The effects of shoulder posture on neck and shoulder musculoskeletal loading and discomfort during smartphone usage

While using their smartphone, users tend to adopt awkward neck and shoulder postures for an extended duration. Such postures impose the risk of MSDs on those body parts. Numerous studies have been undertaken to examine neck posture; however, few studies have investigated shoulder postures. This study examined various shoulder postures during smartphone use and their effect on neck and shoulder kinematics, muscle loading, and neck/shoulder discomfort. Thirty-two asymptomatic young adult smartphone users randomly performed texting tasks for 3 min at four different shoulder flexion angles (15°, 30°, 45°, and 60°), while maintained a neck posture in the neutral position (0° neck flexion angle). Measures were taken of neck and shoulder muscle activity of the cervical erector spinae (CES), anterior deltoid (AD), upper trapezius (UT) and lower trapezius (LT), and kinematic data (angle, distance and gravitational moment). Results showed AD and LT muscle activity significantly increased when the shoulder flexion angle increased with an opposite effect on CES and UT. A recommended shoulder posture was identified as 30° flexion, as this yielded the best compromise between activation levels of the four muscles studied. This angle also induced the lowest neck/shoulder discomfort score. The findings suggest smartphone users hold their device at approximately 30° shoulder flexion angle with their neck in a neutral posture to reduce the risk of shoulder and neck musculoskeletal disorders when smartphone texting.Relevance to industrySmartphone use in the manufacturing and service industries is an integral part of work and useful means of communication tool. Awkward postures during extensive smartphone use impose an increased risk of both neck and shoulder musculoskeletal disorders. Shoulder flexion angles need consideration when making recommendations about safe work postures during smartphone use.     

Integration of active pauses and pattern of muscular activity during computer work

Abstract

Submaximal isometric muscle contractions have been reported to increase variability of muscle activation during computer work; however, other types of active contractions may be more beneficial. Our objective was to determine which type of active pause vs. rest is more efficient in changing muscle activity pattern during a computer task. Asymptomatic regular computer users performed a standardised 20-min computer task four times, integrating a different type of pause: sub-maximal isometric contraction, dynamic contraction, postural exercise and rest. Surface electromyographic (SEMG) activity was recorded bilaterally from five neck/shoulder muscles. Root-mean-square decreased with isometric pauses in the cervical paraspinals, upper trapezius and middle trapezius, whereas it increased with rest. Variability in the pattern of muscular activity was not affected by any type of pause. Overall, no detrimental effects on the level of SEMG during active pauses were found suggesting that they could be implemented without a cost on activation level or variability.

Practitioner Summary: We aimed to determine which type of active pause vs. rest is best in changing muscle activity pattern during a computer task. Asymptomatic computer users performed a standardised computer task integrating different types of pauses. Muscle activation decreased with isometric pauses in neck/shoulder muscles, suggesting their implementation during computer work.     

Interactive effects of acute experimental pain in trapezius and sored wrist extensor on the electromyography of the forearm muscles during computer work

We investigated the interactive effects of shoulder pain and wrist extensor muscle soreness on surface electromyography (EMG) during computer mouse work. On day one, subjects (N = 12) performed computer work with/without acute muscle pain induced in the trapezius muscle. Subsequently, eccentric exercise was performed to induce delayed onset muscle soreness (DOMS) in wrist extensor muscles. In presence of DOMS on day two, computer work recordings with/without pain were repeated. EMG signals were recorded from the descending part of trapezius bilaterally, flexor carpi ulnaris and extensor carpi radialis brevis. Experimental muscle pain in trapezius led to a decrease in the muscular activity of the wrist extensor (P < 0.02) and decreased the relative rest time in the wrist flexor even in presence of DOMS (P < 0.01). The present result suggests that shoulder pain plays a role in the coordination of wrist flexors and extensors during computer work.     

