Durante a infância, a postura sofre uma série de ajustes associados aos estágios de crescimento e aos problemas de equilíbrio que surgem em razão das mudanças nas proporções do corpo. A formação do esquema corporal, durante a infância, ocorre através das experiências motoras e possibilita a estruturação tônico-postural, sendo que desequilíbrios posturais adquiridos nesse período podem perdurar ao longo da adolescência e vida adulta. O objetivo deste estudo foi caracterizar quantitativamente a postura de crianças de 7 e 8 anos e verificar diferenças entre os sexos e idades quanto aos aspectos posturais analisados. Foram avaliadas 230 crianças entre 7 e 8 anos das escolas municipais da cidade de Amparo/SP. A análise postural foi feita por meio de fotografias das crianças em posição ortostática e analisadas com o auxílio de linhas guias traçadas com o software CorelDraw® v. 10.0, baseadas nos pontos ósseos. Foram medidos os seguintes segmentos - tornozelo, joelho, pelve, lombar, torácica, ombro, escápula e cabeça, além do desvio lateral da coluna, do teste do 3o dedo ao chão e da impressão plantar. Os dados foram submetidos a análises descritivas (média, desvio padrão e porcentagem) e ANOVA para verificar diferenças entre os grupos, adotando-se alfa de 5%. Foram definidos valores médios e intervalos de confiança para as variáveis analisadas. Algumas variáveis apresentaram diferenças para o sexo, como terceiro dedo ao chão, postura da cabeça, impressão plantar e distância intermaleolar. Outras apresentaram diferença significativa para a idade - cifose torácica e ombro no plano frontal. Para a lordose lombar, os meninos de 7 anos apresentaram valor médio de 38,49o±15,32 e as demais crianças 42,29o±7,13. A postura da escápula apresentou influência tanto do fator sexo quanto idade, as meninas de 7 anos apresentaram valor médio de 5,29cm±1,82 e as de 8 anos 5,67cm±1,82, os meninos de 7 anos apresentaram 5,74cm±1,97 e os de 8 anos 6,12cm±1,97. As demais variáveis analisadas não apresentaram influência do sexo e da idade, formando apenas um grupo com todas as crianças estudadas - postura de tornozelo (6,67o±4,25), joelho no plano sagital (184,28o±5,46), inclinação pélvica (15,82o±5,46), ombro no plano sagital (6,76cm±1,52), desvio lateral da coluna (3,48o±2,12) e distância intercondilar (1,14cm±1,36). Para o teste do terceiro dedo ao chão, as meninas apresentaram valor médio de 29,15cm±8,80 enquanto os meninos de 27,41cm±10,01 e, para a postura da cabeça, as meninas apresentaram ângulo médio de 49,55o±6,67 e os meninos de 52,16o±7,58. Os valores médios da impressão plantar, pelo Índice de Chipaux-Smirak, classificaram os pés, tanto das meninas (21,02%±19,71) quanto dos meninos (26,31%±22,44), com arco morfologicamente normal. Para cifose torácica, as crianças de 7 anos apresentaram 28,07o±7,73 e as de 8 anos 30,32o±7,73. Não se identificou um padrão de simetria postural para a amostra estudada e observaram-se diferenças entre o sexo e a idade para alguns dos segmentos analisados. Os valores encontrados neste estudo podem servir de auxílio no tratamento fisioterapêutico quando associados a outros fatores da avaliação e da sintomatologia clínica. / During the infancy, the posture undergoes many adjustments related to growth stages due to changes of the body proportions. The formation of the body schema, in childhood, occurs through the motor experiences and allows the tonic-postural structuring, and the postural imbalance acquired in this period can last for the entire adolescence and adult life. The purpose of this study was to characterize quantitatively the posture of children between 7 and 8 years of age and to verify the difference between sex and age for the analyzed postural aspects. Two hundred and thirty children between 7 and 8 years of Amparo/SP city public schools were assessed. The posture evaluation was made through subjects digital photos in orthostatic position and analyzed with the CorelDraw® v. 10.0 software guidelines and the bony landmarks. The following segments were measured - ankle, knee, pelvis, lumbar, thoracic, shoulder, scapula