Dissertations / Theses on the topic 'Human biomechanics'

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2006.
Includes bibliographical references (leaves 108-115).
The human fetal membrane, namely the chorioamnion, is the structural soft tissue retaining the amniotic fluid and the fetus during pregnancy. Its biomechanical integrity is crucial for maintaining a healthy gestation and a successful delivery. The premature rupture of the fetal membrane (PROM) can result in serious perinatal complications. Despite extensive research in this field, the mechanical and biochemical processes governing the membrane deformation and failure remain poorly understood. The aim of this study is to characterize the mechanical behavior of the chorioamnionic tissue along with its biochemical properties, through mechanical testing and biochemical analyses. In order to accomplish this goal, specific mechanical and biochemical testing protocols were developed. In vitro mechanical testing was performed on samples from seven patients under different uniaxial and biaxial loading conditions. Significant relaxation was noted under uniaxial loading while very limited creep was observed under biaxial loading. Biochemical measurements such as collagen and sulfated glycosaminoglycan contents were also obtained. In addition, a microstructurally based constitutive model for the fetal membrane is proposed.
(cont.) The model allows for nonlinear hyperelastic response at large deformation. We also propose a framework to capture the time-dependent response of the tissue. The model was implemented in a finite element formulation to allow three-dimensional simulations of membrane deformation.
by Thibault Philippe Prévost.
S.M.

Includes bibliographical references. The thesis on CD-ROM includes Animate, GaitBib, GaitBook and GaitLab, four quick time movies which focus on the functional understanding of human gait. The CD-ROM is available at the Health Sciences Library.

This thesis reports on work undertaken to study the biomechanics of the human foot during normal daily activity, particularly walking and standing. A literature review is presented on topics related to the subject and several of the areas demanding further investigation are highlighted. Three lines of enquiry were pursued to consider the kinematics, kinetics, passive structural properties and muscle activity associated with the foot. A dynamic pedobarograph with a synchronised video system was used to measure the forces and their distribution under the foot (based on seven marked areas) and six kinematic angles of the foot and lower leg. Sixty-one healthy subjects were assessed and the results are presented. Kinetic and kinematic parameters were found to be consistent and smooth for the test population. Several of the events of the gait cycle were found to be temporally different from values widely reported. In the second investigation, four cadaveric foot specimens were tested dynamically to determine the role of the plantar structures during loading in various positions. A method of sequential dissection was used and the results support many of the theories regarding ligament function. Tests on the effect of three extrinsic muscles on the foot load distribution also support previous studies while a preliminary investigation of two pathological feet partially clarifies the biomechanical effects of a hallux valgus deformity. Eight of the foot extrinsic and intrinsic muscles were assessed for the final investigation. Using electromyographic (EMG) recording techniques on six healthy subjects, the muscle EMG activity was quantified during walking a) barefoot, b) with a moulded heel plate, and c) with soft shoes. The results for the extrinsic muscles generally agree with previous work, while the intrinsic muscle activity is more variable. The intrinsic muscles were more active when shoes were worn and displayed unusual fatigue patterns.