Ergonomic evaluation of the effects of forearm conditions and body postures on trapezius muscle activity during smartphone texting

Neck-shoulder and upper back musculoskeletal symptoms in smartphone users have gained increasing attention. We evaluated trapezius muscle activity and fatigue using an objective method (surface electromyography, sEMG), and discomfort using a subjective method (questionnaire), in smartphone users during the performance of different text-entry tasks. Fifteen participants were recruited to perform six text-entry tasks under different forearm conditions (floating and supported) and body postures (sitting, standing, lying, and walking). We collected upper trapezius (UT) and lower trapezius (LT) sEMG data, and recorded muscle discomfort scores after each task. We found that static postures (especially sitting) during smartphone use predisposed to lower muscle activity with higher fatigue level and discomfort scores than dynamic posture; there was a significant main effect of body posture on average sEMG amplitude (aEMG) and discomfort scores of both muscles (all p < 0.05). Moreover, using a smartphone with the forearm supported can reduce muscle activity, fatigue level, and discomfort scores; there was a significant main effect of the forearm condition on aEMG and discomfort scores of both muscles (all p < 0.05). Our study indicates that smartphone use with the forearm floating for a long time in a static posture should be avoided (especially while sitting).     

Adaptions in back muscle activity in long-haul truck drivers during prolonged driving with and without seat-integrated stimulation

ObjectiveThe aim of this study was to investigate the development of back muscle activity during a simulated 4.5-h truck drive with professional long-haul truck drivers and to assess the effects of a seat-integrated stimulation on muscle activity during the drive.MethodMuscle activity was compared intra-individually between a stimulation condition (with seat-integrated stimulation) and a no-stimulation condition (without seat-integrated stimulation) in a simulated driving study (N = 16). During the drive, sEMGs of the m. trapezius pars descendens, m. trapezius pars ascendens and m. erector spinae were recorded bilaterally and the RMS values of the sEMG amplitudes were analyzed.ResultsThere was a significant increase in muscle activity within 1-h driving periods (in m. trapezius pars descendens and m. trapezius pars ascendens) in both the stimulation and the no-stimulation condition but not within the whole sitting duration (in all muscles). Contrary to our expectations, the RMS values did not differ between conditions.ConclusionShort-term effects on back muscle activity of long-haul truck drivers during 1-h driving periods were found with and without the seat-integrated stimulation. However, interruptions of the driving task seemed to be sufficient to eliminate these effects. These findings on back muscle activity in long-haul drivers reveal new insights as to what affects the musculoskeletal system in prolonged driving.OutlookIn future studies, an uninterrupted driving task under real conditions should be used to investigate possible effects of prolonged driving on truck drivers’ muscle activity in general and of seat-integrated stimulation on back muscle activity in particular.     

Effects of electromyographic and mechanomyographic biofeedback on upper trapezius muscle activity during standardized computer work

The purpose of this laboratory study was to investigate the effects of surface electromyography (EMG)- and mechanomyography (MMG)-based audio and visual biofeedback during computer work. Standardized computer work was performed for 3 min with/without time constraint and biofeedback in a randomized order. Biofeedback was given on the basis of an individual preset threshold value for the right trapezius EMG and MMG signal and a time factor (repetition of events above the threshold). The duration of muscle activity above the preset threshold, the right trapezius EMG and MMG root mean square (RMS) values as well as the work performance in terms of number of completed graph/mouse clicks/errors, the rating of perceived exertion (RPE) and the usefulness of the biofeedback were assessed. The duration of muscle activity above the threshold was significantly lower with MMG compared with EMG as source of biofeedback (p < 0.05). Biofeedback led to a significant decrease in the right trapezius EMG RMS, lower RPE and decreased number of errors and mouse clicks, but also decreased number of completed graphs (p < 0.05). Audio and visual biofeedbacks were as effective. MMG-based biofeedback is a potential reliable alternative to EMG in ergonomics. A lowering of the trapezius muscle activity may contribute to diminish the risk of work related musculoskeletal disorders development.     

