Influence of smartphone use styles on typing performance and biomechanical exposure

Twenty-seven subjects completed 2-min typing tasks using four typing styles: right-hand holding/typing (S-thumb) and two-hand typing at three heights (B-low, B-mid and B-high). The styles had significant effects on typing performance, neck and elbow flexion and muscle activities of the right trapezius and several muscles of the right upper limb (p < 0.0001 by repeated-measure analysis of variance). The subjects typed the fewest words (error-adjusted characters per minute: 78) with the S-thumb style. S-thumb style resulted in similar flexion angles of the neck, elbow and wrist, but significantly increased muscle activities in all tested muscles compared with the B-mid style. Holding the phone high or low reduced the flexion angles of the neck and right elbow compared with the B-mid style, but the former styles increased the muscle activity of the right trapezius. Right-hand holding/typing was not a preferable posture due to high muscle activities and slow typing speed.

Practitioner Summary: Right-hand holding/typing was not favoured, due to increased muscle activities and slower typing speed. Holding the phone high or low reduced the flexion angles of the neck and right elbow, but the former styles increased the muscle activity of the right trapezius compared with holding the phone at chest level.     

Muscle Activity and Comfort Perception on Neck,Shoulder, and Forearm While Using a Tablet Computer at Various Tilt Angles

Tablet computers have become ubiquitous. There is a serious risk that using tablets may lead to musculoskeletal disorders. This research aims to investigate, for tablet computer users, the musculature load and comfort perception of the engaged upper extremity for three angles of viewing and common task types performed at a computer workstation. Thirty healthy adults were recruited. A 3 × 2 repeated experimental design with tilt angle (22.5°, 45°, and 67.5° from horizontal) and task type (movie watching vs. game playing) was employed. The muscular activity of the upper extremity was assessed by electromyography measurement. Subjective comfort ratings were collected using the visual analogue scale. The results showed that when tablets were mounted at a high tilt angle (67.5°), neck muscle activity was low; however, when the tablet computer was mounted at a low tilt angle (22.5°), shoulder forward flexion activity was low, particularly during the game-playing task. This article suggests that users who feel musculoskeletal discomfort in the neck area increase the angle of their tablet computers to decrease neck stress and that users who have musculoskeletal discomfort in the shoulder area position the tablet computer at a lower tilt angle to decrease shoulder stress.     

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.     

A method for analytically generating three-dimensional isocomfort workspace based on perceived discomfort

The purpose of this study was to develop a new method for analytically generating three-dimensional isocomfort workspace for the upper extremities using the robot kinematics. Subjective perceived discomfort scores in varying postures for manipulating four types of controls were used. Fifteen healthy male subjects participated in the experiment. The subjects were asked to hold the given postures manipulating controls for 60 s in the seated position, and to rate their perceived discomfort during the following rest of 60 s using the magnitude estimation. Postures of the upper extremities set by shoulder and elbow motions, types of controls, and left right hand were selected as experimental variables, in which the L32 orthogonal array was adopted. The results showed that shoulder flexion and adduction-abduction, elbow flexion, and types of controls significantly affected perceived discomfort for postures operating controls, but hand used for operating controls did not. Depending upon the types of controls, four regression models predicting perceived discomfort were presented. Using the models, a sweeping algorithm to generate three-dimensional isocomfort workspace was developed, in which the robot kinematics was employed to describe the translational relationships between the upper arm and the lower arm/hand. It is expected that the isocomfort workspace can be used as a valuable design guideline when ergonomically designing three-dimensional workplaces.     

Effects of work surface height on muscle activity and posture of the upper extremity during simulated pipetting

In order to examine the effects of work surface height (WSH) on muscle activity, posture and discomfort during simulated pipetting, an experimental study was conducted using electromyography, electrogoniometry, video techniques and also qualitative data. The experimental design consisted of one independent variable (WSH with six heights) and 13 dependent variables. The levels of muscle strain and discomfort were significantly lower at the shoulder when the WSHs were low but thumb muscle activities and neck flexion levels were markedly higher at these WSHs compared to higher WSHs. To reduce shoulder strain, without raising thumb and neck strain beyond acceptable limits, the findings suggest that the height of a laboratory workbench should be at the level of the pipette tip when held in a standing position with the hand at elbow height. It was also found that pipetting should not be done in a seated posture.