and head, besides lateral spine deviation, fingertip-to-floor test and footprint. Data were analyzed using descriptive statistic (average, standard deviation and percentage) and ANOVA models to verify differences among the groups, adopting alfa of 5%. It was found average values and confidence intervals to the analyzed variables. Some of these variables showed differences to sex, as fingertip-to-floor test, head posture, footprint and intermalleolar distance. The other ones showed significant difference to age - thoracic kyphosis and shoulder in the frontal plane. To lumbar lordosis, boys of 7 years of age showed average value of 38,49o±15,32 and the other children 42,29o±7,13. The scapula posture showed influence of the factors sex and age, girls of 7 years of age showed average value of 5,29cm±1,82 and the one of 8 years 5,67cm±1,82, boys of 7 years of age showed 5,74cm±1,97 and the one of 8 years 6,12cm±1,97. The other analyzed variables do not showed influence of sex and age and they formed only a group with all the studied children - ankle posture (6,67o±4,25), knee in the sagittal plane (184,28o±5,46), pelvic inclination (15,82o±5,46), shoulder in the sagittal plane (6,76cm±1,52), lateral spine deviation (3,48o±2,12) and intercondylar distance (1,14cm±1,36). To the fingertip-to-floor test, girls showed average value of 29,15cm±8,80 while boys showed 27,41cm±10,01 and, to head posture, girls presented average angle of 49,55o±6,67 and boys of 52,16o±7,58. The footprint average values, measured by the Chipaux-Smirak Index, classified the foot, as of the girls ones (21,02%±19,71) as the boys (26,31%±22,44), with normal morphologically arch. To thoracic kyphosis, children of 7 years of age showed 28,07o±7,73 and ones of 8 years of age 30,32o±7,73. It was not identify a pattern of postural symmetry to the studied sample and it was found differences between sex and age for some of the analyzed segments. The values found in this study may help in the physiotherapy treatment when they are associated with other aspects of the clinical assessment and symptomatology.

O controle postural tem como objetivo a orientação e o equilíbrio postural a fim de que o indivíduo realize uma tarefa de maneira estável. Alterações do ajuste postural são relacionadas a disfunções musculoesqueléticas e quedas, corroborando com a importância da avaliação postural completa para a prática clínica, incluindo tanto a postura estática como o comportamento dinâmico. O objetivo deste trabalho foi (1) propor um protocolo de avaliação clínica do ajuste postural compensatório, verificar (2) a confiança inter-examinador e intra-examinador deste protocolo e (3) a concordância entre a avaliação clínica e cinemática, analisar (4) se o deslocamento dos segmentos corporais durante o ajuste postural compensatório está relacionado com a posição dos segmentos na postura quieta ou no momento final do ajuste postural compensatório e (5) a relação entre as posições dos segmentos corporais durante a posição quieta e no momento final do ajuste postural compensatório. Vinte participantes jovens do sexo feminino em pé sobre uma plataforma móvel foram submetidos a perturbações posturais anteriores e posteriores padronizadas. Um quadro inicial e um quadro final representando um momento estável da posição quieta e o fim da perturbação postural, respectivamente, foram selecionados, de maneira que o ajuste postural tenha ocorrido no intervalo entre os quadros. Quatro examinadores realizaram uma avaliação clínica aplicando o protocolo proposto para avaliação clínica do ajuste postural compensatório aos quadros inicial e final de cada teste de cada participante. Os examinadores repetiram a avaliação sete dias após a primeira avaliação. Análise cinemática foi realizada a fim de definir a posição do ângulo tíbiotársico, ângulo do joelho, antepulsão da pelve, anteversão da pelve e posição do tronco. Foi coletada a posição dos segmentos corporais nos quadros inicial e final e a variação da posição dos segmentos corporais durante o ajuste postural compensatório. A confiabilidade inter-examinador