A comparison of trunk biomechanics,musculoskeletal discomfort and productivity during simulated sit-stand office work

Sedentary office work has been shown to cause low back discomfort and potentially cause injury. Prolonged standing work has been shown to cause discomfort. The implementation of a sit–stand paradigm is hypothesised to mitigate discomfort and prevent injury induced by prolonged exposure to each posture in isolation. This study explored the potential of sit–stand to reduce discomfort and prevent injury, without adversely affecting productivity. Twenty-four participants performed simulated office work in three different conditions: sitting, standing and sit–stand. Variables measured included: perceived discomfort, L4–L5 joint loading and typing/mousing productivity. Working in a sit–stand paradigm was found to have the potential to reduce discomfort when compared to working in a sitting or standing only configuration. Sit–stand was found to be associated with reduced lumbar flexion during sitting compared to sitting only. Increasing lumbar flexion during prolonged sitting is a known injury mechanism. Therefore, sit–stand exhibited a potentially beneficial response of reduced lumbar flexion that could have the potential to prevent injury. Sit–stand had no significant effect on productivity.

Practitioner Summary: This study has contributed foundational elements to guide usage recommendations for sit–stand workstations. The sit–stand paradigm can reduce discomfort; however, working in a sit–stand ratio of 15:5 min may not be the most effective ratio. More frequent posture switches may be necessary to realise the full benefit of sit–stand.     

A randomised control trial of the cognitive effects of working in a seated as opposed to a standing position in office workers

Sedentary behaviour is increasing and has been identified as a potential significant health risk, particularly for desk-based employees. The development of sit-stand workstations in the workplace is one approach to reduce sedentary behaviour. However, there is uncertainty about the effects of sit-stand workstations on cognitive functioning. A sample of 36 university staff participated in a within-subjects randomised control trial examining the effect of sitting vs. standing for one hour per day for five consecutive days on attention, information processing speed, short-term memory, working memory and task efficiency. The results of the study showed no statistically significant difference in cognitive performance or work efficiency between the sitting and standing conditions, with all effect sizes being small to very small (all ds < .2). This result suggests that the use of sit-stand workstations is not associated with a reduction in cognitive performance.

Practitioner Summary: Although it has been reported that the use of sit-stand desks may help offset adverse health effects of prolonged sitting, there is scant evidence about changes in productivity. This randomised control study showed that there was no difference between sitting and standing for one hour on cognitive function or task efficiency in university staff.     

Associations of office workers’ objectively assessed occupational sitting,standing and stepping time with musculoskeletal symptoms

We examined the association of musculoskeletal symptoms (MSS) with workplace sitting, standing and stepping time, as well as sitting and standing time accumulation (i.e. usual bout duration of these activities), measured objectively with the activPAL3 monitor. Using baseline data from the Stand Up Victoria trial (216 office workers, 14 workplaces), cross-sectional associations of occupational activities with self-reported MSS (low-back, upper and lower extremity symptoms in the last three months) were examined using probit regression, correcting for clustering and adjusting for confounders. Sitting bout duration was significantly (p < 0.05) associated, non-linearly, with MSS, such that those in the middle tertile displayed the highest prevalence of upper extremity symptoms. Other associations were non-significant but sometimes involved large differences in symptom prevalence (e.g. 38%) by activity. Though causation is unclear, these non-linear associations suggest that sitting and its alternatives (i.e. standing and stepping) interact with MSS and this should be considered when designing safe work systems.

Practitioner summary: We studied associations of objectively assessed occupational activities with musculoskeletal symptoms in office workers. Workers who accumulated longer sitting bouts reported fewer upper extremity symptoms. Total activity duration was not significantly associated with musculoskeletal symptoms. We underline the importance of considering total volumes and patterns of activity time in musculoskeletal research.     

