Evaluating the low back biomechanics of three different office workstations: Seated, standing, and perching

Sitting versus standing work postures during simulated laparoscopic surgery: in terms of user preferences, comfort, performance and biomechanics

Prolonged standing in surgery has been linked to an increased risk of musculoskeletal disorders. The aim of this study was to determine whether sitting could serve as an alternative work posture in laparoscopic procedures. Twenty medical students in their third and fourth years were recruited. Sitting and standing were compared at two task complexity levels on a laparoscopic surgery simulator. Measured variables included user posture preferences, perceived discomfort, performance and biomechanics. Electromyography data from the upper trapezius and erector spinae muscles were analysed. Results showed that posture did not affect surgical performance and erector spinae muscle activation. Sitting showed higher muscle activation at the trapezius muscles; however, perceived discomfort was unaffected. Most participants preferred sitting for the difficult task and standing for the easy task. Findings showed that sitting, with appropriate seat design considerations, could serve as an alternative or even as a preferred work posture for simulated laparoscopic procedures.

A week-long field study of seated pelvis and lumbar spine kinematics during office work

The study objective was to quantify "natural" seated pelvis and lumbar spine kinematics over multiple days of work at individuals' workstations. Twenty participants completed five days of their usual office work while seated time was characterized from a thigh-worn activity monitor. Seated pelvic tilt and lumbar spine flexion-extension were measured from tri-axial accelerometers. Seated time accounted for approximately 90% of participants' workdays. Sitting was characterized by posterior pelvic tilt and lumbar flexion (43-79% of maximum flexion) with an average of 9 shifts and 13 fidgets every 15 min. No significant differences emerged by sex or between days indicating that a single representative day can capture baseline sitting responses in the field. Average field kinematics tended to agree with the laboratory-collected kinematics, but postural variability was larger in the field. These kinematic values could be useful for designing interventions aimed at reducing spine flexion and increasing spine movement in occupational sitting.

Traditional versus dynamic sitting: Lumbar spine kinematics and pain during computer work and activity guided tasks

Dynamic sitting may mitigate low back pain during prolonged seated work. The current study compared pelvis and lumbar spine kinematics, pain, and work productivity, in traditional and dynamic sitting. Sixteen participants completed three 20-min blocks of computer work and activity guided tasks in a traditional office chair or backless and multiaxial rotating seat pan while kinematics were measured from accelerometers on the low back. Pain ratings were recorded on a visual analogue scale every 10 min. Similar pelvis and lumbar kinematics emerged when performing computer work in traditional and dynamic sitting. Pelvis and lumbar sagittal and frontal plane shifts and fidgets were largest for dynamic sitting in the activity guided tasks. Buttocks pain was higher in dynamic sitting, but low back pain and work productivity were unaffected. Dynamic sitting increased spine movement during activity guided tasks, without negatively impacting lumbar kinematics, low back pain, or productivity during seated computer work.

Neck Muscle Coactivation Response to Varied Levels of Mental Workload During Simulated Flight Tasks

OBJECTIVE

To evaluate neck muscle coactivation across different levels of mental workload during simulated flight tasks.

BACKGROUND

Neck pain (NP) is highly prevalent among military aviators. Given the complex nature within the flight environment, mental workload may be a risk factor for NP. This may induce higher levels of neck muscle coactivity, which over time may accelerate fatigue, increase neck discomfort, and affect flight task performance.

METHOD

Three counterbalanced mental workload conditions represented by simulated flight tasks modulated by interstimulus frequency and complexity were investigated using the Modifiable Multitasking Environment (ModME). The primary measure was a neck coactivation index to describe the neuromuscular effort of the neck muscles as a system. Additional measures included perceived workload (NASA TLX), subjective discomfort, and task performance. Participants (n = 60; 30M, 30F) performed three test conditions over 1 hr each while seated in a simulated seating environment.

RESULTS

Neck coactivation indices (CoA) and subjective neck discomfort corresponded with increasing level of mental workload. Average CoAs for low, medium, and high workloads were: .0278(SD = .0232), .0286(SD = .0231), and .0295(SD = .0228), respectively. NASA TLX mental, temporal, effort, and overall scores also increased with the level of mental workload assigned. For ModME task performance, the overall performance score, monitoring accuracy, and resource management accuracy decreased while reaction times increased with the increasing level of mental workload. Communication accuracy was lowest with the low mental workload but had higher reaction times relative to increasing workload.

CONCLUSION

Mental workload affects neck muscle coactivation during combinations of simulated flight tasks within a simulated helicopter seating environment.

APPLICATION

The results of this study provide insights into the physical response to mental workload. With increasing multisensory modalities within the work environment, these insights may assist the consideration of physical effects from cognitive factors.

How are sex-gender differences in chair-and-desk-based postural variability explained? A scoping review

BACKGROUND

Desk-work-related musculoskeletal pain is more prevalent among female workers than male workers. This may be contributed to by sex and/or gender differences in postural variability however, the mechanisms underpinning these differences are poorly understood. This review investigates whether desk-based postural variability studies investigate sex-gender differences and, how they explain the mechanisms behind these differences.

METHODS

A scoping review was conducted with four databases (PubMed, Embase, Scopus and ProQuest) searched in June and July 2023. Studies investigating postural variability among desk-based workers were included and a narrative approach used to synthesise results.

RESULTS

15 studies were included. Only four reported on sex-gender differences. None collected psychological or social information to explore reasons for sex-gender differences.

CONCLUSION

The mechanisms behind postural variability differences between sexes and genders are complex and multifactorial. Studies largely do not consider sex and gender and do not collect the information necessary to explain their results.

Postural shifts and body perceived discomfort during 1-hour sitting when leaning and sitting on an air-filled seat cushion among healthy office workers

This study compared the number of postural shifts and perceived discomfort while leaning and sitting on an air-filled seat cushion for 1 hour. Sixty office workers typed a standard text while leaning on a cushion placed behind the low back, sitting on a cushion placed under the buttocks, and sitting without a cushion (a control condition). The number of postural shifts was collected using a seat pressure mat device. Low back discomfort was assessed using the Borg CR-10 scale. Leaning on a seat cushion (22 shifts/h) led to a significantly higher number of postural shifts than sitting on a seat cushion (18 shifts/h) and the control condition (20 shifts/h). Leaning or sitting on a seat cushion significantly decreased low back discomfort compared to the control condition (p < 0.05). Leaning on a seat cushion placed behind the low back may be an effective means of preventing low back pain among office workers.