A comparison of muscle activity in using touchscreen smartphone among young people with and without chronic neck–shoulder pain

This study aimed to examine differences in muscle activity between young people with and without neck–shoulder pain (n = 20 in each group), when they performed texting on a smartphone. Texting was compared between using both hands (‘bilateral texting’) and with only one hand (‘unilateral texting’). Texting tasks were also compared with computer typing. Surface electromyography from three proximal postural muscles and four distal hand/thumb muscles on the right side was recorded. Compared with healthy controls, young people with neck–shoulder pain showed altered motor control consisting of higher muscle activity in the cervical erector spinae and upper trapezius when performing texting and typing tasks. Generally, unilateral texting was associated with higher muscle loading compared with bilateral texting especially in the forearm muscles. Compared with computer typing, smartphone texting was associated with higher activity in neck extensor and thumb muscles but lower activity in upper and lower trapezius as well as wrist extensors.     

Relationship between trapezius muscle activity and typing speed: taping effect

Clinically, over-activation of upper trapezius (UT) muscular activity is a common cause of symptoms in computer users. The purpose of this study was to investigate the correlation between trapezius muscular activity and typing speed with and without taping. Twelve participants performed a typing task for 15 min with and without taping on the UT muscle. Electromyography (EMG) of the muscular activity of UT and lower trapezius (LT) was recorded. With or without taping, there was a significantly positive correlation (r = 0.40, p = 0.04) between typing speed and UT/LT. Additionally, UT and UT/LT ratios were lower with taping than without taping (difference = 5.2% and 26.9%). The LT ratio was higher with taping than without taping (difference = 5.8%). Taping can alter the muscular activity of the trapezius during typing and may have the potential to be applied in computer users to prevent over-activation of UT muscular activity.

Practitioner Summary: The effect of taping was tested on typing speed and trapezius muscular activity. With or without taping, typing speed was correlated with trapezius activity. The muscle activity of the trapezius, however, was lower with taping than without taping. Thus, taping has the potential to prevent over-activation of UT muscular activity during typing.     

Trapezius muscle motor unit activity in symptomatic participants during finger tapping using properly and improperly adjusted desks

Work-related musculoskeletal disorders in the neck-shoulder area and upper extremities are common among computer users, especially women. We compared temporal changes of motor unit (MU) activation in the trapezius muscle during finger tapping using both appropriate and inappropriate ergonomic desk adjustments. Sixteen intensive and nonintensive computer users with either moderate or severe musculoskeletal disorders participated in the study. Six-channel intramuscular electromyographic (EMG) signals and 2-channel surface EMG were recorded from 2 positions of the trapezius muscle. A statistically significant increase in activity was observed with a desk adjusted 5 cm higher than appropriate and was attributable mainly to increased duration of MU activity. Participants with severe symptoms activated more MUs, and these were also active longer. In women, on average, MUs were active nearly twice as long as in men during the same tapping task. This study demonstrates that it is possible to evaluate ergonomic topics on the MU level and that incorrectly adjusted office equipment, in addition to motor demands imposed by the work task, results in prolonged activity of MUs. A potential application of this research is an increased awareness that certain individuals who work with incorrectly adjusted office equipment may be at greater risk of developing work-related musculoskeletal disorders.     

The effect of an ergonomic computer device on muscle activity of the upper trapezius muscle during typing

OBJECTIVE: Investigate whether an ergonomic computer device, characterised by an inclined working area and keyboard localisation close to the screen (the Up-Line), decreases the muscle activity of the upper trapezius muscle. METHODS: In a crossover design 19 healthy subjects and 19 patients with Whiplash Associated Disorder (WAD) typed during 10 min at the Up-Line and at a standard workstation with 15 min of rest in between. During typing surface EMG was measured of the trapezius muscle. The subjects were asked to rate sitting comfort and complaints. RESULTS: Although most subjects subjectively preferred the Up-Line, on average no significant differences were found in muscle activity between the two workstations for both patients and healthy subjects. Individually in 5 healthy subjects (25%) and in 6 patients (31%) muscle activity was lower when working at the Up-Line. CONCLUSION: Although some subjects subjectively prefer the Up-Line in sitting comfort, on average the Up-Line did not decrease the muscle activity, both in healthy subjects as in patients with WAD.     