Practitioner Summary: An experimental study was conducted to examine the effects of work surface height on upper extremity muscle activity, posture and discomfort during simulated pipetting. The findings suggest that the laboratory workbench height should be at the pipette-tip level when held in a standing position with the hand at elbow height.     

An ergonomic comparison of industrial spray paint guns

Two spray guns were used by 10 subjects in a laboratory. One gun was a `traditional' spray gun. The other was the OMX gun which had `ergonomic' features including reduced gun and hose weight and two triggers (one for horizontal surfaces and one for vertical). The 10 subjects (5 experienced industrial spray painters and 5 inexperienced students) used each gun for 4 h. The criteria used to evaluate the two guns were: (1) Wrist deviation in all three axes, (2) EMG frequency shift of 3 shoulder muscles over the test period, (3) integrated EMG activity of the forearm flexors, and (4) body discomfort ratings.It was found that the OMX gun resulted in significantly less radial/ulnar deviation in the wrist, and moderately increased flexion/extension and pronation/supination deviations from neutral. During the painting period, up to 50% less fatigue in the shoulder muscles was found for the OMX gun. Additionally, the triggering activation levels for sustained grip contractions were found to be acceptable for the OMX gun when using the short trigger. Finally, the amount of discomfort reported by the subjects was statistically lower in the shoulder, upper back, arm, elbow, forearm, wrist, and hand with the OMX gun design. Collectively, these results indicate that the OMX gun would be expected to reduce exposure to occupational risk factors for workers. This study demonstrated how the incorporation of ergonomic design principles can be used to minimize occupationally-related risk.Relevance to industryCumulative trauma disorders (CTDs) are soft tissue disorders resulting from repeated exertions and excessive movements of the body. Industrial spray painting fits the profile of a highly repetitive task. Improving spray paint gun design could potentially reduce the risk of CTDs in industrial spray painting tasks.     

A new table for work with a microscope, a solution to ergonomic problems

Microscope workers are exposed to continuous static muscular work and an increased risk of musculoskeletal disorders in the neck, shoulder and upper extremities. In a Finnish research centre, microscope workers reported pain in the shoulder, neck, lower back and upper back. As a consequence, a programme to solve the ergonomic problems of microscope work was initiated and led to the construction of a new table for microscopes. Ten experienced male microscope workers were chosen as subjects to carry out an experimental study in which the new table and an old one, an ordinary non-adjustable laboratory table, were compared in a standardized microscope task. The dependent variable was the electromyographic activity measured from muscles in the neck–shoulder region. The new table allowed the microscope to be used with the head in an upright position, the forearms supported and with less flexion of the upper arm. Surface electromyographic measurements also confirmed that the changes were ergonomic improvements.     

The effect of upper extremity support on upper extremity posture and muscle activity during keyboard use

Forearm support during keyboard use has been reported to reduce neck and shoulder muscle activity and discomfort. However, the effect of forearm support on wrist posture has not been examined. The aim of this study was to examine the effect of 3 different postures during keyboard use: forearm support, wrist support and "floating". The floating posture (no support) was used as the reference condition. A wrist rest was present in all test conditions. Thirteen participants completed 20 min wordprocessing tasks in each of the test conditions. Electromyography was used to monitor neck, shoulder and forearm muscle activity. Bilateral and overhead video cameras recorded left and right wrist extension, shoulder and elbow flexion and radial and ulnar deviation. The forearm support condition resulted in significantly less ulnar deviation (p < or = 0.007), less time spent in extreme ulnar deviation (p = 0.002) and less reports of discomfort than the "floating" condition (p = 0.002). The wrist support but not the forearm support condition resulted in less trapezius and anterior deltoid muscular activity (p < 0.007). These findings indicate that typing with upper extremity support in conjunction with a wrist rest may be preferable to the "floating" posture implicit in current guidelines.     

