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

Vehicle ergonomics and older drivers

There is a growing population of older people around the world and the population of older drivers is increasing in parallel. UK government figures in 2012 reported that there were more than 15 million people with a driving license aged over 60; more than 1 million of these were over 80. The aim of this thesis is to determine the requirements of older users for an improved driving experience leading to recommendations for the automotive industry. Initially it was necessary to understand some of the key issues concerning the driving experiences of older drivers; therefore a questionnaire survey of drivers of all ages (n=903) was conducted supplemented by interviews with drivers aged ≥ 65 years (n=15). Areas covered included: musculoskeletal symptoms, the vehicle seat, driving performance and driving behaviour. Respondents reported that they were dissatisfied with adjusting specific seat features, for example the head rest height and distance from the head; females reported more difficulty than males. Reaching and pulling the boot door down to close was difficult for 12% of older females. Older males and females also reported more difficulties with parallel parking and driving on a foggy day than younger drivers (p<0.01). Nearly half of the sample (47%) reported that other drivers lights restrict their vision when driving at night. An in depth study was conducted to compare participants own vehicle (familiar) and a test vehicle (unfamiliar) to understand how design of the vehicle cab impacts on posture, comfort, health and wellbeing in older drivers (n=47, ≥50 years). The study involved functional performance assessments, seat set-up process evaluation (observations and postural analysis), ergonomics and emotional design based evaluations of car seat controls. Many issues were identified related to the seat controls such as operating, accessing, reaching and finding, particularly for the head rest height and lumbar support adjustments. Approximately 40% of the participants had difficulty turning their head and body around to adjust the head rest height, and the majority of these were over 80. This led to a series of workshops (including a participatory design exercise) with 18 participants (4 groups, ≥ 65 years).The aim was to explore the optimum positioning and operation of controls for older drivers. This research has provided foundational data and makes design recommendations for the automotive industry with a focus on making seat controls more inclusive (operation, location, type, size, colour and materials) and meet the requirements of older drivers

Including plus size people in workplace design

Over 60% of the adult population in the United Kingdom is now overweight or obese or classed as plus size . This is higher than almost all other developed countries in the world. Even with numerous public health interventions, the incidence of being plus size continues to rise potentially changing the demographics of the working population. This presents a challenge to those involved in workplace design as the design process relies upon the utilization of appropriate anthropometric data to establish the percentage of the user population that will be accommodated by the design. The aim of this thesis is to identify issues affecting plus size people in the working environment, not previously explored within the literature. Furthermore, by understanding the size and shape of this population via the collection of key anthropometric data, this will help inform the design of safe, comfortable, inclusive and productive working environments for plus size people within the United Kingdom. A first stage Scoping Study (n=135) found that fit (equipment, tools, furniture, uniforms and personal protective equipment) and space (circulation and shared spaces within the working environment) were issues of concern to plus size people. This suggests that aspects of the current design of the workplace are not suitable, and may even exclude plus size people. A better understanding of the anthropometric requirements of plus size workers is therefore required. Self-reported anthropometric data is an acceptable way of studying large and geographically diverse populations and may assist in accessing the hard to reach plus size working population. A validation study (n=20) established that self measurement of 14 key anthropometric measurements, using a self measurement instruction guide, was a feasible and acceptable data collection method for a larger scale anthropometric study to further understand the body size and shape of plus size people at work. A unique measure of knee splay (for a non-pregnant population) was included. Defined as the distance between the outer borders of the knees whilst seated in the preferred sitting position it represents the observed sitting postures of plus size individuals not captured in existing anthropometric data sources. The larger scale Plus Size Anthropometry Study (n=101) collected anthropometric data of plus size working age people via self measurement. The findings indicated that the study population was substantially larger in circumference, depth and breadth measurements than the population of existing anthropometric data sources. Knee splay was also identified as a key anthropometric variable for plus size people, however, it is not included in any datasets or literature relating to plus size people at work. These factors may contribute to high exclusion rates from current design practices that seek to accommodate the 5th to 95th or 99th percentile of users and may explain the high incidence of fit and space issues reported by participants with a BMI over 35kg/m2 . Finally, semi structured interviews with stakeholders (n=10) explored how they would like the data from the plus size anthropometry study communicated and any additional requirements of a resource aimed at supporting stakeholders in meeting the needs of plus size people within the working environment. The primary concern from stakeholders was the lack of existing data on the size and shape of the plus size working population and the importance of access to such data in whatever format. A range of ideas were suggested including case studies, guidance and access to training which may assist them in understanding the needs of their end users ultimately supporting the inclusion of plus size people in workplace design

