Upper extremity biomechanics in computer tasks differ by gender

Occupational and non-occupational risk factors correlating with the severity of clinical manifestations of carpal tunnel syndrome and related work disability among workers who work with a computer

The contribution of certain occupational and personal factors to the development of carpal tunnel syndrome (CTS) is still uncertain. We investigated which specific occupational and non-occupational factors correlate with the level of clinical manifestations and work disability related to CTS. The study included 190 workers who work with a computer and have diagnosed CTS (100 men, 90 women, aged 20-65 years). Subjective experience of CTS-related impairments was assessed with the Symptom Severity Scale (SSS) and the Functional Status Scale (FSS) of the Boston Carpal Tunnel Syndrome Questionnaire (BCTQ). The objective, neural impairments were tested with electrodiagnostics (EDX), whereas CTS-related work disability data were collected from medical records. We found a high inter-correlation between BCTQ, EDX, and work disability data. These also showed high correlations with certain occupational factors (duration of computer-working in months and hours spent daily in computer-working, certain ergonomic, microclimatic, and other occupational conditions) and non-occupational factors (demographic and lifestyle factors: nutritional status, diet, smoking, alcohol consumption, and physical activity). Despite its limitations, our study has identified occupational and non-occupational risk factors that can aggravate CTS and work disability, but which can also be improved with workplace and lifestyle preventive and corrective measures. More research is needed, though, to establish the possible causal relationships and the independent influence of each of those risk factors.

The Role of Innovation Technology in the Rehabilitation of Patients Affected by Huntington's Disease: A Scoping Review

Huntington's disease is an autosomal dominant neurodegenerative disease caused by the repetition of cytosine, adenine, and guanine trinucleotides on the short arm of chromosome 4p16.3 within the Huntingtin gene. In this study, we aim to examine and map the existing evidence on the use of innovations in the rehabilitation of Huntington's disease. A scoping review was conducted on innovative rehabilitative treatments performed on patients with Huntington's disease. A search was performed on PubMed, Embase, Web of Science, and Cochrane databases to screen references of included studies and review articles for additional citations. Of an initial 1117 articles, only 20 met the search criteria. These findings showed that available evidence is still limited and that studies generally had small sample sizes and a high risk of bias. Regarding cognitive rehabilitation, it has emerged that VR- and PC-based methods as well as NIBS techniques are feasible and may have promising effects in individuals with Huntington's disease. On the other hand, scarce evidence was found for cognitive and motor training that might have a slight impact on overall cognitive function in individuals with Huntington's disease. Data show that further investigation is needed to explore the effects of innovative rehabilitation tools on cognition, especially considering that cognitive and psychiatric symptoms can precede the onset of motor symptoms by many years.

Objective Evaluation of Active Interactions between the Operator and Display Screen Equipment Using an Innovative Acquisition System

The occupational risk of operators using display screen equipment (DSE) is usually evaluated according to the extent of time spent in active operator-DSE interactions. Risk assessment is based on activity data collected through questionnaires. We evaluated an original and innovative system that can objectively assess active operator-DSE interactions by collecting electrical impulses generated by the activation of mouse, keyboard and a camera that collects attentive eye-screen fixation. The main aim of this study was to evaluate the system's performance on an employee sample involved in the task of active reading and copying at a DSE workstation connected to the system. In the context of mandatory health surveillance at work, we enrolled 38 DSE operators with normal neuropsychological and eye assessments who were required to complete two predefined reading and writing tasks. The obtained results show that the system is able to collect activity data derived from operator-DSE interactions through screen fixation, keyboard tapping and mouse handling. In the copying task, the session duration as recorded by the system was highly related to the screen fixation time. In the copying task, mouse and keyboard activities were more strongly related to session duration than screen fixation. For the copying task, it was also possible to obtain individual profiles of operator-DSE interactions while performing the same standardized tasks. Collected data can allow an objective evaluation of active time spent by DSE operators at their workstations, thus allowing a more accurate occupational health risk assessment and management. Prospective analysis of individual operator-DSE interaction profiles can favor the setup of targeted preventive and organizational interventions from an of even wider worker wellbeing perspective.

The effect of tablet tilt angles and time on posture, muscle activity, and discomfort at the neck and shoulder in healthy young adults

BACKGROUND

Although young adults regularly perform tablet writing, biomechanics during the tablet writing with different tilt angles has not been studied. The objective of this study was to compare posture, muscle activity, and discomfort at the neck and shoulder between tablet writing with 0° (horizontal) and 30° tablet tilt angles over 40 minutes in healthy young adults.

METHODS

Twenty participants wrote continuously for 40 minutes on a tablet with both tilt angles in a randomized order. Between conditions, there was a 5-minute activity break. Differences in neck and shoulder posture, muscle activity, and discomfort between both tablet tilt angles and changes in the outcomes every 10 minutes over 40 minutes were investigated.