Accuracy evaluation of two markerless motion capture systems for measurement of upper extremities: Kinect V2 and Captiv

Motion capturing is a promising method to assess working postures and human movements and, therewith, the risk of musculoskeletal injuries that could occur while performing manual tasks in industrial settings. To obtain a reliable risk assessment, the motion capture system used has to accurately measure body postures adopted by the worker during the task. This study evaluates the accuracy to measure joint angles of upper extremities of two different motion capture systems, namely the Microsoft Kinect V2 and the Captiv system, for angles of upper extremities. For this purpose, an experimental study was conducted involving 12 subjects performing preset static postures and basic movements, including elbow flexion, shoulder flexion, and shoulder abduction. In addition, to examine whether self‐occlusion or occlusion of body parts by work equipment has an impact on the accuracy of the Kinect V2, the subjects handled boxes during some of the tests. As a gold standard, a goniometer for static and an angle scale for dynamic exercises was used. The Captiv system shows high correlation coefficients (r > .93) and small mean absolute errors (<5°) for all movements except for elbow flexion. The Kinect V2 has sufficient results for joint angles captured without occlusion as well, but the accuracy significantly decreases when occlusion occurs.     

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.     

Evaluating posture behavior during seated tasks

A method was developed to evaluate posture behavior of the trunk, neck, eye, and upper extremity in three-dimensional space during the performance of static, seated tasks. Body postures were measured using an ultrasonic measurement system to determine the Cartesian coordinates of joints and the angles between adjacent limbs. Posture preferences for a variety of visual and manual tasks were then determined.

Pilot studies using three subjects performing visual and right-handed tasks showed that the postures were affected by target location, body size, and target size. These experiments suggest that the preferred horizontal location of visual targets is within 10° of the sagittal plane of the head. The preferred vertical location of visual targets is 10° to 35° below the seated eye height. For manual reaches, the target-to-shoulder distance should be at least one-third the length of the upper extremity to avoid extreme elbow flexion. In addition, the seat pan should swivel and should allow a person to move fore and aft in order to adjust to a comfortable work posture.     

The use of mirrors during an assembly task: a study of ergonomics and productivity

Industrial assembly tasks often require awkward, sustained neck and/or shoulder postures that can lead to increased musculoskeletal discomfort and reduced productivity. The aim of this study was to investigate the effects of mirror and periscope visual aids as ergonomic interventions designed to eliminate awkward postures of the cervicobrachial region during assembly tasks. Participants simulated a simple assembly task by using a cordless screwdriver to drive screws into a pre-tapped aluminium block. Trials of 15 min were run for each of four distinct assembly workstation configurations: industry standard (in-line screwdriver, work at elbow height, no visual aid); pistol grip (pistol grip screwdriver, work at shoulder height, no visual aid); mirror (in-line screwdriver, work at elbow height, single mirror visual aid); and periscope (in-line screwdriver, work at elbow height, two-mirror visual aid system). Muscular activity, discomfort, body posture, productivity and operator subjective assessment were recorded to determine the effects of the visual aid interventions. The results show that when comparing the interventions to the industry standard condition, there was a 45% reduction in average cervical erector spinae activity, a 90% reduction in average neck flexion angle and a 72% reduction in neck discomfort with the interventions. When comparing these interventions to the pistol grip condition there was an 80% reduction in activity of the dominant side deltoid, a 92% reduction in shoulder flexion angle and an 81% decrease in shoulder discomfort with the interventions. Productivity was greatest in the industry standard configuration followed by the pistol grip (9% lower), the periscope (13% lower) and the mirror (23% lower) configurations. A follow-up study that compared the productivity of the periscope configuration with that of the industry standard configuration showed that within a 4-h work period this productivity differential decreased by over 33%.     

Technical Note: The use of mirrors during an assembly task: a study of ergonomics and productivity

Industrial assembly tasks often require awkward, sustained neck and/or shoulder postures that can lead to increased musculoskeletal discomfort and reduced productivity. The aim of this study was to investigate the effects of mirror and periscope visual aids as ergonomic interventions designed to eliminate awkward postures of the cervicobrachial region during assembly tasks. Participants simulated a simple assembly task by using a cordless screwdriver to drive screws into a pre-tapped aluminium block. Trials of 15 min were run for each of four distinct assembly workstation configurations: industry standard (in-line screwdriver, work at elbow height, no visual aid); pistol grip (pistol grip screwdriver, work at shoulder height, no visual aid); mirror (in-line screwdriver, work at elbow height, single mirror visual aid); and periscope (in-line screwdriver, work at elbow height, two-mirror visual aid system). Muscular activity, discomfort, body posture, productivity and operator subjective assessment were recorded to determine the effects of the visual aid interventions. The results show that when comparing the interventions to the industry standard condition, there was a 45% reduction in average cervical erector spinae activity, a 90% reduction in average neck flexion angle and a 72% reduction in neck discomfort with the interventions. When comparing these interventions to the pistol grip condition there was an 80% reduction in activity of the dominant side deltoid, a 92% reduction in shoulder flexion angle and an 81% decrease in shoulder discomfort with the interventions. Productivity was greatest in the industry standard configuration followed by the pistol grip (9% lower), the periscope (13% lower) and the mirror (23% lower) configurations. A follow-up study that compared the productivity of the periscope configuration with that of the industry standard configuration showed that within a 4-h work period this productivity differential decreased by over 33%.     