Lateral Pelvis and Lumbar Motion in Seated and Standing Office Work and Their Association With Transient Low Back Pain

OBJECTIVE

To assess frontal plane motion of the pelvis and lumbar spine during 2 h of seated and standing office work and evaluate associations with transient low back pain.

BACKGROUND

Although bending and twisting motions are cited as risk factors for low back injuries in occupational tasks, few studies have assessed frontal plane motion during sedentary exposures.

METHODS

Twenty-one participants completed 2 h of seated and standing office work while pelvic obliquity, lumbar lateral bending angles, and ratings of perceived low back pain were recorded. Mean absolute angles were compared across 15-min blocks, amplitude probability distribution functions were calculated, and associations between lateral postures and low back pain were evaluated.

RESULTS

Mean pelvic obliquity (sit = 4.0 ± 2.8°, stand = 3.5 ± 1.7°) and lumbar lateral bending (sit = 4.5 ± 2.5°, stand = 4.1 ± 1.6°) were consistently asymmetrical. Pelvic obliquity range of motion was 4.7° larger in standing (13.6 ± 7.5°) than sitting (8.9 ± 8.7°). In sitting, 52% (pelvis) and 71% (lumbar) of participants, and in standing, 71% (pelvis and lumbar) of participants, were considered asymmetric for >90% of the protocol. Lateral postures displayed weak to low correlations with peak low back pain (R ≤ 0.388).

CONCLUSION

The majority of participants displayed lateral asymmetries for the pelvis and lumbar spine within 5° of their upright standing posture.

APPLICATION

In short-term sedentary exposures, associations between lateral postures and pain indicated that as the range in lateral postures increases there may be an increased possibility of pain.

Active workstations: A literature review on workplace sitting

The purpose of this paper is to further understand current literature on prolonged sitting, sitting posture and active sitting solutions. This paper is divided into three sections: The first section (Part I) is a comprehensive overview of the literature on how a static prolonged seated posture can affect: spinal health, trunk posture, contact pressure/discomfort development and vascular issues. The second section (Part II) reviews and qualitatively compares the four working postures recognized in ANSI/HFES 100-2007: reclined sitting, upright sitting, declined sitting and standing. The final section (Part III) is a summary of research on active chairs that revolves around the two types of movement patterns: 1- sustaining continual movement over a range of postures, occasionally reaching neutral lordosis, and 2- maintaining high frequency and duration of daily light contractile activity in the legs (or lower limbs).

Gender, Sex and Desk-Based Postural Behaviour: A systematic review re-interpreting biomechanical evidence from a social perspective

BACKGROUND

Biomechanical and pain prevalence differences between sex/gender groups are frequently attributed to biological differences between sexes without considering the influence of socially-constructed gender. This may lead to interventions which are insufficient and culturally unresponsive. This review reinterprets the evidence regarding differences in desk-based postural behaviour between sex/gender groups from a gender-based perspective.

METHODS

Four prominent databases were searched using terms such as 'desk based', 'posture', and 'position'. Articles were included if they objectively investigated desk-based positional variability, postural variability and/or habitual alignment in healthy adults.

RESULTS

Nine studies were included. Differences were found in postural variability and habitual alignment between sex/gender groups and were not explored from a gender-based perspective.

CONCLUSION

Gender-based expectations regarding 'acceptable' posture and movement likely contribute to biomechanical and pain differences between genders. This should be considered by clinicians intending to affect patients' movement and postural patterns and by researchers working in this space.

Alternative to Reduced Stresses on the Upper Extremity in a Standing Workstation

OBJECTIVE

This study evaluated a standing armrest to provide more acceptable ergonomic guidelines that may reduce the cost of standing computer workstations.

BACKGROUND

Of the many advantages of standing workstations, there have been no efforts to minimize the biomechanical cost, such as larger wrist extension and greater forearm muscle activity than sitting.

METHOD

Sixteen participants were asked to perform a typing task under a combination of the following factors: (1) desk shape (rectangular and concave); (2) desk height (0, +5, -5 cm from 90° elbow flexion); and (3) monitor height (0, -10 cm from the eyes). During the trials, the trunk kinematics, muscle activation levels, and CoP were recorded.

RESULTS

Both arms were further away from the upper body under the concave and +5 desk height than under the normal condition, but significant decreases in the extensor carpi radialis (8.6%), anterior deltoid (28.8%), and L4 paraspinals (5.5%) were observed. Similarly, the wrist extension angle decreased by 10.5° (42%) under this condition, but the posture required a 2.2° (19%) increase in wrist adduction angle. The CoP irregularity was greater under the concave workstation, indicating more complex motion.

CONCLUSION

A higher and concave desk can provide an armrest effect while engaged in a standing workstation by reducing the wrist extension and related muscle activation level, but at the cost of a larger wrist adduction angle.

APPLICATION

Providing a standing armrest (+5 cm height and concave desk) could reduce the stresses on the upper extremities, but a split keyboard should be considered to minimize wrist adduction.

Alterations in Physical Demands During Virtual/Augmented Reality-Based Tasks: A Systematic Review

The digital world has recently experienced a swift rise in worldwide popularity due to Virtual (VR) and Augmented Reality (AR) devices. However, concrete evidence about the effects of VR/AR devices on the physical workload imposed on the human body is lacking. We reviewed 27 articles that evaluated the physical impact of VR/AR-based tasks on the users using biomechanical sensing equipment and subjective tools. Findings revealed that movement and muscle demands (neck and shoulder) varied in seven and five studies while using VR, while in four and three studies during AR use, respectively, compared to traditional methods. User discomfort was also found in seven VR and three AR studies. Outcomes indicate that interface and interaction design, precisely target locations (gestures, viewing), design of virtual elements, and device type (location of CG as in Head-Mounted Displays) influence these alterations in neck and shoulder regions. Recommendations based on the review include developing comfortable reach envelopes for gestures, improving wearability, and studying temporal effects of repetitive movements (such as effects on fatigue and stability). Finally, a guideline is provided to assist researchers in conducting effective evaluations. The presented findings from this review could benefit designers/evaluations working towards developing more effective VR/AR products.