The effect of age on in-vivo spine stiffness,postures and discomfort responses during prolonged sitting exposures

Many industrialised working populations are ageing and prolonged sitting exposures are prevalent across occupational sectors. The purpose of this work was to determine the effect of age and sex on passive spine stiffness, postures and discomfort in response to seated work. A total of 34 participants were recruited, with 17 older adults with an average age of (standard deviation) 63.7 (±3.9) years and 17 younger adults aged 23.8 (±5.0) years. Participants were asked to sit continuously for 90?min while typing. Baseline passive spine stiffness was higher in older adults at 40% flexion compared to younger adults (p?=?.0233). Older adults sat in less normalised flexion, at 33.4% (±16.4) compared to 60.9% (±20.2) in the younger group (p?=?.0003). Discomfort was higher among older adults in the neck, right shoulder and middle back regions (p?<?.0086). An understanding of age-specific responses to workplace exposures is essential to determine whether age-specific interventions are warranted.

 

Practitioner summary: Older adults had higher passive spine stiffness and sat with less flexion during prolonged sitting. Discomfort was higher among older adults and occurred earlier in the simulation compared to younger participants, indicating that interventions, such as walking breaks may need to be implemented earlier during sitting for aged workers.     

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     

A comfort assessment of existing cervical orthoses

Purpose: Identify location and intensity of discomfort experienced by healthy participants wearing cervical orthoses.

Method: Convenience sample of 34 healthy participants wore Stro II, Philadelphia, Headmaster, and AspenVista^® cervical orthoses for four-hour periods. Participants reported discomfort level (scale 0–6) and location.

Results: Participants reported mean discomfort for all orthoses over the four-hour test between ‘a little discomfort’ and ‘very uncomfortable’ (mean discomfort score = 1.64, SD = 1.50). Seven participants prematurely stopped tests due to pain and six reported maximum discomfort scores. Significant linear increase in discomfort with duration of wear was found for all orthoses. Significantly less discomfort was reported with Stro II than Headmaster and Philadelphia. Age correlated with greater perceived discomfort. Orthoses differed in the location discomfort was experienced.

Conclusion: Existing cervical orthoses cause discomfort influenced by design and duration of wear with orthoses’ design the more significant factor. This work informed the design of a new orthosis and future orthoses developments.

Practitioner Summary: The purpose of this study was to gain greater knowledge about the discomfort caused by wearing of existing neck orthoses in order to inform the design and development of a new neck orthosis. This study gathers empirical data from a surrogate population and concludes that orthosis design is more influential than the duration of wear.     

Association between objectively measured static standing and low back pain – a cross-sectional study among blue-collar workers*

This study aims to investigate the cross-sectional association between objectively measured total time and temporal patterns of static standing (short bouts: 0–5 min; moderate bouts: >5–10 min; and long bouts: >10 min) during work and leisure and low back pain (LBP) among 698 blue-collar workers. Workers reported LBP on a 0–10 scale. The association between time spent on static standing and LBP was tested with linear regression. A positive association with LBP intensity was found for long bouts of static standing (β = 0.27) during total day (work + leisure), and total static standing time at leisure (β = 0.12). No significant associations were found for static standing during work and LBP intensity. These findings indicate that particularly long bouts of static standing over the entire day contribute to LBP in blue-collar workers.

Practitioner Summary: The association between LBP and static standing time was investigated. This study indicates that prolonged time standing during total day and standing during leisure are positively associated with LBP among blue-collar workers. Therefore, practitioners should consider long periods of standing as a potential risk factor for LBP.     

An investigation into four different sit–stand workstation use schedules

Twelve office workers participated in a study investigating effects of four sit/stand schedules (90-min sit/30-min stand, 80/40, 105/15, and 60/60) via several objective and subjective measures (muscle fatigue, foot swelling, spinal shrinkage, and self-reported discomfort). Results showed that there were no significant differences in shoulder and low back static muscle activities between sitting and standing. Muscle fatigue was developed during workday under all schedules. The longest standing schedule seemed to have a tendency of reducing muscle fatigue. None of the schedules helped or worsened foot swelling and spinal shrinkage. More active break-time activities seemed reducing muscle fatigue and foot swelling. While the self-reported bodily discomfort levels were generally low, the preferred schedules among the participants were varied, although the least standing schedule was the least preferred. We may conclude that effects of using sit–stand workstation to improve musculoskeletal health may be limited but promoting more active break-time activities can help.