Perceived discomfort functions based on joint moment for various joint motion directions of the upper limb

The aim of the present study was to formulate the relationship between the perceived discomfort and the joint moment ratio for twelve joint motion directions of the upper limb by considering the between-subject variability, and to investigate the effect of joint motion direction. Three approximation models (i.e., linear, exponential, and logistic function models) were compared in terms of the accuracy of predicting the perceived discomfort, and the logistic function was selected because its average error was lowest. The concept of L-R fuzzy number was used to consider the individual variability of perceived discomfort, and a simplified distribution of perceived discomfort was represented. Cluster analysis showed that the twelve discomfort functions formed two clusters: one for elbow flexion and a second for the remaining joint motions. The data show that elbow flexion is more sensitive than other joint motions to increases in the joint moment ratio.     

Shoulder and neck muscle activities during typing with articulating forearm support at different heights

Use of forearm support is known to reduce physical stress of computer users, but research about how to properly position the forearm support is insufficient. This study was aimed to determine whether the height of forearm support influences muscular loads during typing. Twenty four subjects performed a typing task with a pair of articulating forearm support at three different heights as well as without any support, while shoulder, neck and forearm muscle activities and posture data were recorded. Typing with the support at resting elbow height produced significantly (p < 0.05) lower shoulder and neck muscle activities than that of no support condition. Typing with the support at heights higher than the resting elbow height produced significantly greater shoulder and neck muscle activities compared to the no support condition. Results suggest that forearm support can help computer users lessen physical stress in typing, but only when the supports are positioned at resting elbow height.

Practitioner Summary: Use of forearm support is known to alleviate physical stress of PC users in computer works such as typing. This experimental study addressed the importance of proper positioning of forearm support by comparing neck and upper extremity muscle activities between conditions with varying heights of forearm support in keyboard typing.     

Evaluation of the loading of neck and shoulder musculature in overhead pushing and pulling exertions

Despite substantial epidemiological evidence relating overhead exertions with work‐related musculoskeletal disorders (WMSD) of the neck, effects of such exertions on the loading of neck or cervical spine musculature are not well understood. In this study, the effects of overhead pushing and pulling exertions on the loading of the cervical spine were evaluated using electromyography (EMG) and subjective discomfort ratings. Additionally, the role of gender as well as individual strength on the loading of neck musculature during such exertions was evaluated. Twenty‐four healthy individuals (12 men and 12 women) participated in this study. Each participant performed overhead pushing and pulling exertions, exerting 25%, 50%, and 75% of their respective maximum strengths. Overhead pushing exertions were found to be significantly more strenuous to the neck musculature than were the pulling exertions. Gender had no significant effect on the activities of the neck muscles. Participants with high strength, however, were able to exert more force at comparatively low muscle activation levels. Subjective discomfort ratings were strongly correlated with the EMG data. At various workplaces, avoiding overhead exertions is rather impossible due to material, interface, and site constraints. Based on the results of this study, however, during such exertions, an interchange between directions of force application could prevent sustained loading of the neck muscles, fatigue, and consequently the probability of neck WMSD incidents. © 2011 Wiley Periodicals, Inc.     

LUBA: an assessment technique for postural loading on the upper body based on joint motion discomfort and maximum holding time.

This paper presents a technique for postural loading on the upper body assessment (LUBA). The proposed method is based on the new experimental data for composite index of perceived discomfort (ratio values) for a set of joint motions, including the hand, arm, neck and back, and the corresponding maximum holding times in static postures. Twenty male subjects participated in the experiment designed to measure perceived joint discomforts. The free modulus technique of the magnitude estimation method was employed to obtain subjects' discomforts for varying joint motions. The developed postural classification scheme was based on the angular deviation levels from the neutral position for each joint motion. These were divided into groups with the same degree of discomforts based on the statistical analysis. Each group was assigned a numerical discomfort score relative to the perceived discomfort value of elbow flexion, which exhibited the lowest level among all joint motions investigated in this study, and, therefore, was set as a reference point. The criteria for evaluating stresses of working postures were proposed based on the four distinct action categories, in order to enable practitioners to apply appropriate corrective actions. The proposed scheme can be used for evaluating and redesigning static working postures in industry.     