The relationship between a child's postural stability and manual dexterity

The neural systems responsible for postural control are separate from the neural substrates that underpin control of the hand. Nonetheless, postural control and eye-hand coordination are linked functionally. For example, a stable platform is required for precise manual control tasks (e.g. handwriting) and thus such skills often cannot develop until the child is able to sit or stand upright. This raises the question of the strength of the empirical relationship between measures of postural stability and manual motor control. We recorded objective computerised measures of postural stability in stance and manual control in sitting in a sample of school children (n = 278) aged 3–11 years in order to explore the extent to which measures of manual skill could be predicted by measures of postural stability. A strong correlation was found across the whole sample between separate measures of postural stability and manual control taken on different days. Following correction for age, a significant but modest correlation was found. Regression analysis with age correction revealed that postural stability accounted for between 1 and 10 % of the variance in manual performance, dependent on the specific manual task. These data reflect an interdependent functional relationship between manual control and postural stability development. Nevertheless, the relatively small proportion of the explained variance is consistent with the anatomically distinct neural architecture that exists for ‘gross’ and ‘fine’ motor control. These data justify the approach of motor batteries that provide separate assessments of postural stability and manual dexterity and have implications for therapeutic intervention in developmental disorders

작업 관련 근골격계 질환의 위험성 저감을 위한 작업 자세 및 동작의 인간공학 연구

학위논문(박사) -- 서울대학교대학원 : 공과대학 산업공학과, 2022.2. 박우진.육체적 부하가 큰 자세 및 동작으로 작업을 수행하는 것은 작업자의 근골격계 질환의 위험성을 증가시킨다. 작업자의 근골격계에 가해지는 육체적 부하의 양상은 수행하는 작업의 종류에 따라 달라진다. 장시간 앉은 자세로 작업을 수행하는 경우, 작업자의 근육, 인대와 같은 연조직에 과도한 부하가 발생하여 목, 허리 등 다양한 신체 부위에서 근골격계 질환의 위험성이 증가할 수 있다. 따라서, 착좌 시 발생할 수 있는 근골격계 질환의 위험성을 저감하기 위해서는 작업자의 착좌 자세를 실시간으로 모니터링하고, 이에 대한 피드백을 제공하는 것이 필요하다. 들기 작업과 같은 동적인 움직임이 포함된 작업을 수행하는 경우, 작업자의 체중이 신체적 부하에 영향을 미칠 수 있다. 전세계적인 비만의 유행으로 인해 많은 작업자들이 체중 증가를 겪고 있고, 들기 작업과 같은 동적인 작업에서 비만은 신체적 부하에 악영향을 미칠 수 있다. 따라서, 비만과 작업 관련 근골격계 질환의 위험성은 잠재적인 연관성을 가지고 있고, 비만이 들기 작업에 미치는 생체역학적 영향을 논의할 필요성이 있다. 작업장에서의 근골격계 질환의 위험성을 저감하기 위해 다양한 연구들이 수행되어 왔지만, 작업 시스템의 인간공학적 설계 측면에서 추가적인 연구가 필요하다. 장시간 의자에 앉아 정적인 작업을 수행하는 작업자의 근골격계 질환을 저감하기 위한 유망한 방법 중 하나로, 작업자의 자세를 실시간으로 모니터링하고 분류하는 시스템을 개발하는 것이 제안되고 있다. 이러한 시스템은 작업자가 근골격계 질환의 위험성이 낮은 자세를 작업 시간 동안 유지하도록 돕는 데 활용될 수 있을 것이다. 기존의 대부분의 자세 모니터링 시스템에서는 분류할 자세를 정의하는 과정에서 인간공학적 문헌이 거의 고려되지 않았고, 사용자가 실제로 활용하기에는 여러 한계점들이 존재하였다. 