RESULTS

With the tilted tablet, there were lower neck flexion (Z = -4.637, P<0.001), lower shoulder extension (Z = -3.734, P<0.001), and lower neck Visual Analogue Scale (VAS) (left; Z = -4.699, P<0.001 and right; Z = -3.874, P<0.001) as compared to the no tilt condition. However, the right upper trapezius muscle activity was higher in the tilted condition as compared to the no tilt one. Over 40 minutes, the neck VAS (left; χ2(4) = 30.235, P<0.001 and right; χ2(4) = 32.560, P<0.001) and heart rate variability (χ2(4) = 12.906, P = 0.012) showed notable increases after 20 minutes compared to baseline.

CONCLUSION

In conclusion, adjusting the tablet tilt to 30° and limiting time spent to 20 minutes are recommended for young adults during the tablet writing to prevent neck problems.

The role of at home workstation ergonomics and gender on musculoskeletal pain

BACKGROUND

The recent mandate for university faculty and staff to work-from-home (WFH) during the COVID-19 pandemic has forced employees to work with sub-optimal ergonomic workstations that may change their musculoskeletal discomfort and pain. As women report more work-related musculoskeletal discomfort (WMSD), this effect may be exacerbated in women.

OBJECTIVE

The purpose of this study was to describe university employee at-home office workstations, and explore if at-home workstation design mediates the effect of gender on musculoskeletal pain.

METHODS

University employees completed a survey that focused on the WFH environment, at home workstation design and musculoskeletal pain. Descriptive statistics and regression analysis were used to analyze the responses.

RESULTS

61% of respondents reported an increase in musculoskeletal pain, with the neck, shoulders and lower back being reported most frequently. Women reported significantly greater musculoskeletal pain, but this relationship was significantly mediated by poor ergonomic design of the home workstation. Improper seat-height and monitor distance were statistically associated with total-body WMSD.

CONCLUSIONS

WFH has worsened employee musculoskeletal health and the ergonomic gap between women and men in the workspace has persisted in the WFH environment, with seat height and monitor distance being identified as significant predictors of discomfort/pain.

Interaction between hand span and different sizes of keyboards on EMG activity in pianists: An observational study

The availability of keyboards with reduced key width has been recently promoted as an ergonomic aid for small-handed pianists to overcome any potential physical disadvantages that may restrict their piano repertoire. However, a lack of biomechanical data exists to support whether reduced piano key size is effective in achieving this outcome. This research investigates the effect of playing on three different key width size pianos (5.5-inch octave, 6.0-inch octave and conventional size with 6.5-inch octave) on hand, arm and shoulder muscle activity levels according to the hand size of the pianists. Results indicate that piano key size affects the muscle activity levels of selected muscles. Furthermore, this effect of different key sizes changed according to the players' hand spans. Small-handed pianists may benefit from using smaller-sized keyboards to reduce muscular exertion during performance. This investigation provides preliminary EMG data supporting the use of different size keyboards to improve the ergonomic fit according to the dimensions of individual pianists.

Effects of Sensor Types and Angular Velocity Computational Methods in Field Measurements of Occupational Upper Arm and Trunk Postures and Movements

Accelerometer-based inclinometers have dominated kinematic measurements in previous field studies, while the use of inertial measurement units that additionally include gyroscopes is rapidly increasing. Recent laboratory studies suggest that these two sensor types and the two commonly used angular velocity computational methods may produce substantially different results. The aim of this study was, therefore, to evaluate the effects of sensor types and angular velocity computational methods on the measures of work postures and movements in a real occupational setting. Half-workday recordings of arm and trunk postures, and movements from 38 warehouse workers were compared using two sensor types: accelerometers versus accelerometers with gyroscopes-and using two angular velocity computational methods, i.e., inclination velocity versus generalized velocity. The results showed an overall small difference (<2° and value independent) for posture percentiles between the two sensor types, but substantial differences in movement percentiles both between the sensor types and between the angular computational methods. For example, the group mean of the 50th percentiles were for accelerometers: 71°/s (generalized velocity) and 33°/s (inclination velocity)-and for accelerometers with gyroscopes: 31°/s (generalized velocity) and 16°/s (inclination velocity). The significant effects of sensor types and angular computational methods on angular velocity measures in field work are important in inter-study comparisons and in comparisons to recommended threshold limit values.

Wrapping technique and wrapping height interact to modify physical exposures during manual pallet wrapping

Occupational tasks often involve musculoskeletal demands that contribute to injury risk. In pallet wrapping tasks, 36% of workplace claims involve over exertion and repetitive exposures (Workplace Safety and Prevention Services, 2012). Tools that modify how the wrap is handled by workers have been introduced to help mitigate over exertion and extreme postures wherever possible. A novel device has been introduced that places the required tension on the roll to mitigate these factors. However, the effect of reducing the necessary tension on the roll during pallet wrapping in limiting muscular demand and extreme postures is unknown. Fourteen healthy university aged participants completed 12 wrapping trials on a simulated pallet (2 repetitions of 2 wrapping techniques (device, hand wrapping) at 3 wrapping heights (low, medium, high)). Surface electromyography (sEMG) was measured on 6 shoulder and 2 low back muscles; anterior and middle deltoids, biceps brachii, infraspinatus, supraspinatus, upper trapezius, and erector spinae (T8 & L3). Kinematic data were collected for the torso and upper extremity and global to torso, and torso to upper arm angles were computed. Repeated measures ANOVAs were performed for the following experimental factors: 1) technique used (device or hand wrapping) and 2) the wrapping height (low, medium, high) for each muscle (8), angle (5), rating of perceived discomfort (1) and rating of perceived exertion (1). Pallet wrapping without a device required greater trunk flexion at lower heights and thoracohumeral elevation at higher wrapping heights as compared to using the device. Muscular activation increased when using the device, specifically at the higher and lower heights. Posture and muscular demands during pallet wrapping tasks are sensitive to both wrapping technique and wrapping height. Ergonomics interventions such as this device may mitigate postural risks associated with manual material handling tasks.

