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Are hybrid sit-stand postures a good compromise between sitting and standing?
Ergonomics
Abstract
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 one-minute 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 < 0.01). Anterior-posterior forces were the highest in perching (p < 0.001), requiring approximately 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.
... As an alternative to sit-stand rotation, hybrid sit-stand chairs have been proposed to avoid end-range spine flexion in sitting (Antle et al., 2015;Chester et al., 2002;Ebara et al., 2008;Kingston et al., 2016;Le and Marras, 2016;Sartika and Dawal, 2010). However, recommendations for appropriately positioning the spine in these hybrid chairs are more recent (Buchman--Pearle et al., 2023;Noguchi et al., 2019) and there is little evidence that simply opening up the trunk-thigh angle in hybrid chairs will elicit less spine flexion than a traditional 90-90-90 sitting posture. Unlike hybrid chairs which primarily aim to decrease spine flexion in sitting, 'dynamic' or 'active' chairs aim to decrease spine flexion while also promoting movement. ...
... Force data were padded (Howarth and Callaghan, 2009) and then smoothed using a dual-pass second order low-pass Butterworth filter with an effective cutoff frequency of 10 Hz (Noguchi et al., 2019) and expressed as a percentage of body weight. The force in the vertical and anterior-posterior direction were computed separately to indicate if individuals tended to forward brace on their legs. ...
... These findings are consistent with the seat pan being able to tilt anteriorly (De Carvalho and Callaghan, 2023b) and are similar to lumbar flexion angles previously observed with dynamic sitting on a multiaxial rotating seat pan (Frey et al., 2021). Additionally, the lack of change in lumbar spine angles is consistent with suggestions that the trunk-thigh angle needs to approach 145 • in females and 160 • in males before there are any corresponding decrease in lumbar flexion (Noguchi et al., 2019). Pelvic obliquity and lumbar lateral bending were not different between the chairs during the seated computer work, wherein mean lateral bending angles of 16 %MaxBend were observed for each of the three blocks (Fig. 4). ...
... A tilted seat pan either forward or backward transfers some of the intervertebral disc loading to the floor or backrest, respectively (Kayis and Hoang 1999) and induces muscle fatigue and tissue shear forces that may be uncomfortable or even harmful (Rasmussen et al., 2009). A perching position improved lumbopelvic angles when compared to sitting, it also resulted in: 1-a significant increase in ground reaction anterior/posterior shear force (an increase in shear force has been associated with the development of discomfort); 2-a significant increase in vastus medialis obliquus activity when compared to standing; and 3little to no change in trunk extensor activity when compared to both sitting and standing (Noguchi et al., 2019). A perching position does not influence trunk muscle activation, but requires greater muscular activity of the knee and ankle extensors, leading to increased load on the lower limbs (Hamaoui et al., 2015;Mastalerz and Palczewska 2010) and leg swelling (Antle et al., 2015). ...
... Sitting on a perching stool can improve lumbar posture due to the more open trunk-thigh angle, however, the literature shows that sitting on a perching stool increases perceived discomfort in the leg muscles as they are forced to act as static postural stabilizers (Mastalerz and Palczewska 2010) and increases the tissue shear forces on a sloped seat (Noguchi et al., 2019). ...
... To interrupt sedentary sitting time and change posture, the active sitting concepts based on perching have proven popular, and if one is able to take frequent walking breaks, they can be used throughout the day. The purpose of this analysis is not to diminish their value to interrupt sedentary time but to point out that a decline seat does not provide a significant increase in movement (Commissaris et al., 2014) or trunk muscle activation (Noguchi et al., 2019) and is not suitable for all-day use. ...
... Unfortunately, seated breaks may not effectively relieve standing-induced low back pain (Gallagher, Campbell, and Callaghan 2014), and, in practice, individuals often fail to comply with sit-stand recommendations as they do not stand often enough (Graves et al. 2015;Pronk et al. 2012;Robertson, Ciriello, and Garabet 2013;Wilks, Mortimer, and Nyl� en 2006). Hybrid postures, which situate the lumbar spine in a mid-range 'goldilocks' posture (Le and Marras 2016;Noguchi et al. 2019) through the use of less traditional office chairs, such as the lean support, perch, stool, or prop (ANSI (American National Standards Institute) 2019), may offer an alternative to sit-stand rotation and prolonged sedentary exposures near end ranges of motion. ...
... Hence, a hybrid posture intended to replicate the lumbopelvic posture in standing (Keegan 1953) may not reduce low back pain development. One study which characterised lumbopelvic angles at trunk-thigh angle increments of 10 � between sitting (90 � ) and standing (180 � ) found that the lumbopelvic posture at trunk-thigh angles between 145 and 175 � for males and 160-175 � for females differed from both sitting and standing (Noguchi et al. 2019). While this study provides a range of sex-specific trunk-thigh angles to define a hybrid posture, it falls short in defining where physiological neutral may occur based on the mechanical properties of the spine. ...
... lumped flexor stiffness) moment-angle curve. From previous analyses of sexbased differences in extensor stiffness (Beach et al. 2005;De Carvalho and Callaghan 2011;Tennant et al. 2020) and the observation that males adopt smaller trunk-thigh angles at the flexion boundary in perched seats (Noguchi et al. 2019), it was hypothesised that males would demonstrate greater extensor stiffness as well as greater lumbar flexion and smaller trunk-thigh angles at the neutral zone flexion breakpoint only. The second objective of this study was to examine if the lumbar angle in upright standing, and the corresponding trunk-thigh angle, fell within the neutral zone and if angular displacement relative to the extension boundary was different between the sexes. ...
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
... This position presents several advantages over Staffel's, such as tilting the pelvis forwards (anteversion), maintaining lumbar lordosis, and decreasing intradiscal pressure (Noro et al., 2012). Common ergonomic designs that promote these beneficial posturesas well as alternation and movement -have used higher chairs with forward slopes, saddle chairs, and adjustable height desks (Mandal, 1991;Roossien et al., 2017;Kuster et al., 2018;Noguchi et al., 2019;Chambers et al., 2019;Vaucher et al., 2015;Johnston et al., 2019). Demonstrated across different populations -from dentists (Gouvêa et al., 2018) to school children (Castellucci et al., 2016a,b) -hybrid sitting interventions incorporate furniture and equipment that allow users to modify their sitting posture according to their preference, work-related use, and comfort. ...
... Demonstrated across different populations -from dentists (Gouvêa et al., 2018) to school children (Castellucci et al., 2016a,b) -hybrid sitting interventions incorporate furniture and equipment that allow users to modify their sitting posture according to their preference, work-related use, and comfort. Moreover, they have been shown to be more effective than any single static posture (Noguchi et al., 2019). Based on the above, "new" fundamental design principles to bear under the framework of Dynamic Sitting, i.e., posture changes among sitting, standing, and half-standing positions, also known as semi-sitting or perching, should be included in office settings (Bendix and Bridger, 2004). ...
... The studies that do discuss it define perching as a trunk/thigh angle of at least 105 • (Fig. 1b) to promote neutral pelvis and spine lumbar positions (Bendix and Bridger, 2004). Other authors have suggested an ideal trunk/thigh angle of 120 • (Fig. 1c) (Mandal, 1991;Noro et al., 2012), while others consider perching at a trunk/thigh angle of at least 135 • (Fig. 1d) (Keegan, 1953;Mandal, 1981;Noguchi et al., 2019;Rohlmann et al., 2011). ...
Anthropometry is critical for product and workplace design. Highly prevalent, office work is associated with sedentarism and physical discomfort due to prolonged sitting. Dynamic seating (alternating across sitting, perching, and standing) has been suggested as an alternative to overcome those problems. The current study tested a large sample of anthropometric data for mismatch levels against national and international office furniture standards using dynamic seating as a framework with traditional and perching mismatch equations, applied to three recommended dynamic seating components. Dimensions present in the standards used did not match the majority of the sample. For sitting, seat width and depth individually presented the lowest levels of match, as well as under cumulative fit of all office furniture dimensions. However, these were alleviated when incorporating adjustability. Perching was shown to be generally impeded given commercially-available chair height options. Limitations in state-of-the-art perching equations are discussed, and two new models are proposed as design alternatives. Further research should focus on testing the criteria presented in this research through discomfort and objective measures.