e intra-examinador do protocolo proposto foi calculada e as respostas da avaliação clínica e as medidas cinemáticas dos quadros inicial e final, foram comparadas. A relação entre a posição dos segmentos corporais nos quadros inicial e final e a variação da posição dos segmentos corporais durante o ajuste postural compensatório, assim como a relação entre as posições dos segmentos corporais nos quadros inicial e final, foram observadas. A análise do Protocolo de Avaliação Clínica do Ajuste Postural Compensatório revelou bom nível de confiança inter-examinador e intraexaminador, com concordância entre a avaliação clínica e cinemática. O padrão de movimento do ajuste postural compensatório não se relacionou com a posição dos segmentos corporais na postura quieta ou no momento final do ajuste postural compensatório. Houve uma forte relação entre os segmentos do membro inferior tanto durante a posição quieta como no momento final do ajuste postural compensatório. Esta relação deve ser considerada para o melhor entendimento do padrão de movimento na manutenção do equilíbrio e na prática clínica para o tratamento de disfunções musculoesqueléticas do membro inferior. / Postural control aims postural orientation and equilibrium in order an individual accomplishes a task in a stable way. Alterations of postural adjustment are related to musculoskeletal diseases and falls, supporting the importance of a complete posture evaluation in clinical practice, including static and dynamic components of posture. The aim of this study was (1) to present a protocol to clinical evaluation of compensatory postural adjustment, to verify (2) interexaminer and intraexaminer reliability of this protocol and (3) agreement between clinical and kinematics evaluation, analyze (4) if the displacement of body segments during compensatory postural adjustment is related to posture during quiet stance or at final moment of compensatory postural adjustment and (5) the relationship between body segments during quiet stance and postural adjustment. Twenty healthy young non-athletic female participants standing upon a moveable support surface underwent to standardized backward and forward postural perturbation. An initial and a final frame representing the stable moment of quiet stance and the end of the postural perturbation, respectively, were selected, in a way that postural adjustment has occurred between these frames. Four independent examiners have made a clinical evaluation of initial and final frames of each participant using the protocol proposed for compensatory postural adjustment clinic evaluation. Examiners have repeated this evaluation seven days after the first evaluation. Kinematics analyses have been done to verify the ankle angle, knee angle, pelvic antepulsion, pelvic anteversion and trunk position. Measures of body segments position at initial and final frame and displacement of body segments during compensatory postural adjustment were acquired. Interexaminer and intraexaminer reliability of the proposed protocol was analyzed and answers of clinical evaluation and kinematics measures of initial and final frames were compared. The relationship between body segments position at initial and final frames and displacement of body segments during compensatory postural adjustment, as well as the relationship between body segments position at initial and final frames, were observed. The protocol proposed for compensatory postural adjustment clinic evaluation showed good inter-examiner and intra-examiner reliability with good agreement between clinical and kinematics evaluation. Motion pattern during compensatory postural adjustment was not related to posture during quiet stance or at final moment of compensatory postural adjustment. There is a strong relationship between lower limb segments either during quiet stance or at final moment of compensatory postural adjustment. This relationship should be considered to better understanding of motion pattern during maintenance of balance and treatment of lower limb musculoskeletal diseases in clinical practice.