Increasing movement during office work at sit-stand workstations: A novel seating device to facilitate transitions

A novel active office chair (Movably Pro) was designed to facilitate frequent sit-stand movement 1) through auditory and tactile prompts and 2) with minimal-to-no work surface adjustment when transitioning. The purpose of this study was to compare lumbopelvic kinematics, discomfort, and task performance between the novel chair and traditional sitting/standing. Sixteen participants completed three separate 2-h sedentary exposures. Although participants transitioned every 3 min between sitting and standing with the novel chair, productivity was not affected. When standing in the novel chair, the lumbopelvic angles fell in between traditional sitting and standing (p < 0.01). Movement and/or postural changes that occurred with the novel chair reduced low back and leg discomfort for pain developers (PDs) (p < 0.01). All participants classified as PDs in traditional standing were non-PDs with the novel chair. This intervention was effective in reducing sedentary time without the time loss associated with desk movement.

Exploring the Interaction Between Head-Supported Mass, Posture, and Visual Stress on Neck Muscle Activation

OBJECTIVE

Assess neck muscle activity for varying interactions between helmet, posture, and visual stress in a simulated "helo-hunch" posture.

BACKGROUND

Military aviators frequently report neck pain (NP). Risk factors for NP include head-supported mass, awkward postures, and mental workload. Interactions between these factors could induce constant low-level muscle activation during helicopter flight and better explain instances of NP.

METHOD

Interactions between physical loading (helmet doffed/donned), posture (symmetric/asymmetric), and visual stress (low/high contrast) were studied through neck muscle electromyography (EMG), head kinematics, subjective discomfort, perceived workload, and task performance. Subjects (n = 16) performed eight 30-min test conditions (varied physical loading, posture, and visual stress) while performing a simple task in a simulated "helo-hunch" seating environment.

RESULTS

Conditions with a helmet donned had fewer EMG median frequency cycles (which infer motor unit rotation for rest/recovery, where more cycles are better) in the left cervical extensor and left sternocleidomastoid. Asymmetric posture (to the right) resulted in higher normalized EMG activity in the right cervical extensor and left sternocleidomastoid and resulted in less lateral bending compared with neutral across all conditions. Conditions with high visual stress also resulted in fewer EMG cycles in the right cervical extensor.

CONCLUSION

A complex interaction exists between the physical load of the helmet, postural stress from awkward postures, and visual stress within a simulated "helo-hunch" seating environment.

APPLICATION

These results provide insight into how visual factors influence biomechanical loading. Such insights may assist future studies in designing short-term administrative controls and long-term engineering controls.

Defining the lumbar and trunk-thigh neutral zone from the passive stiffness curve: application to hybrid sit-stand postures and chair design

Minimal data exist on the neutral position for the lumbar spine, trunk, and thighs when adopting a hybrid posture. This study examined sex differences in the neutral zone lumbar stiffness and the lumbar and trunk-thigh angle boundaries of the neutral zone, and determined if the standing lumbar angle fell within the neutral zone. Passive lumbar flexion and extension moment-angle curves were generated for 31 participants (13 M, 18 F), pooled from two datasets, with trunk-thigh angles available for 10 participants. The neutral zone was defined as the low stiffness zone from both the flexion and extension curves. Males demonstrated significantly greater extensor stiffness. Neutral lumbar and trunk-thigh angles ranged on average -22.2 to 0.2° and 124.2 to 159.6° for males and -17.8 to -1.3° and 143.2 to 159.5° for females, respectively. Standing lumbar angles fell outside the neutral zone for 44% of participants. These neutral zone boundaries may inform kinematics for hybrid chair designs.Practitioner summary: Adoption of a neutral spinal posture may be achieved through hybrid chair design, yet minimal data exists on a physiologically defined neutral zone. Using measures of in vivo lumbar stiffness, the lumbar and trunk-thigh angular boundaries of the neutral zone were defined for both males and females.Abbreviations: EMG: electromyography; MVC: maximal voluntary contraction.

Effects of Postural Shifting Frequency on Perceived Musculoskeletal Discomfort During 1-Hour Sitting in Office Workers

OBJECTIVE

The purpose of this study was to evaluate the effects of postural shifting frequency on perceived musculoskeletal discomfort during 1 hour of sitting in healthy office workers.

METHODS

An experimental study comparing 3 different postural shifting frequencies was conducted on 60 healthy office workers who were asked to sit for an hour. The effects of 3 postural shifts (ie, 10, 20, and 30 times/h) on discomfort, measured by Borg's CR-10 scale, were compared. A seat pressure mat was used to confirm an individual's postural shift.

RESULTS

Postural shifting frequency of 10 to 30 times/h had significant effects on perceived discomfort in the neck, shoulder, and upper and lower back during 1-hour sitting. At the neck and shoulder, a postural shifting frequency of 30 times/h significantly reduced perceived discomfort compared to a postural shifting frequency of 10 times/h during 1-hour sitting. At the upper and lower back, a postural shifting frequency of 20 to 30 times/h significantly reduced perceived discomfort compared to a postural shifting frequency of 10 times/h.

CONCLUSION

Postural shifts of 30 times/h provided buffering effects on perceived musculoskeletal discomfort at the neck, shoulder, and upper and lower back.

Innovative seated vertical lumbar traction allows simultaneous computer work while inducing spinal height changes similar to supine lying

BACKGROUND

Lumbar intervertebral disc height loss has been associated with spinal height change (SHC) and low back pain (LBP), including stenosis. Non-invasive methods to improve disc height loss require forms of lying down, which are unconducive to computer work.

OBJECTIVE

Intermittent vertical traction (VT) integrated with seated computer work may provide ergonomic alternatives for increasing SHC to promote LBP relief. The primary aim was to develop and introduce a safe VT prototype and dosage to induce and measure SHC. Prototype comfort and LBP ratings were exploratory secondary aims.

METHODS

Forty-one participants were stadiometry-measured for pre- and post-intervention SHC from seated VT at 35% body weight removed, supine lying (SL), and sitting at a computer (SIT) without VT. Pain ratings were recorded for those self-reporting LBP. VT prototype evaluations were compiled from a 3-question, 7-point Likert-style survey.