Effects of shoulder rotation combined with elbow flexion on discomfort and EMG activity of ECRB muscle

Work related MusculoSkeletal Disorders (WMSDs) are injuries or dysfunctions caused by occupational or non occupational tasks involving bad postures, high frequency of exertions or high force levels. In the present study, the effects of shoulder flexion/extension combined with elbow flexion angle on discomfort score were investigated for repetitive gripping task. A laboratory experimental simulation was conducted. Ten male participants volunteered in this study. Four levels of shoulder flexion/extension (−45° extension, 0° neutral, 45° & 90° flexion) with three levels of elbow flexion angle (45°, 90° & 135°) were taken as levels of independent variables. There were 12 combinations available for each participant and the experiment was conducted on the basis of random order of experimental combinations for each participant. Discomfort score on 100 mm visual analogue scale (VAS) and Electromyography (EMG) activity of Extensor Carpi Radialis Brevis (ECRB) muscle were dependent variables for the analyses. The task for the experiment was of 150N ± 5N grip force at a frequency of 15 exertions/minute for five minutes duration. After performing the MANOVA on the recorded data, the results showed that the shoulder flexion/extension and elbow flexion both were highly significant (p < 0.001). Also it was found that −45° shoulder extension combined with 45° elbow flexion angle was the most discomfort posture. The practical relevance of the study is that, in industrial tasks such posture should be avoided to minimize risk of WMSDs.Relevance to industryThe findings in terms of relationship between discomfort/EMG vs. shoulder rotation combined with elbowflexion are important to design Industrial tasks with the reduced risk of WMSDs. Such as, sheet metal cutting, fabrication of sheet metal work, die casting, and drilling operations may require the shoulder movements in extenion/flexion combined with elbowflexion.     

Effect of a desk attachment board on posture and muscle activity in women during computer work

Working at a computer is part of a large number of jobs and has been associated with upper extremity musculoskeletal disorders and back pain. The study evaluated the effects of a board attachment on upper extremity and back. The findings are mixed in that the board may have a positive effect in preventing back pain, but may be detrimental to upper extremities. Effect of a desk attachment board on upper extremity and trunk posture, and muscle activity was assessed in women video display terminal users. Participants completed a standard 20-min computer task under two conditions: 1) using a standard desk; 2) using a desk attachment board designed to support the forearms. Bilateral electromyography of the trapezius, multifidus and longissimus muscles and the right anterior deltoid and forearm extensor muscles was recorded. 3-D trunk and upper extremity posture was monitored. Participants were tested before and after 2 weeks of familiarisation with the board in their workplace. Perceived tension and discomfort were recorded before and after use of the board. Use of the board tended to increase muscle activity in the right trapezius and forearm extensor and to decrease muscle activity in the back. Perceived tension in the low back decreased slightly with the board. The board may be useful in reducing tension in the low back during computer work, but may adversely affect the upper extremities.     

Exploring time‐dependent symptom outcomes in office staff

This article illustrates the application of a new mathematical model developed for the study of time‐dependent health outcomes for office staff during computer work. The model describes the time‐dependent associations of computer usage with outcomes expressed as discomfort in multiple body regions. The association is explicitly presented with a functional relationship that is parameterized by body regions. The validation of the model demonstrated accuracy in reproducing the observed quantities for the study population. Therefore, we used this model to assess the impact of computer‐related work exposure on discomfort in different body regions among office staff to better understand the behavior of musculoskeletal and other symptoms. The exposures and outcomes were recorded parallel in time as usage of keyboard and mouse and with diaries of discomfort. The body regions of neck/shoulders, eyes, head, shoulder joint/upper arm, and upper back were identified to have the highest discomfort levels and rates for the development of discomfort parallel with exposures. Most of our findings are consistent with the literature. The developed mathematical methodology may be used to understand how the human body reacts to computer work to further prevent potential musculoskeletal and other disorders. © 2009 Wiley Periodicals, Inc.