The knee joint is an integral component of the musculoskeletal system, aiding the absorption and transition of weight bearing forces. It is often subjected to injury or disease, with osteoarthritis (OA) being the most prevalent disease, particularly amongst the elderly population. It is now understood that OA is a whole-joint disease affecting the entire osteochondral unit at a molecular and cellular level; however to what extent this effects material properties is mostly unexplored. This thesis firstly aimed to comprehensively review the current knowledge of whole human knee joint material properties in young versus old and healthy versus OA samples, and their subsequent macro-scale application into existing finite element (FE) models. Results indicated unambiguous gaps in the literature for material properties, particularly evident in the aged and OA samples. Consequently, existing human knee FE models apply material properties from a variety of animal and human cohorts, obtained from differing anatomical localities and diverse cadaver demographics, reducing the biological accuracy of resultant mechanical behaviour predicted from such models. Secondly, this thesis aimed to determine the effects of multiple freeze-thaw cycles on cartilage material properties in an attempt to justify a reliable storage and perseveration technique for future work. Results showed that cartilage can undergo up to three freeze-thaw cycles without statistically compromising the integrity of samples. Although data should be interpreted and subsequently applied to future research with consideration in relation to its particular application due to high biological variability across samples. Finally, this thesis aimed to collect and analyse new primary material property data of spatially distributed cartilage, subchondral bone and trabecular bone by nanoindentation techniques, and the four primary knee joint ligaments by tensile testing. Samples were obtained from cadaveric specimens with a wide age range (31-88 years) and OA grade (International Cartilage Repair Society grades 0-4) to provide varying demographics that were evidently missing from the literature. Cartilage shear storage and loss modulus and subchondral bone elastic modulus significantly decreased with increasing age and grade of OA. Furthermore, a change in cartilage shear storage and loss modulus was correlated with a change in subchondral bone elastic modulus in site-matched samples. Trabecular bone elastic modulus was not correlated with age or OA. Results also showed preferential regional development of OA in the medial knee compartment and a decrease in cartilage shear storage modulus at site-specific locations. Additionally, the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) material properties had correlations with age, and linear and failure mechanics showed some correlations with increasing OA grade. The medical collateral ligament (MCL) and lateral collateral ligament (LCL) failure mechanics also showed some correlated with an increase in age and OA grade. This thesis has provided, for the first time, whole-joint multiple tissue material properties from the same cadavers during ageing and disease, concluding that both age and OA affect the material properties of the entire osteochondral unit. Such valuable data can be applied to future FE modelling of the human knee to produce more accurate predication of mechanical behaviour. Current data can also be applied therapeutically, including the use of biomimetic materials, joint replacement and pharmacological interventions.

Includes abstract.
Includes bibliographical references (p. 137-148).
The human tongue is composed mainly of skeletal-muscle tissue, and has a complex architecture. Its anatomy is characterised by interweaving, yet distinct muscle groups. It is a significant contributor to the phenomenon of Obstructive Sleep Apnea (OSA). OSA is a pathological condition defined as the partial or complete closing of any part of the human upper airway (HUA) during sleep. OSA syndrome affects a significant portion of the population. Patients with OSA syndrome experience various respiratory problems, an increase in the risk of heart disease, a significant decrease in productivity, and an increase in motor-vehicle accidents [58]. The aim of this work is to report on a constitutive model for the human tongue, and to demonstrate its use in computational simulations for OSA. A realistic model of the constitution of the tongue and computational simulations are also important in areas such as linguistics and speech therapy [44]. The detailed anatomical features of the tongue have been captured using data from the Visible Human Project (VHP) [102]. The geometry of the tongue, and each muscle group of the tongue, are visually identified, and its geometry captured using Mimics [100]. Various image processing tools available in Mimics, such as image segmentation, region-growing and volume generation were used to form the three-dimensional model of the tongue geometry. Muscle fibre orientations were extracted from the same dataset, also using Mimics.The muscle model presented here is based on Hill’s three-element model for representation of the constituent parts of muscle fibres. This Hill-type muscle model also draws from recent work in muscle modelling, by Martins [88]. The model is implemented in an Abaqus user element (UEL) subroutine [24]. The transversely isotropic behaviour of the muscle tissue is accounted for, as well as the influence of muscle activation. The mechanics of the model is limited to static, small-strain, anisotropic, linear-elastic behaviour, and the governing equations are suitably linearized. The body position of the patient during an apneic episode is accounted for in the simulations, as well as the effect of gravity. The focus of this study is on tongue muscle behaviour under gravitational loading, simulating a simplified OSA event. Future models will incorporate airway pressure as well. The behaviour of the model is illustrated in a number of benchmark tests, and computational examples.