RESULTS

SHC increased by 3.9 ± 3.4 mm in VT, 1.7 ± 3.4 mm in SIT, and 4.3 ± 3.1 mm in SL (P< 0.000). Post hoc findings were significant between VT and SIT (P< 0.000), and SL and SIT (P< 0.000). VT and SL LBP ratings both decreased, but not SIT.

CONCLUSION

Intermittent seated VT is a promising alternative for postural relief during seated computer work, producing SHC similar to lying down without compromising workflow.

Evaluating the biomechanics of an in-between posture to create a multi-posture office environment

BACKGROUND

Prolonged sitting during work is common and has been shown to cause health issues. However, changing working postures has been reported to reduce musculoskeletal issues and impact other health issues; thus, there is a need for an office environment with multiple choices of working postures.

OBJECTIVE

The purpose of this study was to evaluate changes in body position, body loading, and blood perfusion while in a seated, standing, and new office seating position, termed the in-between position.

METHODS

Ground reaction forces, joint angles, pelvic tilt, openness angle (angle between the pelvis plane and thorax), and blood perfusion were evaluated for three positions. A motion capture system with markers was used to capture the position of anatomical landmarks. A six-axis force plate was used to collect the ground reaction forces, and a laser doppler perfusion monitor was used to obtain the blood perfusion.

RESULTS

Data showed that the in-between position articulated the hips, which provided a hip and lumbar position closer to a standing posture than a seated posture. The average vertical ground reaction force in the in-between position was larger than the seated position but significantly smaller than during standing (p < 0.0001). There were no significant differences in anterior/posterior ground reaction forces between the seated and the in-between positions (p = 0.4934). Lastly, blood perfusion increased during the dynamic transitions between positions indicating changes in blood flow.

CONCLUSION

The in-between position provides benefits of both standing (larger pelvic tilt and increased lumbar lordosis) and sitting (reduction in ground reaction forces).

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.

Impact of task variation and microbreaks on muscle fatigue at seated and standing postures

BACKGROUND

Prolonged and sustained work posture among computer users is one of the main factors that contributes to musculoskeletal discomfort. Rest-break interventions such as task variation and microbreaks may help prevent muscle fatigue and work-related musculoskeletal disorder.

OBJECTIVE

We aimed to investigate the effects of task variation and microbreaks at seated and standing workstations on forearm muscle activity, namely extensor digitorum communis, extensor carpi ulnaris, flexor digitorum superficialis, and flexor carpi ulnaris; mouse operation force (vertical compression force); mouse operation parameters; and perceived body discomfort during mouse operation.

METHODS

Twelve healthy right-handed young adults were recruited (male: n = 7, 21.6±1.4 years; female: n = 5, 21.4±1.7 years). Participants performed three blocks of computer tasks (computer mouse operation and typing) in both seated and standing postures with each block lasting for 30 min. Surface electromyography (EMG) of the forearm muscles and operation force were monitored during computer mouse operation. Body discomfort rating was recorded at the end of each block.

RESULTS

With simulated task variation and microbreaks, work posture and work time showed no significant difference with EMG amplitude and mouse operation force.

CONCLUSION

Task variation and microbreaks could be of benefit to computer users by reducing muscle fatigue during long hours of computer work at both seated and standing workstations.

Computational lumbar spine models: A literature review

BACKGROUND

Computational spine models of various types have been employed to understand spine function, assess the risk that different activities pose to the spine, and evaluate techniques to prevent injury. The areas in which these models are applied has expanded greatly, potentially beyond the appropriate scope of each, given their capabilities. A comprehensive understanding of the components of these models provides insight into their current capabilities and limitations.

METHODS

The objective of this review was to provide a critical assessment of the different characteristics of model elements employed across the spectrum of lumbar spine modeling and in newer combined methodologies to help better evaluate existing studies and delineate areas for future research and refinement.

FINDINGS

A total of 155 studies met selection criteria and were included in this review. Most current studies use either highly detailed Finite Element models or simpler Musculoskeletal models driven with in vivo data. Many models feature significant geometric or loading simplifications that limit their realism and validity. Frequently, studies only create a single model and thus can't account for the impact of subject variability. The lack of model representation for certain subject cohorts leaves significant gaps in spine knowledge. Combining features from both types of modeling could result in more accurate and predictive models.

INTERPRETATION

Development of integrated models combining elements from different model types in a framework that enables the evaluation of larger populations of subjects could address existing voids and enable more realistic representation of the biomechanics of the lumbar spine.

The biomechanical benefits of active sitting

This cross-sectional study examined the biomechanical effects of two active chairs (AC1: had the feature to pedal and slide forward on the seat pan; AC2: a multiaxial motion seat pan) compared to a traditional office chair and standing workstation. Twenty-four healthy participants worked at each of the workstations for 60-min. The following equipment was used: Motion Capture, Electromyography, Ratings of Perceived Discomfort Questionnaire, and Exit Survey. The active protocol had positive effects on the body, including increased neuromuscular activity in the gastrocnemius, increased overall movement, and a more open trunk-thigh angle. Greater discomfort in the buttocks due to the lack of seat pan contour was reported for the AC1 which identified a need for a design modification. While standing, participants' shoulders were less flexed than when sitting in any of the three seats, however, greater discomfort was reported in the lower legs after 1 h of computer work. Practitioner summary: A comparison of four different workstations was conducted to further understand the use of active workstations. Active sitting was found to have positive effects on the body, such as allowing sitters to increase movement while sitting without the high activation of muscular activity. Standing can also provide a positive break from sitting.

The Effects of Standing Working Posture on Operation Force and Upper Limb Muscle Activation When Using Different Pointing Devices

This study investigated how sitting and standing working postures affected operation force, upper limb muscle activation, and task performance using different pointing devices. Fifteen male participants completed cursor aiming and dragging tasks using a conventional mouse, a vertical mouse, and a trackball at sitting and standing workstations. A custom-made force plate was used to measure operation forces applied to the pointing devices. Surface electromyography (EMG) was used to capture the activation of the biceps brachii, triceps brachii, deltoid, and trapezius. Task performance was measured by task success rates, and subjective ratings were obtained for the force required for operation, smoothness of operation, accuracy, and local fatigue in the upper limb. We quantified the following significant outcomes: (1) greater operation forces were found when standing; (2) standing reduced EMG amplitudes of the triceps and trapezius muscles for all tasks; (3) during the aiming task, the vertical mouse had greater operation forces; (4) during the dragging task, both the vertical mouse and trackball had greater operation forces; and (5) task success rates differed for pointing devices only when sitting. This study revealed the distinct biomechanical properties of standing working posture and suggested limited beneficial effects of alternative pointing devices in terms of task performance and subjective ratings.