Sex differences in muscle activity and motor variability in response to a non-fatiguing repetitive screwing task

Background

Musculoskeletal disorders are more prevalent among women than among men, which may be explained by aspects of motor control, including neuromuscular requirements and motor variability. Using an exploratory approach, this study aimed to evaluate sex differences in neuromuscular responses and motor variability during a repetitive task performed on 3 days.

Methods

Thirty women and 27 men performed the non-fatiguing, repetitive, 1-h screwing task. For neuromuscular responses, the mean and difference values of static, median, and peak percentile muscle activity levels (normalized to a reference voluntary contraction force) and, for motor variability, the mean and difference values of relative and absolute cycle-to-cycle variability across days were compared between both sexes for each muscle. A mixed-design analysis of variance was used to assess differences between both sexes.

Results

The non-fatiguing character of the screwing task was confirmed by the absence of decreased force levels in maximal voluntary contractions performed before and after the task and by absence of electromyographic signs of muscle fatigue. The static and median muscle activity levels tended to be higher among women (on average 7.86 and 27.23 %RVE) than men (on average 6.04 and 26.66 %RVE). Relative motor variability of the flexor and biceps muscles and absolute motor variability of both upper arm muscles were lower in women (on average 0.79 and 29.70 %RVE) than in men (on average 0.89 and 37.55 %RVE). The median activity level of both upper arms muscles tended to decrease within days among women (on average - 2.63 %RVE) but increase among men (on average + 1.19 %RVE). Absolute motor variability decreased within days among women (on average - 5.32 to - 0.34%RVE), whereas it tended to decrease less or increase within days among men (on average - 1.21 to + 0.25 %RVE).

Conclusion

Women showed higher levels of muscle activity and lower initial relative and absolute motor variability than males when performing the same occupational task, implying women may have a higher risk for developing disorders and point to both sexes using different intrinsic motor control strategies in task performance. Clearly, biological aspects alone cannot explain why women would be at higher risk for developing disorders than men. Therefore, a wider range of individual and environmental factors should be taken into account for optimizing work station designs and organizations by taking into account sex differences.

Surgeons' posture and muscle strain during laparoscopic and robotic surgery

Background

It is assumed that conventional laparoscopy (LAP) and robotic-assisted laparoscopic surgery (RALS) differ in terms of the surgeon's comfort. This study compared muscle workload, work posture and perceived physical exertion of surgeons performing LAP or RALS.

Methods

Colorectal surgeons with experience in advanced LAP and RALS performed one of each operation. Bipolar surface electromyography (EMG) recordings were made from forearm, shoulder and neck muscles, and expressed relative to EMG maximum (%EMGmax). The static, median and peak levels of muscle activity were calculated, and an exposure variation analysis undertaken. Postural observations were carried out every 10 min, and ratings of perceived physical exertion before and after surgery were recorded.

Results

The study included 13 surgeons. Surgeons performing LAP showed higher static, median, and peak forearm muscle activity than those undertaking RALS. Muscle activity at peak level was higher during RALS than LAP. Exposure variation analysis demonstrated long-lasting periods of low-level intensity muscle activity in the shoulders for LAP, in the forearms for RALS, and in the neck for both procedures. Postural observations revealed a greater need for a change in work posture when performing LAP compared with RALS. Perceived physical exertion was no different between the surgical modalities.

Conclusion

Minimally invasive surgery requires long-term static muscle activity with a high physical workload for surgeons. RALS is less demanding on posture.

Going Short: The Effects of Short-Travel Key Switches on Typing Performance, Typing Force, Forearm Muscle Activity, and User Experience

This study examined the effects of 4 micro-travel keyboards on forearm muscle activity, typing force, typing performance, and self-reported discomfort and difficulty. A total of 20 participants completed typing tasks on 4 commercially available devices with different key switch characteristics (dome, scissors, and butterfly) and key travels (0.55, 1.3, and 1.6 mm). The device with short-travel (0.55 mm) and a dome-type key switch mechanism was associated with higher muscle activities (6%-8%, P < .01), higher typing force (12%, P < .01), slower typing speeds (8%, P < .01), and twice as much discomfort (P < .05), compared with the other 3 devices: short-travel (0.55 mm) and butterfly switch design and long travel (1.3 and 1.6 mm) with scissor key switches. Participants rated the devices with larger travels (1.3 and 1.6 mm) with least discomfort (P = .02) and difficulty (P < .01). When stratified by sex/gender, these observed associations were larger and more significant in the female participants compared with male participants. The devices with similar travel but different key switch designs had difference in outcomes and devices with different travel were sometimes not different. The results suggest that key travel alone does not predict typing force or muscle activity.