들기 작업의 경우, 체질량 지수(BMI) 40 이상의 초고도 비만 작업자의 동작 패턴을 논의한 연구는 거의 찾아볼 수 없었다. 또한, 다양한 들기 작업 조건 하에서 전신 관절들의 움직임을 생체역학적 측면에서 분석한 연구는 부족한 실정이다. 따라서, 본 연구에서의 연구 목적은 1) 다양한 센서 조합을 활용한 실시간 착좌 자세를 분류하는 시스템을 개발하고, 2) 들기 작업 시 초고도 비만이 개별 관절의 움직임과 들기 동작 패턴에 미치는 영향을 이해하여, 다양한 종류의 작업에서 발생할 수 있는 근골격계 질환의 위험성을 저감하는 것이다. 연구 목적을 달성하기 위해 다음의 두 가지 연구를 수행하였다. 첫번째 연구에서는 실시간으로 착좌 자세를 분류하는 스마트 의자 시스템을 개발하였다. 스마트 의자 시스템은 각각 여섯 개의 거리 센서와 압력 센서를 조합하여 구성되었다. 착좌 관련한 근골격계 질환에 대해 문헌 조사를 수행하였고, 이를 바탕으로 결정된 자세들에 대해 서른 여섯 명의 데이터를 수집하였다. 스마트 의자 시스템에서 자세를 분류하기 위해 kNN 알고리즘을 활용하였고, 성능을 검증하기 위해 단일 종류의 센서로 구성된 기준 모델들과 비교를 수행하였다. 분류 성능을 비교한 결과, 센서를 조합한 스마트 의자 시스템이 가장 우수한 결과를 보였다. 두번째 연구에서는 들기 작업을 수행할 때 초고도 비만이 개별 관절의 움직임과 동작 패턴에 미치는 영향을 분석하기 위해 모션 캡쳐 실험을 수행하였다. 들기 실험에는 근골격계 질환 이력이 없는 서른 다섯 명이 참여하였다. 수집된 데이터를 바탕으로 주요 관절(발목, 무릎, 엉덩이, 허리, 어깨, 팔꿈치) 별 운동역학적 변수들과, 들기 동작의 패턴을 표현하는 동작 지수들을 계산하였다. 들기 작업 조건과 비만 수준에 따라, 대부분의 변수에서 통계적으로 유의한 차이를 보였다. 전체적으로 비만인은 정상체중인에 비해 다리 보다 허리를 사용하여 들기 작업을 수행하였고, 동작 수행 시 상대적으로 적은 관절 각도 변화와 느린 움직임을 보였다. 들기 작업에서 박스의 이동에 개별 관절이 기여하는 비율도 정상체중인과 비만인은 다른 패턴을 보였다. 본 연구의 결과를 활용하여 다양한 종류의 신체적 부하에 노출된 작업자들의 근골격계 질환의 위험성을 저감할 수 있고, 궁극적으로 업무의 생산성과 개인의 건강을 제고할 수 있을 것이다. 첫번째 연구에서 개발된 스마트 의자 시스템은 기존 자세 분류 시스템의 단점들을 완화하였다. 개발된 시스템은 저렴한 소수의 센서만을 활용하여 근골격계 측면에서 중요한 자세들을 높은 정확도로 분류하였다. 이러한 자세 분류 시스템은 작업자에게 실시간으로 자세 피드백을 제공하여, 근골격계 질환의 위험성이 낮은 자세를 유지하는 데 활용될 수 있을 것이다. 두번째 연구의 결과는 동적인 작업 시 초고도 비만으로 인한 잠재적인 근골격계 질환의 위험성을 이해하는 데 활용될 수 있다. 초고도 비만인과 정상체중인 간 관절의 움직임과 동작의 차이를 이해하여, 비만을 고려한 인간공학적 작업장 설계와 동작 가이드라인을 제공할 수 있을 것이다.Working in stressful postures and movements increases the risk of work-related musculoskeletal disorders (WMSDs). The physical stress on a worker’s musculoskeletal system depends on the type of work task. In the case of sedentary work, stressful sitting postures for prolonged durations could increase the load on soft connective tissues such as muscles and ligaments, resulting in the incidence of WMSDs. Therefore, to reduce the WMSDs, it is necessary to monitor a worker’s sitting posture and additionally provide ergonomic interventions. When the worker performs a task that involves dynamic movements, such as manual lifting, the worker’s own body mass affects the physical stress on the musculoskeletal system. In the global prevalence of obesity in the workforce, an increase in the body weight of the workers could adversely affect the musculoskeletal system during the manual lifting task. Therefore, obesity could be associated with the development of WMSDs, and the impacts of obesity on workers’ movement during manual lifting need to be examined. Despite previous research efforts to prevent WMSDs, there still exist research gaps concerning ergonomics design of work systems. For sedentary workers, a promising solution to reduce the occurrence of WMSDs is the development of a system capable of monitoring and classifying a seated