Previous analyses of mandibular biomechanics have incorporated a wide variety of approaches and variables in attempts at describing the relationships between the forces generated by the muscle and the forces of resistance at the dentition and temporomandibular joints. The most difficult element to determine in man has been the role of the joint forces which require indirect analyses. A critical literature review points out the problems associated with previous analyses of mandibular mechanics and predictions of joint loading and the need for the incorporation of all relevant anatomical and physiological parameters in order to realistically quantify these relationships. A computerized mathematical model of human mandibular biomechanics for static functions is presented which allows the determination of forces occurring at the dentition and the joints due to the individual muscle force contributions. Utilizing the principles of static equilibrium the model provides for the determination of these forces for any individual for whom the necessary input parameters have been derived. Anatomically, this model requires the designation of the three dimensional coordinates of the origin and insertion points of nine pairs of masticatory muscles, any position of tooth contact, and the temporomandibular joint positions. Determination of the forces generated by the individual muscle groups, and therefore the overall muscle force resultant acting on the system, is given by the product of a number of physiological parameters. These include the physiological cross-section, the intrinsic force per unit of cross-sectional area, and the relative activation level of each muscle for the specific static function. Also required is the three dimensional orientation of tooth resistance force at the designated position of tooth contact, as well as that of the left joint force in the frontal plane. This information reduces the variables in the equilibrium equations to a determinate number which has a single unique solution for each of the tooth and two joint resistance forces. The magnitudes as well as three dimensional orientations of the resultant vectors of the muscles, the tooth resistance force and the two temporomandibular joints are thereby determined mathematically. Both bilaterally symmetrical and unilateral clenching functions as well as three intervals near the intercuspal position of chewing were tested with this model using data derived from literature sources from real subjects. This data was incorporated into a hypothetical average individual data file. Using this data, derivation of the magnitudes and orientations of muscle and tooth forces were made providing predictions as to the nature of temporomandibular joint loading for this individual. The extent of muscle force generated for static maximal clenching tasks modeled was a maximum of 1000 to 1200 N during intercuspal clenching. The orientation of muscle force with respect to the occlusal plane varied from about 90 degrees in the lateral plane, for more posterior molar functions, to 64 degrees for incisal functions. Maximal tooth resistance forces were around 500 to 600 N at the molars versus only 130 to 140 N at the incisors. Unilateral functions showed the working side joint to be more heavily loaded than the balancing side especially for a more posterior function (i.e. molar). Less muscle and therefore tooth force was produced unilaterally but with the benefit of even less residual joint force. Thus, unilateral functions appear to be much more efficient in terms of the distribution of forces between the dentition and joints. Variation in tooth orientation produced variations in both the orientation and magnitudes of the joint forces exhibiting a functional interrelationship of these forces. Based on the analysis in general, the joints were predicted to be capable of resisting up to 300 N of force per side directed anterosuperiorly at about 60 to 100 degrees in the lateral plane. More divergent forces at the joints were found to be of substantially lower magnitude in the lateral and frontal planes. These findings are in good agreement with other studies.
Dentistry, Faculty of
Graduate

Computational modeling is an important tool for studying the structure and function of human anatomy in biomedicine. In this thesis, a dynamic, anatomically accurate model of the human mandibular and laryngeal structures is presented. The complexities of the infra-mandibular anatomy are discussed along with previous approaches to jaw modeling and a detailed description of dynamic modeling techniques. Forward dynamic simulations, created with the model's comprehensive user-interface, are reported that show consistency with previously published jaw modeling literature. Laryngeal motion during swallowing was simulated and shows plausible upward displacement consistent with published recordings. Simulation of unilateral chewing was also performed with the model to study mastication mechanics. A novel open-source modeling platform, ArtiSynth, is described in the context of its use and extension in the construction and simulation of the biomechanical jaw and laryngeal model.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

This thesis addresses the reliability of Goldmann-type applanation tonometers (GAT). It deals with the investigation of the relation between predicted intraocular pressure, IOPG and true pressure, IOPT. The problem of the accuracy of GAT readings has acquired special importance over the last two decades as new types of surgical procedures to correct vision disorders are being explored and gain universal acceptance. The overall aim of the present study is to assess the effects of individual variations in the corneal central thickness (CCT), material properties of the involved tissues and paracentral applanation on the accuracy of IOPG. Two finite element models have been constructed: a two-dimensional axisymmetric model of the cornea and a three-dimensional model of the whole corneoscleral envelope. Various material descriptions were adopted for the cornea in 2D, whereas the 3D model accounted for collagen microstructure and represented a hyperelastic ber reinforced material. Nonlinear analyses were carried out using the commercial general-purpose finite element software ABAQUS. An extensive literature survey and consultations with ophthalmologists and clinicians were the platform for establishing relevant modelling procedures. The results reveal a clear association between all considered parameters and measured IOPG. The effect of assumed CCT is highly dependent on the corneal material properties. Material model alone has a profound effect on predicted IOPG. Variations in tonometer tip application produce clinically signi cant errors to IOPG measurements. Potential effects of corneal stiffness and paracentral applanation on GAT readings are larger than the impact of CCT. The behaviour of the models is broadly in agreement with published observations. The proposed procedures can be a useful tools for suggesting the magnitudes of corrections for corneal biomechanics and possible human errors. The present modelling exercise has an ability to reproduce the behaviour of human cornea and trace it under IOP and GAT, providing potentially useful information on the distribution of stresses and strains. Some recommendations can be drawn in pursuit of the clinical imperatives of ophthalmologists.
QC 20100729