... All accelerometer data were input into a custom Matlab program (2020b, The MathWorks Inc., Natick, MA) for processing. Raw voltage data were padded [27,28] and then filtered using a dual-pass fourth order low-pass Butterworth filter and an effective cutoff frequency of 3 Hz [29,30]. Using data from the six calibration trials, all accelerometer channels were calibrated with respect to gravity. ...
... Marker position data, including calculated anatomical landmarks of the pelvis, were input to Visual3D™ motion analysis software (Version 2020, C-Motion, Germantown, MA). Raw position data were padded [27,28] and then smoothed with a dual-pass fourth order low-pass Butterworth filter with an effective cutoff frequency of 3 Hz [29,30]. Marker position data acquired from the standing calibration trial were used to construct a linkedsegment model containing the trunk, pelvis, thigh, and shank segments. ...
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.
... All accelerometer data were input into a custom Matlab program (2020b, The MathWorks Inc., Natick, MA) for processing. Raw voltage data were padded [27,28] and then filtered using a dual-pass fourth order low-pass Butterworth filter and an effective cutoff frequency of 3 Hz [29,30]. Using data from the six calibration trials, all accelerometer channels were calibrated with respect to gravity. ...
... Marker position data, including calculated anatomical landmarks of the pelvis, were input to Visual3D™ motion analysis software (Version 2020, C-Motion, Germantown, MA). Raw position data were padded [27,28] and then smoothed with a dual-pass fourth order low-pass Butterworth filter with an effective cutoff frequency of 3 Hz [29,30]. Marker position data acquired from the standing calibration trial were used to construct a linkedsegment model containing the trunk, pelvis, thigh, and shank segments. ...
Background:
Adherence to sit-stand workstation usage has been shown to decrease post-intervention, with the reported reasons related to fatigue, cumbersome workstation adjustments, and focus.
Objective:
To characterize the mechanical work and total energy required to perform transitions from a traditional office chair and a dynamic chair designed specifically for sit-stand workstations. The whole-body, thigh, and shank centre-of-mass (CoM) were evaluated.
Methods:
Fifteen participants (8 male; 7 female) performed three intermittent sit-to-stand and stand-to-sit transitions from the traditional and dynamic chairs. Kinematic data of the trunk, pelvis, and lower extremities were collected using an optoelectronic motion capture system and triaxial accelerometers. The change in total energy and work between the sitting and standing postures were evaluated for each CoM point. Lumbar spine range-of-motion was further assessed between chair conditions.
Results:
Chair designs facilitated opposite work and energy responses for a given transition. Transitions performed from the dynamic chair reduced the work and total energy of the whole-body CoM, by ±8.5J and ±214.6J (p < 0.001), respectively. The work and energy of the thigh CoM differed within transitions (p < 0.001), but the positive and negative components were similar between chairs (work =±0.18J, energy =±0.55J). The dynamic chair increased the total energy (±38.3J, p < 0.001) but not the work of the shank CoM (±1.1J, p≥0.347).
Conclusion:
The required mechanical work and energy of sit-to-stand and stand-to-sit transitions was modified by chair design. These outcomes have the potential to address identified reasons for the disuse of sit-stand workstations.
... Using a sit-stand stool can reduce the weight load in nurses' legs, feet and back providing better body weight distribution, improving venous flow and reducing spinal loading 2,6 . A 2019 study (n=24) documented a hybrid position between sitting and standing as a favourable position for both genders (p<0.005) in creating natural pelvic and lumbar angles and reducing body weight tension and loading 10 . While it is not always acceptable for the instrument or circulating nurse to use this equipment, a sit-stand stool should be used when appropriate 10 . ...
... A 2019 study (n=24) documented a hybrid position between sitting and standing as a favourable position for both genders (p<0.005) in creating natural pelvic and lumbar angles and reducing body weight tension and loading 10 . While it is not always acceptable for the instrument or circulating nurse to use this equipment, a sit-stand stool should be used when appropriate 10 . ...
... В рамках более широких тематических исследований нами проводилось наблюдение на здоровых добровольцах, с целью исследования электромиографических (ЭМГ) и постурографических параметров, связываемых с балансом тела в "гибридных позах" (по типу "стоячего сидения", например: [11]) в экзоскелете, по сравнению с внешне похожими позициями без экзоскелета. Прогнозируемый полезный результат связывался с адаптацией известных физиологических способов (стабилометрия, ЭМГ) для исследования баланса тела человека в экзоскелетах, а также с установлением возможной связи отдельных особенностей сенсорного обеспечения вертикальной позы со стабильностью человека в "гибридных позах". ...
... Первый этап включал 2 фазы исследованияобычное стояние добровольца в вертикальной позе, голова прямо, руки свободно опущены вдоль туловища, с открытыми и закрытыми глазами, по 30 с; в которых изучали влияние зрительной афферентации на контроль позы. Второй и третий этапы -по 1 фазе в 30 с, где доброволец последовательно принимал 2 варианта вертикальной позы в виде "стоячего сидения" (по типу "гибридных поз" [11]), при этом за счет конструктивных свойств пассивного экзоскелета изменя- ...
... There is evidence that the surface electromyography variables depend on the length of lumbar erector spinae muscles due to their complex anatomy (Petrofsky et al., 1982). Flexion/extension movement of the back is linked to changes in the distance between the origins and insertions of lumbar erector spinae muscles and, consequently, the length of the muscle, which can bias the results (Noguchi et al., 2019). Also, such factors as the proportion of muscle fibres (Gerdle et al., 1997;Kupa et al., 1995) and unwanted signals from surrounding muscles, e.g., crosstalk (Lowery, Stoykov & Kuiken, 2003), play a role in the analysis and assessment of muscle contraction. ...
Background
Musculoskeletal disorders (MSDs), especially in the lumbar spine, are a leading concern in occupational health. Work activities associated with excessive exposure are a source of risk for MSDs. The optimal design of workplaces requires changes in both sitting and standing postures. In order to secure such a design scientifically proved quantitative data are needed that would allow for the assessment of differences in spine load due to body posture and/or exerted force. Intradiscal pressure (IP) measurement in the lumbar spine is the most direct method of estimating spinal loads. Hence, this study aims at the quantitative evaluation of differences in lumbar spine load due to body posture and exerted forces, based on IP reported in publications obtained from a comprehensive review of the available literature.
Methodology
In order to collect data from studies measuring IP in the lumbar spine, three databases were searched. Studies with IP for living adults, measured in various sitting and standing postures, where one of these was standing upright, were included in the analysis. For data to be comparable between studies, the IP for each position was referenced to upright standing. Where different studies presented IP for the same postures, those relative IPs (rIP) were merged. Then, an analysis of the respective outcomes was conducted to find the possible relationship of IPs dependent on a specific posture.
Results
A preliminary analysis of the reviewed papers returned nine items fulfilling the inclusion and exclusion criteria. After merging relative IPs from different studies, rIP for 27 sitting and 26 standing postures was yielded. Some of the data were useful for deriving mathematical equations expressing rIP as a function of back flexion angle and exerted force in the form of a second degree polynomial equation for the standing and sitting positions. The equations showed that for the standing posture, the increase in IP with increasing back flexion angle is steeper when applying an external force than when maintaining body position only. In a sitting position with the back flexed at 20°, adding 10 kg to each hand increases the IP by about 50%. According to the equations developed, for back flexion angles less than 20°, the IP is greater in sitting than in standing. When the angle is greater than 20°, the IP in the sitting position is less than in the standing position at the same angle of back flexion.
Conclusions
Analysis of the data from the reviewed papers showed that: sitting without support increases IP by about 30% in relation to upright standing; a polynomial of the second degree defines changes in IP as a function of back flexion for for both postures. There are differences in the pattern of changes in IP with a back flexion angle between sitting and standing postures, as back flexion in standing increases IP more than in sitting.
... While health care costs and individual worker health are important, providing data about how changing a task will affect performance or customer satisfaction is vital for the successful adoption of changes. It will also be important to identify different equipment for standing, such as perch/leaning chairs (Buchman-Pearle et al., 2022;Noguchi et al., 2019), and ensure that standing aids are available such as anti-fatigue matting (Winberg et al., 2022) or foot rests (Fewster et al., 2017(Fewster et al., , 2019, in a way that does not adversely affect safety (tripping, blocking egress routes, etc.). ...
