Armrests and back support reduced biomechanical loading in the neck and upper extremities during mobile phone use

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.

Perceived Discomfort, Neck Kinematics, and Muscular Activity During Smartphone Usage: A Comparative Study

OBJECTIVE

The present study aims to evaluate the effects of posture, task, and handgrip style on discomfort, neck kinematics, and concomitant muscular activity when using a smartphone (SP).

BACKGROUND

Along with the popularity of smartphones, musculoskeletal disorders have become prevalent among smartphone users. However, comprehensive aspects of discomfort, kinematics, and electromyographic responses across various conditions remain to be investigated.

METHOD

Twenty-four young smartphone users performed typing, video watching, and reading tasks while holding the smartphone both with one hand and with two hands while either sitting or standing. Neck kinematics and muscular activities were simultaneously recorded.

RESULTS

Working with SPs led to higher discomfort in the neck (p = 0.01), lower back (p = 0.01), and shoulder (p = 0.04) while sitting as compared to standing. Sitting was associated with greater neck flexion and more minor lateral bending for all tasks and grip styles (p < 0.05). Electromyographic analysis indicated significant differences between sitting and standing, with alterations being dependent on the test condition. Moreover, neck kinematics and muscular activities significantly differed based on the task nature, handgrip, and interactions.

CONCLUSION

This study highlights the risk of using smartphones in increased neck angle flexion and muscular activities fatigue. Thus, posture and handgrip should be considered while using SPs. As each test condition affects a specific dependent variable, a holistic approach is required to evaluate the responses of SP users' musculoskeletal systems.

APPLICATION

Results can be applied to develop guidelines for musculoskeletal disorders/discomfort prevention among SP users, especially with the rise of smartphone use during the COVID-19 pandemic.

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.

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.

A passive upper-limb exoskeleton reduced muscular loading during augmented reality interactions

The aim of this study was to evaluate a passive upper-limb exoskeleton as an ergonomic control to reduce the musculoskeletal load in the shoulders associated with augmented reality (AR) interactions. In a repeated-measures laboratory study, each of the 20 participants performed a series of AR tasks with and without a commercially-available upper-limb exoskeleton. During the AR tasks, muscle activity (anterior, middle, posterior deltoid, and upper trapezius), shoulder joint postures/moment, and self-reported discomfort were collected. The results showed that the exoskeleton significantly reduced muscle activity in the upper trapezius and deltoid muscle groups and self-reported discomfort. However, the shoulder postures and task performance measures were not affected by the exoskeleton during the AR interactions. Given the significant decrease in muscle activity and discomfort without compromising task performance, a passive exoskeleton can be an effective ergonomic control measure to reduce the risks of developing musculoskeletal discomfort or injuries in the shoulder regions.

Effects of lying posture and task type on muscle fatigue, visual fatigue, and discomfort while using a smartphone on the bed

BACKGROUND

Neck-shoulder and arm musculoskeletal disorders in smartphone use have attracted increasing attention.

OBJECTIVE

This study aimed to examine the effect of different lying postures and task types by comparing the electrooculography (EOG) responses, perceived discomfort, and the activity of neck-shoulder and arm muscles while using a smartphone on the bed.

METHODS

Twenty participants were recruited to perform 30-min tasks (texting/ watching video) while holding the smartphone in three different lying postures (half-lying/lying/side-lying). Subjective discomfort, muscular activities including the abductor pollicis brevis (APB), upper trapezius (UT), and extensor carpi radialis (ECR), and EOG signals were simultaneously monitored.

RESULTS

The results showed that the perceived discomfort of measured body parts increased significantly over time in all postures. Watching video significantly increases muscle activities of APB and UT and decreases blink frequency and blink duration. Compared to lying or half-lying, the side-lying posture has the highest blink frequency, blink duration, and muscle activities in ECR and UT.

CONCLUSION

The findings of this study indicate that side-lying posture should be avoided while using a smartphone on the bed. It provides an understanding of the association between the postures of using smartphones on the bed and fatigue, which can help prevent muscle and visual fatigue in smartphone use.

Laptop use and muscle activity in adult females: Ground sitting has lower muscular demand than using a chair

BACKGROUND

With progressing technology in the portable computing field, laptops are now integral for work, home and social settings. Different working postures adopted by laptop users impose different loads on the relevant muscles, which can be associated with musculoskeletal discomfort in the various body regions. Some Arabic and Asian cultures adopted postures are not well investigated, particularly for the 20-30 years age-group.

OBJECTIVE

This study compared muscle activity in the cervical spine, arm, and wrist among different laptop workstation setups.

METHODS

In this cross-sectional study, 23 healthy female university students (age = 24.2±2.28 years, range 20-26 years) performed a standardized 10 minute typing task in four different laptop workstation setups: DESK, SOFA, GROUND sitting with back support, and laptop table (LAP-Tab). Differences between electromyography (EMG) muscle activity recorded in the trapezius (TR), cervical extensors (CE), deltoid (DEL), and wrist extensors (WE) were determined using one-way repeated ANOVA measures with a post-hoc Bonferroni test.