Practitioner Summary: Sit–stand workstations are used to reduce work-related musculoskeletal disorders. This study shows that office workers prefer sit/stand durations in the range between 1:1 and 3:1. Longer standing may have the potential to reduce muscle fatigue. However, active break-time activities may be more effective in reducing muscle fatigue and foot swelling.     

Biomechanical investigation of prolonged driving in an ergonomically designed truck seat prototype

A postural evaluation during a prolonged driving task was conducted to determine the ergonomic validity of a new freely adjustable truck seat prototype. Twenty participants were recruited to perform two 2-h simulated driving sessions. Postures were assessed using motion capture, accelerometers and pressure pads. Subjective discomfort was also monitored in 15-min increments using ratings of perceived discomfort (RPD) and the Automotive Seating Discomfort Questionnaire. Participants had a more neutral spine posture during the first hour of the drive and reported lower RPDs while sitting in the prototype. Pairing the gluteal backrest panel with the adjustable seat pan helped reduce the average sitting pressure. The industry-standard truck seat may lead to the development of poor whole body posture, and the proposed ergonomic redesign of a new truck seat helped improve sitting posture and reduce perceived discomfort.

Practitioner Summary: A new freely adjustable truck seat prototype was compared to an Industry standard seat to assess hypothesised improvements to sitting posture and discomfort for long haul driving. It was found that the adjustable panels in the prototype helped promote spine posture, reduce sitting pressure and improved discomfort ratings.     

The impact of different seats and whole-body vibration exposures on truck driver vigilance and discomfort

Laboratory studies have shown that exposure to whole-body vibration (WBV) increases physical and mental fatigue, which are common issues professional drivers face. The objective of this study was to determine whether altering WBV exposures had any effect on driver vigilance and discomfort. A repeated measures crossover design of five truck drivers with regular 10-h routes was used. Active and passive suspension truck seats were evaluated. For each seat, WBV exposures were measured. Participants completed a discomfort questionnaire and a reaction time task before and after their shift for two weeks, one week per seat. Compared with the passive seat, the active seat significantly reduced WBV exposures, decrements in the optimal and mean reaction times (p = 0.02, 0.047, respectively), and discomfort in the lower back and wrist(s)/forearm(s) (p < 0.01, 0.01, respectively). Study results indicated that reducing WBV helps reduce discomfort and maintain vigilance, which may improve drivers’ health and reduce the risk of truck collisions.

Practitioner Summary: The active suspension seat used in this study reduced truck drivers’ exposure to whole-body vibration (WBV) by over 33% in relation to their current industry standard passive suspension seat. This study demonstrated that reducing truck drivers’ exposure to WBV reduced fatigue and discomfort development over a workday.     

Integrating a hip belt with body armour reduces the magnitude and changes the location of shoulder pressure and perceived discomfort in soldiers*

Soldiers carry heavy loads that may cause general discomfort, shoulder pain and injury. This study assessed if new body armour designs that incorporated a hip belt reduced shoulder pressures and improved comfort. Twenty-one Australian soldiers completed treadmill walking trials wearing six different body armours with two different loads (15 and 30 kg). Contact pressures applied to the shoulders were measured using pressure pads, and qualitative assessment of comfort and usability were acquired from questionnaires administered after walking trials. Walking with hip belt compared to no hip belt armour resulted in decreased mean and maximum shoulder pressures (p < 0.005), and 30% fewer participants experiencing shoulder discomfort (p < 0.005) in best designs, although hip discomfort did increase. Laterally concentrated shoulder pressures were associated with 1.34-times greater likelihood of discomfort (p = 0.026). Results indicate body armour and backpack designs should integrate a hip belt and distribute load closer to shoulder midline to reduce load carriage discomfort and, potentially, injury risk.