Occupational Applications
In this paper, we provide a framework for practitioners when (re)designing tasks that historically have required standing in the workplace. While the goal is not to remove standing from all jobs, practitioners must work with management to align health and safety outcomes related to standing at work with the enterprise's main outcomes. Practitioners should also be made aware that in many of these jobs, standing has been required because, in the enterprise’s judgment, it improves performance and customer service. Understanding common beliefs about customer interactions and job performance in the workplace will be vital to implementing changes that have previously been difficult to navigate.
This study investigates the criteria defining sit-standing postures offered by Chairless chair devices through comparative analysis. It evaluates the applicability of conventional sitting posture criteria, including balance, body segment orientation, and biomechanics, in defining unconventional postures. Findings indicate that sit-standing postures exhibit a distinct center of gravity, unique support polygons, and specific body segment geometries. Devices such as those developed by Noonee and Archelis facilitate a posture that is intermediate between sitting and standing, enhancing visual control and interaction with the workspace. This research underscores the potential ergonomic and functional benefits of these innovative seating solutions, warranting further exploration
The environment of companies, especially large companies, is complex and rapidly changing. In addition to the technical and economic conditions that directly influence the operation, the effects of external factors also fundamentally change the operation of companies. The corporate processes affecting occupational health and safety (OHS) have also become complex, and this represents a serious challenge for the managers. Knowing the factors and processes affecting the company's OHS performance is necessary for managerial decisions that improve its effectiveness. The purpose of this work is to delve into the methods companies use to monitor and manage OHS performance. A systematic literature review was conducted of studies published in the field of OHS performance management. This overview provides knowledge about which methods determine the OHS management of companies. The review highlights and discusses performance management strategies and the main difficulties, constraints and challenges managers face in influencing OHS performance. The study concludes that improving OHS performance has become a complex task for medium and large companies. Most of the literature investigating safety performance management focuses on the technical issues of overall measurement. Limited attention is paid to the use of information from the measurement of OHS performance, and to the factors influencing managerial decisions resulting in improved performance.
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).
In vivo lumbar passive stiffness is often used to assess time-dependent changes in lumbar tissues and to define the neutral zone. We tested the hypothesis that flexing the hips would alter tension in hip and spine musculature, leading to a more extended passive stiffness curve (i.e., right-shifted), without changes in lumbar stiffness. Twenty participants underwent side-lying passive testing with the lower limbs positioned in Stand, Kneel, and Sit representative postures. Moment-angle curves were constructed from the lumbar angles and the moment at L4/5 and partitioned into three zones. Partially supporting our hypothesis, lumbar stiffness within the low and transition stiffness zones was similar between the Stand and Sit. Contrary to our hypothesis, lumbar angles were significantly larger in the Sit compared to the Stand and Kneel postures at the first and second breakpoints, with average differences of 9.3° or 27.2% of passive range of motion (%PassRoM) in flexion and 5.6° or 16.6 %PassRoM in extension. Increased flexion in the Sit may be linked to increased posterior pelvic tilt and associated lower lumbar vertebrae flexion. Investigators must ensure consistent pelvis and hip positioning when measuring lumbar stiffness. Additionally, the adaptability of the neutral zone to pelvis posture, particularly between standing and sitting, should be considered in ergonomic applications.
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, 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.
This article analyzes the current state of studies of aspects of the neurophysiological control of parameters of atypical postures in humans associated with the use of external exoskeleton-type devices. The main results of studies in the last five years relate to the formation of scientific concepts of neurophysiological rearrangements of the motor control system on use of robotic devices. The resulting information can be used in sports physiology, motor rehabilitation, development of upper and lower limb exoskeletons, organizing the work of operators, and training to specific movements.
Once fully automated driving has been implemented, passengers will be able to take advantage of not only the sitting posture but also standing and perching postures. Physical workload of these postures should be investigated in order to design car seats that provide passengers appropriate physical workload. This study aimed to investigate the feasibility of simulation-based physical workload evaluation of these postures by a musculoskeletal model. Twelve male students participated, and four electromyograms (EMGs) of the rectus femoris, tibialis anterior, gastrocnemius, and erector spinae were recorded with varying seat angle against the horizontal surface: 0° (i.e., sitting), 30°, 45°, 60° (i.e., perching), and 90° (i.e., standing). Results showed that the effect of the seat angle condition was significant for the EMGs of rectus femoris and erector spinae. In particular, the EMG of rectus femoris was relatively higher than the other three EMGs. The EMG of rectus femoris increased with the increase in seat angle in the range from 0° to 60°and decreased in the range of 60° to 90°. The musculoskeletal analysis was carried out with the same condition as the EMG measurement. The average height and weight of the participants were applied to the analysis model, and the muscle activities of the four muscles were estimated. As expected, the trend of muscle activity in the rectus femoris estimated by the musculoskeletal analysis agreed with the experimental result. The average absolute error of muscle activity in the rectus femoris between the experiment and the analysis was approximately 2.5%. From these results, it is suggested that musculoskeletal analysis can be utilized to estimate muscle activity of a spectrum of static posture from sitting to standing through perching.
Close interface between humans and inanimate objects (furniture, assistive devices, and external loads) can obstruct line-of-sight in biomechanics studies that utilize optoelectronic motion capture systems. This specific problem is frequently encountered with the pelvis segment. This study sought to compare joint and pelvis angles computed from a pelvis-fixed local coordinate system (LCS) that was constructed from optically tracked pelvis landmarks (gold standard) and landmarks derived from angular deviations calculated from triaxial accelerometer data. One participant performed seven tasks: sitting, forward bend, sit-to-stand-to-sit, forward lunge, symmetrical squat, asymmetrical squat, and gait. The root mean square error (RMSE) and coefficient of determination (R²) were examined for the pelvis, lumbar spine, and hip joint angles calculated using the standard and accelerometer-based methods for creating a LCS. The RMSE values for global pelvis angles ranged from 2.2° (gait; R² = 0.47) to 4.9° (sit-to-stand-to-sit; R² = 0.98), 0.6° (sitting; R² = 0.88) to 7.4° (gait; R² = 0.39), and 1.5° (forward bend; R² = 0.99) to 2.9° (sit-to-stand-to-sit; R² = 0.99) for motion about the X, Y, and Z axes, respectively. The magnitude of error observed for adjacent joint motion was lowest about the Z axis for all tasks. In conclusion, the accelerometer-based LCS offers an alternative method for computing pelvis and adjacent joint angles without the reliance on a visual line-of-sight. For motion about the X and Y axes, time-series data derived with the accelerometer-based method may be less representative of discrete events, particularly for gait and lunging tasks.
Beyond formal training and coaching supervision, the coaching literature has had relatively little to say about what it means for coaches' to be fit for purpose. As such, this article explores what it might mean for coaches to be in a state of readiness for the work they undertake. It does this by isolating listening as a core skill set, whilst also identifying its challenges and the various demands it places upon the listener. In respect of these challenges, attention is then drawn to the importance of energy management, with a model of dialogical fitness presented and briefly discussed to help identify practices that might build such a state of fitness. The paper concludes with some possibilities for initiating research in this area.
Few studies have demonstrated that seating modifications reduce low back pain (LBP). One recent study found that a forward-inclined seatpan reduced low back discomfort (LBD), however this was only examined in people with flexion-related LBP. No study has yet investigated its effectiveness among people with extension-related LBP. This crossover study examined 12 subjects with extension-related LBP. Sitting discomfort and surface electromyography of three trunk muscles were recorded during a 10-minute typing task while sitting with two different seatpan inclinations, both with and without a backrest. LBD (p < 0.001) and overall body discomfort (OBD) (p = 0.016) were significantly greater on the forward-inclined seatpan. The backrest did not alter trunk muscle activation or sitting discomfort. The results demonstrate that in a specific subgroup of people with extension-related LBP, increasing forward seatpan inclination significantly increased LBD and OBD. Future research should consider matching ergonomics prescriptions according to the individual presentation of people with LBP.