Local dynamic stability of the trunk after prolonged seating with axial load

Fatigue from prolonged seating with an axial load on the trunk may impair neuromuscular control and spine stability which may elevate risk of low back pain (LBP) for dynamic tasks following seating. The objective of this study was to assess local dynamic trunk stability using the maximum Lyapunov exponent (λ_MAX) with corresponding coactivation patterns to understand possible effects from prolonged seating. An increase in λ_MAX would indicate decreased stability. Twenty participants (10 male, 10 female) performed a controlled, cyclic sagittal flexion task at 40 cycles per minute before and after three hours of seating in a simulated helicopter-seating environment with a weighted vest. A statistically significant decrease was seen in λ_MAX (bits/s) (Pre-Test = 0.654 ± 0.172; Post-Test = 0.829 ± 0.268, p = 0.002), trunk cumulative coactivation index (unitless/s) (Pre-Test = 1.71 ± 0.97; Post-Test = 1.59 ± 0.96, p = 0.0095), and abdominal activation (normalized) (Pre-Test = 0.46 ± 0.17, Post-Test = 0.41 ± 0.18, p = 0.0146) post-seating exposure. Trunk extension was reduced (∼4°, p = 0.0004) during the post-seating cyclic test with slight corresponding increases in flexion. This study provides evidence of potential effects of fatigue from prolonged seating to neuromuscular control, which may have implications for occupations requiring highly dynamic tasks after prolonged seated postures. Future studies would repeat the tests with dynamic environments (i.e., vibration), test the cyclic flexion protocols with different seating interventions, and continue to test the approach to develop a tool to assess back impairment or intervention effectiveness.

A Systematic Review on Evaluation Strategies for Field Assessment of Upper-Body Industrial Exoskeletons: Current Practices and Future Trends

With rising manual work demands, physical assistance at the workplace is crucial, wherein the use of industrial exoskeletons (i-EXOs) could be advantageous. However, outcomes of numerous laboratory studies may not be directly translated to field environments. To explore this discrepancy, we conducted a systematic review including 31 studies to identify and compare the approaches, techniques, and outcomes within field assessments of shoulder and back support i-EXOs. Findings revealed that the subjective approaches [i.e., discomfort (23), usability (22), acceptance/perspectives (21), risk of injury (8), posture (3), perceived workload (2)] were reported more common (27) compared to objective (15) approaches [muscular demand (14), kinematics (8), metabolic costs (5)]. High variability was also observed in the experimental methodologies, including control over activity, task physics/duration, sample size, and reported metrics/measures. In the current study, the detailed approaches, their subject-related factors, and observed trends have been discussed. In sum, a new guideline, including tools/technologies has been proposed that could be utilized for field evaluation of i-EXOs. Lastly, we discussed some of the common technical challenges experimenters face in evaluating i-EXOs in field environments. Efforts presented in this study seek to improve the generalizability in testing and implementing i-EXOs.

Use of an inflatable mat to reduce body discomfort development when performing computer work at a standing desk

This study aimed to determine the effects of inflatable mat design on body discomfort, task performance, and musculoskeletal exposures during standing computer work. Twenty-seven healthy adults completed three 2-hour standing trials on different mediums (concrete floor, foam mat, and inflatable mat) on different days in an experimental laboratory. Both mats were associated with reduced discomfort in all lower-body regions and increased typing performance compared to the concrete floor. Perceived discomfort in lower extremities (except thighs) was further alleviated while standing on the inflatable mat than on the foam mat. Use of the inflatable mat led to increased lower-body muscle activity, a flexed lower back, and a wide range of sagittal knee movements. As standing time increased, body discomfort increased, typing accuracy decreased, and there were increased variations in muscle activity and postural movements in the lower body. The inflatable mat shows potential to improve the ergonomic experience during prolonged standing. Practitioner summary: Incorporating standing postures in office-based workplaces can reduce sitting time and may mitigate the health hazards associated with sedentary behaviour. With adequate weight-shifting movements, using an inflatable mat for standing could be an effective way to lessen discomfort and accumulated musculoskeletal strain due to constrained standing, without jeopardising task productivity. Abbreviations: APDF: amplitude probability distribution function. AVR: average rectified value. CI: confidence interval. CMRR: common mode rejection ratio. COP: center of pressure. CV: coefficient of variation. EA: electrical activity. EMG: electromyography. FL: fibularis longus. GM: gluteus medius. LBP: lower back pain. LES: lumbar erector spinae. MVC: maximum voluntary contraction. PD: pain developer. rANOVA: repeated-measures analysis of variance. SOL: soleus. VAS: visual analog scale. WPM: words per minute.

An innovative sit-standing seat in urban buses: A new design to prevent falls and non-collision injuries

BACKGROUND: Due to the rapid growth of metropolises and the insufficiency of public transportation, nowadays, many people travel on these vehicles in a standing position. This position leads to discomfort and the risk of falling or non-collision incidents for the passengers. OBJECTIVE: The present study was conducted to analyze an innovative sit-standing seat to prevent falls and non-collision injuries in standing passengers. METHODS: A total of sixteen participated in this study. EMG signal and Borg scale were used to assess muscle activity and discomfort, respectively. RESULTS: The mean Borg scale score for perceived discomfort was lower in the sit-standing position than the standing position in all body organs, except for the hips. Also, in the sit-standing position compared to the standing position, the muscle activity of the soleus and medial gastrocnemius muscles was significantly lower in the constant velocity and entire phases in both legs, lower in the right leg in the acceleration phase and lower in the left leg in the deceleration phase. CONCLUSIONS: So, this seat can be used as an innovative idea to improve the ergonomic condition of standing passengers to prevent falls and non-collision injuries on transit buses.

