performance than the quadratic regression especially in the high postural discomfort group. The MLP regression also showed better performance in predicting postural discomfort among individuals who had a variability of subjective rating among different postures compared to the quadratic regression. The deep learning for postural discomfort prediction would be useful for the efficient job risk assessment for various industries that involve prolonged static postures. CONCLUSIONS: The deep learning for postural discomfort prediction would be useful for the efficient job risk assessment for various industries that involve prolonged static postures. This information would be meaningful as basic research data to study in predicting psychophysical data in ergonomics.

The effects of target size and error rate on the cognitive demand and stress during augmented reality interactions.

This study investigated the effects of target size and error rate on cognitive demand during augmented reality (AR) interactions. In a repeated-measures laboratory study, twenty participants performed two AR tasks (omni-directional pointing and cube placing) with different target sizes and error rates. During the AR tasks, we measured cerebral oxygenation using functional near-infrared spectroscopy (fNIRS), perceived workload using the NASA-TLX questionnaire, stress using the Short Stress State Questionnaire, and task performance (task completion time). The results showed that the AR tasks with more interaction errors increased cerebral oxygenation, perceived workload, and task completion time while the target size significantly affected physical demand and task completion time. These results suggest that appropriate target sizes and low system errors may reduce potential cognitive demand in AR interactions.

A deep learning-based method for grip strength prediction: Comparison of multilayer perceptron and polynomial regression approaches.

The objective of this study was to accurately predict the grip strength using a deep learning-based method (e.g., multi-layer perceptron [MLP] regression). The maximal grip strength with varying postures (upper arm, forearm, and lower body) of 164 young adults (100 males and 64 females) were collected. The data set was divided into a training set (90% of data) and a test set (10% of data). Different combinations of variables including demographic and anthropometric information of individual participants and postures was tested and compared to find the most predictive model. The MLP regression and 3 different polynomial regressions (linear, quadratic, and cubic) were conducted and the performance of regression was compared. The results showed that including all variables showed better performance than other combinations of variables. In general, MLP regression showed higher performance than polynomial regressions. Especially, MLP regression considering all variables achieved the highest performance of grip strength prediction (RMSE = 69.01N, R = 0.88, ICC = 0.92). This deep learning-based regression (MLP) would be useful to predict on-site- and individual-specific grip strength in the workspace to reduce the risk of musculoskeletal disorders in the upper extremity.

Effects of passive back-support exoskeletons on physical demands and usability during patient transfer tasks.

The objective of this study was to evaluate and compare the effects of three passive back-support exoskeletons (FLx ErgoSkeleton, V22 ErgoSkeleton, and Laevo V2.5) and patient transfer methods on physical demands in the low back and shoulders during patient transfer. Twenty professional caregivers (17 females and 3 males) performed a series of simulated patient transfer tasks between a wheelchair and a bed with three different patient transfer methods including the squat pivot, stand pivot, and scoot with two directions (wheelchair to bed and vice versa). The passive exoskeletons (FLx ErgoSkeleton, V22 ErgoSkeleton, and Laevo V2.5) significantly affected trunk postures (forward flexion and lateral flexion), shoulder postures (flexion and abduction), hand pull forces, muscle activities of erector spinae and middle deltoid (p-values < 0.01). The muscle activities of the erector spinae were significantly lower (up to 11.2%) with the FLx and V22 ErgoSkeletons compared to no exoskeleton condition (p-values < 0.002). However, the trunk and shoulder flexion angles with the passive exoskeleton use were greater (up to 77.3%) than those without the exoskeletons (p-values < 0.03). The biomechanical benefits and usability varied by passive exoskeleton designs (p-values < 0.01). The lower muscle activities of the erector spinae suggest that the back-support exoskeletons may be a viable intervention to reduce the low back strain during patient transfer tasks. More research would be needed to reduce the adverse effects of back-support exoskeletons on the postures such as increased trunk and shoulder flexions during patient handling.

Classification of Whole-Body Postural Discomfort Using Cluster Analysis.

The objectives of this study were to evaluate the effect of gender and postures of the neck, trunk, and knee on overall postural discomfort, and to classify combined postures into different postural discomfort groups. A total of 95 participants (42 males and 53 females) performed 45 different static postures, which were a combination of 3 neck angles, 5 trunk angles, and 3 knee angles, and rated the perceived postural discomfort. Non-hierarchical K-means cluster analysis was employed to classify the 45 different combined postures into several postural discomfort groups. Postural discomfort was significantly affected by gender and postures of the neck, trunk, and knee (p < 0.001). Three clusters (high, medium, and low discomfort) were identified and the postural discomfort was significantly different between clusters (p < 0.001). The high discomfort group consisted of mostly males with high knee and trunk flexion angles and a moderate neck flexion angle. The low discomfort group was female-dominant with low neck and trunk flexion angles and a moderate knee flexion angle. The different flexibility (stiffness) of the joint motions between genders may affect the gender difference in postural discomfort. The knee and trunk postures were critical to the postural balance, which may affect the perception of whole-body discomfort. This result will be useful for developing and improving postural observation tools.