Unlabelled:
Low back pain (LBP) is a common musculoskeletal disorder and prolonged sitting often aggravates LBP. A novel dynamic ergonomic chair ('Back App'), which facilitates less hip flexion while sitting on an unstable base has been developed. This study compared lumbar posture and trunk muscle activation on this novel chair with a standard backless office chair. Twelve painfree participants completed a typing task on both chairs. Lumbar posture and trunk muscle activation were collected simultaneously and were analysed using paired t-tests. Sitting on the novel dynamic chair significantly (p < 0.05) reduced both lumbar flexion and the activation of one back muscle (Iliocostalis Lumborum pars Thoracis). The discomfort experienced was mild and was similar (p > 0.05) between chairs. Maintaining lordosis with less muscle activation during prolonged sitting could reduce the fatigue associated with upright sitting postures. Studies with longer sitting durations, and in people with LBP, are required.
Practitioner summary:
Sitting on a novel dynamic chair resulted in less lumbar flexion and less back muscle activation than sitting on a standard backless office chair during a typing task among pain-free participants. Facilitating lordotic sitting with less muscle activation may reduce the fatigue and discomfort often associated with lordotic sitting postures.
Loading is important to maintain the balance of matrix turnover in the intervertebral disc (IVD). Daily cyclic diurnal assists
in the transport of large soluble factors across the IVD and its surrounding circulation and applies direct and indirect stimulus
to disc cells. Acute mechanical injury and accumulated overloading, however, could induce disc degeneration. Recently, there
is more information available on how cyclic loading, especially axial compression and hydrostatic pressure, affects IVD cell
biology. This review summarises recent studies on the response of the IVD and stem cells to applied cyclic compression and
hydrostatic pressure. These studies investigate the possible role of loading in the initiation and progression of disc degeneration
as well as quantifying a physiological loading condition for the study of disc degeneration biological therapy. Subsequently,
a possible physiological/beneficial loading range is proposed. This physiological/beneficial loading could provide insight
into how to design loading regimes in specific system for the testing of various biological therapies such as cell therapy,
chemical therapy or tissue engineering constructs to achieve a better final outcome. In addition, the parameter space of ‘physiological’
loading may also be an important factor for the differentiation of stem cells towards most ideally ‘discogenic’ cells for
tissue engineering purpose.
KeywordsIntervertebral disc–Disc generation–Dynamic loading–Axial compression–Hydrostatic pressure–Mechanobiology
A relationship between low back pain (LBP) and prolonged standing or prolonged sitting at work has not been clearly shown, despite its biological plausibility. Because sitting and standing postures vary as to duration and freedom to alternate postures, and standing postures vary as to mobility, associations between specific working postures and LBP were explored using multiple logistic regression. Associations between work factors and self-reported LBP during the previous 12 months that interfered with usual activities were examined among 4493 standing workers and 3237 sitting workers interviewed in the 1998 Quebec Health and Social Survey; 24.5% reported significant LBP. Since the same conditions can correspond to different physiological demands for sitting compared with standing workers, analyses were performed separately for the two groups. Standing without freedom to sit was associated with LBP. Different occupational physical and psychosocial factors were associated with LBP in sitting compared with standing populations.
Asymptomatic volunteers underwent magnetic resonance imaging to investigate how different positions affect lumbar intervertebral discs.
To quantify sagittal migration of the lumbar nucleus pulposus in 6 functional positions.
Previous studies of the intervertebral disc response in the sagittal plane were limited to imaging of recumbent positions. Developments of upright magnetic resonance imaging permit investigation of functional weight-bearing positions.
T2-weighted sagittal scans of the L1-L2 to L5-S1 discs were taken of 11 volunteers in standing, sitting (upright, flexed, and in extension), supine, and prone extension. Sagittal migration of the nucleus pulposus was measured (mm) as distance from anterior disc boundary to peak pixel intensity. Lumbar lordosis (Cobb angle) was measured in each position.
Fifteen comparisons between positions showed significant positional effects (14 at L4-L5, L5-S1, the most mobile segments). Prone extension and supine lying induced significantly less posterior migration than sitting. Flexed and upright sitting, significantly more than standing at L4-L5, as did flexed sitting compared with extended.
These results support for the first time the validity of clinical assumptions about disc behavior in functional positions: sitting postures may increase risk of posterior derangement, and prone and supine may be therapeutic for symptoms caused by posterior disc displacement.
Background:
Approximately 50% of a sample population will develop prolonged standing induced low back pain. The cause of this pain may be due to their lumbar spine posture. The purpose of this study was to investigate differences in lumbar posture between 17 participants categorized as a pain or non-pain developers during level ground standing. A secondary purpose was to evaluate the influence of two standing aids (an elevated surface to act as a foot rest and declined sloped surface) on lumbopelvic posture.
Methods:
Four sagittal plane radiographs were taken: a normal standing position on level ground, when using an elevated foot rest, using a declined sloped surface, and maximum lumbar spine extension as a reference posture. Lumbosacral lordosis, total lumbar lordosis, and L1/L2 and L5/S1 intervertebral joint angles were measured on each radiograph.
Findings:
There was a significant difference between the lumbosacral lordosis angle and L5/S1 angles in upright versus maximum extension; however, this was independent of pain group. The elevated surface was most effective at causing lumbosacral spine flexion.
Interpretation:
Potentially successful postures for eliminating low back pain during prolonged standing mainly influence the lower lumbar lordosis. Future work should assess the influence of hip posture on low back pain development during standing.
The objective of this study was to evaluate how different workstations may influence physical behavior in office work through motion and how that may affect spinal loads and discomfort. Twenty subjects performed a typing task in three different workstations (seated, standing, and perching) for one hour each. Measures of postural transitions, spinal loads, discomfort, and task performance were assessed in order to understand the effects of workstation interaction over time. Results indicated that standing had the most amount of motion (6–8 shifts/min), followed by perching (3–7 shifts/min), and then seating (<1 shift/min). Standing had the highest reports of discomfort and seating the least. However, spinal loads were highest in A/P shear during standing (190N posterior shear, 407N anterior shear) compared to perching (65N posterior shear, 288N anterior shear) and seating (106N posterior shear, 287 anterior shear). These loads are below the risk threshold for shear, but may still elicit a cumulative response. Perching may induce motion through supported mobility in the perching stool, whereas standing motion may be due to postural discomfort. Office workstation designs incorporating supported movement may represent a reasonable trade-off in the costs-benefits between seating and standing.
Highlights
• Perching was associated with lower spinal loads compared to standing.
• Supported movement resulted in lower discomfort relative to prolonged standing.
• Heart rate variability may provide an objective understanding of discomfort.
While alternating standing position on a sloped surface has proven successful at reducing low back pain during standing, the purpose of this study was to evaluate standing solely on a declining surface to isolate the influence of the postural change. Seventeen participants performed two 75-min prolonged standing occupational simulations– level ground and declining surface. Fifty-three percent of participants (9/17) were categorized as pain developers during the level ground standing condition. For these same pain developers, their average maximum pain scores were 58% lower during sloped standing. All participants showed greater hip flexion, trunk-to-thigh angle flexion, and posterior translation of the trunk center of gravity when standing on the sloped surface. These postural changes could cause the muscles crossing the hip posteriorly to increase passive stiffness and assist with stabilizing the pelvis. This study stresses the importance of hip kinematics, not just lumbar spine posture, in reducing prolonged standing induced low back pain.
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.
Previous research points to the lack of movement during prolonged standing as a pre-disposing factor to low back pain (LBP). Such movements could be at the level of the lumbar spine or at the foot-ground interface. The primary purpose of this in vivo study was to determine if there were differences in magnitude, region, and frequency of movement patterns between non-pain developers (non-PDs) and standing induced pain developers (PDs). Thirty-two participants reported their LBP development using a visual analog scale over 2-h of prolonged standing. Time-varying lumbar spine kinematics were used to assess the magnitude and frequency of lumbar spine fidgets and shifts. Ground reaction forces were used to assess the magnitude and frequency of whole body weight transfers and anterior-posterior center of pressure movements. Fourteen of 32 participants (43.75%) were categorized as PDs. The first 15min of standing distinguished the two pain groups, as non-PD performed a higher frequency of lumbar spine flexion/extension fidgets and large body weight transfers. Both of these differences may be pre-disposing factors for transient LBP development, as they both occurred prior to PDs reaching the 10mm visual analog scale threshold for LBP classification.
