Time-varying changes in the lumbar spine from exposure to sedentary tasks and their potential effects on injury mechanics and pain generation

General body discomfort increases over time during prolonged sitting and it is typically accepted that no single posture can be comfortably maintained for long periods. Despite this knowledge, workplace exposure to prolonged sitting is very common. Sedentary occupations that expose workers to prolonged sitting are associated with an increased risk of developing low back pain (LBP), disc degeneration and lumbar disc herniation. Given the prevalence of occupations with a large amount of seated work and the propensity for a dose-response relationship between sitting and LBP, refining our understanding of the biomechanics of the lumbar spine during sitting is important. Sitting imposes a flexed posture that, when held for a prolonged period of time, may cause detrimental effects on the tissues of the spine. While sitting is typically viewed as a sedentary and constrained task, several researchers have identified the importance of investigating movement during prolonged sitting. The studies in this thesis were designed to address the following two global questions: (1) How do the lumbar spine and pelvis move during sitting? (2) Can lumbar spine movement and postures explain LBP and injury associated with prolonged sitting? The first study (Study 1) examined static X-ray images of the lower lumbo-sacral spine in a range of standing and seated postures to measure the intervertebral joint angles that contribute to spine flexion. The main finding was that the lower lumbo-sacral joints approach their total range of motion in seated postures. This suggests 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. Study 2 compared external spine angles measured using accelerometers from L3 to the sacrum with corresponding angles measured from X-ray images. While the external and internal angles did not match, the accelerometers were sensitive to changes in seated lumbar posture and were consistent with measurements made using similar technology in other studies. This study also provided an in-depth analysis of the current methods for data treatment and how these methods affect the outcomes. A further study (Study 3) employed videofluoroscopy to investigate the dynamic rotational kinematics of the intervertebral joints of the lumbo-sacral spine in a seated slouching motion in order to determine a sequence of vertebral motion. The pelvis did not initiate the slouching motion and a disordered sequence of vertebral rotation was observed at the initiation of the movement. Individuals performed the slouching movement using a number of different motion strategies that influenced the IVJ angles attained during the slouching motion. From the results of Study 1, it would appear as though the lowest lumbar intervertebral joint (L5/S1) contribute the most to lumbo-sacral flexion in upright sitting, as it is at approximately 60% of its end range in this posture. However, the results from Study 3 suggest that there is no consistent sequence of intervertebral joint rotation when flexing the spine from upright to slouched sitting. When moving from standing to sitting, lumbar spine flexion primarily occurs at the lowest joint (i.e. L5/S1); however, a disordered sequence of vertebral motion the different motion patterns observed may indicate that different joints approach their end range before the completion of the slouching movement. In order to understand the biomechanical factors associated with sitting induced low back pain, Study 4 examined the postural responses and pain scores of low back pain sufferers compared with asymptomatic individuals during prolonged seated work. The distinguishing factor between these two groups was their respective time-varying seated lumbar spine movement patterns. Low back