Evaluation of the biomechanical stress in the neck and shoulders during augmented reality interactions.

This study aimed to characterize the biomechanical stresses in the neck and shoulder, self-reported discomfort, and usability by different target distance or size during augmented reality (AR) interactions. In a repeated-measures laboratory-based study, 20 participants (10 males) performed three standardized AR tasks (3-dimensional (3-D) cube, omni-directional pointing, and web-browsing tasks) with three target distances (0.3, 0.6, and 0.9 m from each participant denoted by near, middle, far targets) for the 3-D cube and omni-directional pointing tasks or three target sizes: small (30% smaller than default), medium (default: 1.0 × 1.1 m), and large (30% larger than default) for the web-browsing task. Joint angle, joint moment, muscle activity, self-reported discomfort and comfort in the neck and shoulders; and subjective usability ratings were measured. The results showed that shoulder angle (flexion and abduction), shoulder moment (flexion), middle deltoid muscle activity significantly increased as the target distance increased during the 3-D cube task (p's < 0.001). Self-reported neck and shoulder discomfort significantly increased after completing each task (p's < 0.001). The participants preferred the near to middle distance (0.3-0.6 m) or the medium to large window size due to task easiness (p's < 0.005). The highest task performance (speed) was occurred at the near distance or the large window size during the 3-D cube and web-browsing tasks (p's < 0.001). The results indicate that AR interactions with the far target distance (close to maximum reach envelop) may increase the risk for musculoskeletal discomfort in the shoulder regions. Given the increased usability and task performance, the near to middle distance (less than 0.6 m) or the medium to large window size (greater than 1.0 × 1.1 m) would be recommended for AR interactions.

Air-assisted devices reduce biomechanical loading in the low back and upper extremities during patient turning tasks.

This laboratory study evaluated different assistive devices for reducing biomechanical loading during patient turning tasks. Twenty caregivers (18 females and 2 males) performed standardized patient turning tasks with two simulated patients (body mass: 74 kg and 102 kg). The turning tasks were performed in two turning directions (toward vs. away relative to caregivers) using five device conditions: draw sheet, friction-reducing turning sheet, air-assisted transfer device, air-assisted turning device, and no assistive device. Low back and upper extremity muscle activity, trunk and shoulder postures, low back moment, and self-reported usability ratings were evaluated. While all assistive devices reduced trunk flexion, both air-assisted transfer and turning devices reduced the trunk flexion (p's < 0.001) and muscle activity (p's < 0.001) in the erector spinae and triceps compared to no assistive device condition. These results suggest that the air-assisted devices have potential as an effective intervention to considerably reduce physical risk factors associated with caregivers' musculoskeletal disorders in low back and upper extremities.

Determination of maximum acceptable and comfortable height during one-handed lifting.

BACKGROUND: One-handed lifting commonly occurs in the industry. Specific guidelines of proper heights during one-handed lifting could be valuable information to design or to assess the risk of work environment. OBJECTIVE: The objective of this study was to determine the maximum acceptable height and comfortable height during one-handed vertical lifting by gender, participant height, hand, and object weight. METHODS: Based on the psychophysical method, 72 males and 50 females, divided into four different height groups, determined their maximum acceptable and comfortable heights by each hand (left and right) and various object weights (1 kg, 3 kg, 5 kg, and 8 kg). RESULTS: Males revealed significantly greater maximum acceptable heights (males: 157 cm; females: 135 cm) and higher comfortable heights (males: 104 cm; females: 96 cm) compared to females. The participants' heights, which hand was used to lift, and the object weight were significant factors in determining the maximum acceptable height for both males and females. The multiple linear regression model of the maximum acceptable height showed more robust predictive power (R2 = 0.55) compared to the comfortable height (R2 = 0.20) as a function of gender, participant height, hand, and object weight. CONCLUSIONS: Results suggest that gender, participant height, hand, and object weight are important variables to consider when determining the proper surface height of one-handed vertical lifting. Using the robust predictive model, an appropriate maximum acceptable height could be suggested based on the material handler's anthropometric information and object weight.

The effects of target location on musculoskeletal load, task performance, and subjective discomfort during virtual reality interactions.

The objective of this study was to evaluate the effect of different target locations on musculoskeletal loading and task performance during virtual reality (VR) interactions. A repeated-measures laboratory study with 20 participants (24.2 ± 1.5 years; 10 males) was conducted to compare biomechanical exposures (joint angle, moment, and muscle activity in the neck and shoulder), subjective discomfort, and task performance (speed and accuracy) during two VR tasks (omni-directional pointing and painting tasks) among different vertical target locations (ranged from 15° above to 30° below eye height). The results showed that neck flexion/extension angle and moment, shoulder flexion angle and moment, shoulder abduction angle, muscle activities of neck and shoulder muscles, and subjective discomfort in the neck and shoulder significantly varied by target locations (p's < 0.001). The target locations at 15° above and 30° below eye height demonstrated greater shoulder flexion (up to 52°), neck flexion moment (up to 2.7Nm), anterior deltoid muscle activity, and subjective discomfort in the neck and shoulder as compared to the other locations. This result indicates that excessive vertical target locations should be avoided to reduce musculoskeletal discomfort and injury risks during VR interactions. Based on relatively lower biomechanical exposures and trade-off between neck and shoulder postures, vertical target location between eye height and 15° below eye height could be recommended for VR use.