Visually deficient working conditions and reduced work performance in office workers: Is it mediated by visual discomfort?

IntroductionThe main purpose of this cross-sectional study was to investigate whether visual discomfort acts as a mediating factor between perceived visual ergonomic working conditions and self-rated visual performance among office workers who carry out administrative tasks and computer-based work at the Swedish Tax Agency.MethodsA questionnaire was sent to 94 office workers addressing: 1) perceived visual quality of the visual display units; 2) prevalence of eye symptoms; and 3) self-rated visual performance. Eighty-six persons (54 women (63%), 31 men (36%), and 1 of unspecified sex) answered the questionnaire. Multiple regression analysis investigated the association between visual ergonomic working conditions and visual performance, both with and without visual discomfort as a mediator.ResultsThe group mean of the Indexed survey questions indicated a reasonably good quality of visual ergonomic working conditions, a relative absence of eye symptoms, and acceptable self-rated visual performance. Results from multiple regression analysis showed a significant association between perceived visual ergonomic working conditions and self-rated visual performance (r² = 0.30, β = 0.327, p < 0.01). When visual discomfort was used as a mediator, the association between perceived visual ergonomic working conditions and self-rated visual performance remained the same (r² = 0.32, β = 0.315, p < 0.01).DiscussionIt was remarkable to discover that self-rated visual performance was independent of visual discomfort. Possible explanations include exposure factors not included in the current study, such as dry air and sensory irritation in the eyes, psychosocial stress, time spent performing near work activities, or time exposed to visually deficient working conditions.Relevance to industryThe strong connection between satisfaction with visual ergonomic working conditions and productivity in this study has implications for workplace profitability and staff satisfaction. If productivity is enhanced by better visual ergonomic working conditions, then managers of workplaces may be able to improve work outcomes by optimizing the physical work environment.     

Effects of portable computing devices on posture,muscle activation levels and efficiency

Very little research exists on ergonomic exposures when using portable computing devices. This study quantified muscle activity (forearm and neck), posture (wrist, forearm and neck), and performance (gross typing speed and error rates) differences across three portable computing devices (laptop, netbook, and slate computer) and two work settings (desk and computer) during data entry tasks. Twelve participants completed test sessions on a single computer using a test–rest–test protocol (30 min of work at one work setting, 15 min of rest, 30 min of work at the other work setting). The slate computer resulted in significantly more non-neutral wrist, elbow and neck postures, particularly when working on the sofa. Performance on the slate computer was four times less than that of the other computers, though lower muscle activity levels were also found. Potential or injury or illness may be elevated when working on smaller, portable computers in non-traditional work settings.     

Discomfort and load on the upper trapezius muscle when operating a word processor

Abstract

Surface electromyogram recordings from the descending part of the trapezius muscle and discomfort ratings were assessed for six female VDT wordprocessor operators during their work. Each operator was studied during three work periods of 3 to 5 hours on different days. During one of the work periods, short pauses (15 s) were introduced every sixth minute. A static local muscular load of 32 and 30% of the maximal voluntary contraction was found on the right and the left side, respectively. The median and peak muscular loads during work were low. There was a significant negative correlation between pauses and static load on the right upper trapezius muscle. The rating of perceived discomfort was less after the work periods with short pauses than after the work periods without.     