Workstation configuration and container type influence upper limb posture in grocery bagging

INTRODUCTION

Repetitive movements and awkward postures are two persistent injury risk factors for grocery store cashiers. Due to the recent rise in popularity of environmentally-friendly grocery bagging options, current recommendations for cashiers are likely outdated. Correspondingly, the objective of this study was to examine the effects of cashier-specific work demands, workstation configuration, and container type on upper limb postures during typical job activities.

METHODS

Fifteen experienced cashiers bagged groceries at varying combinations of workstation height (low, medium, high) and container type (reusable bins, reusable bags, plastic bags). Upper limb movement was quantified with motion capture and amplitude probability distribution functions of humeral elevation and humeral axial internal rotation were used to assess the static (10th percentile), median (50^th percentile), and peak (90^th percentile) postural demands, which were then interpreted in the context of existing postural guidelines.

RESULTS

High workstation height and reusable bags increased right arm elevation at peak posture by 15.7° compared to the low workstation height and reusable bin combination. However, reusable bins increased internal rotation demands of the right arm by 4.3° compared to other container types. Left arm elevation and internal rotation were consistently lower than right arm angles.

CONCLUSION

Cashiers are encouraged to adjust the workstation to decrease the arm elevation and internal rotation required by higher workstation heights and tall containers, and to use both arms for scanning and packing, when possible, to reduce undesirable arm postures.

Predicting Forearm Physical Exposures During Computer Work Using Self-Reports, Software-Recorded Computer Usage Patterns, and Anthropometric and Workstation Measurements

Objectives

Alternative techniques to assess physical exposures, such as prediction models, could facilitate more efficient epidemiological assessments in future large cohort studies examining physical exposures in relation to work-related musculoskeletal symptoms. The aim of this study was to evaluate two types of models that predict arm-wrist-hand physical exposures (i.e. muscle activity, wrist postures and kinematics, and keyboard and mouse forces) during computer use, which only differed with respect to the candidate predicting variables; (i) a full set of predicting variables, including self-reported factors, software-recorded computer usage patterns, and worksite measurements of anthropometrics and workstation set-up (full models); and (ii) a practical set of predicting variables, only including the self-reported factors and software-recorded computer usage patterns, that are relatively easy to assess (practical models).

Methods

Prediction models were build using data from a field study among 117 office workers who were symptom-free at the time of measurement. Arm-wrist-hand physical exposures were measured for approximately two hours while workers performed their own computer work. Each worker's anthropometry and workstation set-up were measured by an experimenter, computer usage patterns were recorded using software and self-reported factors (including individual factors, job characteristics, computer work behaviours, psychosocial factors, workstation set-up characteristics, and leisure-time activities) were collected by an online questionnaire. We determined the predictive quality of the models in terms of R2 and root mean squared (RMS) values and exposure classification agreement to low-, medium-, and high-exposure categories (in the practical model only).

Results

The full models had R2 values that ranged from 0.16 to 0.80, whereas for the practical models values ranged from 0.05 to 0.43. Interquartile ranges were not that different for the two models, indicating that only for some physical exposures the full models performed better. Relative RMS errors ranged between 5% and 19% for the full models, and between 10% and 19% for the practical model. When the predicted physical exposures were classified into low, medium, and high, classification agreement ranged from 26% to 71%.

Conclusion

The full prediction models, based on self-reported factors, software-recorded computer usage patterns, and additional measurements of anthropometrics and workstation set-up, show a better predictive quality as compared to the practical models based on self-reported factors and recorded computer usage patterns only. However, predictive quality varied largely across different arm-wrist-hand exposure parameters. Future exploration of the relation between predicted physical exposure and symptoms is therefore only recommended for physical exposures that can be reasonably well predicted.

Gender and posture are significant risk factors to musculoskeletal symptoms during touchscreen tablet computer use

[Purpose] To investigate the prevalence of neck and shoulder symptoms during the use of tablet computer, and to identify the risk factors associated with these symptoms. [Subjects and Methods] A cross-sectional survey was conducted to study tablet computer usage, posture during use, and neck and shoulder symptoms in 412 participants in a school setting. Significant risk factors for musculoskeletal symptoms during tablet computer use were identified. [Results] Overall prevalence of musculoskeletal symptoms during tablet computer use was 67.9% with greater prevalence of neck symptoms (neck: 84.6%; shoulder/upper extremity: 65.4%). Significant risk factors associated with symptoms during use were: current musculoskeletal symptoms, gender, roles, and postural factors including: sitting without back support, sitting with device in lap, and lying on the side and on the back during tablet computer use. A multivariate analysis further showed that the odds for females to have symptoms were 2.059 times higher than males. [Conclusion] The findings revealed that female gender and other postural factors were significantly associated with musculoskeletal symptoms during the use of tablet computer. Among all postural factors, sitting without back support was identified as the most important risk factor for having musculoskeletal symptoms.