Orientador: Danilo Florentino Pereira / Coorientador: Leda Gobbo de Freitas Bueno / Coorientador: Ricardo César Gonçalves Sant'ana / Resumo: O Brasil é o 3º maior produtor de ovos da América e para produzir é necessário que a cadeia produtiva esteja organizada para fornecer produtos com qualidade, além de ter bons níveis de produtividade. Os consumidores apresentam-se cada vez mais exigentes e a avicultura de postura precisa se adaptar para atender essa demanda. A rastreabilidade é um sistema que possibilita rastrear todas as informações relacionadas a um produto, desde o início da cadeia produtiva até o consumidor final e pode respaldar esse momento vivido pela indústria. Requisitos de qualidade referentes a avicultura de postura são apresentados em documentos orientadores como da EMBRAPA e da União Brasileira da Avicultura, que abrangem todas as etapas do processo produtivo, desde a origem dos insumos até etapas posteriores a produção. A fim de complementar as informações de qualidade, outras legislações, que regulamentam diversos processos produtivos, que tratam de rastreabilidade foram utilizadas. Apontados os requisitos que podem alimentar um sistema de rastreabilidade, tanto de qualidade, quanto informacional, a próxima etapa refere-se a coleta de dados, descrita no Ciclo de Vida dos Dados que dará suporte para o início da implantação de um sistema que seja capaz de rastrear as informações de produção dos ovos. O objetivo geral desse trabalho foi avaliar a viabilidade de coleta de dados para implantação de um sistema de rastreabilidade de informações do produto na cadeia de ovos, identificando os pontos crít... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Brazil is the 3rd largest producer of eggs in America and to produce it is necessary that the production chain is organized to provide quality products in addition to having good levels of productivity. Consumers are becoming increasingly demanding and poultry keeping has to adapt to meet this demand. Traceability is a system that makes it possible to trace all information related to a product, from the beginning of the production chain to the final consumer, and can support this momentum experienced by the industry. Quality requirements for layinghens are presented in guidance documents such as EMBRAPA and the Brazilian Poultry Union, which cover all stages of the production process, from the origin of the inputs to the later stages of production. In order to complement quality information, other legislation, which regulates various production processes, dealing with traceability has been used. Given the requirements that can feed a traceability system, both quality and information, the next step refers to the data collection, described in the Data Life Cycle that will support the beginning of the implantation of a system that is capable to track egg production information. The overall objective of this work was to evaluate the viability of data collection for the implementation of a system of traceability of product information in the egg chain, identifying the critical points of this data collection. And, as specific objectives identify the main requirements for information, quality and legislation are required to implement a system of traceability of eggs on a farm; identify through interviews the critical points for collecting traceability information; validate the identified requirements; and, propose improvements in the quality system and in the process of data collection. (Complete abstract click electronic access below) / Mestre

The role of digital humans in product design and assessment is ever increasing. Accurate digital human models are used to provide feedback on virtual prototypes of products, thus reducing costs and shortening the design cycle. An essential part of product assessment in the virtual world is the ability of the human model to interact correctly and naturally with the product model. This involves reaching, grasping and manipulation. This work addresses the difficult problem of grasp planning for digital humans. We develop a semi-interactive system for synthesizing grasps based on the object's shape, and implement this system for SantosTM, the digital human developed at the Virtual Soldier Research Program at the University of Iowa. The system is composed of three main parts: First, a shape matching module that creates an initial power grasp for the object based on a database of pre-calculated grasps. Second, an optimization based module provides control of the fingertip locations. This can be used to synthesize precision grasps under the user's guidance. Finally, a grasp quality module provides feedback about the grasp's mechanical stability. The novelty of our approach lies in the fact that it takes into consideration the upper body posture when planning the grasp, so the whole arm and the torso are involved in the grasp.