pain sufferers moved more than asymptomatic individuals did during 90 minutes of seated work and they reported increased low back pain over time. Frequent shifts in lumbar spine posture could be a mechanism for redistributing the load to different tissues of the spine, particularly if some tissues are more vulnerable than others. However, increased movement did not completely eliminate pain in individuals with pre-existing LBP. The LBP sufferers’ seated spine movements increased in frequency and amplitude as time passed. It is likely that these movements became more difficult to properly control because LBP patients may lack proper lumbar spine postural control. The results of this study highlight the fact that short duration investigations of seated postures do not accurately represent the biological responses to prolonged exposure. Individuals with sitting-induced low back pain and those without pain differ in how they move during seated work and this will have different impacts on the tissues of the lumbar spine. A tissue-based rational for the detrimental effects on the spinal joint of prolonged sitting was examined in Study 5 using an in vitro spine model and simulated spine motion patterns documented in vivo from Study 4. The static protocol simulated 2 hours of sitting in one posture. The shift protocol simulated infrequent but large changes in posture, similar to the seated movements observed in a group of LBP sufferers. The fidget protocol replicated small, frequent movements about one posture, demonstrated by a group of asymptomatic individuals. Regardless of the amount of spine movement around one posture, all specimens lost a substantial amount of disc height. Furthermore, the passive range of motion of a joint changed substantially after 2 hours of simulated sitting. Specifically, there were step-like regions of reduced stiffness throughout the passive range of motion particularly around the adopted “seated flexion” angle. However, small movements around a posture (i.e. fidgeting) may mitigate the changes in the passive stiffness in around the seated flexion angle. The load transferred through the joint during the 2-hour test was varied either by changing postures (i.e. shifting) or by a potential creep mechanism (i.e. maintaining one static posture). Fidgeting appeared to reduce the variation of load carriage through the joint and may lead to a more uniform increase in stiffness across the entire passive range of motion. These changes in passive joint mechanics could have greater consequences for a low back pain population who may be more susceptible to abnormal muscular control and clinical instability. Nevertheless, the observed disc height loss and changes in joint mechanics may help explain the increased risk of developing disc herniation and degeneration if exposure to sitting is cumulative over many days, months and years. In summary, this work has highlighted that seated postures place the joints of the lumbar spine towards their end range of motion, which is considered to be risky for pain/injury in a number of tissue sources. In-depth analyses of both internal and external measurements of spine postures identified different seated motion patterns and self-selected seated postures that may increase the risk for developing LBP. The model of seated LBP/discomfort development used in this thesis provided evidence that large lumbar spine movements do not reduce pain in individuals with pre-existing LBP. Tissue-based evidence demonstrated that 2 hours of sitting substantially affects IVJ mechanics and may help explain the increased risk of developing disc herniation and degeneration if exposure to sitting is cumulative over many days, months and years. The information obtained from this thesis will help develop and refine interventions in the workplace to help reduce low back pain during seated work