The work reported in this thesis was carried out to investigate the mechanisms of ligamentous action in the human foot during the functions of standing and walking. A comprehensive literature review of the relevant subject areas was presented and a need for further work demonstrated. Ligament strain patterns in cadaveric feet were measured for a number of foot positions and static and dynamic loading patterns, including simulations of standing and gait. Levels of functional strain have been established for each ligament and it has been shown that the plantar ligaments of the tarsus are especially sensitive to the motions of inversion and eversion. Maximum strain levels were witnessed during the toe-off phase of the gait cycle where values of approximately 4 times those seen during standing were found. The action of the extrinsic musculature was able to supplement passive support mechanisms by reducing strain in the subject ligaments. Uniaxial tension testing of isolated preparations of the subject ligaments was then carried out utilising measurements of local strain. In addition to providing a record of the load-deformation responses of the tissues tested, these experiments allowed derivation of a range of functional force estimates for intact normal feet. Stress-strain relationships were also derived and these were compared to contemporary models of ligament mechanics. Functional values of stress were also reported. A mathematical model representing the foot during stance was developed. Forcedeformation data and measured anatomical data provided the necessary information to solve the model for the stance condition. The effect of simulated ligament rupture through injury and the effects of surgical ligament release on the strain and force patterns of the unaffected ligament structures were identified. The results of this investigation served as a record of the quantitative biomechanics of the ligaments in the human foot.

Introduction: The forearm is a complex biological unit, which has allowed man's evolution. This PhD commenced with an analysis of the normal biomechanical functioning of the key components of the forearm: notably the distal radioulnar joint (DRUJ), interosseous ligament (IOL) and proximal radioulnar joint (PRUJ). Understanding normal forearm physiology, a clinical study followed to delineate the pathophysiology of a new clinical entity, related to DRUJ dysfunction. Methods: Biomechanical Study: A biomechanical testing jig was developed to facilitate collection of data about normal functioning of the DRUJ, IOL and PRUJ in both unloaded and loaded states. This permitted testing throughout the range of forearm pronosupination. Thawed fresh frozen cadaveric upperlimbs were mounted into the jig. Using Microstrain® strain gauges and Tekscan™ pressure sensors, the functional anatomy of the key components of the forearm was delineated, both with the forearm flexed at 90° and maximally extended at the elbow. Clinical Study: A series of 3-Tesla MRI scans was undertaken on patients symptomatic of an intermittent ulnar neuropathy. The causative pathophysiology was determined using 3D qualitative and quantitative analyses. Results: Biomechanical Study: Reproducible patterns of force transmitted and joint contact area have been determined for the DRUJ, and for the first time, the PRUJ. With the exception of PMax and P60 for the PRUJ, application of load increases contact areas and transmitted forces across the joints (P<0.05). The converse is true for PMax and P60 in the PRUJ. The IOL is lax during pronation, strain gradually increasing as the arm moves to neutral. In neutral the middle-portion of the IOL (m-IOL) demonstrates most strain, this decreasing again in supination, whilst the distal and proximal portions (d- & p-IOL) exhibit more strain (P<0.05). Axial loading consistently increases strain in all ligaments (P<0.05). Observed behaviour patterns across the joints and in the ligaments alter with elbow extension (P<0.05). Clinical Study: Salient symptoms of the new syndrome were described. Displacement of the ulnar nerve from its normal course was seen with compression/distraction in the distal forearm and Guyon’s canal. This was considered causative of the syndrome. As a by-product of the research, a new clinical device was also developed, which improves the patient pathway when investigating DRUJ dysfunction. Conclusions and Outcomes: This research has analysed normal forearm biomechanics determining that the PRUJ is a load-bearing joint, interrelated with the DRUJ and IOL. Elbow extension has been shown to alter the normal biomechanics of the forearm. A clinical entity of a dysfunctional forearm has been defined, called subluxation-related ulnar neuropathy or SUN syndrome. Finally, a new clinical device has been developed, which it is anticipated will translate into visible improvements in patient care.

