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

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Prolonged Standing-Induced Low Back Pain Is Linked to Extended Lumbar Spine Postures: A Study Linking Lumped Lumbar Spine Passive Stiffness to Standing Posture

Postural assessments of the lumbar spine lack valuable information about its properties. The purpose of this study was to assess neutral zone (NZ) characteristics via in vivo lumbar spine passive stiffness and relate NZ characteristics to standing lumbar lordosis. A comparison was made between those that develop low back pain during prolonged standing (pain developers) and those that do not (nonpain developers). Twenty-two participants with known pain status stood on level ground, and median lumbar lordosis angle was calculated. Participants were then placed in a near-frictionless jig to characterize their passive stiffness curve and location of their NZ. Overall, both pain developers and nonpain developers stood with a lumbar lordosis angle that was more extended than their NZ boundary. Pain developers stood slightly more extended (in comparison to nonpain developers) and had a lower moment corresponding to the location of their extension NZ boundary. Overall, in comparison to nonpain developers, pain developers displayed a lower moment corresponding to the location of their extension NZ boundary which could correspond to greater laxity in the lumbar spine. This may indicate why pain developers have a tendency to stand further beyond their NZ with greater muscle co-contraction.

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

OBJECTIVE

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

APPLICATION

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

Lower limb postures resembling sitting and standing alter lumbar angles along the passive stiffness curve

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.

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

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

In vivo through-range passive stiffness of the lumbar spine: a meta-analysis of measurements and methods

Passive spinal stiffness is an important property thought to play a significant role in controlling spinal position and movement. Measuring through-range passive stiffness in vivo is challenging with several methods offered in the literature. Currently, no synthesis of values or methods exists to which to compare literature to. This study aims to provide a contemporary review and quantitative synthesis of the through-range in vivo passive lumbar spinal stiffness values for each of the cardinal planes of movement. A structured systematic search, following PRISMA guidelines, of 28 electronic databases was conducted in 2022. Articles were restricted to peer-reviewed English language studies investigating in vivo through-range passive stiffness of the lumbar spine. Thirteen studies were included, ten relating to flexion/extension, four to lateral bending and five to axial rotation. Average stiffness values, as weighted means and confidence intervals, for each of the four sections of the moment-movement curves were synthesised for all planes of movement. Lateral bending was found to be the comparatively stiffest movement followed by flexion and then axial rotation. Future research should focus on the validity and reliability of measurement techniques. Axial rotation would also benefit from further study of its latter stages of range.

Graphical abstract

The Relationship Between the NSP and the Individual and Work Organizational Variables: A Cross-Sectional Study

Objectives

To investigate the characteristics of neck-shoulder pain (NSP) and explore the potentional relationship between the NSP and the individual and work organizational variables.

Methods

A cross-sectional study was performed in the tertiary general hospitals in Hunan Province, China between May 2019 and July 2019. A total of 2,030 healthcare workers were enrolled randomly in this study based on a three-stage stratified sampling method. The Neck Disability Index (NDI) was used to measure disability in subjects with neck pain. A self-administered questionnaire was used to assess the characteristics of individual and work organizational variables. The Mann-Whitney U test and the Kruskal-Wallis H test were applied to analyze the prevalence of pain intensity among groups. Multivariate linear regression analysis was performed to explore the potentional relationship between NSP and individual and work organizational variables using the NDI score as the dependent variable.

Results

2,008 of 2,030 healthcare workers filled out the survey questionnaires online. In the past 12 months, 1,489 participants (74.2%) complained of pain in the cervical-shoulder region. NDI score increased by 0.10 for each year of age, with healthcare workers working in Obstetrics and Gynecology, and the Operating Room less likely to have NSP than those working in other departments. In contrast, female healthcare workers with a history of pregnancy were more likely to have NSP. In terms of organizational factors, workers who received concern from their supervisor about their health, who had the choice to change their shift status to off duty when they were not feeling well, or who were informed about WMSDs were less likely to have NSP.