Low back pain and sickness absence among sedentary workers: the influence of lumbar sagittal movement characteristics and psychosocial factors

Introduction: Low back pain remains a burden for society, since it can lead to sickness absence and work disability. Physical occupational risk factors can contribute to the development of back pain, yet little is known about any risks in sedentary jobs posed by sitting. The influence of psychosocial factors on back pain and sickness absence amongst sedentary workers is also unclear. The aim of this study was to measure work activities, lumbar movement characteristics, symptoms and psychosocial factors in order to determine associations with low back pain and sickness absence. Methods: Phase 1: involved validation of a fibre-optic goniometer system that attaches to the lumbar spine and hip to continuously measure: (1) activities (sitting, standing, walking); and (2) lumbar movement characteristics (notably sitting postures and kinematics). New questionnaires were also validated to measure aspects of low back discomfort. Phase 2: consisted of a cross-sectional survey of call centre workers (n=600) to collect data on: demographics, clinical and occupational psychosocial factors, and symptoms. An experimental sample (n=140) wore the goniometer system during work. Phase 3: involved a 6-month follow-up survey to collect back pain and sickness absence data (n=367). Logistic regression was used to determine associations (P<0.05) between data. Results: Workers spent 83% of work-time sitting, 26% of which was spent adopting a lordotic lumbar posture. Current back pain (>24hrs: yes/no) was associated with a kyphotic sitting posture (time spent with a lumbar curve ≥180°) (R2 0.05), although future back pain was not. Using multivariable models: limited variety of lumbar movement whilst sitting was associated with future (persistent) LBP, dominating other variables (R2 0.11); yet high levels of reported back discomfort, physical aggravating factors and psychological demand at work were stronger predictors of sickness absence, and dominated other variables (R2 0.24). Interpretation: Workers do not follow the advice from employers to maintain a lumbar lordosis whilst sitting, as recommended by statutory bodies. Furthermore, sitting with a kyphotic posture did not increase the risk of back pain, although a relative lack of lumbar movement did. Thus, ergonomic advice encouraging lumbar movement-in-sitting appears to be justified. Predictors of sickness absence were multi-factorial, and consideration of work-relevant biomedical and psychosocial factors would be more useful than adopting more narrow screening approaches

Evaluation of a novel thoracic support for police officers during prolonged simulated driving exposures

Background: There is a high prevalence of injury and low back pain prevalence associated with professional drivers, including mobile police officers. In particular, the reduction in lumbar lordosis has been hypothesized as a contributing risk factor for injury during prolonged seated periods. Furthermore, the use of the mobile data terminal (MDT) and the protective equipment worn by officers creates a unique interface between the occupant and the car seat. Purpose: To evaluate a novel thoracic support that was designed to address the unique seated working demands of mobile police officers. Methods: Fourteen participants: 7 male (21.3 (1.9) years, 1.71 (0.06) m, 75.1 (9.3) kg) and 7 female (23.3 (4.4) years, 1.69 (0.06) m, 68.2 (7.7) kg) were recruited from a university student population. Participants attended two 120 minute driving simulations on separate days; using a standard Crown Victoria Interceptor seat and the same seat equipped with a retrofitted surface mounted thoracic support. Time-varying spine postures, seat pressure measures and perceived discomfort were measured. Results: The introduction of a thoracic support changed postures, reduced lower seat back interface pressures but did not reduce discomfort compared to a standard seat during a 2 hour exposure period. Average discomfort scores were low with all values below 10mm out of a possible 100mm for both seating conditions. Discomfort was found to have small increases over time in the neck and right thigh with the support, but mean values remained low (under 3mm). Lumbar angles became more flexed with the support compared to a standard seat. Posterior pelvic rotation was reduced in female participants while in males there was greater posterior pelvic rotation with the support. There was a reduction in interface pressures on the bottom half of the seat back, the area where the duty belt is in contact with the seat. Conclusions: The postural and seat interface information support further field evaluations using a retrofitted thoracic insert as an in-vehicle ergonomic intervention for police officers. Further investigations focussed on prolonged exposure to the intervention will guide future design iterations

비만인의 발 도달 작업에 관한 인간공학 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 산업공학과, 2022. 8. 박우진.세계보건기구(World Health Organization)에 따르면, 비만이란 과도하게 신체에 지방이 축적된 물리적 상태로 정의된다. 비만을 정의하는 변수 중 널리 쓰이는 것으로 BMI(Body mass index)가 있으며, 체중을 키의 제곱으로 나눈 값으로 계산된다. BMI가 30 이상인 경우 비만으로 분류되고, 35 이상인 경우 고도비만으로 분류된다. 비만 인구는 매년 증가하는 추세로, WHO에 따르면 2016년 성인 중 19억명이 과체중(BMI 25 이상 30 이하)에 해당한다. 이 중 6억 5천만명이 비만으로 분류되어, 전체 성인 중 13%에 달한다. 2020년 기준 5세 이하의 아동 3900만명이 과체중이거나 비만인 것으로 추정되며, 3억 4천만명의 청소년 인구도 과체중이거나 비만으로 집계되고 있어 앞으로도 계속 비만인구는 증가할 것으로 예측되었다. 비만인구가 증가함에 따라 비만인 작업자의 비율도 꾸준히 증가하고 있으며, 결국 비만으로 발생하는 작업자의 능률 및 지각불편도에 대한 연구가 점점 더 필요한 실정이다. 많은 일상 생활과 작업활동에서 인간은 계속해서 육체적 과업 또는 자세를 유지하는 과업을 수행하고 있다. 따라서, 비만인들이 이런 육체적 과업을 수행할 때, 어떠한 양상을 보이는지에 대해 연구하는 것은 매우 중요하다고 할 수 있다. 기존 인간공학 연구에서 비만 관련 연구는 주로 자세 유지나 걷기 등과 같은 기초적인 것에 국한되어 있었다. 위에서 언급한 중요성에도 불구하고, 아직까지 일반적인 과업을 수행할 때, 비만이 신체적 능력 및 불편도에 어떠한 영향을 미치는지에 대한 연구는 미흡한 실정이다. 특히, 발 도달 작업 같은 기본적인 동작 같은 경우에도 비만의 영향을 알아본 연구는 전무하다. 따라서, 본 연구의 목적은 발 도달 작업에서 비만이 미치는 영향에 관해 파악하는 것이다. 이러한 연구 목적의 달성을 위해 크게 3가지 주요 연구가 수행되었다. 연구 1에서는 앉은 자세에서 발 도달 작업을 수행할 때 비만이 미치는 영향에 대해서 파악하였다. 비만인 그룹과 일반인 그룹을 모집하여 다양한 타겟의 위치 배치에 따른 발 도달 능력을 알아보았다. 실험 결과, 비만인 그룹과 일반인 그룹간 반응 시간, 이동 시간, 과업 수행 시간에 통계적으로 유의한 차이가 나타남을 확인할 수 있었다. 지각불편도는 비만인 그룹과 일반인 그룹간 유의한 차이가 나타나지 않았다. 연구 2에서는 연구 1의 확장으로 자세 요인을 추가적으로 넣어 실험을 수행하였다. 기존 연구 1의 데이터를 활용하여, 추가적인 비만인 모집을 수행한 후 데이터 수집을 진행하였다. 실험 분석 결과, 서 있는 자세에서도 앉은 자세와 마찬가지로 비만의 영향이 나타남을 확인할 수 있었다. 앉은 자세에서 먼 거리를 이동하는 발 도달 과업의 경우, 더 많은 이동 시간이 발생함을 알 수 있었다. 앉아 있는 자세에서 발 도달 과업을 수행할 때 지각불편도가 더 큰 값을 보임을 관측하였다. 연구 3에서는 연구1, 2의 결과 데이터를 통해 예측 발 도달 과업 범위를 제안하는 연구를 수행하였다. 기존 도달 범위 모델의 경우 대부분 손을 활용한 도달 범위를 제안하는 경우가 많았다. 일부 모델 생성 연구에서 최적 발 도달 범위를 제안하는 연구가 있었지만, 비만과 같은 인적 변수를 고려하지 않고 신체치수 등과 같은 변수만을 활용하였다. 본 연구의 데이터를 활용하여, 인적 요인에 따른 최적 발 도달 범위값을 제안하였다. 회귀분석을 통해 수행시간과 불편도에 대한 높은정확도의 예측추정식을 제안하였다. 앉은 자세일 때 수용될 수 있는 최대기준값이 더 작게 나타나는 것으로 보이며, 이를 고려한 발 도달 작업 가이드라인을 제시하였다. 본 연구의 결과를 통해 비만이 발 도달 과업에서 미치는 영향에 대한 이해를 향상시켰으며, 비만인 작업자들을 위해 최적의 발 도달 작업을 할 수 있는 작업장 설계에 도움이 되는 방법론을 제시하였다. 또한, 본 연구를 통해 기존 발 도달 작업 관련 인간공학 분야에 도움이 되는 지식을 제공할 수 있을 것으로 기대하고 있다. 비만이 발 도달 작업에 미치는 영향을 알 수 있게 되며, 발 도달 작업에서 발생하는 주관적 불편도에 대한 예측 모델을 생성할 때 비만요인과 작업자세를 적용할 수 있을 것으로 기대하고 있다. 또한 본 연구를 통해 실제 산업현장에서 비만인을 위한 작업 설계를 도와줄 수 있을 것이다. 추후 여성 작업자들의 발도달 작업 데이터를 수집하여 모든 작업자들에 대한 디지털 휴먼 모델링을 생성하는 것을 기대하고 있다. 