Practitioner Summary: Soldiers carry heavy loads that increase their risk of discomfort and injury. New body armour designs are thought to ease this burden by transferring the load to the hips. This study demonstrated that designs incorporating a hip belt reduced shoulder pressure and shoulder discomfort compared to the current armour design.     

Predictive discomfort of supine humans in whole-body vibration and shock environments

This work presents a predictive model to evaluate discomfort associated with supine humans during transportation, where whole-body vibration and repeated shock are predominant. The proposed model consists of two parts: (i) static discomfort resulting from body posture, joint limits and ambient discomfort; and (ii) dynamic discomfort resulting from the relative motion between the body segments as a result of transmitted vibration. Twelve supine subjects were exposed to single and 3D random vibrations and 3D shocks mixed with vibrations. The subjects’ reported discomfort and biodynamic response were analysed under different support conditions, including a rigid surface, a stretcher and a stretcher with a spinal backboard. The results demonstrated good correlations between the predictive discomfort and the reported discomfort for the different conditions under consideration, with R² = 0.69–0.94 for individual subjects and R² = 0.94 for the group mean. The results also indicated a strong relationship between the head-neck and trunk angular velocities and discomfort during supine transportation.

Practitioner Summary: The quantification of discomfort of supine humans under vibration and shocks by using a predictive model is an important contribution to this field, whereby the efficacy of different transport systems can be compared. The predictive discomfort model can be used as design criteria for ergonomic enhancement in supine transportation of humans.     

Muscle activity patterns and spinal shrinkage in office workers using a sit–stand workstation versus a sit workstation

Reducing sitting time by means of sit–stand workstations is an emerging trend, but further evidence is needed regarding their health benefits. This cross-sectional study compared work time muscle activity patterns and spinal shrinkage between office workers (aged 24–62, 58.3% female) who used either a sit–stand workstation (Sit–Stand group, n = 10) or a traditional sit workstation (Sit group, n = 14) for at least the past three months. During one typical workday, muscle inactivity and activity from quadriceps and hamstrings were monitored using electromyography shorts, and spinal shrinkage was measured using stadiometry before and after the workday. Compared with the Sit group, the Sit–Stand group had less muscle inactivity time (66.2 ± 17.1% vs. 80.9 ± 6.4%, p = 0.014) and more light muscle activity time (26.1 ± 12.3% vs. 14.9 ± 6.3%, p = 0.019) with no significant difference in spinal shrinkage (5.62 ± 2.75 mm vs. 6.11 ± 2.44 mm). This study provides evidence that working with sit–stand workstations can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.

Practitioner Summary: This cross-sectional study compared the effects of using a sit–stand workstation to a sit workstation on muscle activity patterns and spinal shrinkage in office workers. It provides evidence that working with a sit–stand workstation can promote more light muscle activity time and less inactivity without negative effects on spinal shrinkage.     

Thermal and cardiovascular strain imposed by motorcycle protective clothing under Australian summer conditions

Motorcycle protective clothing can be uncomfortably hot during summer, and this experiment was designed to evaluate the physiological significance of that burden. Twelve males participated in four, 90-min trials (cycling 30 W) across three environments (25, 30, 35 °C [all 40% relative humidity]). Clothing was modified between full and minimal injury protection. Both ensembles were tested at 25 °C, with only the more protective ensemble investigated at 30 and 35 °C. At 35 °C, auditory canal temperature rose at 0.02 °C min^?1 (SD 0.005), deviating from all other trials (p < 0.05). The thresholds for moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 min (SD 20.6) and 180 min (SD 33.0), respectively. Profound hyperthermia might eventuate in ~10 h at 30 °C, but should not occur at 25 °C. These outcomes demonstrate a need to enhance the heat dissipation capabilities of motorcycle clothing designed for summer use in hot climates, but without compromising impact protection.