Schedules of standing and sitting directed by musculoskeletal discomfort in workers transitioning to sit-stand workstations: a cross-sectional study

Sit-stand workstations are growing in popularity, however limited guidelines exist regarding optimal schedules of sitting and standing. This was the first known study to observe sit-stand workstation schedules when postural change is based on maintaining musculoskeletal discomfort within 'acceptable' levels. Fourteen healthy adults new to sit-stand workstations completed computer-based work at a sit-stand desk for half a workday. Participants changed between standing and sitting postures each time discomfort reached the maximum acceptable threshold. On average, the amount of standing and sitting was greatest in the first standing (median 40 minutes, interquartile range 40 minutes) and sitting (median 30 minutes, interquartile range 115 minutes) bouts. Average durations spent standing and sitting were lower in all consecutive bouts. Stand-sit ratios indicated an equal amount of standing to sitting or somewhat less standing. The schedules had substantial inter-participant variability. Future studies should consider that optimal schedules may vary with regard to time and be individual-specific.

Different sit:stand time ratios within a 30-minute cycle change perceptions related to musculoskeletal disorders

Regular standing interruptions to sedentary work are recommended, but their dosage is understudied. To measure perception variations associated with different sit:stand ratios, 16 people used six ratios (30:0, 27:3, 24:6, 21:9, 18:12 and 15:15) within 30-min cycles in their normal office environment. At start and end of each workday, study participants recorded their perception of 11 factors on a 10-point scale. Musculoskeletal discomfort in 10 body regions was measured before and after exposure to sit-stand ratios. Overall preferred ratios were recorded. Sit:stand ratio affected all perceived factors, with impact varying. Standing at least 6 min improved results most overall; however, individual perceived factors were least impacted by any of 30:0, 27:3, 24:6 or 21:9. Preferred sit:stand ratios were 15:15, 18:12 and 21:9. Typically, least liked ratios involved briefest standing (30:0, 27:3, 24:6) although two participants least liked 15:15. Understanding these variations contributes to appropriate standing dosage recommendations.

Determining the interactions between postural variability structure and discomfort development using nonlinear analysis techniques during prolonged standing work

PURPOSE

Nonlinear analysis techniques provide a powerful approach to explore dynamics of posture-related time-varying signals. The aim of this study was to investigate the fundamental interactions between postural variability structure and discomfort development during prolonged standing.

METHODS

Twenty participants, with equal distribution for gender and standing work experience (SWE), completed a simulated long-term standing test. Low back and legs discomfort, center of pressure, lumbar curvature, and EMG activity of trunk and leg muscles were monitored. Nonlinear measures including largest lyapunov exponent, multi-scale entropy, and detrended fluctuation analysis were applied to characterize the variability structure (i.e., complexity) in each signal. The size (i.e., amount) of variability was also computed using traditional linear metrics.

RESULTS

With progress of low back and legs discomfort over standing periods, significant lower levels were perceived by the participants having SWE. The amount of variability in all signals (except external oblique EMG activity) were significantly increased with the time progress for all participants. The structure of variability in most signals demonstrated a lower complexity (more regularity) with fractal properties that deviated from 1/f noise. The SWE group showed a higher complexity levels.

CONCLUSIONS

Overall, the findings verified variations in structure and amount of the postural variability. However, nonlinear analysis identified postural strategies according to the perceived discomfort in a different way. These results provide supports for future application of nonlinear tools in evaluating standing tasks and related ergonomics interventions as it allows further insight into how discomfort development impact the structure of postural changes.

The effects of prolonged sitting, standing, and an alternating sit-stand pattern on trunk mechanical stiffness, trunk muscle activation and low back discomfort

Sit-stand desks continue to be a popular intervention for office work. While previous studies have reported changes in subjective measures, there is limited understanding of how sit-stand work differs from prolonged sitting or standing work, from a biomechanical standpoint. The objective of this study was to investigate the effects of prolonged sitting, prolonged standing, and a sit-stand paradigm on changes in trunk stiffness, low back discomfort, and trunk muscle activation. Twelve healthy participants performed 2 h of computer-based tasks in each protocol, on three different days. The sit-stand protocol was associated with a significant increase in trunk stiffness and a decrease in muscle activation of lumbar multifidus and longissimus thoracis pars thoracis, compared to both prolonged sitting and standing. Both sitting and standing were associated with increased low back discomfort. These findings may be worth exploring in more detail, for why alternating sit-stand patterns may help alleviate low back pain. Practitioner summary: We explored changes in objective and subjective measures related to low back discomfort following prolonged sitting, standing, and alternating sit-stand patterns. Alternating sit-stand pattern was associated with increased trunk stiffness and decreased back muscle activity. Hence, sit-stand desks may have benefits in terms of preventing/mitigating low back pain. Abbreviations: DOF: degree of freedom; EMG: electromyogram; ILL: iliocostalis lumborum pars lumborum; LTL: longissimus thoracis pars lumborum; LTT: longissimus thoracis pars thoracis; LBP: low back pain; LM: lumbar multifidus; MVEs: maximum isometric voluntary exertions; RANOVA: repeated-measure analysis of variance; RMS: root mean square.

Effects of Prolonged Sitting with Slumped Posture on Trunk Muscular Fatigue in Adolescents with and without Chronic Lower Back Pain

Background and Objectives: This study investigated the effects of prolonged sitting on trunk muscular fatigue and discomfort in participants with and without chronic lower back pain (LBP). Material and Methods: This study included 15 patients with LBP and 15 healthy controls. All participants were instructed to sit on a height-adjustable chair with their knee and hip joints bent at 90° for 30 min, in slumped sitting postures. Surface electromyography was used to assess the median frequency of the internal obliques (IO)/transversus abdominis (TrA) and multifidus (MF) muscles. Perceived discomfort was measured using a Borg category ratio-scale. Median frequency of the trunk muscles and perceived discomfort after 30 min of sitting were compared with baseline. Result: There were no significant differences within the group and between both groups in the median frequency of bilateral IO and MF muscles. The LBP group showed significantly greater perceived discomfort after prolonged sitting, as compared to the control group. Conclusions: Prolonged sitting with slumped posture could increase the risk of experiencing lower back discomfort.

Does objectively measured prolonged standing for desk work result in lower ratings of perceived low back pain than sitting? A systematic review and meta-analysis

BACKGROUND

Prolonged sitting has been shown to induce transient low back pain (LBP). Height adjustable office desks now present the opportunity to replace sitting with standing in the workplace. Since standing has also been associated with LBP, this may not be an advisable alternative.

OBJECTIVE

To determine if objectively measured prolonged exposures to desk work while standing, compared to sitting, results in lower perceived LBP in healthy adults.