worker's posture in real-time, which could be utilized to provide feedback to the worker to maintain a posture with a low-risk of WMSDs. However, the previous studies in relation to such a posture monitoring system lacked a review of the ergonomics literature to define posture categories for classification, and had some limitations in widespread use and user acceptance. In addition, only a few studies related to obesity impacts on manual lifting focused on severely obese population with a body mass index (BMI) of 40 or higher, and, analyzed lifting motions in terms of multi-joint movement organization or at the level of movement technique. Therefore, the purpose of this study was to: 1) develop a sensor-embedded posture classification system that is capable of classifying an instantaneous sitting posture as one of the posture categories discussed in the ergonomics literature while not suffering from the limitations of the previous system, and, 2) identify the impacts of severe obesity on joint kinematics and movement technique during manual lifting under various task conditions. To accomplish the research objectives, two major studies were conducted. In the study on the posture classification system, a novel smart chair system was developed to monitor and classify a worker’s sitting postures in real-time. The smart chair system was a mixed sensor system utilizing six pressure sensors and six infrared reflective distance sensors in combination. For a total of thirty-six participants, data collection was conducted on posture categories determined based on an analysis of the ergonomics literature on sitting postures and sitting-related musculoskeletal problems. The mixed sensor system utilized a kNN algorithm for posture classification, and, was evaluated in posture classification performance in comparison with two benchmark systems that utilized only a single type of sensors. The mixed sensor system yielded significantly superior classification performance than the two benchmark systems. In the study on the manual lifting task, optical motion capture was conducted to examine differences in joint kinematics and movement technique between severely obese and non-obese groups. A total of thirty-five subjects without a history of WMSDs participated in the experiment. The severely obese and non-obese groups show significant differences in most joint kinematics of the ankle, knee, hip, spine, shoulder, and elbow. There were also significant differences between the groups in the movement technique index, which represents a motion in terms of the relative contribution of an individual joint degree of freedom to the box trajectory in a manual lifting task. Overall, the severely obese group adopted the back lifting technique (stoop) rather than the leg lifting technique (squat), and