Normative kinematics of reaching and dexterity tasks: moving towards a quantitative baseline for Functional Capacity Evaluations (FCEs)

Purpose: This work generates a comprehensive description of upper extremity and torso kinematics of a healthy population during reaching and dexterity Functional Capacity Evaluation (FCE) tasks. Methods: Upper limb and torso kinematic data were collected from 30 young, healthy participants as they performed three common FCE tasks: repetitive reaching, fingertip dexterity, and hand and forearm dexterity. Kinematic profiles were created for all clinically relevant angles of the torso, shoulder, elbow, and wrist. Results: These provocative tasks require large ranges of motion and create high demand postures for the upper limb, specifically at the shoulder. Arm elevation was up to 90°, while humeral internal rotation of 25° was observed. Torso angles were typically below 30° from neutral and elbow flexion remained within 90°–120° for nearly all tasks. Wrist ulnar deviation ranged from 0° to 26° for both wrists. Conclusion: The normative data created in this investigation provide a description of healthy motion during reaching and dexterity tasks. These normative curves are the initial step towards understanding movement that would contraindicate return to work during an FCE. This work supports a future clinical goal of being able to identify persons at risk of further injury or disability if returned to work too early.

Electromyographic analysis of relevant muscle groups during completion of computer tasks using different computer mouse positions

BACKGROUND

We analyzed muscular activity for different computer mouse positions during the completion of a timed computer task and determined whether the different mouse positions could affect muscular activity, productivity and perceived fatigue.

METHODS

The subjects were nine healthy young men. Two mouse positions were studied: the distal position (DP), with the forearm rested on the desk; the proximal position (PP), with only the wrist rested on the desk. The subjects performed a 16-min task in each position. Surface electromyography data were recorded for the upper back and shoulder muscles. Work productivity and muscular activity were measured for each mouse position. A visual analog scale was used to assess subjective fatigue.

RESULTS

Muscular activity was higher in muscle (m.) deltoideus (posterior) for the DP, while it was significantly higher in m. inferior infraspinatus for the PP. The visual analog scale score was significantly higher and work productivity was lower in the PP.

CONCLUSIONS

We found that using a mouse in the DP rather than the PP leads to less activity of the external rotators, less perceived fatigue and more productivity. This suggests that the DP is preferable to the PP for computer work involving a mouse.

A literature review of the effects of computer input device design on biomechanical loading and musculoskeletal outcomes during computer work

BACKGROUND

Extended use of conventional computer input devices is associated with negative musculoskeletal outcomes. While many alternative designs have been proposed, it is unclear whether these devices reduce biomechanical loading and musculoskeletal outcomes.

OBJECTIVE

To review studies describing and evaluating the biomechanical loading and musculoskeletal outcomes associated with conventional and alternative input devices.

METHODS

Included studies evaluated biomechanical loading and/or musculoskeletal outcomes of users' distal or proximal upper extremity regions associated with the operation of alternative input devices (pointing devices, mice, other devices) that could be used in a desktop personal computing environment during typical office work.

RESULTS

Some alternative pointing device designs (e.g. rollerbar) were consistently associated with decreased biomechanical loading while other designs had inconsistent results across studies. Most alternative keyboards evaluated in the literature reduce biomechanical loading and musculoskeletal outcomes. Studies of other input devices (e.g. touchscreen and gestural controls) were rare, however, those reported to date indicate that these devices are currently unsuitable as replacements for traditional devices.

CONCLUSIONS

Alternative input devices that reduce biomechanical loading may make better choices for preventing or alleviating musculoskeletal outcomes during computer use, however, it is unclear whether many existing designs are effective.

Effects of mouse slant and desktop position on muscular and postural stresses, subject preference and performance in women aged 18-40 years

This study compared muscular and postural stresses, performance and subject preference in women aged 18-40 years using a standard mouse, a vertical mouse and a slanted mouse in three different computer workstation positions. Four tasks were analysed: pointing, pointing-clicking, pointing-clicking-dragging and grasping-pointing the mouse after typing. Flexor digitorum superficialis (FDS) and extensor carpi radialis (ECR) activities were greater using the standard mouse compared to the vertical or slanted mouse. In all cases, the wrist position remained in the comfort zone recommended by standard ISO 11228-3. The vertical mouse was less comfortable and more difficult to use than the other two mice. FDS and ECR activities, shoulder abduction and wrist extension were greater when the mouse was placed next to the keyboard. Performance and subject preference were better with the unrestricted mouse positioning on the desktop. Grasping the mouse after typing was the task that caused the greatest stress. Practitioner Summary: In women, the slanted mouse and the unrestricted mouse positioning on the desktop provide a good blend of stresses, performance and preference. Unrestricted mouse positioning requires no keyboard, which is rare in practice. Placing the mouse in front of the keyboard, rather than next to it, reduced the physical load.