Conclusion

The prevalence of NSP within the previous year was high in this population. Individual factors including history of neck-shoulder diseases, age, and history of pregnancy and organizational factors including being adequately informed regarding WMSDs, concern from supervisors about workers' health, and the ability of workers to change their shift status to off duty when they were not feeling well were shown to induce significant effects to NSP.

Passive stiffness changes in the lumbar spine following simulated automotive low speed rear-end collisions

BACKGROUND

Historically, there has been a lack of focus on the lumbar spine during rear impacts because of the perception that the automotive seat back should protect the lumbar spine from injury. As a result, there have been no studies involving human volunteers to address the risk of low back injury in low velocity rear impact collisions.

METHODS

A custom-built crash sled was used to simulate rear impact collisions. Randomized collisions were completed with and without lumbar support. Measures of passive stiffness were obtained prior to impact (Pre), immediately post impact (Post) and 24 h post impact (Post-24). Low back pain reporting was monitored for 24 h following impact exposure.

FINDINGS

None of the participants developed clinically significant levels of low back pain after impact. Changes in the passive responses persisted after impact for the length of the low stiffness flexion and extension zone. The length of the low stiffness zone was longer in the Post and Post-24 trial for low stiffness flexion and longer in the Post-24 for low stiffness extension.

INTERPRETATION

Findings from this investigation demonstrate that during a laboratory-simulation of an 8 km/h rear-impact collision, young healthy adults did not develop low back pain. Changes in the low stiffness zone of the passive flexion/extension curves were observed following impact and persisted for 24 h. Changes in passive stiffness may lead to changes in the loads and load distributions during movement within the passive structures such as the ligaments and intervertebral discs following impacts.

Prediction and comparison of postural discomfort based on MLP and quadratic regression

OBJECTIVE

The objective of this study was to predict postural discomfort based on the deep learning-based regression (multilayer perceptron [MLP] model).

METHODS

A total of 95 participants performed 45 different static postures as a combination of 3 neck angles, 5 trunk angles, and 3 knee angles and rated the whole-body discomfort. Two different combinations of variables including model 1 (all variables: gender, height, weight, exercise, body segment angles) and model 2 (gender, body segment angles) were tested. The MLP regression and a conventional regression (quadratic regression) were both conducted, and the performance was compared.

RESULTS

In the overall regression analysis, the quadratic regression showed better performance than the MLP regression. For the postural discomfort group-specific analysis, MLP regression showed greater performance than the quadratic regression especially in the high postural discomfort group. The MLP regression also showed better performance in predicting postural discomfort among individuals who had a variability of subjective rating among different postures compared to the quadratic regression. The deep learning for postural discomfort prediction would be useful for the efficient job risk assessment for various industries that involve prolonged static postures.

CONCLUSIONS

The deep learning for postural discomfort prediction would be useful for the efficient job risk assessment for various industries that involve prolonged static postures. This information would be meaningful as basic research data to study in predicting psychophysical data in ergonomics.

Passive stiffness characteristics and neutral zone quality of the scoliotic lumbar torso in the principle anatomical planes of motion

BACKGROUND

The 1-10% prevalence rate of adult scoliosis frequently requires expensive therapy and surgical treatments and demands further research into the disease, especially with an aging population. Most studies examining the mechanics of scoliosis have focused on in vitro testing or computer simulations. This study quantitatively defined the passive stiffness properties of the in vivo scoliotic spine in three principle anatomical motions and identified differences relative to healthy controls.

METHODS

Adult scoliosis (n = 14) and control (n = 17) participants with no history of spondylolisthesis, spinal fracture, or spinal surgery participated in three different tests (torso lateral side bending, torso axial rotation, and torso flexion/extension) that isolated mobility to the in vivo lumbar spine. The spinal stiffnesses and spinal neutral zone width were calculated. These parameters were statistically compared between factor of population and within factor of direction.

FINDINGS

Torque-rotational displacement data were fit using a double sigmoid function, resulting an in excellent overall fit (Avg. R² = 0.95). There was a significant interaction effect between populations when comparing axial twist neutral zone width vs. lateral bend neutral zone width and axial twist stiffness vs. lateral bend stiffness. The axial twist neutral zone width magnitude was significantly larger in scoliosis patients.