비만인들의 부상 및 근골격계 질환 위험을 예방하여 경제적 이득을 가져올 수 있으며, 실제 비만인 작업자의 능률을 향상시켜 작업자의 사용자경험(UX) 개선에 도움이 될 것으로 기대하고 있다.Obesity is prevalent worldwide and the obese population continues to increase. Therefore, research is needed to find out the impacts of obesity in basic tasks, and, it could help with ergonomic design in the workplace. Existing ergonomic studies have examined the basic physical abilities of obese people, such as walking and balancing. Through an understanding of the physical capabilities of obese individuals, it is possible to design a workplace that is suitable for obese individuals. Foot reach work is a basic movement that occurs frequently in the workplace. In light of the results of ergonomic research related to obesity, it is possible that the foot reach task will exhibit a different result. Despite the importance mentioned above, understanding how obesity impacts physical performance and discomfort rating is still insufficient. Particularly, no studies have been found that have examined the effects of obesity on foot reach. Therefore, this study aims to investigate the impact of obesity on foot reach and develop a method to improve the performance of obese groups. To accomplish the objectives, three major studies were conducted. In the study 1, the impact of obesity was investigated in the foot target reach in a seated position. Task performance and discomfort rating data were analyzed. The differences between the participant groups (non-obese, obese) were compared statistically. It was found that the obese group had a statistical difference from the non-obese group in reaction time, movement time, and task completion time. In terms of discomfort rating, there was no significant difference between the obese and the non-obese group. In the study 2, the impact of obesity in standing posture was investigated as an expanding study of study 1. In the standing position, the movement time decreased, but the reaction time increased. There was no significant interaction effect between participant group and posture factors. Foot reach in a seated position was more uncomfortable. As a result of task performance time analysis, a significant interaction effect between posture and target distance was observed. In the study 3, a study was conducted to propose the prediction model. It describes the possible range of foot reach for workers using the existing prediction model. Task performance time data is used to present an area that optimizes the foot reach task of obese/non-obese workers. It was found that obese people have a smaller foot reach area. The above-mentioned findings investigate the impact of obesity on foot reach task and provide an understanding that helps design workplaces for obese people. Based on the findings from study 1, it was possible to understand how obesity affects foot reach in a seated position. The findings provided in the study 2 would be helpful to provide an understanding of the possible changes in performance in standing posture. The results of study 3 provide inspiration for workplace improvements for obese workers. For obese workers, it is possible to propose increasing the size of the target where the reduced foot reach performance is evident.Chapter 1 Introduction 1 1.1 Research Background 1 1.2 Research Objectives 3 1.3 Dissertation Outline 4 Chapter 2 Literature Review 7 2.1 Obesity Effects on Physical Function and Performance 7 2.2 Literature Review on Foot Target Reach Task 10 2.3 Literature Review on Reaction time 13 Chapter 3 Obesity Effects on Seated Foot Reaches 15 3.1 Introduction 15 3.2 Research Methods 17 3.3 Results 24 3.4 Discussions 29 Chapter 4 The effects of obesity and posture on foot reach tasks: task performance and perceived discomfort 37 4.1 Introduction 37 4.2 Research Methods 40 4.3 Results 45 4.4 Discussions 56 Chapter 5 Models for predicting standing and seated foot target reach movement times of obese and non-obese operators 66 5.1 Introduction 66 5.2 Research Methods 70 5.3 Results 74 5.4 Discussions 91 Chapter 6 Conclusion 95 6.1 Summary 95 6.2 Implications 97 6.3 Future Research Ideas 99 Bibliography 102 Appendix A. The ANOVA tables 123 A.1 The ANOVA results for reaction time 123 A.2 The ANOVA results for movement time 124 A.3 The ANOVA results for task performance time 125 A.4 The ANOVA results for discomfort rating 126 국문초록 130박