showed less joint range of excursions and slow movements compared to the non-obese group. The findings mentioned above could be utilized to reduce the risk of WMSDs among workers performing various types of tasks, and, thus, improve work productivity and personal health. The mixed sensor system developed in this study was free from the limitations of the previous posture monitoring systems, and, is low-cost utilizing only a small number of sensors; yet, it accomplishes accurate classification of postures relevant to the ergonomic analyses of seated work tasks. The mixed sensor system could be utilized for various applications including the development of a real-time posture feedback system for preventing sitting-related musculoskeletal disorders. The findings provided in the manual lifting study would be useful in understanding the potential risk of WMSDs for severely obese workers. Differences in joint kinematics and movement techniques between severely obese and non-obese groups provide practical implications concerning the ergonomic design of work tasks and workspace layout.Chapter 1. Introduction 1 1.1 Research Background 1 1.2 Research Objectives 5 1.3 Dissertation Outline 6 Chapter 2. Literature Review 8 2.1 Work-related Musculoskeletal Disorders Among Sedentary Workers 8 2.1.1 Relationship Between Sitting Postures and Musculoskeletal Disorders 8 2.1.2 Systems for Monitoring and Classifying a Seated Worker's Postures 10 2.2 Impacts of Obesity on Manual Works 22 2.2.1 Impacts of Obesity on Work Capacity 22 2.2.2 Impacts of Obesity on Joint Kinematics and Biomechanical Demands 24 Chapter 3. Developing and Evaluating a Mixed Sensor Smart Chair System for Real-time Posture Classification: Combining Pressure and Distance Sensors 27 3.1 Introduction 27 3.2 Materials and Methods 33 3.2.1 Predefined posture categories for the mixed sensor system 33 3.2.2 Physical construction of the mixed sensor system 36 3.2.3 Posture Classifier Design for the Mixed Sensor System 38 3.2.4 Data Collection for Training and Testing the Posture Classifier of the Mixed Sensor System 41 3.2.5 Comparative Evaluation of Posture Classification Performance 43 3.3 Results 46 3.3.1 Model Parameters and Features 46 3.3.2 Posture Classification Performance 47 3.4 Discussion 50 Chapter 4. Severe Obesity Impacts on Joint Kinematics and Movement Technique During Manual Load Lifting 57 4.1 Introduction 57 4.2 Methods 61 4.2.1 Participants 61 4.2.2 Experimental Task 61 4.2.3 Experimental Procedure 64 4.2.4 Data Processing 65 4.2.5 Experimental Variables 67 4.2.6 Statistical Analysis 71 4.3 Results 72 4.3.1 Kinematic Variables 72 4.3.2 Movement Technique Indexes 83 4.4 Discussion 92 Chapter 5. Conclusion 102 5.1 Summary 102 5.2 Implications 105 5.3 Limitations and Future Directions 106 Bibliography 108 국문초록 133박