METHODS

A systematic search of several databases was conducted. Two independent reviewers screened titles/abstracts and conducted a quality assessment. The results of three studies were pooled using an inverse variance random-effects meta-analysis. Heterogeneity was tested using the Chi-squared test and I2 statistic.

RESULTS

Objectively measured prolonged standing postures during desk work did not induce significantly less perceived LBP compared to seated postures (standardized mean difference 0.60, 95% CI -0.68 to 1.87, p = 0.36.) There was significant heterogeneity, I2 = 90%).

CONCLUSIONS

It appears that replacing seated desk work postures with standing for prolonged periods of time would not be recommended. Larger studies, including a wider age range and health history, conducted in the field with objective measures is recommended to obtain more generalizable data on which to base ergonomic standards for work postures.

The effect of aircraft seat pitch on comfort

This study explores the relationship between seat pitch and comfort, and the influencing factors, like space experience and anthropometric measurements. Two hundred ninety-four participants experienced economy class seats in a Boeing 737 with 28-inch, 30-inch, 32-inch and 34-inch seat pitches. Anthropometric measurements of the participants were measured. Participants completed a questionnaire on comfort (10-scale), discomfort (CP-50) and space experience and the results were analysed using SPSS 25. This study showed a significant relationship between seat pitch and comfort as well as discomfort. Additionally, it was found that the mean rank of discomfort of each pitch size for the middle seat was higher than the window and aisle seat, though seat pitch did affect the (dis)comfort more compared with seat location. It was also found that anthropometric sizes significantly affect the (dis)comfort on smaller pitch sizes, and all space experience questions had a correlation to the pitch sizes.

The musculoskeletal and cognitive effects of under-desk cycling compared to sitting for office workers

Alternate work positions are being considered as a way to address sedentary behaviour for office workers. This study evaluated the effect of two hours of just-sitting versus sitting while under-desk cycling on musculoskeletal discomfort and cognitive function (sustained attention and creative problem solving). To consider mechanisms, muscle fatigue, kinematics and mental state were also measured. Discomfort increased significantly across all body areas with knee and ankle discomfort greater (in a clinically meaningful manner) in under-desk cycling. Sustained attention reaction time was the only cognitive measure to show a difference between conditions (slower for under-desk cycling [β-34.82 CI (-62.12 to -7.53)]). There was no evidence of muscle fatigue, while kinematic differences between conditions were identified. Mental state deteriorated over time in both conditions. This study found no clear benefit of under-desk cycling compared to just-sitting for musculoskeletal health and cognitive function measures.

The effect of sit-stand desks on office worker behavioral and health outcomes: A scoping review

This scoping review examines the effects of sit-stand desks (SSDs) on six domains: behavior (e.g. time sitting and standing), physiological, work performance, psychological, discomfort, and posture. Fifty-three articles met criteria. We determined the percentage of significant results for each domain. Forty-seven studies were experimental trials. Sample sizes ranged from six to 231 participants. Follow-up time-frames ranged from one day to one year. Sixty-one percent of behavioral (24 studies), 37% of physiological (28 studies), 7% of work performance (23 studies), 31% of psychological (11 studies), 43% of discomfort (22 studies), and 18% of posture domain results (4 studies) were significant. We conclude that SSDs effectively change behaviors, but these changes only mildly effect health outcomes. SSDs seem most effective for discomfort and least for productivity. Further study is needed to examine long-term effects, and to determine clinically appropriate dosage and workstation setup.

Are hybrid sit-stand postures a good compromise between sitting and standing?

Potential alternatives for conventional sitting and standing postures are hybrid sit-stand postures (i.e. perching). The purposes of this study were (i) to identify where lumbopelvic and pelvic angles deviate from sitting and standing and (ii) to use these breakpoints to define three distinct postural phases: sitting, perching, and standing, in order to examine differences in muscle activations and ground reaction forces between phases. Twenty-four participants completed 19 1-min static trials, from sitting (90°) to standing (180°), sequentially in 5°trunk-thigh angle increments. The perching phase was determined to be 145-175° for males and 160-175° for females. For both sexes, knee extensor activity was lower in standing compared to perching or sitting (p < .01). Anterior-posterior forces were the highest in perching (p < .001), requiring ∼15% of body-weight. Chair designs aimed at reducing the lower limb demands within 115-170° trunk-thigh angle may improve the feasibility of sustaining the perched posture. Practitioner summary: Individuals who develop low back pain in sitting or standing may benefit from hybrid sit-stand postures (perching), yet kinematic and kinetic changes associated with these postures have not been investigated. Perching can improve lumbar posture at a cost of increased lower limb demands, suggesting potential avenues for chair design improvement. Abbreviations: A/P: anterior-posterior; M/L: medial-lateral; LBP: low back pain; EMG: electromyography; TES: thoracic erector spinae; LES: lumbar erector spinae; VMO: vastus medialis obliquus; MVC: maximum voluntary contraction; ASIS: anterior superior iliac spine; PSIS: posterior superior iliac spine; BW: body weight; RMSE: root mean square error; SD: standard deviation; ROM: range of motion.

The effects of sedentary behaviour interventions on work-related productivity and performance outcomes in real and simulated office work: A systematic review

This review examined the impact of environmental, behavioral, and combined interventions to reduce occupational sedentary behaviour on work performance and productivity outcomes. Productivity outcomes were defined as variables assessing work-related tasks (e.g., typing, mouse), whereas performance outcomes were categorized as any variables assessing cognition that did not mimic work-related tasks. Nine databases were searched for articles published up to January 2018. Sixty-three studies were identified that met the inclusion criteria: 45 examined a productivity outcome (i.e., typing, mouse, work-related tasks, and absenteeism), 38 examined a performance outcome (i.e., memory, reading comprehension, mathematics, executive function, creativity, psychomotor function, and psychobiological factors), and 30 examined a self-reported productivity/performance outcome (i.e., presenteeism or other self-reported outcome). Overall, standing interventions do not appear to impact productivity/performance outcomes, whereas walking and cycling interventions demonstrate mixed null/negative associations for productivity outcomes. Hence, standing interventions to reduce occupational sedentary behaviour could be implemented without negatively impacting productivity/performance outcomes.