Copyright © 2015 Elsevier B.V. All rights reserved.
There has been a major shift toward office workstations that accommodate standing postures. This shift is attributable to negative health and musculoskeletal issues from sedentary exposures. However, changing exposures from sitting to standing does not eliminate these issues, as evidence indicates prolonged standing also induces problems. Reducing seated exposure and rotating frequently between sitting and standing has been shown to result in positive health outcomes, reduced discomfort, and increased work performance. Implementing sit-stand workstations has promise to mitigate work-related health issues, if the users are provided with training that includes accommodations for individual work patterns and preferences.
Use of logical constraints among hypotheses and correlations among test statistics can greatly improve the power of step-down tests. An algorithm for uncovering these logically constrained subsets in a given dataset is described. The multiple testing results are summarized using adjusted p values, which incorporate the relevant dependence structures and logical constraints. These adjusted p values are computed consistently and efficiently using a generalized least squares hybrid of simple and control-variate Monte Carlo methods, and the results are compared to alternative stepwise testing procedures.
Sit-stand stools are available for use in industrial settings, but there is a lack of quantitative evidence
demonstrating benefits for lower limb, back and/or neck/shoulder outcomes. In this paper we describe
an experiment conducted to compare and contrast posture and time-related differences in muscular and
vascular outcomes during 34 min of manual repetitive work performed in either standing or sit-standing
work posture. We measured vascular parameters in the lower limbs, and muscular parameters in the
trunk and neck/shoulder, and discomfort in the three regions as participants accomplished a repetitive
box-folding task. Results show that blood flow in the foot (p ¼ 0.022) and ankle mean arterial pressure
(p < 0.001) were greater during standing. Left gluteus medius and external oblique activation was higher
during standing, while sit-standing work resulted in higher levels of co-activation between the left
erector spinae and external oblique muscle pair (p ¼ 0.026). Neck/shoulder muscle activity was not
significantly different between the conditions. Reported discomfort did not differ significantly for the
trunk and neck/shoulder region, but standing resulted in higher level of reported discomfort in the lower
limb. The sit-stand posture used in this experiment appears to prevent the undesirable lower limb
outcomes associated with static standing work posture.
Relevance to industry: This work demonstrates quantitative evidence to support the potential use of a sitstand
stool for industrial work operations, at least over relatively short durations.
Little is known about the number of spinal movements in the sagittal plane in daily life, mainly due to the lack of adequate techniques to assess these movements. Our aim was to measure these movements in asymptomatic volunteers. Two sensor strips based on strain gauge technology (Epionics SPINE system) were fixed on the skin surface of the back parallel to the spine on a total of 208 volunteers without back pain. First, the lordosis angle was determined during relaxed standing. The volunteers were then released to daily life. The increases and decreases in the back lumbar lordosis angle over a period of 24 h were determined and classified into 5A degrees increments. Changes in the lordosis angle greater than 5A degrees were considered. The median number of spinal movements performed within 24 h was approximately 4,400. Of these movements, 66 % were between 5A degrees and 10A degrees. The proportions of higher-magnitude lordosis angle changes were much lower (e.g., 3 % for the 20-25A degrees movement bin). Surprisingly, the median total number of movements was significantly higher (29 %) in women than in men. Large inter-individual differences were observed in the number of movements performed. The volunteers spent a median of 4.9 h with the lumbar spine flexed between 20A degrees and 30A degrees and only 24 min with the spine extended relative to the reference standing position. A median of 50 movements reached or exceeded full-flexion angle and zero movements full-extension angle. These data illustrate the predominantly small range of movement of the spine during daily activities and the small amount of time spent in extension. These unique data strongly contribute to the understanding of patients' everyday behavior, which might affect the development and testing of spinal implants and the evaluation of surgical and nonsurgical treatments.
With the recent attention to 'sitting disease', health practitioners and scientists are promoting standing in the workplace to decrease sedentary time, despite a high prevalence of low back pain (LBP) development during prolonged standing. The purpose of this study was to assess how a seated break inserted between bouts of prolonged standing would influence LBP development, posture and movement. A total of 20 participants stood for 45 minutes, sat for 15 minutes and repeated this sequence while lumbar and thoracic angles were measured, and LBP visual analogue scale reports were taken. Of the sample, 55% participants reported LBP in standing. A stand to sit ratio of 3:1 did not provide lasting recovery of LBP from standing and pain developers utilised a limited range of their lumbar spine angle and increased thoracic extension, resulting in static postures that caused tissue aggravation that was not resolved after 15 minutes of sitting. Prolonged standing in the workplace has the potential to result in LBP for some workers and alternate ways to reduce sedentary time should be investigated.
Gender differences in lumbar and pelvic posture have been reported previously in prolonged sitting, both in an office chair and automobile seat. To date, it is not known whether these postural exposures during prolonged driving affect the passive lumbar spine flexion stiffness. The purpose of this study was to examine time-varying responses of passive lumbar spine stiffness, lumbar spine and pelvic postures during a 2 h simulated driving trial. Secondary goals investigated the influence of gender on lumbar spine stiffness, discomfort scores and seat pressure profiles. Twenty (10 males, 10 females) subjects were recruited to complete a 2 h simulated driving task. Passive lumbar range of motion was measured on a customized frictionless jig before, halfway through and at the end of 2 h. During driving there was a time-varying difference in the lumbar flexion angles adopted by the gender groups. A significant interaction (p = 0.0458) was found for gender and time with women being found to sit significantly different than males in the second hour of driving exhibiting greater maximum lumbar flexion (60.0% ROM (±1.27) than men 50.0% ROM (±1.5). Both men and women demonstrated similar passive stiffness changes characterized by an initial increase in transitional zone stiffness after 1 h (+0.1 Nm/degree for males and +0.3 Nm/degree for females, p = 0.2372). Over 2 h of driving there was a non-significant trend of genders to respond differently to the seated exposure. Specifically transitional zone stiffness was found to increase in males (0.86 (SD 0.31) to 0.92 (SD 0.31) Nm/degree) and decrease in females (0.81 (SD0.88) to 0.73 (SD 0.52) Nm/degree) (p = 0.1178). Differences in lumbar posture and passive stiffness over 2 h of simulated driving were demonstrated between genders in this study.
Use of logical constraints among hypotheses and correlations among test statistics can greatly improve the power of step-down tests. An algorithm for uncovering these logically constrained subsets in a given dataset is described. The multiple testing results are summarized using adjusted p values, which incorporate the relevant dependence structures and logical constraints. These adjusted p values are computed consistently and efficiently using a generalized least squares hybrid of simple and control-variate Monte Carlo methods, and the results are compared to alternative stepwise testing procedures.
Prolonged standing in an occupational setting has long been associated with the development of low back pain. In response to this, researchers have investigated various interventions that can alleviate low back pain and discomfort, such as anti-fatigue mats, shoe insoles, and more recently, sloped platforms. The purpose of this study was to investigate the effects of a sloped surface on kinematics and trunk muscle thickness during quiet and prolonged occupational standing. Eleven participants performed 1-min quiet standing tasks on three surfaces - level ground, incline, and decline - followed by 16-min of prolonged standing in each condition. Trunk, lumbar, and global pelvis angles were measured during each standing condition, and muscle thickness measurements of erector spinae and the lateral abdominal wall were taken during the quiet standing task. During quiet standing, there were systematic changes in trunk, lumbar, and pelvis angles with the different surfaces; however, these changes were not accompanied by systematic changes in muscle thickness. The responses found during the quiet standing were consistent during prolonged standing. As a result, the reduced perceived low back pain found when using sloped platforms is likely not the result of changes in morphology of the trunk musculature, but might be related to the altered kinematics caused by standing on these platforms.