Effects of electromyographic and mechanomyographic biofeedback on upper trapezius muscle activity during standardized computer work

The purpose of this laboratory study was to investigate the effects of surface electromyography (EMG)- and mechanomyography (MMG)-based audio and visual biofeedback during computer work. Standardized computer work was performed for 3 min with/without time constraint and biofeedback in a randomized order. Biofeedback was given on the basis of an individual preset threshold value for the right trapezius EMG and MMG signal and a time factor (repetition of events above the threshold). The duration of muscle activity above the preset threshold, the right trapezius EMG and MMG root mean square (RMS) values as well as the work performance in terms of number of completed graph/mouse clicks/errors, the rating of perceived exertion (RPE) and the usefulness of the biofeedback were assessed. The duration of muscle activity above the threshold was significantly lower with MMG compared with EMG as source of biofeedback (p < 0.05). Biofeedback led to a significant decrease in the right trapezius EMG RMS, lower RPE and decreased number of errors and mouse clicks, but also decreased number of completed graphs (p < 0.05). Audio and visual biofeedbacks were as effective. MMG-based biofeedback is a potential reliable alternative to EMG in ergonomics. A lowering of the trapezius muscle activity may contribute to diminish the risk of work related musculoskeletal disorders development.     

The impact of working technique on physical loads—an exposure profile among newspaper editors

The aim of this study was to investigate the possible associations between working technique, sex, symptoms and level of physical load in VDU-work. A study group of 32 employees in the editing department of a daily newspaper answered a questionnaire, about physical working conditions and symptoms from the neck and the upper extremities. Muscular load, wrist positions and computer mouse forces were measured. Working technique was assessed from an observation protocol for computer work. In addition ratings of perceived exertion and overall comfort were collected. The results showed that subjects classified as having a good working technique worked with less muscular load in the forearm (extensor carpi ulnaris p=0.03) and in the trapezius muscle on the mouse operating side (p=0.02) compared to subjects classified as having a poor working technique. Moreover there were no differences in gap frequency (number of episodes when muscle activity is below 2.5% of a reference contraction) or muscular rest (total duration of gaps) between the two working technique groups. Women in this study used more force (mean force p=0.006, peak force p=0.02) expressed as % MVC than the men when operating the computer mouse. No major differences were shown in muscular load, wrist postures, perceived exertion or perceived comfort between men and women or between cases and symptom free subjects. In conclusion a good working technique was associated with reduced muscular load in the forearm muscles and in the trapezius muscle on the mouse operating side. Moreover women used more force (mean force and peak force) than men when operating the click button (left button) of the computer mouse.     

Influence of mouse position on muscular activity in the neck, shoulder and arm in computer users

Anecdotal reports of shoulder and arm discomfort related to computer mouse use are common. The aim of this study of ten subjects was to examine the influence of mouse position, relative to the keyboard, on shoulder and arm muscular activity and working posture. Surface electromyography and the Rapid Upper Limb Assessment were used to determine the differences in muscle activity and posture during an editing task in each of three mouse positions. Significantly less anterior (p = 0.01) and middle (p = 0.03) deltoid electromyographic activity was demonstrated when the computer mouse was positioned adjacent to a keyboard without a numeric pad when compared to performance of an identical task with the mouse adjacent to a standard keyboard. Electromyographic activity in trapezius muscle did not differ between mouse positions. Working posture of right handed mouse users is improved by removal of the numeric keypad.     

Neck and shoulder muscle activity among ophthalmologists during routine clinical examinations

Muscular demands during common clinical ophthalmologic activities may contribute to the high prevalence of musculoskeletal health outcomes observed among ophthalmologists and other eye care physicians. Characterizations of the muscle activation patterns in the live ophthalmologic environment are lacking. This study was conducted to (i) characterize the frequencies and durations of common activities performed by ophthalmologists during routine clinical examinations, (ii) characterize neck and shoulder muscle activation patterns during the whole clinical work day, and (iii) explore differences in neck and shoulder muscle activation patterns between common clinical activities. Fifteen ophthalmologists performed routine patient examinations in an outpatient ophthalmology clinic while continuous surface electromyography measurements of the upper trapezius and anterior deltoid muscles were obtained. Results indicated that while computer use was the most frequently performed clinical activity, use of the indirect ophthalmoscope, followed by use of the slit lamp biomicroscope, required greater muscular demands than computer use or other clinical activities. Results provide evidence that the clinical activities of indirect ophthalmoscope and slit lamp biomicroscope use are appropriate for ergonomic intervention.     