Comfort evaluation of a subject-specific seating interface formed by vibrating grains

Sitting is the most common posture for work in offices, and spinal cord injury (SCI) patients who are wheelchair dependent spend 10.6 h per day seated in wheelchairs. Thus, the comfort of subject-specific interfaces is increasingly important for the well-being of patients and office workers. This paper introduces a new method of forming a subject-specific interface, based on vibrating grains. Twenty subjects (10 females and 10 males) participated in the sitting test. Interface comfort was evaluated using the pressure distribution and subjective rating methods. Five seating interface types were compared. The results showed that compared with a flat interface, the interfaces formed by vibrating grains had a significantly reduced peak contact pressure (PeakCP) (by more than 58.03%), and that PeakCP was highly correlated with the comfort rating (R = -0.533) and discomfort rating(R = -0.603). This new method shows promise for guiding the future development of customized seating interfaces.

The Short Term Musculoskeletal and Cognitive Effects of Prolonged Sitting During Office Computer Work

Office workers are exposed to high levels of sedentary time. In addition to cardio-vascular and metabolic health risks, this sedentary time may have musculoskeletal and/or cognitive impacts on office workers. Participants (n = 20) undertook two hours of laboratory-based sitting computer work to investigate changes in discomfort and cognitive function (sustained attention and problem solving), along with muscle fatigue, movement and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.43 [1.33–1.53]) reaching clinically meaningful levels in the low back and hip/thigh/buttock areas. Creative problem solving errors increased (β = 0.25 [0.03–1.47]) while sustained attention did not change. There was no change in erector spinae, trapezius, rectus femoris, biceps femoris and external oblique median frequency or amplitude; low back angle changed towards less lordosis, pelvis movement increased, and mental state deteriorated. There were no substantial correlations between discomfort and cognitive function. The observed changes suggest prolonged sitting may have consequences for musculoskeletal discomfort and cognitive function and breaks to interrupt prolonged sitting are recommended.

A detailed description of the short-term musculoskeletal and cognitive effects of prolonged standing for office computer work

Due to concerns about excessive sedentary exposure for office workers, alternate work positions such as standing are being trialled. However, prolonged standing may have health and productivity impacts, which this study assessed. Twenty adult participants undertook two hours of laboratory-based standing computer work to investigate changes in discomfort and cognitive function, along with muscle fatigue, movement, lower limb swelling and mental state. Over time, discomfort increased in all body areas (total body IRR [95% confidence interval]: 1.47[1.36-1.59]). Sustained attention reaction time (β = 18.25[8.00-28.51]) deteriorated, while creative problem solving improved (β = 0.89[0.29-1.49]). There was no change in erector spinae, rectus femoris, biceps femoris or tibialis anterior muscle fatigue; low back angle changed towards less  lordosis, pelvis movement increased, lower limb swelling increased and mental state decreased. Body discomfort was positively correlated with mental state. The observed changes suggest replacing office work sitting with standing should be done with caution. Practitioner Summary: Standing is being used to replace sitting by office workers; however, there are health risks associated with prolonged standing. In a laboratory study involving 2 h prolonged standing discomfort increased (all body areas), reaction time and mental state deteriorated while creative problem-solving improved. Prolonged standing should be undertaken with caution.

Implementation of Active Workstations in University Libraries-A Comparison of Portable Pedal Exercise Machines and Standing Desks

Sedentary behaviors are an important issue worldwide, as prolonged sitting time has been associated with health problems. Recently, active workstations have been developed as a strategy to counteract sedentary behaviors. The present study examined the rationale and perceptions of university students’ and staff following their first use of an active workstation in library settings. Ninety-nine volunteers completed a self-administered questionnaire after using a portable pedal exercise machine (PPEM) or a standing desk (SD). Computer tasks were performed on the SD (p = 0.001) and paperwork tasks on a PPEM (p = 0.037) to a larger extent. Men preferred the SD and women chose the PPEM (p = 0.037). The appreciation of the PPEM was revealed to be higher than for the SD, due to its higher scores for effective, useful, functional, convenient, and comfortable dimensions. Younger participants (<25 years of age) found the active workstation more pleasant to use than older participants, and participants who spent between 4 to 8 h per day in a seated position found active workstations were more effective and convenient than participants sitting fewer than 4 h per day. The results of this study are a preliminary step to better understanding the feasibility and acceptability of active workstations on university campuses.

The impact of office chair features on lumbar lordosis, intervertebral joint and sacral tilt angles: a radiographic assessment

BACKGROUND

The purpose of this study was to determine which office chair feature is better at improving spine posture in sitting.

METHOD

Participants (n = 28) were radiographed in standing, maximum flexion and seated in four chair conditions: control, lumbar support, seat pan tilt and backrest with scapular relief. Measures of lumbar lordosis, intervertebral joint angles and sacral tilt were compared between conditions and sex.

RESULTS

Sitting consisted of approximately 70% of maximum range of spine flexion. No differences in lumbar flexion were found between the chair features or control. Significantly more anterior pelvic rotation was found with the lumbar support (p = 0.0028) and seat pan tilt (p < 0.0001). Males had significantly more anterior pelvic rotation and extended intervertebral joint angles through L1-L3 in all conditions (p < 0.0001).

CONCLUSION

No one feature was statistically superior with respect to minimising spine flexion, however, seat pan tilt resulted in significantly improved pelvic posture. Practitioner Summary: Seat pan tilt, and to some extent lumbar supports, appear to improve seated postures. However, sitting, regardless of chair features used, still involves near end range flexion of the spine. This will increase stresses to the spine and could be a potential injury generator during prolonged seated exposures.

A biomechanical and physiological study of office seat and tablet device interaction

Twenty subjects performed typing tasks on a desktop computer and touch-screen tablet in two chairs for an hour each, and the effects of chair, device, and their interactions on each dependent measure were recorded. Biomechanical measures of muscle force, spinal load, and posture were examined, while discomfort was measured via heart rate variability (HRV) and subjective reports. HRV was sensitive enough to differentiate between chair and device interactions. Biomechanically, a lack of seat back mobility forced individuals to maintain an upright seating posture with increased extensor muscle forces and increased spinal compression. Effects were exacerbated by forward flexion upon interaction with a tablet device or by slouching. Office chairs should be designed with both the human and workplace task in mind and allow for reclined postures to off-load the spine. The degree of recline should be limited, however, to prevent decreased lumbar lordosis resulting from posterior hip rotation in highly reclined postures.