INTERPRETATION

The present study is the first investigation to quantify the whole trunk neutral zone of the scoliotic lumbar spine. Future research is needed to determine if lumbar spine mechanical characteristics can help explain progression of scoliosis and complement scoliosis classification systems.

A Comparison of Clinical Spinal Mobility Measures to Experimentally Derived Lumbar Spine Passive Stiffness

Spinal stiffness and mobility assessments vary between clinical and research settings, potentially hindering the understanding and treatment of low back pain. A total of 71 healthy participants were evaluated using 2 clinical assessments (posteroanterior spring and passive intervertebral motion) and 2 quantitative measures: lumped mechanical stiffness of the lumbar spine and local tissue stiffness (lumbar erector spinae and supraspinous ligament) measured via myotonometry. The authors hypothesized that clinical, mechanical, and local tissue measures would be correlated, that clinical tests would not alter mechanical stiffness, and that males would demonstrate greater lumbar stiffness than females. Clinical, lumped mechanical, and tissue stiffness were not correlated; however, gradings from the posteroanterior spring and passive intervertebral motion tests were positively correlated with each other. Clinical assessments had no effect on lumped mechanical stiffness. The males had greater lumped mechanical and lumbar erector spinae stiffness compared with the females. The lack of correlation between clinical, tissue, and lumped mechanical measures of spinal stiffness indicates that the use of the term "stiffness" by clinicians may require reevaluation; clinicians should be confident that they are not altering mechanical stiffness of the spine through segmental mobility assessments; and greater resting lumbar erector stiffness in males suggests that sex should be considered in the assessment and treatment of the low back.

The effect of age, prolonged seated work and sex on posture and perceived effort during a lifting task

The purpose of this investigation was to determine the effect of prolonged seated work, lift task, age and sex on normalized lumbar angles, thoracic angles, perceived effort and duration of lifts. A total of 17 young and 17 mature participants were recruited with an average (standard deviation) age of 23.8 (5.0) years and 63.7 (3.9) years, respectively. Participants completed 3 different floor to knuckle lifts before and following 90 min of seated work. The lifts included; (i) 7 kg symmetrical, (ii) 4.5 kg symmetrical and (iii) 4.5 kg asymmetrical. Prolonged seated work and age interacted to affect normalized peak lumbar angles (p = 0.0469) where older adults adopted 56(15)% flexion after seated work compared to 67(16)% among younger adults. Older adults took significantly longer to complete the lifting tasks compared to younger adults while age did not affect perceived effort across lifting tasks. Older workers may require age specific interventions given age specific responses.

Influence of creep deformation on sub-regional lumbar spine motion during manual lifting

Prolonged or repetitive spine flexion induces creep deformation of posterior spine tissues allowing for increased intervertebral motion beyond 'normal' limits, which may influence sub-regional (intersegmental) spine motion during subsequent manual lifting tasks. Using spine skin-surface kinematics, intersegmental lumbar spine motion was recorded over 20 minutes of prolonged static spine flexion and a subsequent manual lifting task (2 lifts every 3 minutes, 30 minutes total) in 14 participants. Results demonstrated that mid to lower lumbar intersegmental levels (i.e. L₂/L₃ to L₄/L₅) experienced the greatest overall creep deformation and range of motion during both prolonged flexion and manual lifting; however, overall range of motion during manual lifting was unaffected. Additionally, creep deformation did not completely recover within 30 minutes. Future work should continue to investigate the influence of this residual creep, as well as how overall creep deformation impacts spine neuromuscular control and stability, and ultimately the development of low back disorders. Practitioner summary: Mid to lower lumbar spine levels (i.e. L₂/L₃ to L₄/L₅) experienced the greatest creep deformation and range of motion during both prolonged flexion and manual lifting. Repeated lifting following prolonged flexion may limit creep recovery; however, overall lifting kinematic motion remained unchanged.