Understanding factors that influence preferred sitting postures is considered important to prevent low-back pain (LBP) associated with seated exposures. The purpose of this study was to examine the influence of gender and flexibility (hip, hamstring, and low-back) on lumbo-pelvic postures adopted when performing laboratory-simulated computer work and automobile driving. Ten female and 9 male volunteers were exposed to 10 minutes each of the abovementioned sitting conditions. Sagittal lumbo-pelvic kinematics were recorded during each sitting condition. Correlation analyses were per-formed between lumbo-pelvic postures and various measures of hip, hamstring, and low-back flexibility. When driving, females exhibited 9.8 degrees more posterior pelvic tilt (p = 0.0329) and 10.5 degrees more lumbar flexion (p = 0.0116) than males with respect to their lumbo-pelvic alignments in upright standing. When performing seated computer work, it was males who experienced greater posterior pelvic tilt (p = 0.0048). Individuals with greater hip flexibility, typically fe-males, adopted lumbar flexion postures closer to their voluntary end-range while driving (r = 0.5709; p = 0.0107). Indi-viduals who exhibited greater posterior pelvic tilt in office chair sitting, typically males, were those with less hip (r = – 0.5484; p = 0.0150) and hamstring (r = –0.4690; p = 0.0496) flexibility. Given that differences exist between males and females with respect to various indices of hip, hamstring, and low-back flexibility, it is possible that gender-based differ-ences in seated postures are related to inherent differences in flexibility between the sexes. These findings suggest that strategies to prevent LBP associated with sitting may depend on both individual flexibility characteristics and the type of seated exposure.
This study determined the differences in lower leg swelling, discomfort, and fatigue for three different conditions: sitting, standing, and using a sit–stand chair. On three different days, 18 subjects with no previous lower extremity problems sat in (1) an office chair, (2) a sit/stand chair, and (3) stood for 90 min. Leg volume changes the most when using the sit/stand chair (81.7 cm3) and least when sitting (38.2 cm3). The largest percent change in circumference occurred while sit/standing (2.9%) and the least when standing (1.7%). Subjective comfort ratings show that sitting is the most comfortable, using the sit/stand chair causes slight discomfort in the upper back, hips, and upper legs, and standing causes the most discomfort in the entire lower body, the feet in particular. Sitting causes the least fatigue and standing causes the most.Relevance to industryThe forward-sloping chair is a new concept starting to be introduced to the industries where standing for long periods of time is required. This data can be used to aid in the decision to use sit/stand chairs in industry.
Sitting is frequently assumed to cause high spinal loads because people with sedentary work often suffer from low back pain. It is assumed that the posture while sitting, as well as several seat parameters, also affects the spinal loads.
To measure the loads on a spinal implant for different upper body inclinations, backrest declinations, seat heights, types of seat, and arm positions.
Loads on a vertebral body replacement during sitting were measured in five patients with telemeterized implants.
The telemeterized vertebral body replacement measures all six load components. It was implanted into five patients suffering from compression fractures of a lumbar vertebral body. Loads were measured when the patients were sitting on a stool and inclining their upper body between 15° flexion and 10° extension in steps of 5°; on a chair with an adjustable backrest that allowed declination angles between 108° and 180°; on an office chair while the seat height was varied between 40 and 60 cm in steps of 5 cm; and successively on seven different types of seats. The effect of the arm position was also studied.
The resultant implant force was increased on the average by 48% for 15° flexion and decreased by 19% for 10° extension of the trunk. When sitting on a chair with an adjustable backrest, the loads decreased with an increasing backrest declination angle. The seat height had in most cases only a minor effect on implant loads. In comparison to sitting on a stool, the loads were reduced when sitting on a bench (7%) or a stool with a padded wedge (9%), a knee stool (19%), a chair (35%), and an office chair (41%). Sitting on a physiotherapy ball increased the loads by 7%. Placing the hands on the thighs reduced the implant loads on the average by 19% in comparison to arms hanging on the sides.
Spinal loads can be reduced by leaning against the backrest, placing the arms on the armrest or the thighs, and by decreasing the flexion angle of the upper body.
This study measured gluteus medius (GM) strength and endurance before and after a 2 h prolonged standing task in previously asymptomatic individuals, to compare between individuals who did and did not report pain in the low back. Twenty-four participants without a history of low back pain stood in a constrained area for 2h. Before and after the standing protocol, participant's maximal hip abduction strength (N) and side-bridge endurance (seconds and GM myoelectric fatigue) were measured. Continuous surface EMG was collected from GM during the 2-h protocol for analysis of bilateral co-activation. Pain in the low back was rated every 15 min with a visual analog scale (VAS). Seventeen of 24 (71%) previously asymptomatic participants developed pain in the low back during the standing protocol. These participants had lower side-bridge endurance (p = .002), and higher gluteus medius (GM) co-activation (p = .002) compared to participants who did not develop pain in the low back. Hip abduction strength decreased for both groups following prolonged standing, with no between groups' difference. Lower side-bridge endurance and hip abduction strength were significantly associated with higher GM co-activation (adjusted r(2) = .34), but not pain levels. Side-bridge endurance and GM co-activation, but not hip abduction strength, may have utility in identifying participants likely to develop pain in the low back during prolonged standing. The best training program for increasing GM endurance is unclear.
Forces acting on the body via various external surfaces during locomotion are needed to support the body under gravity, control posture, and overcome inertia. Examples include the forces acting on the body via the seating surfaces during wheelchair propulsion, the forces acting on the plantar foot tissues via the insole during gait, and the forces acting on the residual-limb tissues via the prosthetic socket during various movement activities. Excessive exposure to unwarranted stresses at the body-support interfaces could lead to tissue breakdowns commonly known as pressure ulcers, often presented as deep-tissue injuries around bony prominences or as surface damage on the skin. In this article, we review the literature that describes how the involved tissues respond to epidermal loading, taking into account both experimental and computational findings from in vivo and in vitro studies. In particular, we discuss related literature about internal tissue deformation and stresses, microcirculatory responses, and histological, cellular, and molecular observations.
Background:
Occupations that require prolonged periods of standing have been associated with increased reports of musculoskeletal disorders including low back pain. Previous work has utilized a prospective design of functionally inducing low back pain in previously asymptomatic individuals during a prolonged standing task. Increased trunk and gluteus medius muscle co-activation has been found in previously asymptomatic individuals who developed pain during standing compared with individuals who did not develop pain.
Purpose:
The purpose of this study was to investigate the subjective and biomechanical responses of known pain developers and non-pain developers (previously determined during level standing) when exposed to the same prolonged standing task protocol completed while standing on a +/-16 degrees sloped surface.
Results:
Overall low back pain scores were reduced by 59.4% for the pain development group, identified in level standing, when using the sloped surface. There was a marked decrease in the co-activation of the bilateral gluteus medius muscles in the known pain developers when standing on the sloped surface compared with level standing. However the non-pain developer group responded in the opposite direction by having an increase in the co-activation of these muscles, although they did not have a commensurate increase in low back pain. There were changes in both the postural and joint-loading variables examined. These changes were minimal and in most cases the sloped surface produced responses that bracketed the postures and loading magnitudes found in level standing depending on whether the participant was standing on the +16 degrees or -16 degrees surface.
Conclusions:
The sloped surface resulted in decreased subjective low back pain during prolonged standing. There were also associated biomechanical changes resulting from using a sloped surface during prolonged standing. These positive findings were supported in an exit survey satisfaction rating with 87.5% indicating that they would use the sloped surface if they were in an occupational setting that required prolonged standing work.
In vivo measurements of low back flexion posture and muscle activity before, during, and after static flexion.
To identify the occurrence of creep and muscle fatigue development in the low back during static upper body deep flexion that resembled an above ground work posture.
Static lumbar flexion has been related to the development of low back disorders, and its injury mechanism has been focused on the changes in passive spinal tissues. Potential influences of muscle fatigue of extensor muscles have not been explored.
A total of 20 asymptomatic subjects performed submaximal isometric trunk extension exertions and an isokinetic trunk flexion before and immediately after 5-minute static flexion while the trunk sagittal flexion angle and the myoelectric activities (electromyography [EMG]) of back extensor muscles were recorded simultaneously. Changes in the flexion-relaxation onset angle, maximum flexion angle, muscle activity level, and the median power frequency of EMG associated with the static flexion were evaluated.