Comparison of the postural and physiological effects of two dynamic workstations to conventional sitting and standing workstations

Increasing evidence is being found for the association of health risk factors with work-related physical inactivity. An increasing number of people are being exposed to this form of inactivity, and as a result, various interventions aimed at increasing physical activity during working hours are being developed. This study aims to investigate the differences in postural, muscular and physical activities resulting from two dynamic workstations, namely an elliptical trainer and a treadmill workstation, compared with a conventional sitting and standing workstation. Twelve participants completed five standardised office tasks in a laboratory setting at all workstations. No significant effect was found regarding changes in posture and the muscular activity was only significantly higher for the trapezius muscle (50th percentile: 8.1 %MVC) at the dynamic workstations. For the dynamic workstations, physical activity ranged from 4.0 to 14.9 × 10(-2) g, heart rate from 14.3 to 27.5 %HRR and energy expenditure from 1.8 to 3.1 METs. Practitioner Summary: Work-related physical inactivity is associated with health risk factors. In this study, physiological and postural effects of dynamic workstations were assessed in comparison to conventional workstations. No significant effects were found regarding changes in posture and muscular activity. Physical activity, heart rate and energy expenditure increased for the dynamic workstations.

Wrist rotations about one or two axes affect maximum wrist strength

Most wrist strength studies evaluate strength about one axis, and postural deviations about that same axis. The purpose of this study was to determine if wrist posture deviations about one axis (e.g. flexion/extension), or two axes (e.g. flexion/extension and pronation/supination), affect the strength about another axis (e.g. ulnar deviation). A custom-built instrumented handle was used to measure maximum static isometric torque exertions at 18 wrist postures (combinations of flexion/extension, radial/ulnar deviation, and pronation/supination). Ulnar deviation torques were highest when the wrist was in neutral. This pattern was not maintained for the other torque directions; the generated torque tended to be highest when the wrist posture was not neutral. The effects were similar for male and female subjects, although male subjects exerted significantly larger torques in all directions. This study illustrates that there is a complex relationship between wrist posture and maximal wrist torques.

Wrist Hypothermia Related to Continuous Work with a Computer Mouse: A Digital Infrared Imaging Pilot Study

Computer work is characterized by sedentary static workload with low-intensity energy metabolism. The aim of our study was to evaluate the dynamics of skin surface temperature in the hand during prolonged computer mouse work under different ergonomic setups. Digital infrared imaging of the right forearm and wrist was performed during three hours of continuous computer work (measured at the start and every 15 minutes thereafter) in a laboratory with controlled ambient conditions. Four people participated in the study. Three different ergonomic computer mouse setups were tested on three different days (horizontal computer mouse without mouse pad; horizontal computer mouse with mouse pad and padded wrist support; vertical computer mouse without mouse pad). The study revealed a significantly strong negative correlation between the temperature of the dorsal surface of the wrist and time spent working with a computer mouse. Hand skin temperature decreased markedly after one hour of continuous computer mouse work. Vertical computer mouse work preserved more stable and higher temperatures of the wrist (>30 °C), while continuous use of a horizontal mouse for more than two hours caused an extremely low temperature (<28 °C) in distal parts of the hand. The preliminary observational findings indicate the significant effect of the duration and ergonomics of computer mouse work on the development of hand hypothermia.

Prediction of trapezius muscle activity and shoulder, head, neck, and torso postures during computer use: results of a field study

BACKGROUND

Due to difficulties in performing direct measurements as an exposure assessment technique, evidence supporting an association between physical exposures such as neck and shoulder muscle activities and postures and musculoskeletal disorders during computer use is limited. Alternative exposure assessment techniques are needed.

METHODS

We predicted the median and range of amplitude (90th-10th percentiles) of trapezius muscle activity and the median and range of motion (90th-10th percentiles) of shoulder, head, neck, and torso postures based on two sets of parameters: the distribution of keyboard/mouse/idle activities only ("task-based" predictions), and a comprehensive set of task, questionnaire, workstation, and anthropometric parameters ("expanded model" predictions). We compared the task-based and expanded model predictions based on R2 values, root mean squared (RMS) errors, and relative RMS errors calculated compared to direct measurements.

RESULTS

The expanded model predictions of the median and range of amplitude of trapezius muscle activity had consistently better R2 values (range 0.40-0.55 compared to 0.00-0.06), RMS errors (range 2-3%MVC compared to 3-4%MVC), and relative RMS errors (range 10-14%MVC compared to 16-19%MVC) than the task-based predictions. The expanded model predictions of the median and range of amplitude of postures also had consistently better R2 values (range 0.22-0.58 compared to 0.00-0.35), RMS errors (range 2-14 degrees compared to 3-22 degrees), and relative RMS errors (range 9-21 degrees compared to 13-42 degrees) than the task-based predictions.

CONCLUSIONS

The variation in physical exposures across users performing the same task is large, especially in comparison to the variation across tasks. Thus, expanded model predictions of physical exposures during computer use should be used rather than task-based predictions to improve exposure assessment for future epidemiological studies. Clinically, this finding also indicates that computer users will have differences in their physical exposures even when performing the same tasks.