This thesis analyzes the wrist joint of the human hand by using a realistic threedimensional wrist model. Load distributions among carpal bones, forces on ligaments and joints were examined by using three-dimensional model. Wrist injuries and required surgical operations were examined with the model. The most crucial point of the study was that, using three-dimensional model of the wrist, hand surgeons would be able to predict results of surgical operation. Surgery planning may be done and mechanical results may be Evaluated on the wrist model.

Introduction: Claims that foot orthoses can resolve low-back pain are common in the marketing of these devices. The claims are based on the notion that wearing the orthoses will limit excess pronation at the subtalar joint thus reducing excessive internal tibial and femoral rotations. Excess leg rotations increase the anterior tilt of the pelvis and subsequently the degree of lumbar lordosis. Since lumbar lordosis has been suggested as a cause of low-back pain, it is speculated that foot orthoses could be used to treat and prevent pain to the low-back by reducing the forward curvature of the spine. This mechanical link between foot function and the low-back has not been investigated by experimental studies. Purpose: The purpose of this thesis was to investigate whether increased internal rotation of the femur induced an anterior tilt of the pelvis thus increasing the degree of lumbar lordosis and if external rotation induced a posterior pelvic tilt thus decreasing the degree of lumbar lordosis. Methods: In order to internally and externally rotate the femur, participants placed their feet in 18 different foot positions. Seven of these positions ranged from 15 degrees of foot eversion to 15 degrees of foot inversion and 11 positions ranged from 40 degrees of external foot rotation to 40 degrees of internal foot rotation. Six cameras surrounded the motion capture area and angles of pelvic tilt and lumbar lordosis were calculated. Results: Foot eversion and inversion did not have a statistically significant effect on pelvic tilt and lumbar lordosis. In-toeing had a statistically significant linear relationship with anterior pelvic tilt (R2=0.35, F1,131=69.79, p=0.00). Internally and externally rotating the feet had no effect on lumbar lordosis (R2=0.001, F1,153=0.09, p=0.77). Conclusion: Internally rotating the legs caused the pelvis to tilt anteriorly but only at extreme ranges of motion, much greater than what would normally be seen during gait. At which point, lumbar angles remained unaffected. This study does not dispute the effectiveness of foot orthoses to treat low-back pain but the results do not support the mechanical link proposed as the mechanism by which they work.