The influence of whole-body vibration and postural support on activity interference in standing rail passengers

Travel time has generally been regarded as an unproductive period, representing a means-to-an-end in order to engage in activities at specific destinations. Rapid developments in mobile technology have provided people with innovative ways to multi-task and engage in meaningful activities while travelling. Rail transportation specifically, offers passengers advantages over other means of transportation as there is no need to focus on driving tasks. Due to the increase in passenger numbers and limited seating availability in train carriages, over one third of rail passengers are required to stand while travelling (DfT, 2013). The vibration to which rail passengers are exposed has been shown to interfere with the performance of activities and for standing passengers, it is often necessary to use postural supports such as holding on to grab rails or leaning on walls in order to maintain stability. The overall aim of the research is to evaluate the influence of whole-body vibration (WBV) exposure and standing posture on the performance of manual control tasks and the associated subjective workloads experienced by rail passengers. The use of supports, such as a backrest in seated postures, has been found to influence the response of the human body to WBV exposure, yet no reported studies have investigated the effects of postural supports on the response of the body in standing postures. Understanding how the body is affected in these conditions would increase the current state of knowledge on the biomechanical responses of the human body to vibration exposure and provide improved representation of standing postures within vibration standards (for example, ISO2631-4 (2001)) and guidelines for device interface design. A field study, using direct observation, was conducted to assess the behaviour of standing rail passengers and determine the characteristics of typical vibration exposures. This information provided the basis for the design of four subsequent laboratory studies. The main investigations of the laboratory studies were the influence of WBV exposure on objective performance measures, such as task completion time and error rate, and subjective workloads (for example, NASA TLX) for a range of manual control tasks. One of these laboratory studies evaluated the influence of various postural supports (for example, backrests) on the biomechanical responses of standing individuals. Measurements obtained during the field investigation indicated that the vibration exposures did not exceed the EU Physical Agents Exposure Action Value (EAV) and therefore posed little risk of injury. Vibration magnitudes in the horizontal directions (x- and y-axes) were higher than in the vertical direction (z-axis) and it was necessary for standing passengers to alter behaviours and use supports in order to maintain stability while travelling. The results of the laboratory studies indicated that in conditions where decrements in task performance occurred, the extent to which performance was degraded increased progressively with increases in vibration magnitude. There were conditions (for example, in the continuous control task and the Overhead Handle supported posture in the serial control task) where vibration exposure showed no significant influence on performance measures. This suggested that individuals were able to adapt and compensate for the added stress of vibration exposure in order to maintain performance levels however, this occurred at the expense of mental workload. The workload experienced by the participants increased with corresponding increases in magnitude. Vibration frequency-dependent effects in performance and workload were found to match the biomechanical responses (apparent mass and transmissibility) of the human body and resemble the frequency weightings described in the standards (ISO2631-1 (1997)). During the serial control task, the postures which demonstrated the greatest decrements to performance (for example, Lean Shoulder and Lean Back ) corresponded to the same postures that showed the greatest influence on the biomechanical responses of the body. It was concluded therefore, that measurements of the biomechanical responses to WBV could be used to offer predictions for the likelihood of activity interference. Consideration should however, be given to the applicability of this research before these results can be generalised to wider contexts. Further validation is recommended for future work to include different conditions in order to substantiate the findings of this research

A cross-culture, cross-gender comparison of perspective taking mechanisms

Being able to judge another person's visuo-spatial perspective is an essential social skill, hence we investigated the generalizability of the involved mechanisms across cultures and genders. Developmental, cross-species, and our own previous research suggest that two different forms of perspective taking can be distinguished, which are subserved by two distinct mechanisms. The simpler form relies on inferring another's line-of-sight, whereas the more complex form depends on embodied transformation into the other's orientation in form of a simulated body rotation. Our current results suggest that, in principle, the same basic mechanisms are employed by males and females in both, East-Asian (EA; Chinese) and Western culture. However, we also confirmed the hypothesis that Westerners show an egocentric bias, whereas EAs reveal an other-oriented bias. Furthermore, Westerners were slower overall than EAs and showed stronger gender differences in speed and depth of embodied processing. Our findings substantiate differences and communalities in social cognition mechanisms across genders and two cultures and suggest that cultural evolution or transmission should take gender as a modulating variable into account

A Stimulation Method to Assess the Contractile Status of the Lumbar Extensors in a Seated Posture

The purpose of present study was to develop and evaluate methods to assess stimulation responses of the lumbar extensors, as part of a longer‐term goal of detecting fatigue during prolonged sitting. Three stimulation frequencies (2, 5, and 8 Hz) were tested in separate stages, which include 3 stimulation trains and 4 sampling blocks. Repeated measures analyses of variance were used to determine whether any significant differences in mean stimulation responses occurred with respect to stimulation frequency, sampling block, and stimulation train. Reliability of measured stimulation responses was assessed within and between sampling blocks using intraclass correlation coefficients. Stimulation frequencies significantly affected the stimulation responses and time‐to‐potentiation differed between the 3 stimulation frequencies; it was highest for 2 Hz stimulation. All 3 stimulation frequencies resulted in excellent reliability within and between sampling blocks. Use of the current protocol at 2 Hz is recommended as appropriate to measure the lumbar extensors status during prolonged sitting.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/115927/1/hfm20584.pd