The position of a standard optical computer mouse affects cardiorespiratory responses during the operation of a computer under time constraints

OBJECTIVES

This study investigated the association between task-induced stress and fatigue by examining the cardiovascular responses of subjects using different mouse positions while operating a computer under time constraints.

MATERIAL AND METHODS

The study was participated by 16 young, healthy men and examined the use of optical mouse devices affixed to laptop computers. Two mouse positions were investigated: (1) the distal position (DP), in which the subjects place their forearms on the desk accompanied by the abduction and flexion of their shoulder joints, and (2) the proximal position (PP), in which the subjects place only their wrists on the desk without using an armrest. The subjects continued each task for 16 min. We assessed differences in several characteristics according to mouse position, including expired gas values, autonomic nerve activities (based on cardiorespiratory responses), operating efficiencies (based on word counts), and fatigue levels (based on the visual analog scale - VAS).

RESULTS

Oxygen consumption (VO(2)), the ratio of inspiration time to respiration time (T(i)/T(total)), respiratory rate (RR), minute ventilation (VE), and the ratio of expiration to inspiration (Te/T(i)) were significantly lower when the participants were performing the task in the DP than those obtained in the PP. Tidal volume (VT), carbon dioxide output rates (VCO(2)/VE), and oxygen extraction fractions (VO(2)/VE) were significantly higher for the DP than they were for the PP. No significant difference in VAS was observed between the positions; however, as the task progressed, autonomic nerve activities were lower and operating efficiencies were significantly higher for the DP than they were for the PP.

CONCLUSIONS

Our results suggest that the DP has fewer effects on cardiorespiratory functions, causes lower levels of sympathetic nerve activity and mental stress, and produces a higher total workload than the PP. This suggests that the DP is preferable to the PP when operating a computer.

The effect of aging on muscle activation and postural control pattern for young and older computer users

A lot of older adults try to learn to use computers and might use different ways to perform a computer task compared to younger people. Fifteen healthy young and 15 healthy older adults participated in this study and all performed a series of mouse tasks. A three dimensional motion capture system and electromyographic analysis were used to obtain kinematic and kinetic data during performing the computer tasks. Three-way analysis of variance with repeated measures on task and time factors was used to analyze all dependent measurements. Older adults had higher RMS of forearm muscles compared to the young adults. The RMS of the finger extensor was highest when performing a dragging task. Compared with young adults, the older adults had greater cranial-cervical angle and neck flexion, but smaller head flexion, shoulder angle, elbow angle and ulnar deviation. Consequently, the older adults might have a greater risk of developing musculoskeletal disorder.

A monitoring tool of workers' activity at Video Display Terminals for investigating VDT-related risk of musculoskeletal disorders

Today the risk factors related to the use of Video Display Terminals (VDT) are assessed by investigating the actual activities at the VDT through subjective questionnaires and/or quantitative measurements. Questionnaire outcomes are quite imprecise and seldom objective. Quantitative measurements (EMG recordings, electrogoniometers, motion analysis systems) mostly prevent subjects from moving freely while working at the VDT. The paper presents an automatic tool for the monitoring of activity at VDTs, using a quantitative, objective approach. The suitability of the proposed tool was fully tested in the laboratory, both in terms of functionalities, accuracy of the tool, and acceptance by the subjects involved. The outcomes show that the tool allows for a detailed analysis of VDT activities and may be used to improve VDT-related risk analysis with high accuracy and good acceptance by workers.

Comparison of posture and muscle control pattern between male and female computer users with musculoskeletal symptoms

The primary purpose of this study was to compare the posture and muscle control patterns between male and female computer users with musculoskeletal symptoms. Forty computer users were recruited. Each subject performed a preferred speed typing, a fast speed typing, and a repetitive mouse task. The independent variables were gender, typing speed, and time. There were significant differences between genders for head and neck flexion angles when they were performing the preferred speed typing task. Significant differences between genders were also found for upper extremity angles when they were performing the repetitive mouse task. Male computer users had a smaller root mean square of the right extensor digitorium than females. In general, postural differences were significant between genders, even when the subjects' table and chair were adjusted to meet their anthropometry. Our results suggest that modifications of the computer working environment may be different between genders.

Observed differences in upper extremity forces, muscle efforts, postures, velocities and accelerations across computer activities in a field study of office workers

This study, a part of the PRedicting Occupational biomechanics in OFfice workers (PROOF) study, investigated whether there are differences in field-measured forces, muscle efforts, postures, velocities and accelerations across computer activities. These parameters were measured continuously for 120 office workers performing their own work for two hours each. There were differences in nearly all forces, muscle efforts, postures, velocities and accelerations across keyboard, mouse and idle activities. Keyboard activities showed a 50% increase in the median right trapezius muscle effort when compared to mouse activities. Median shoulder rotation changed from 25 degrees internal rotation during keyboard use to 15 degrees external rotation during mouse use. Only keyboard use was associated with median ulnar deviations greater than 5 degrees. Idle activities led to the greatest variability observed in all muscle efforts and postures measured. In future studies, measurements of computer activities could be used to provide information on the physical exposures experienced during computer use. Practitioner Summary: Computer users may develop musculoskeletal disorders due to their force, muscle effort, posture and wrist velocity and acceleration exposures during computer use. We report that many physical exposures are different across computer activities. This information may be used to estimate physical exposures based on patterns of computer activities over time.