Flexion-relaxation onset angle in isokinetic flexion and EMG amplitude of isometric extension were significantly greater after static flexion, indicating creep of spinal tissues in static flexion. Median power frequency of lumbar erector spinae EMG during isometric extension was significantly lower after static flexion, suggesting the development of muscle fatigue. Consistent but low level of EMG was observed together with sporadic muscle spasms during the static flexion period.
Fatigue of low back extensor muscles may occur in static flexion due to prolonged passive stretching of the muscles. Low back extensor muscles are required to generate more active forces in weight holding or lifting after static flexion to compensate for the reduced contribution of creep deformed passive tissues in maintaining spinal stability and the posture. The degraded force generating capacity of the fatigued muscles can be a significant risk factor for low back pain.
Purpose and scope:
Low back pain development has been associated with static standing postures in occupational settings. Previous work has demonstrated gluteus muscle co-activation as a predominant pattern in previously asymptomatic individuals who develop low back pain when exposed to 2-h of standing. The purpose of this work was to investigate muscle co-activation as a predisposing factor in low back pain development while including a multifactorial approach of clinical assessment tools and psychosocial assessments to identify individuals who are at risk for pain development during standing.
Results:
Forty percent of participants developed low back pain during the 2-h of standing. Pain developers demonstrated bilateral gluteus medius and trunk flexor-extensor muscle co-activation prior to reports of pain development. Pain developers and non-pain developers demonstrated markedly different patterns of muscle activation during the 2-h of standing. A novel screening test of active hip abduction was the only clinical assessment tool that predicted pain development.
Conclusions:
Gluteus medius and trunk muscle co-activation appears to be a predisposing rather than adaptive factor in low back pain development during standing. A combination of a positive active hip abduction test and presence of muscle co-activation during standing may be useful for early identification of at-risk individuals.
Seated postures are achieved with a moderate amount of lumbo-sacral flexion and sustained lumbo-sacral spine flexion has been associated with detrimental effects to the tissues surrounding a spinal joint. The purpose of this study was to determine if the lower intervertebral joints of the lumbo-sacral spine approach their end ranges of motion in seated postures.
Static sagittal digital X-ray images of the lumbo-sacral region from L3 to the top of the sacrum were obtained in five standing and seated postures from 27 participants. Vertebral body bony landmarks were manually digitized and intervertebral joint angles were calculated for the three lower lumbo-sacral joints.
In upright sitting, the L5/S1 intervertebral joint was flexed to more than 60% of its total range of motion. Each of the lower three intervertebral joints approached their total flexion angles in the slouched sitting posture. These observations were the same regardless of gender. The results support the idea that lumbo-sacral flexion is driven by rotation of the pelvis and lower intervertebral joints in seated postures.
This is the first study to quantitatively show that the lower lumbo-sacral joints approach their total range of motion in seated postures. While not directly measured, the findings suggest that there could be increased loading of the passive tissues surrounding the lower lumbo-sacral intervertebral joints, contributing to low back pain and/or injury from prolonged sitting.
In this study the influence of chair characteristics on comfort, discomfort, adjustment time and seat interface pressure is investigated during VDU and non-VDU tasks: The two investigated office chairs, both designed according to European and Dutch standards are different regarding: 1) seat cushioning and shape, 2) backrest angle and 3) controls. Thirty subjects in total, both male and female, participated in two experiments: twenty in the first and ten in the second. Significant differences are found for ease of adjustment and adjustment time of controls, independent of the tasks. Related to tasks, a significant difference was found for the backrest range of motion. For non-VDU tasks a larger range of backrest motion was preferred by 70% of the subjects. The chair design differences were most clear for comfort and adjustment time of controls, followed by comfort of backrest angle. No differences are found between seat pan comfort and discomfort, first impressions and peak interface pressure.
A brief review of kinesiological research with special reference to electromyographic kinesiology is presented. The review deals with, among other things, the use of electromyography in functional anatomical studies, in biomechanical studies on muscular force, in neurophysiological studies on muscular fatigue, in applied kinesiologic studies and in vocational studies.
A descriptive comparative study was done to validate the use of the treadmill as an experimental device to investigate the electromyographic (EMG) signal during human locomotion. Eight subjects walked on a walkway and on a treadmill and EMG recordings of several consecutive strides were made during each procedure. These recordings were made from the soleus, rectus femoris, biceps femoris, vastus medialis and tibialis anterior muscles. By using the correlation coefficient and the value of the slope of the regression line resulting from correlating the linear envelopes (digitized at 50 Hz) of EMG activity from the two walk modes, it was shown that similar profiles of EMG activity exist between the walkway and treadmill. This was so for most muscles investigated with one exception, the biceps femoris. Furthermore, there was a tendency for the treadmill data to indicate slightly larger EMG amplitudes, but lower variation, than did the walkway data. However, in view of the overall similarity of the profiles obtained from both conditions, it is concluded that the treadmill is a valid laboratory instrument to study gait.
Cadaveric lumbar intervertebral joints were loaded to simulate the erect standing posture (lordosis), and the erect sitting posture (slightly flexed). The results show that, after the intervertebral disc has been reduced in height by a period of sustained loading, the apophysial joints resist about 16 per cent of the intervertebral compressive forces in the erect standing posture, whereas in the erect sitting posture they resist none. The implications of this in relationship to degenerative changes and to low backache are discussed.
This paper presents an inexpensive and simple system to measure the way of use of the backrest. The system can be also used in field studies. It is based on a set of electrodes which, attached to the subject's back and the backrest, allows the contact area to be measured. A laboratory test was performed to validate the system. In the test the spontaneous use of the backrest in standard office chairs and tasks was studied. Four different types of backrest use have been detected, and it has been shown that they determine the lumbar curvature and pelvic inclination angles, as well as postural mobility. The comfort levels observed in the four types of backrest use were also different. Consequently, the system can be used as an indicator of back posture and comfort.
The biomechanics, histology and electromyography of the lumbar viscoelastic tissues and multifidus muscles of the in vivo feline were investigated during 20 min of static as well as cyclic flexion under load control and during 7 h of rest following the flexion. It was shown that the creep developed in the viscoelastic tissues during the 20 min of static or cyclic flexion did not fully recover over the 7 h of following rest. It was further seen that a neuromuscular disorder with five distinct components developed during and after the static and cyclic flexion. The neuromuscular disorder consisted of a decreasing magnitude of reflexive EMG from the multifidus upon flexion as well as of superimposed spasms. The recovery period was characterized by an initial muscle hyperexcitability, a slowly increasing reflexive EMG and a delayed hyperexcitability. Histological data from the supraspinous ligament demonstrate significant increase (x 10) in neutrophil density in the ligament 2 h into the recovery and even larger increase (x 100) 6 h into the recovery from the 20 min flexion, indicating an acute soft tissue inflammation. It was concluded that sustained static or cyclic loading of lumbar viscoelastic tissues may cause micro-damage in the collagen structure, which in turn reflexively elicit spasms in the multifidus as well as hyperexcitability early in the recovery when the majority of the creep recovers. The micro-damage, however, results in the time dependent development of inflammation. In all cases, the spasms, initial and delayed hyperexcitabilities represent increased muscular forces applied across the intervertebral joints in an attempt to limit the range of motion and unload the viscoelastic tissues in order to prevent further damage and to promote healing. It is suggested that a significant insight is gained as to the development and implications of a common idiopathic low back disorder as well as to the development of cumulative trauma disorders.
The most common cause of low-back pain related to seating is posterior protrusion or extrusion of lower lumbar intervertebral discs.
The normal curve of the lumbar spine in adult man is determined by maintenance of the trunk-thigh and the knee angles at approximately 135 degrees.
Alteration of this normal lumbar curve, either an increase in standing erect or a decrease in sitting or stooping, is caused largely by the limited length and consequent pull of the trunk-thigh muscles of the opposite side.
The most important postural factor in the causation of low-back pain in sitting is decrease of the trunk-thigh angle and consequent flattening of the lumbar curve.
The next most important cause of low-back pain in sitting is lack of primary back support over the vulnerable lower lumbar intervertebral discs.
Added factors of comfort in seating are the shortness of the seat, a rounded narrow front border, an open space beneath for better positioning of the legs, and permissive change of position in the seat.