Neck and shoulder muscle activity during standardized work-related postural tasks

The aim of the present study was to assess the activity levels of the sternocleidomastoid muscle and upper trapezius muscle during static postures under controlled and standardized conditions, and to determine whether the muscle activity differed between sexes. Electromyographic (EMG) activity was recorded unilaterally from the sternocleidomastoid and upper trapezius muscle in 17 participants whilst they were performing various postural tasks. EMG amplitude was measured by the root mean square values of the raw signals and normalized to peak maximum contractile values for each muscle (%MVC). The intensity of muscle activity was ranked as light (<3%MVC), moderate (3%MVC ≤ EMG ≤ 8%MVC), and substantial (>8%MVC). During most tasks the two muscles contracted light to moderately. Head leaning and shoulder shrugging postures yielded substantial muscle activity in both muscles. Muscle activity did not differ significantly between male and female participants (F = 3.1; p = 0.078). Our findings provided normative values, which will enhance future studies of muscle activity during work in a natural, unrestrained environment.     

Relationship between trapezius load and the incidence of musculoskeletal illness in the neck and shoulder

A relationship between m. trapezius load measured by electromyography (EMG) and the incidence of musculoskeletal illness in the neck and shoulder regions, was investigated both for assembly workers and VDT operators. For assembly workers, the static trapezius load (probability 0.1 of the amplitude probability distribution function, APDF) was significantly reduced from 4.3% MVC (Maximum Voluntary Contraction) to 1.4% MVC as a group median value after an ergonomic adaptation of their work places. Musculoskeletal sickleave was significantly reduced from 22.9 days to 1.8 days as a medium duration per-man-labour year for the same group.

Three groups of VDT operators were examined in terms of trapezius load and pain intensity and duration before and after an ergonomic intervention. All groups reported significant less intensity or duration of pain either in the neck or in the shoulder regions after the intervention. The trapezius load was reduced for all groups post vs. prior intervention. This reduction was measured in terms of a decrease in the static level of APDF and an increase in the number of periods per minute and total duration of muscle activity below 1% MVC. The results from this study indicate that the trapezius load may be a predictor for development of musculoskeletal illness in the neck and shoulder regions.     

Upper trapezius muscle activity in healthy office workers: reliability and sensitivity of occupational exposure measures to differences in sex and hand dominance

Patterns of cervical muscle activity may contribute to overuse injuries in office workers. The purpose of this investigation was to characterise patterns of upper trapezius muscle activity in pain-free office workers using traditional occupational exposure measures and a modified Active Amplitude Probability Distribution Function (APDF), which considers only periods of active muscle contraction. Bilateral trapezius muscle activity was recorded in 77 pain-free office workers for 1–2 full days in their natural work environment. Mean amplitude, gap frequency, muscular rest and Traditional and Active APDF amplitudes were calculated. All measures demonstrated fair to substantial reliability. Dominant muscles demonstrated higher amplitudes of activity and less muscular rest compared to non-dominant, and women demonstrated less muscular rest with no significant difference in amplitude assessed by Active APDF compared to men. These findings provide normative data to identify atypical motor patterns that may contribute to persistence or recurrence of neck pain in office workers.

Practitioner Summary: Upper trapezius muscle activity was characterised in a large cohort of pain-free workers using electromyographic recordings from office environments. Dominant muscles demonstrated higher activity and less rest than non-dominant, and women demonstrated less rest than men. Results may be used to identify atypical trapezius muscle activity in office workers.