Developing a framework for predicting upper extremity muscle activities, postures, velocities, and accelerations during computer use: the effect of keyboard use, mouse use, and individual factors on physical exposures

Prediction models were developed based on keyboard and mouse use in combination with individual factors that could be used to predict median upper extremity muscle activities, postures, velocities, and accelerations experienced during computer use. In the laboratory, 25 participants performed five simulated computer trials with different amounts of keyboard and mouse use ranging from a highly keyboard-intensive trial to a highly mouse-intensive trial. During each trial, muscle activity and postures of the shoulder and wrist and velocities and accelerations of the wrists, along with percentage keyboard and mouse use, were measured. Four individual factors (hand length, shoulder width, age, and gender) were also measured on the day of data collection. Percentage keyboard and mouse use explained a large amount of the variability in wrist velocities and accelerations. Although hand length, shoulder width, and age were each significant predictors of at least one median muscle activity, posture, velocity, or acceleration exposure, these individual factors explained very little variability in addition to percentage keyboard and mouse use in any of the physical exposures investigated. The amounts of variability explained for models predicting median wrist velocities and accelerations ranged from 75 to 84% but were much lower for median muscle activities and postures (0-50%). RMS errors ranged between 8 to 13% of the range observed. While the predictions for wrist velocities and accelerations may be able to be used to improve exposure assessment for future epidemiologic studies, more research is needed to identify other factors that may improve the predictions for muscle activities and postures.

A critical review on physical factors and functional characteristics that may explain a sex/gender difference in work-related neck/shoulder disorders

The objective of this paper is to critically review recent literature on physical and functional sex/gender (s/g) differences, with focus on physical determinants associated with neck/shoulder musculoskeletal injuries. It is well known that there are s/g differences in anthropometrical and functional body characteristics (e.g. size and strength). However, s/g differences may be wrongly attributed if data analysis does not include appropriate corrections (e.g. by strength for endurance). Recent literature on motor control shows that there may indeed be s/g differences in muscle coordination and movement strategies during upper limb tasks that are not currently explained by methodological inadequacies. Moreover, recent studies have shown differences between men and women in sensory hypersensitivity characteristics associated with neck/shoulder injuries. Taken together, the literature points to the importance of accounting for possible s/g differences at all levels of the biopsychosocial system in order to better understand sex- and gender-specific issues relevant to workplace health.

PRACTITIONER SUMMARY

This article critically reviews recent literature and a conceptual model highlighting s/g differences in physical and functional characteristics related to neck/shoulder musculoskeletal disorders (NSMSD). Findings have implications on understanding how personal factors may affect NSMSD risk. With better understanding, practitioners can make more appropriate decisions to prevent work-related NSMSD.

Increased physical work loads in modern work--a necessity for better health and performance?

Shifting workforce proportions to sedentary occupations and technology developments in traditionally physically demanding occupations have resulted in low physical workloads for many workers. Insufficient physical stress is known to have detrimental short- and long-term effects on health and physical capacity. It is argued herein that many modern workers are at risk of insufficient physical workload. Further, it is argued that the traditional physical ergonomics paradigm of reducing risk by reducing physical loads ('less is better') is not appropriate for many modern occupations. It is proposed that a new paradigm is required, where 'more can be better'. The potential for work to be seen as an arena for improving physical health and capability is discussed and the types of changes to work that may be required are outlined. The paper also discusses challenges and responsibilities presented by this new paradigm for ergonomists, employers, health and safety authorities and the community. The majority of workers in affluent communities now face the significant threat to health of insufficient physical workload. Ergonomics can design work to a prescription that can not only reduce injury risk but enhance health and capacity. However, this will require a change in paradigm.

Inertia artefacts and their effect on the parameterisation of keyboard reaction forces

Reaction force measurements collected during typing on keyboard trays contain inertia artefacts due to dynamic movements of the supporting work surface. To evaluate the effect of these artefacts, vertical forces and accelerations were measured while nine volunteers touch-typed on a rigid desk and a compliant keyboard tray. Two signal processing methods were evaluated: 1) low pass filtering with 20 Hz cut-off; 2) inertial force cancellation by subtracting the accelerometer signal. High frequency artefacts in the force signal, present on both surfaces, were eliminated by low pass filtering. Low frequency artefacts, present only when subjects typed on the keyboard tray, were attenuated by subtracting the accelerometer signal. Attenuation of these artefacts altered the descriptive statistics of the force signal by as much as 7%. For field measurements of typing force, reduction of low frequency artefacts should be considered for making more accurate comparisons across groups using work surfaces with different compliances. Direct measures of physical risk factors in the workplace can improve understanding of the aetiology of musculoskeletal disorders. Findings from this study characterise inertia artefacts in typing force measures and provide a method for eliminating them. These artefacts can add variability to measures, masking possible differences between subject groups.