The design of all seats, regardless of model or size, should be based on this knowledge.
Prolonged sitting may alter the passive stiffness of the lumbar spine. Consequently, performing full lumbar flexion movements after extended periods of sitting may increase the risk of low back injury.
The purpose was to quantify time-varying changes in the passive flexion stiffness of the lumbar spine with exposure to prolonged sitting and to link these changes to lumbar postures and trunk extensor muscle activation while sitting. A secondary objective was to determine whether men and women responded differently to prolonged sitting.
Passive lumbar flexion moment-angle curves were generated before, during and after 2 hours of sitting. Lumbar flexion/extension postures and extensor muscle activation levels were measured while sitting.
Twelve (6 men, 6 women) university students with no recent low back pain were studied.
Quantified changes in the shapes of the passive flexion moment-angle curves (slopes, breakpoints and maximum lumbar flexion angles) were the outcome measures. While sitting, average lumbar flexion/extension angles, the distribution of lumbar flexion/extension postures, average electromyogram (EMG) amplitude, the number and average length of EMG gaps, and trunk extensor muscle rest levels were measured.
Participants performed deskwork for 2 hours while sitting on the seat pan of an office chair. Moment-angle relationships for the lumbar spine were derived by pulling participants through their full voluntary range of lumbar flexion on a customized frictionless table.
Lumbar spine stiffness increased in men after only 1 hour of sitting, whereas the responses of women were variable over the 2-hour trial. Men appeared to compensate for this increase in stiffness by assuming less lumbar flexion in the second hour of sitting.
Changes in the passive flexion stiffness of the lumbar spine may increase the risk of low back injury after prolonged sitting and may contribute to low back pain in sitting.
Individuals may respond differently to various chair designs and the factors that influence these sitting behaviours are not well understood. There is very little information in the scientific literature regarding the observation and documentation of gender differences in seated postures. In particular, anecdotal observations of potential gender-specific sitting behaviours led us to test the influence of gender on the postural responses to different seated conditions.
Sixteen healthy university students (8 males and 8 females) were tested on four different chair configurations. Upper body kinematics (spine angles and centre of mass) and seat pressure profiles (centre of pressure, peak pressure) were obtained during each testing session.
Regardless of the chair used or the task performed, average lumbar and trunk angles were significantly more flexed for males than for females (P=0.047 and P=0.0026, respectively). Males exhibited average lumbar spine and trunk angles of 65.4 degrees (SD 16.2 degrees ) and 29.8 degrees (SD 28.3 degrees ), respectively, while female lumbar spine and trunk angles were 49.6 degrees (SD 23.1 degrees ) and -3.3 degrees (SD 20.4 degrees ), respectively. The pelvis was posteriorly rotated for males (7.6 degrees (SD 8.2 degrees )) and anteriorly rotated for females (-5.5 degrees (SD 9.3 degrees )) (P=0.0008). Significant gender *chair interactions of the location of the individual on the chair seat were most marked for the pivoting chair with a back rest. Females positioned their centre of mass and hip joints anterior to the chair pivot point while males' centre of mass (P=0.0003) and hip joints (P=0.0039) were located posterior to the pivot point. Females also sat with their centre of mass closer to the seat pan centre of pressure than males when a back rest was present (P=0.0012).
Males and females may be exposed to different loading patterns during prolonged sitting and may experience different pain generating pathways. Therefore, gender-dependent treatment modalities and/or coaching should be implemented when considering methods of reducing the risk of injury or aggravation of an existing injury.
Trunk electromyographic signals (EMG) are often contaminated with heart muscle electrical activity (ECG) due to the proximity of the collection sites to the heart and the volume conduction characteristics of the ECG through the torso. Few studies have quantified ECG removal techniques relative to an uncontaminated EMG signal (gold standard or criterion measure), or made direct comparisons between different methods for a given set of data. Understanding the impacts of both untreated contaminated EMG and ECG elimination techniques on the amplitude and frequency parameters is vital given the widespread use of EMG. The purpose of this study was to evaluate four groups of current and commonly used techniques for the removal of ECG contamination from EMG signals. ECG recordings at two intensity levels (rest and 50% maximum predicted heart rate) were superimposed on 11 uncontaminated biceps brachii EMG signals (rest, 7 isometric and 3 isoinertial levels). The 23 removal methods used were high pass digital filtering (finite impulse response (FIR) using a Hamming window, and fourth-order Butterworth (BW) filter) at five cutoff frequencies (20, 30, 40, 50, and 60 Hz), template techniques (template subtraction and an amplitude gating template), combinations of the subtraction template and high pass digital filtering, and a frequency subtraction/signal reconstruction method. For muscle activation levels between 10% and 25% of maximum voluntary contraction, the template subtraction and BW filter with a 30 Hz cutoff were the two best methods for maximal ECG removal with minimal EMG distortion. The BW filter with a 30 Hz cutoff provided the optimal balance between ease of implementation, time investment, and performance across all contractions and heart rate levels for the EMG levels evaluated in this study.
The objective of the study was to evaluate the differences between sitting on a stability ball and in an office chair in terms of trunk muscle activation and lumbar spine posture.
Stability balls have become increasingly popular as an alternative to office chairs to help reduce the prevalence of low back pain; however, little research has been conducted on their use as office chairs.
The 14 participants (7 men, 7 women) were required to sit on both a stability ball and an office chair for 1 hour each while performing various computer workstation tasks throughout the sitting periods. The activation of eight muscles and lumbar spine posture were measured and analyzed.
Increased muscle activation in thoracic erector spinae (p = .0352), decreased pelvic tilt (p = .0114), and increased perceived discomfort (p < .0001) while sitting on the stability ball were observed.
The small changes in biological responses when sitting on a stability ball as compared with an office chair, combined with the increased reported discomfort while on the ball, suggests its use for prolonged sitting may not be advantageous.
Prolonged sitting on a stability ball does not greatly alter the manner in which an individual sits, yet it appears to increase the level of discomfort. Therefore, it is important to fully explore a new chair design and consult scientific research before implementing its use.
Positional magnetic resonance imaging (MRI) study of control subjects.
To determine dimensional changes in the lumbar dural sac as a function of posture, and to establish changes between the supine, erect and seated positions.
Studies using computerized tomography and MRI were done to determine the mechanical effects on the lumbar spinal canal in the different positions. There has been no consecutive study, however, in which normal individuals were investigated for positional changes of the dural sac, including true standing position.
Thirty-two male asymptomatic volunteers were recruited. The examination was performed using a new MRI system. All subjects were examined with sagittal T2 and axial T1-weighted spin-echo images. The subjects were studied in the supine, standing, and sitting positions. The measurements were made using OSIRIS software (Digital Imaging Unit University Hospital of Geneva, Geneva, Switzerland). On axial images, dural sac cross-sectional area and anteroposterior (AP) dural sac diameter were measured at the level of the L3/4, L4/5, and L5/S1 discs. On midsagittal images, AP dural sac diameter and the upper-endplate angles of L1 and S1 were measured.
We found a disc degeneration or disc protrusion in 41% (12/29) of the subjects, but there was no obvious compression of the dural sac. Depending on the postures, the mean dural sac cross-sectional area and AP dural sac diameter changed. At all levels, mean dural sac cross-sectional area in the supine position was significantly smaller than in other postures. The dural area decreased most at the L5/S1 level due to positional change from standing to supine. The largest dural area at the L5/S1 level was in sitting extended. AP dural sac diameter on axial and midsagittal images showed a similar tendency.
A significant posture-dependent difference of the dural sac cross-sectional area at the level of intervertebral disc in asymptomatic volunteers has been demonstrated. When the posture changed from supine to standing position, lumbar dural sac volume expanded by the increased pressure of cerebrospinal fluid, and the dural sac cross-sectional area increased. The smallest values were found in the supine position.
The Relationships of Prolonged Standing Induced Low Back Pain Development with Lumbopelvic Posture and Movement Patterns.” PhD diss
- K M Gallagher
Spine Biomechanics of Prolonged Sitting: Exploring the Effect Chair Features, Walking Breaks and Spine Manipulation Have on Posture and Perceived Pain in Men and Women
- D Carvalho
- E Diana