RESULTS

Significantly higher muscle activity was observed respectively in the workstations of DESK > LAP-Tab > SOFA > GROUND. Significant differences were found between WE muscle activity and the three other muscle groups (p < 0.001). There was a significant interaction between workstations and muscle activity (F(9,264) = 3.81, p < 0.001, = 0.11), where the WE and DEL muscles showed respectively higher and lower muscle activity in all setups.

CONCLUSION

Muscles showed variable activity in different workstations such that the GROUND workstation provided the minimum load, while the DESK workstation showed the maximum load on the measured muscle groups. These findings require further investigation in different cultural and gender specific groups.

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.

Fatigue due to smartphone use? Investigating research trends and methods for analysing fatigue caused by extensive smartphone usage: A review

BACKGROUND: The easy accessibility of smartphones has led to a fivefold increase in their use. People use smartphones almost anywhere, including during travelling and studying. During the global COVID-19 pandemic, the average smartphone screen time has increased from 2.25 to 4.8 hours per day. In India, smartphone usage increased by 68%, and the average screen time increased from 2.42 to 6.9 hours. This dependency on smartphones has led to smartphone addiction. Inappropriate postures during the prolonged use of smartphones can exert adverse effects such as musculoskeletal disorders, digital eye strain, loss of focus and attention. OBJECTIVES: This study was undertaken to understand the effects of prolonged smartphone utilisation and explored fatigue measurement techniques. METHODS: A total of 130 studies examining the effects of smartphone utilisation published in the previous 10 years were identified from the following databases: IEEE, Science Direct, PubMed, PubMed Central, and Google Scholar are reviewed. This study was conducted from September 2019 to January 2021. RESULTS: One in every four adolescents were prone to smartphone addiction, which causes poor mental health. Moreover, India’s research on the effects of excessive smartphone usage is limited. CONCLUSIONS: Studies are required to establish the correlation between fatigue levels and smartphone usage patterns.

A predictive model to quantify joint torques and support reaction forces when using a smartphone while standing with support

The present study had a dual objective: (1) to present and validate a predictive model of standing posture in the sagittal plane, joint torques and support forces for a smartphone user built from biomechanical principles; (2) propose risk scales for joint torques and reaction forces based on simulations in order to use them into the musculoskeletal disorders prevention. Comparison of the modelled data with experimental measurements (400 tested postures with sample size verification) for calling and texting tasks highlights the model's ability to correctly estimate posture and reaction forces on the ground. The model was able to provide estimates of the range of variation of each parameter for a wide range of environmental conditions as a function of the user body mass index (setting between 12.5 and 50). Joint torques risk scales have been constructed, especially for shoulder and elbow, to characterise the risks incurred by the users. Practitioner summary: The proposed model enables the postures, joint torques and reaction forces to be estimated from subject's body mass index and environmental configuration without resorting to experimentation, which is relevant in industry. This approach allows the proposition of new scales based on joint torques to reinforce the recommendations for MSDs prevention. Abbreviations: BMI: body mass index; LUBA: postural loading on the upper body assessment; MSDs: musculoskeletal disorders; RULA: rapid upper limb assessment; WHO: World Health Organization.

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.

Ergonomic arm support prototype device for smartphone users reduces neck and shoulder musculoskeletal loading and fatigue

Smartphone use is a risk factor for both neck and shoulder musculoskeletal disorders. The objective of this study was to evaluate an ergonomic arm support prototype device, which may help improve posture while using a smartphone, by determining its effect on muscle activity, muscle fatigue, and neck and shoulder discomfort. Twenty-four healthy young adult smartphone users performed 20 min of smartphone game playing under two different conditions, smartphone use with support prototype device (i.e. intervention condition) and without (i.e. control condition), while neck and shoulder posture were controlled at 0° neck flexion and 30° shoulder flexion. Activity and fatigue of four muscles were measured using surface electromyography (sEMG), these were: anterior deltoid (AD), cervical erector spinae (CES), upper trapezius (UT) and lower trapezius (LT). The intervention condition showed significantly decreased activity of all muscles. Fatigue of all muscles, except LT, significantly increased over time compared to the start point in the control condition. There was no significant difference in muscle fatigue between each time point in the intervention condition. In conclusion, the ergonomic arm support prototype device can be used as ergonomic intervention to reduce neck and shoulder muscle loading and fatigue.