The pedestrian is one of the most vulnerable road users. According to the World Health Organization (WHO), traffic accidents cause about 1.34 million fatalities annually across the world. This is the eighth leading cause of death across all age groups. Among these fatalities, pedestrians represent 23% (world), 27% (Europe), 40% (Africa), 34% (Eastern Mediterranean), and 22% (Americas) of total traffic deaths. In the United States, approximately 6,227 pedestrians were killed in road crashes in 2018, the highest number in nearly three decades. To protect pedestrians during Car-to-Pedestrian Collisions (CPC), subsystem impact tests, using impactors corresponding to the pedestrian's head and upper/lower leg were included in regulations. However, these simple impact tests cannot capture the complex vehicle-pedestrian interaction, nor the pedestrian injury mechanisms, which are crucial to understanding pedestrian kinetics/kinematics responses in CPC accidents. Numerous variables influence injury variation during vehicle-pedestrian interactions, but current test procedures only require testing in the limited scenarios that mostly focus on the anthropometry of the 50th percentile male subject. This test procedure cannot be applied to real-world accidents nor the entire pedestrian population due to the incredibly specific nature of the testing. To better understand the injury mechanisms of pedestrians and improve the test protocols, more pre-impact variables should be considered in order to protect pedestrians in various accident scenarios. In this study, simplified finite element (FE) models corresponding to 5th percentile female (F05), 50th percentile male (M50), and 95th percentile male (M95) pedestrians were developed and validated in order to investigate the kinetics and kinematics of pedestrians in a cost-effective study. The model geometries were reconstructed from medical images and exterior scanned data corresponding to a small female, mid-sized male, and tall male volunteers, respectively. These models were validated based on post mortem human surrogate (PMHS) test data under various loading including valgus bending at knee joint, lateral/anterior-lateral impact at shoulder, pelvis, thorax, and abdomen, and lateral impact during CPC. Overall, the kinetic/kinematic responses predicted by the pedestrian FE models showed good agreement against the corresponding PMHS test data. To predict injuries from the tissue level up to the full-body, detailed pedestrian models, including sophisticated musculoskeletal system and internal organs, were developed and validated as well. Similar validations were performed on the detailed pedestrian models and showed high-biofidelic responses against the PMHS test data. After model development and validation, the effect of pre-impact variables, such as anthropometry, pedestrian posture, and vehicle type in CPC impacts were investigated in different impact scenarios. The M50-PS model's posture was modified to replicate pedestrian gait posture. Five models were developed to demonstrate pedestrian posture in 0, 20, 40, 60, and 80 % of the gait cycle. In a sensitivity study, the 50th percentile male pedestrian simplified (M50-PS) model in gait predicted various kinematic responses as well as the injury outcomes in CPC impact with different vehicle type. The pedestrian FE models developed in this work have the capability to reproduce the kinetic/kinematic responses of pedestrians and to predict injury outcomes in various CPC impact scenarios. Therefore, this work could be used to improve the design of new vehicles and current pedestrian test procedures, which eventually may reduce pedestrian fatalities in traffic accidents.
Doctor of Philosophy
The pedestrian is one of the most vulnerable road users. According to the World Health Organization, traffic accidents cause about 1.34 million fatalities annually across the world. This is the eighth leading cause of death across all age groups. Among these fatalities, pedestrians represent 23% (world), 27% (Europe), 40% (Africa), 34% (Eastern Mediterranean), and 22% (Americas) of total traffic deaths. In the United States, approximately 6,227 pedestrians were killed in road crashes in 2018, the highest number in nearly three decades. To protect pedestrians in traffic accidents, subsystem impact tests, using impactors corresponding to the pedestrian’s head and upper/lower leg were included in regulations. However, these simple impact tests cannot capture the complex vehicle-pedestrian interaction, nor the pedestrian injury mechanisms, which are crucial to understanding pedestrian kinetics/kinematics responses in traffic accidents. Numerous variables influence injury variation during vehicle-pedestrian interactions, but current test procedures only require testing in the limited scenarios that mostly focus on the anthropometry