The lack of adequate equipment and measurement tools in whole-body vibration has imposed significant constraints on what can be measured and what can be investigated in the field. Most current studies are limited to single direction measurements while focusing on simple postures. Besides the limitation in measurement, most of the current biomechanical measures, such as the seat-to-head transmissibility, have discrepancies in the way they are calculated across different labs. Additionally, this field lacks an important measure to quantify the subjective discomfort of individuals, especially when sitting with different postures or in multiple-axis vibration. This work begins by explaining discrepancies in measurement techniques and uses accelerometers and motion capture to provide the basis for more accurate measurement during single- and three-dimensional human vibration responses. Building on this concept, a new data collection method is introduced using inertial sensors to measure the human response in whole-body vibration. The results indicate that measurement errors are considerably reduced by utilizing the proposed methods and that accurate measurements can be gathered in multiple-axis vibration. Next, a biomechanically driven predictive model was developed to evaluate human discomfort during single-axis sinusoidal vibration. The results indicate that the peak discomfort can be captured with the predictive model during multiple seated postures. The predictive model was then modified to examine human discomfort to whole-body vibration on a larger scale with random vibrations, multiple postures, and multiple vibration directions. The results demonstrate that the predictive measure can capture human discomfort in random vibration and during varying seated postures. Lastly, a new concept called effective seat-to-head transmissibility is introduced, which describes how to combine the human body's biodynamic response to vibration from multiple directions. This concept is further utilized to quantify the human response using many different vibration conditions and seated postures during 6D vibration. The results from this study demonstrate how complicated vibrations from multiple-input and multiple-output motions can be resolved into a single measure. The proposed effective seat-to-head transmissibility concept presents an objective tool to gain insights into the effect of posture and surrounding equipment on the biodynamic response of the operators. This thesis is timely as advances in seat design for operators are increasingly important with evolving armrests, backrests, and seat suspension systems. The utilization of comprehensive measurement techniques, a predictive discomfort model, and the concept of effective seat-to-head transmissibility, therefore, would be beneficial to the fields of seat/equipment design as well as human biomechanics studies in whole-body vibration.

Studies of human response to whole-body vibration, such those encountered in heavy machinery and ground and aerial transportation, have highlighted the critical role of the head-neck posture of seated human occupants and the role of the transport system of a supine human on the severity of the transmitted vibration to the human body. Novel passive and muscle-based models are introduced in this work to predict the biodynamical response of the human under whole-body vibration in seated and supine postures. Planar and three-dimensional models representing the human head-neck system under different seated postures and fore-aft and multiple-axis whole-body vibration are first introduced. In these models, the head-neck system is represented by rigid links connected via spring-damper components representing the soft-tissue and connecting elements between the bones. Additional muscle components are added to some models. The muscle components comprise additional mass, spring, and damper elements arranged in a special order to capture the effect of changes in the displacement, velocity, acceleration, and jerk. The results show that the proposed models are able to predict the displacement and acceleration of the head under different vibration files, with the muscle-based models showing better performance than the passive models. The second set of models is introduced in this work to investigate the effect of the underlying transport system conditions on the response of supine humans under vertical and multiple-axis whole-body vibration. In these models, the supine human body is represented by three rigid links representing the head, torso/arms, and legs. The links are connected via rotational and translational joints, and therefore, it is expected that the models can capture the coupling effects between adjacent segments. The joints comprise translational and rotational spring-damper components that represent the soft tissue and the connecting elements between the segments. The contact surfaces between the supine human and the underlying transport system were modeled using spring-damper elements. Two underlying transport systems were considered, including a rigid support and a long spinal board attached to a military litter. The results showed that the proposed models were able to predict the effect of the transport systems on the human response under different vibration conditions.

Mechanical loading can modulate tissue plasticity and has potential applications in rehabilitation science and regenerative medicine. To safely and effectively introduce mechanical loads to human cells, tissues, and the entire body, we need to understand the optimal loading environment to promote growth and health. The purpose of this research was 1) to validate a limb vibration and compression system; 2) to determine the effect of limb vibration on neural excitability measured by sub-threshold TMS-conditioned H-reflexes and supra-threshold TMS; 3) to determine changes in center of pressure, muscle activity, and kinematics during a postural task following limb vibration; 4) to determine the effect of vibration on accuracy and long latency responses during a weight bearing visuomotor task. The major findings of this research are 1) the mechanical system presented in the manuscript can deliver limb vibration and compression reliably, accurate, and safely to human tissue; 2) sub-threshold cortical stimulation reduces the vibration-induced presynaptic inhibition of the H-reflex. This reduction cannot be attributed to an increase in cortical excitability during limb vibration because the MEP remains unchanged with limb vibration; 3) limb vibration altered the soleus and tibialis EMG activity during a postural control task. The vibration-induced increase in muscle activity was associated with unchanged center of pressure variability and reduced center of pressure complexity; 4) healthy individuals were able to accommodate extraneous afferent information due to the vibration interventions They maintained similar levels of accuracy of a visuomotor tracking task and unchanged long latency responses during an unexpected perturbation.