Influence of neck flexion angle on gravitational moment and neck muscle activity when using a smartphone while standing

This study compares the effects of different neck flexion angles on neck gravitational moment and muscle activity of users that stand and operate a smartphone. Thirty-two healthy young adult smartphone users performed texting tasks for three minutes at four different neck flexion angles (0°, 15°, 30°, and 45°) while standing. Neck gravitational moment and cervical erector spinae (CES) and upper trapezius (UT) activity were investigated. When the neck flexion angle increased, the gravitational moment of the neck increased significantly. The muscle activity of CES significantly increased when the neck flexion angle increased, whereas that of UT decreased. The lowest gravitational moment of the neck at 0° flexion was consistent with the lowest CES muscle activity and the lowest neck discomfort score. In conclusion, for texting while standing, adults should maintain their neck posture at 0° flexion to reduce the gravitational force acting on the cervical spine and alleviate neck discomfort. Practitioner Summary: During smartphone use when standing, excessive neck flexion (30° and 45° flexion) should be avoided. The suggested neck posture when operating a smartphone while standing is 0° flexion. Abbreviations: CES: cervical erector spinae; UT: upper trapezius; COG: centre of gravity; MSDs: musculoskeletal disorders; CROM: cervical range of motion; sEMG: surface electromyography; VAS: visual analogue scale; MVCs: maximum voluntary contractions.

Effects of environmental illumination and screen brightness settings on upper limb and axial skeleton parameters: how do users adapt postures?

79% of smartphone users carry their phone 22 hours a day. In this context, the main task worldwide, texting, is performed under a wide range of light and position conditions. The aim of this study was to test the effects of environmental illumination and screen brightness settings on upper limb and axial skeleton parameters. Twelve subjects performed three trials of texting under three experimental positions, two screen luminance settings and three environmental light conditions. 3 D axial skeleton and upper limb angles, smartphone orientation and face-to-smartphone distance were used as dependent variables. High environmental illumination and/or low screen brightness resulted in an increase in interaction time and a reduction in the face-to-smartphone distance by approximately 10%. Subjects attempted to compensate for the unfavourable effects of such light conditions by adopting postures rated 5 in the Rapid Upper Limb Assessment, indicating an increased risk of developing musculoskeletal disorders. Practitioner's summary: The purpose of the study was to quantify the joint angles of the upper body in experimental conditions that represent daily life. Postures were influenced by ambient illumination and display brightness. The most harmful postures were observed when the display brightness was minimum, and the ambient light was similar to a sunny day. Abbreviations: ST: seated with table; SWT: seated without any support; STA: standing; 0L: in the dark, no light; AL: ambient light; SL: strong light; BrightMin: minimum display brightness; BrightMax: maximum display brightness (BrightMax); ISB: International Society of Biomechanics; RULA: rapid upper limb assessment; MSDs: musculoskeletal disorders.

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.

A field study on spinal postures and postural variations during smartphone use among university students

This field study compared the real-time spinal movements and postural variations during smartphone-use versus non-use in university students. Ten males and eight females (mean age of 21.5 ± 2.6 years) participated, with similar daily phone use time between the two sexes. Five inertial motion sensors were attached to the cervical, thoracic and lumbar spinal regions, and kinematics was recorded for 3 h while participants went about their usual academic activities within the university campus. Significantly greater degrees of cervical and upper thoracic flexion were adopted during phone use versus non-use time (p < 0.01). There were also significantly greater frequency of postural variations (zero crossing per min) in all spinal regions in the sagittal plane (all p < 0.05), and in some of the movements in transverse and frontal planes comparing phone use vs non-use. The postural variables also showed some significant correlations with self-reported pre-existing neck and upper back pain scores.

Mobile phones and "inattention" injuries: the risk is real

OBJECTIVE

Mobile phones though indispensable have a flip side, in that they adversely affecting our ergonomics and mobility. They share an etiologic burden on the changed profile of inattention injuries and now have proven to be a necessary evil in the changing lifestyles. We aim to evaluate the role of mobile phones as a causative factor in these head and neck injuries.

METHODOLOGY

We evaluated various injury statistics published throughout the world that attributed the concurrence of neurological injuries to portable handheld communication devices. We evaluated the dangers posed by simultaneous engagement on phone and mobility and examined the impact on walking and field of view. We have also reviewed the current management strategies to combat this new mode of injury. The recent sensation Pokemon Go has been discussed as a case study of a spike in the incidence of injuries due to mobile phone use.

RESULTS

Age>35 yrs is a risk factor for mobile phone use and injuries as they have a higher chance of being distracted (81%) when compared to millennials (70% distracted). The highest incidence was that of head injuries being 33.1% of the estimated total followed by face, including eyelid, eye area, and nose (32.7%); and neck (12.5%). The most common injury diagnoses included laceration (26.3% of estimated total), contusion/abrasion (24.5%), and internal organ injury (18.4%). A heightened sense of self-protection and a multitasking attitude remains at the core of the trouble despite having knowledge of the required behavior.

CONCLUSIONS

The health hazard of mobile phone use driving or walking needs to be highlighted with special emphasis on public education, law adherence, and technological solutions to mitigate the risk. The onus lies on the public as any technological advance would only work on the multitasking strategy and the price would be paid by the vulnerable road users.

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.