Practitioner’s Summary:

Motorcycle protective clothing can be uncomfortably hot during summer. This experiment was designed to evaluate the physiological significance of this burden across climatic states. In the heat, moderate (>38.5 °C) and profound hyperthermia (>40.0 °C) were predicted to occur within 105 and 180 min, respectively.     

Measuring mental workload: ocular astigmatism aberration as a novel objective index

This study assessed the effect of two perceptually matched mental tasks with different levels of mental demand on ocular aberrations in a group of young adults. We measured ocular aberration with a wavefront sensor, and total, internal and corneal RMS (root mean square) aberrations were calculated from Zernike coefficients, considering natural and scaled pupils (5, 4.5, and 4 mm). We found that total, internal and corneal astigmatism RMS showed significant differences between mental tasks with natural pupils (p < .05), and this effect was maintained with 5 mm scaled pupils (total RMS astigmatism, p < .05). Consistently, pupil size, intraocular pressure, perceived mental load and cognitive performance were influenced by the level of mental complexity (p < .05 for all). The findings suggest that ocular astigmatism aberration, mediated by intraocular pressure, could be an objective, valid reliable index to evaluate the impact of cognitive processing in conjunction with others physiological markers in real world contexts.

Practitioner Summary: The search continues for a valid, reliable, convenient method of measuring mental workload. In this study we found ocular astigmatism aberration is sensitive to the cumulative effect of mental effort. It shows promise of being a novel ocular index which may help to assess mental workload in real situations.     

Stand up: comparison of two electrical screed levelling machines to reduce the work demands for the knees and low back among floor layers

Electrical screed levelling machines are developed to reduce kneeling and trunk flexion of sand–cement-bound screed floor layers. An observational intervention study among 10 floor layers was performed to assess the differences between a self-propelled and a manually moved machine. The outcome measures were work demands, production time, perceived load, discomfort and applicability. Compared to the self-propelled machine, the duration of kneeling (?13 min; p = 0.003) and trunk flexion (?12 min; p < 0.001) was shorter using the manually moved machine, and the duration of pushing and pulling increased (?39 min; p < 0.001). No significant or relevant differences were found for production time, perceived load and discomfort. Nine out of ten floor layers found the manually moved machine applicable and three out of ten found the self-propelled machine applicable. When compared with the traditional manner of floor laying, both electrical machines reduced the exposure towards kneeling and trunk flexion.

Practitioner Summary: Electrical machines may help to reduce high physical work demands on floor layers. A manually moved machine is better applicable for the installation of screed floors in residences with smaller floor areas. A self-propelled machine is better applicable on large floor areas with a minimum width of 4 m.     

Frequency-dependence of discomfort caused by vibration and mechanical shocks

The frequency content of a mechanical shock is not confined to its fundamental frequency, so it was hypothesised that the frequency-dependence of discomfort caused by shocks with defined fundamental frequencies will differ from the frequency-dependence of sinusoidal vibration. Subjects experienced vertical vibration and vertical shocks with fundamental frequencies from 0.5 to 16 Hz and magnitudes from ±0.7 to ±9.5 ms^–2. The rate of growth of discomfort with increasing magnitude of motion decreased with increasing frequency of both motions, so the frequency-dependence of discomfort varied with the magnitudes of both motions and no single frequency weighting will be ideal for all magnitudes. At the frequencies of sinusoidal vibration producing greatest discomfort (4–16 Hz), shocks produced less discomfort than vibration with same peak acceleration or unweighted vibration dose value. Frequency-weighted vibration dose values provided the best predictions of the discomfort caused by different frequencies and magnitudes of vibration and shock.