Epidemiological evidence suggests an association between exposure to non-neutral working postures and work-related musculoskeletal disorders (MSDs) of the low back and shoulder. Accurate and precise quantitative estimation of exposure to non-neutral working postures is, therefore, essential for evaluating worker risk, developing and testing ergonomic interventions, and improving worker health and well-being. Current methods used to directly estimate occupational exposure to non-neutral postures may be obtrusive, often lack sufficient portability for field use, and have limited accuracy and precision when used to measure dynamic or complex motions. Inertial measurement units (IMUs) are emerging instrumentation devices that measure and report an object's orientation and motion characteristics using multiple electromechanical sensors (i.e., accelerometers, gyroscopes, and/or magnetometers). They have been observed to accurately monitor body kinematics over periods of relatively short duration in comparison to laboratory-based optical motion capture systems. Limited research, however, has been performed comparing exposure information obtained with IMUs to exposure information obtained with other field-capable direct measurement exposure assessment methods. Furthermore, insufficient information on the repeatability of IMU-based estimates over a substantial time period (e.g., a full work shift) and inadequate knowledge regarding the effects of different IMU sensor configurations and processing methods on the accuracy and repeatability of estimates of exposure obtained with IMU systems contributes to a lack of their use in epidemiological field studies. This thesis was designed to address these issues and expand upon the current scientific literature regarding the use of IMU sensors as direct measurement devices for assessing exposure to non-neutral working postures in the field. Chapter I provides a background and justification for the work. Chapter II presents the findings of a laboratory-based, manual material handling study that was performed to compare estimates of thoracolumbar trunk motion obtained with a commercially available IMU system with estimates of thoracolumbar trunk motion obtained with a field-capable reference system, the Lumbar Motion Monitor (LMM). The effects of alternative sensor configurations and processing methods on the agreement between LMM and IMU-based estimates of trunk motion were also explored. Chapter III presents the results of a study performed to evaluate the accuracy and repeatability of estimates of trunk angular displacement and upper arm elevation obtained with the IMU system examined in Chapter II over the course of an eight-hour work shift in both a laboratory and field-based setting. The effects of alternative sensor configurations and processing methods on the accuracy and repeatability of estimates of trunk angular displacement and upper arm elevation obtained with the IMU system were also studied. Chapter IV presents the results of a randomized, repeated measures intervention that demonstrates the utility of the IMU system examined in Chapters II and III as a direct measurement instrument for comparing "ergonomic" and conventional examination equipment commonly used by ophthalmologists. Finally, Chapter V summarizes the major findings, discusses their practical implications, and provides suggestions for future research.

Quantifying human posture and range of motion remains challenging due to the need for specific technologies, time for data collection and analysis, and space requirements. The demand for affordable and accessible human body position measurement requires alternative methods that cost less, are portable, and provide similar accuracy to expensive multi-camera systems. This thesis developed and evaluated a novel augmented reality mobile app for human posture measurement to bring marker-based body segment measurement to the point of patient contact. The augmented reality app provides live video of the person being measured, AprilTag2 fiducial markers locations in the video, processes marker data, and calculates angles and distances between markers. Results demonstrated that the mobile app can identify, track, and measure angles and distances between AprilTag2 markers attached to a human body in real-time with millimetre accuracy, thereby allowing researchers and clinicians to quantify posture measurements anywhere, at anytime.