of the average male subject. This test procedure cannot be applied to real-world accidents nor the entire pedestrian population due to the incredibly specific nature of the testing. To better understand the injury mechanisms of pedestrians and improve the test protocols, more pre-impact variables should be considered in order to protect pedestrians in various accident scenarios. In this study, simplified pedestrian computational models corresponding to small female, average male, and large male pedestrians were developed and validated in order to investigate the kinetics and kinematics of pedestrians in a cost-effective study. Overall, the kinetic/kinematic responses predicted by the pedestrian models showed good agreement against the corresponding test data. To predict injuries from the tissue level up to the full-body, detailed pedestrian computational models, including sophisticated musculoskeletal system and internal organs, were developed and validated as well. Similar validations were performed on the detailed pedestrian models and showed high-biofidelic responses against the test data. After model development and validation, the pre-impact variables were examined using the average male pedestrian model, which was modified the position to replicate pedestrian gait posture. In a sensitivity study, the average male pedestrian model in gait predicted various kinematic responses as well as the injury outcomes in lateral impact with different vehicle types. The pedestrian models developed in this work have the capability to reproduce the kinetic/kinematic responses of pedestrian and to predict injury outcomes in various pedestrian impact scenarios. Therefore, this work could be used to improve the design of new vehicles and current pedestrian test procedures, which eventually many reduce pedestrian fatalities in traffic accidents.
The pedestrian is one of the most vulnerable road users. According to the World Health Organization, traffic accidents cause about 1.34 million fatalities annually across the world. This is the eighth leading cause of death across all age groups. Among these fatalities, pedestrians represent 23% (world), 27% (Europe), 40% (Africa), 34% (Eastern Mediterranean), and 22% (Americas) of total traffic deaths. In the United States, approximately 6,227 pedestrians were killed in road crashes in 2018, the highest number in nearly three decades. To protect pedestrians in traffic accidents, subsystem impact tests, using impactors corresponding to the pedestrian’s head and upper/lower leg were included in regulations. However, these simple impact tests cannot capture the complex vehicle-pedestrian interaction, nor the pedestrian injury mechanisms, which are crucial to understanding pedestrian kinetics/kinematics responses in traffic accidents. Numerous variables influence injury variation during vehicle-pedestrian interactions, but current test procedures only require testing in the limited scenarios that mostly focus on the anthropometry of the average male subject. This test procedure cannot be applied to real-world accidents nor the entire pedestrian population due to the incredibly specific nature of the testing. To better understand the injury mechanisms of pedestrians and improve the test protocols, more pre-impact variables should be considered in order to protect pedestrians in various accident scenarios. In this study, simplified pedestrian computational models corresponding to small female, average male, and large male pedestrians were developed and validated in order to investigate the kinetics and kinematics of pedestrians in a cost-effective study. Overall, the kinetic/kinematic responses predicted by the pedestrian models showed good agreement against the corresponding test data. To predict injuries from the tissue level up to the full-body, detailed pedestrian computational models, including sophisticated musculoskeletal system and internal organs, were developed and validated as well. Similar validations were performed on the detailed pedestrian models and showed high-biofidelic responses against the test data. After model development and validation, the pre-impact variables were examined using the average male pedestrian model, which was modified the position to replicate pedestrian gait posture. In a sensitivity study, the average male pedestrian model in gait predicted various kinematic responses as well as the injury outcomes in lateral impact with different vehicle types. The pedestrian models developed in this work have the capability to reproduce the kinetic/kinematic responses of pedestrian and to predict injury outcomes in various pedestrian impact scenarios. Therefore, this work could be used to improve the design of new vehicles and current pedestrian test procedures, which eventually many reduce pedestrian fatalities in traffic accidents.