Influence of the wearable posture correction sensor on head and neck posture: Sitting and standing workstations.

BACKGROUND: Flexed head and neck postures are associated with the development of neck pain in the office environment. There is little evidence regarding whether a wearable posture sensor would improve the head and neck postures of office workers. OBJECTIVE: The aim of this study was to evaluate the effect of the wearable posture sensor on the posture and physical demands on the head and neck during office work. METHODS: Nineteen participants performed a typing task with and without the wearable sensor in the sitting and standing positions. They were allowed to adjust their workstation during the experiment based on a psychophysical method. The flexion angles of the head and neck, the gravitational moment on the neck, and the positions of the workstation components were measured. RESULTS: On average, participants with the wearable sensor had 8% lower neck flexion angles and 14% lower gravitational moments on the neck than those of participants without the wearable sensor. The effect of the wearable sensor on reducing postural stress of the neck was more significant when using the standing workstation compared to the sitting workstation. CONCLUSIONS: The wearable posture sensor could be an effective tool to alleviate the postural stress of the neck in the office setting.

Job satisfaction and job-related stress among nurses: The moderating effect of mindfulness.

BACKGROUND: Job stress can positively influence individuals' work motivation; however, it is more typical for job stress to have adverse physical and psychological effects, which in turn undermine job satisfaction. OBJECTIVE: The present study has two purposes: to evaluate the effect of the health-promotion lifestyle and job stress to job satisfaction and turnover intention, respectively; and to investigate the moderating effect of mindfulness on each relationship. METHODS: The present study surveyed 200 nurses employed at small-to-medium-sized hospitals in South Korea. To verify the internal consistency, the reliability of the scales that was administered with the Cronbach's alpha. Correlations between mindfulness, health-promotion lifestyle, job satisfaction, stress factors, and turnover intention were analyzed. The moderating effect of mindfulness on the relationships among aforementioned measures were evaluated. RESULTS: We found significant associations between the health-promotion lifestyle and job satisfaction (p < 0.001), and mindfulness had a moderating effect on the relationship between the health-promotion lifestyle and job satisfaction (p < 0.05). CONCLUSIONS: The enhancing effect of mindfulness in these relationships can suggest an important role of mindfulness in the relationship between life style and job attitude.

Commercially Available Friction-Reducing Patient-Transfer Devices Reduce Biomechanical Stresses on Caregivers' Upper Extremities and Low Back.

OBJECTIVE: The aim of this study was to evaluate the efficacy of commercially available friction-reducing patient-transfer devices in reducing biomechanical stresses on caregivers and patients. BACKGROUND: Caregivers suffer from high prevalence of work-related musculoskeletal disorders, which is associated with manual patient handling. However, there is not enough information available on the efficacy of various friction-reducing devices in reducing biomechanical stresses in the upper extremities and low back. METHOD: During patient-transfer tasks performed by 20 caregivers, we measured hand force; shoulder and trunk posture; shoulder moment; muscle activity in the flexor digitorum superficialis, extensor digitorum communis, biceps, triceps, trapezius, and erector spinae; and usability ratings from four devices: a draw sheet, a repositioning sheet, a slide board, and an air-assisted device. In addition, triaxial head acceleration of mock patients was measured to evaluate patients' head acceleration. RESULTS: The slide board and air-assisted device significantly reduced hand force (p < .001), shoulder flexion (p < .001), shoulder moment (p < .001), muscle activities of caregivers (p < .004), and patients' head acceleration (p < .023) compared with the draw sheet. However, no significant differences in biomechanical measures were found between the repositioning and draw sheets. The air-assisted device consistently showed the lowest biomechanical stresses and was most preferred by participants. CONCLUSION: Reduction in caregivers' biomechanical stresses and mock patients' head acceleration indicates that a slide board and an air-assisted device can be effective engineering controls to reduce risk of injury. APPLICATION: The study results can provide a recommendation for engineering controls to reduce biomechanical stresses for both caregivers and patients.

Investigation of grip strength by various body postures and gender in Korean adults.

BACKGROUND: Grip strength is an objective measure of a person's hand functionality and upper limb strength. In Asia, there is a lack of normative data for grip strength among the population, especially in South Korea. OBJECTIVE: The objective of this study was to evaluate the grip strength in various body postures and gender in the adult South Korean population. METHODS: A total of 100 male and 64 female subjects participated in this study. Their grip strengths were measured using a standard adjustable Jamar handle dynamometer. RESULTS: The results showed that their grip strength differed statistically by gender, handedness, and posture. Their gender and right-hand length were the most significant predictors of their grip strength. The Asian population, including South Korea, showed a lower grip strength than the European and American populations in previous studies. CONCLUSIONS: The present study showed that the maximal isometric grip strength is affected by gender, handedness, posture, and population. Thus, gender-, population-, and posture-specific grip strength data are essential for clinical and industrial applications.