Practitioner Summary: Human responses to vibration and shock vary according to the frequency content of the motion. The ideal frequency weighting depends on the magnitude of the motion. Standardised frequency-weighted vibration dose values estimate discomfort caused by vibration and shock but for motions containing very low frequencies the filtering is not optimum.     

Specific flexion-related low back pain and sitting: comparison of seated discomfort on two different chairs

No study has examined the effectiveness of prescribing seating modifications according to the individual clinical presentation of people with low back pain (LBP). A dynamic, forward-inclined chair (‘Back App’) can reduce seated paraspinal muscle activation among pain-free participants. This study examined 21 participants whose LBP was specifically aggravated by prolonged sitting and was eased by standing. Low back discomfort (LBD) and overall body discomfort (OBD) were assessed every 15 min while participants sat for 1 h on both the dynamic, forward-inclined chair and a standard office chair. LBD increased significantly more (p = 0.005) on the standard office chair, with no significant difference (p = 0.178) in OBD between the chairs. The results demonstrate that, in a specific flexion-related subgroup of people with LBP, increased LBD during sitting can be minimised through modifying chair design. Mechanisms that minimise seated discomfort may be of relevance in LBP management, as part of a biopsychosocial management plan.

Practitioner summary: This study examined low back discomfort (LBD) during a typing task among people with low back pain (LBP). Sitting on a dynamic, forward-inclined chair resulted in less seated LBD than sitting on a standard office chair. Further research is required to examine the long-term effectiveness of ergonomics interventions in LBP.     

Glasses-type wearable computer displays: usability considerations examined with a 3D glasses case study

This study presents usability considerations and solutions for the design of glasses-type wearable computer displays and examines their effectiveness in a case study. Design countermeasures were investigated by a four-step design process: (1) preliminary design analysis; (2) design idea generation; (3) final design selection; and (4) virtual fitting trial. Three design interventions were devised from the design process: (1) weight balance to reduce pressure concentrated on the nose, (2) compliant temples to accommodate diverse head sizes and (3) a hanger mechanism to help spectacle users hang their wearable display on their eye glasses. To investigate their effectiveness, in the case study, the novel 3D glasses adopting the three interventions were compared with two existing 3D glasses in terms of neck muscle fatigue and subjective discomfort rating. While neck muscle fatigue was not significantly different among the three glasses (p = 0.467), the novel glasses had significantly smaller discomfort ratings (p = 0.009).

Relevance to Industry: A four-step design process identified usability considerations and solutions for the design of glasses-type wearable computer displays. A novel 3D glasses was proposed through the process and its effectiveness was validated. The results identify design considerations and opportunities relevant to the emerging wearable display industry.     

Perceptions of performance and satisfaction after relocation to an activity-based office

Many companies move from open-plan offices (OPO) to activity-based workplaces (ABWs). However, few studies examine the benefits and drawbacks following such a change. The aim of this study was to explore how physical conditions, office use, communication, privacy, territoriality, satisfaction and perceived performance change following a company’s relocation from an OPO to an ABW. A mixed methods approach included pre- and post-relocation questionnaires and post-relocation focus groups, individual interviews and observations. The questionnaires enabled comparisons over time (n = 34) and broader analyses based on retrospective ratings of perceived change (n = 66). Results showed that satisfaction with auditory privacy, background noise, air quality, outdoor view and aesthetics increased significantly after relocation. Negative outcomes, such as lack of communication within teams, were perceived as being due to the high people-to-workstation ratio and lack of rules. Overall satisfaction with the physical work environment increased in the ABW compared to the OPO. Perceived performance did not change significantly.

Practitioner Summary: Activity-based workplaces (ABWs) are commonly implemented although their effects on performance and well-being are unclear. This case study gives advice to stakeholders involved in office planning. Despite shortcomings with the people-to-workstation ratio and rules, employees showed improved satisfaction with auditory privacy and aesthetics in the ABW compared with the previous open-plan office.