Computer technology has advanced rapidly in the past few decades and computers have become a very important and powerful tool in our everyday lives. Prolonged computer use by office workers has been reported to result in an increased risk of developing Work-related Neck and Upper Limb Disorders (WRNULD) (Bernard et al.. 1994: Faucett & Rempel. 1994: Tittiranonda et al.. 1999). The occupational risk factors associated with prolonged computer use include static posture and the speed and force of keyboard operation. Past studies have examined different aspects of these risk factors through measuring muscle electrical activity (EMG), kinematics and keyboard forces. However, most of these studies have been conducted on healthy painfree subjects and even the few Case-Control studies have not clearly established any direct relationships between the risk factors and WRNULD. The present research project consisted of a series of three studies aimed at investigating whether there were intrinsic differences among different individuals in response to different physical stressors. These intrinsic differences may have important implications to help explain why some individuals would develop WRNULD while others do not. The individuals' responses to the demands of three physical stressors: static posture, speed and force of keyboard operation were assessed. The internal exposure measures of kinematics, EMG, keyboard dynamics and subjective discomforts were used to evaluate the inter-individual differences. Study I was a field investigation comparing the neck-shoulder kinematics between symptomatic ("Case", n=8) and asymptomatic ("Control", n=8) office workers. Results showed trends for consistently greater head tilt and neck flexion angles, and greater ranges of movements in the Case Group than the Control Group. / The Case Group also exhibited a trend for increased acromion protraction compared to the Control Group. The Case Group also reported significantly greater discomfort scores compared to the Control Group. Neither the discomforts nor the kinematics displayed any significant changes over a working day. Study 2 was a laboratory study comparing the responses of Case and Control Groups in terms of EMG, kinematics and subjective discomforts, while a standardised computer task was performed continuously for one hour. The responses of Case (n=23) and Control (n=20) Groups were compared to examine the effects of static posture. The results showed similar trends to those in Study I, with increased neck flexion mean angles and ranges of movements in the Case Group compared to the Control Group. In terms of EMG results, there were trends for EMG amplitude differences in the right upper trapezius (UT) and cervical erector spinae (CES) muscles between Case and Control Groups. These trends became statistically significant when the Case subjects were sub-divided into the High (n=15) and Low (n=8) Groups based on their mean discomfort scores. Study 3 was also a laboratory study to compare the Case (n=21) and Control (n=20) Groups when they were challenged by the physical stressors of speed and force of keyboard operation. In this study, each subject's EMG and discomforts were examined in three typing conditions of normal speed and force, increased typing speed and increased typing force. The Case Group showed trends for higher increases in both UT and CES muscle activities than the Control Group, and when divided into the High-Low Groups, the High Group (n=8) showed trends for much higher muscle activities in all three conditions. / Beside muscle activity changes, the High Group subjects also demonstrated a trend for much higher within-subject Speed and Force Variabilities in their keystroke performance, compared to the Low Group and the Control Group. This result implied that the High Group subjects had a more erratic motor control of the keystroke actions. Based on these results, conceptual models were developed to describe the relationships among the physical stressors, internal exposure responses and discomforts. The Altered Motor Control Model refers to the programmed changes in motor control strategies involving muscle recruitment and joint movement patterns, and these changes were closely related to the subjects' musculoskeletal discomforts. The Heightened Sensitivity Model describes the higher sensitivity levels of individuals with more severe discomforts, in response to the demands of physical stressors. These models are closely related and heightened sensitivity may be an 'effect-modifier" of the motor control mechanisms and the perception of discomforts or pains within the individual. In conclusion, the present research has identified important differences between individuals on the basis of their motor control strategies which may contribute to the development of WRNULD. While the present research has mainly examined the individual responses to three physical stressors, it is possible that the models developed may be applicable to other physical stressors. These findings may also have important implications for future ergonomic research, emphasising the need to address interindividual differences in ergonomic interventions to workers. Further research should be directed towards better understanding of these intrinsic individual differences in both physical and non-physical factors that contribute to the development of WRNULD.