The research presented in this thesis investigates eye injuries caused by blunt impacts and blast overpressure. This research represents part of an ongoing investigation to accurately quantify and predict eye injuries and injury mechanisms for various loading schemes. It has been shown that blunt trauma can cause severe eye injuries but it remains undecided whether blast overpressure alone can cause eye injury. Presented herein are four experimental studies that quantify eye injuries and implement a technique for predicting injury risk. Isolated porcine or human eyes were subjected to various loading conditions consisting of blunt projectiles, water streams, remote control helicopter blades, and blast overpressure. All eyes were prepared in a similar manner that required the insertion of a miniature pressure sensor into the globe through the optic nerve. This sensor measured intraocular pressure throughout each event. Using previously published injury risk curves, this intraocular pressure data was used to predict the injury risk for four eye injuries: hyphema, lens damage, retinal damage, and globe rupture. Injuries sustained were quantified upon direct inspection of the globe following testing. No serious eye injuries were observed for any of the tests and all tests resulted in low predicted injury risks consistent with the lack of observed injury. The research presented in this thesis provides a robust low injury level dataset for eye injuries. This data could be useful for designing and validating computational models and anthropomorphic test device eyes, and serves as a basis for future work with more dangerous projectiles and higher pressure levels.
Master of Science

Advances in technology and research have been employed in recent years to develop efficient mechanisms to deliver home-based exercise therapy to patients suffering from knee osteoarthritis, a degenerative disease associated with aging. Essential to the success of a therapeutic home-exercise program is the quality of the motion performed by the patient. The unsupervised nature of home-based exercise may lead to incorrect exercise performance by patients; however, current home-based exercise programs do not provide mechanisms for monitoring the quality of motion performed or for providing feedback to the patient. This lack of support has been found to be a factor in patient non-compliance to home exercise programs. Our goal is to provide a motion sensor-based system that can evaluate the quality of exercise to support home rehabilitation. We introduce the Quality Assessment Framework (QAF) that uses low-cost motion sensors with data processing and machine learning techniques to assess the quality of human motion performed during therapeutic exercises. Data from fifteen persons with knee osteoarthritis were collected in a laboratory environment, and a classifier was trained using multi-label learning methods to detect descriptive characteristics of the patient's motion. These characteristics represent errors in the exercise performance as well as variables, such as speed, that are regularly monitored by the patient's therapist. Results from multi-label learning are presented and recommendations are made on requirements for an in-home therapeutic exercise system. A classifier, using Ensembles of Classifier Chains with a Support Vector Machine base classifier, provides the best method for assessing human motion quality in the QAF. Leave-one-out and leave-half-out testing provided us with information on the achievable level of generalizability for new patients whose motion is not contained in the training set. We found that a small amount of new patient data is required for good recognition of characteristics in exercise performances. The QAF can be adapted to the home therapy needs of conditions other than knee OA. We present a preliminary design of the InForm Exercise System that utilizes the QAF and has the potential to present feedback to patients completing home exercise programs.

Intramuscular pressure (IMP), which is closely correlated with both active and passive muscle tension, may become a useful supplement to current clinical tools as a means to quantify individual muscle-generated force. A continuing challenge associated with this measure is its non-uniform distribution, which is not yet fully understood. Several studies have observed that pressure increases with muscle depth. Conservation of mass suggests that these regional pressure differences may result from non-uniformly distributed changes in local tissue volume. Therefore, the overarching goal of this work was to characterize volumetric strain distribution in skeletal muscle as a means to better understand the mechanism driving the non-uniform IMP distribution.

Three-dimensional volumetric strain distribution had not been previously quantified in skeletal muscle; therefore the bulk of this thesis work revolved around developing and validating a method for this purpose using cine Phase Contrast (CPC) magnetic resonance imaging (MRI). CPC MRI has been previously used to quantify 2D strain distribution in skeletal muscle. Fortunately, the method lends itself to 3D measurements using multiple slice data collection, but this requires a lengthy data acquisition time. We chose to develop the method during passive tension of the human tibialis anterior (TA), because passive tension is closely correlated with IMP and the motion repeatability is more readily controlled and maintained for an extended duration than active tension.

As hypothesized, volumetric strain was found to be non-uniformly distributed during passive tension of the human TA with a decreasing trend from the anterior (superficial) to the posterior (deep) muscle regions. These data align with previously observed trends of decreasing IMP near the muscle surface and may provide important insight into ideal sensor placement regions to maximize measurement repeatability. These results advance our understanding of the tension-IMP relationship in muscle by providing insight into the mechanism behind the non-uniform distribution of IMP. Furthermore, this work has strong potential to contribute to a computational model relating IMP to muscle tension by way of volumetric strain.

Every year, more than 2.4 million eye injuries occur in the United States, with over 30,000 of those injured left blind in at least one eye as a result. Computer modeling is one of the most versatile ways to study ocular trauma, however, existing models lack accurate stress and strain properties for ocular globe rupture. A pressure system was built to examine static and dynamic globe rupture pressures for healthy postmortem human and porcine (pig) eyes. Maximum rupture stress for the quasi-static tests was found to be 11.17MPa for human tissue and 12.08MPa for porcine tissue, whereas stress for the dynamic tests was found to be 30.18MPa for human tissue and 26.01MPa for porcine tissue. Maximum rupture stress results correlate well with static material properties used in published research (9.4MPa), and dynamic properties of 23MPa found in published research. Healthy postmortem human eyes were ruptured statically and dynamically to determine the relationship between stress and strain for the ocular globe under intraocular pressure loading. Stress-strain relationships were investigated and values for the elastic modulus were found to be slightly lower than that previously published. This research shows that it is important to differentiate between tissue type, and static versus dynamic failure properties before drawing conclusions from computer models and other published research. Now that rupture can be accurately determined, safety systems designed to protect eyesight in automotive, sports, and military applications can also be applied to protect the quality of life for humans in these applications.
Master of Science

More than 50% of intervertebral discs in the third and fourth decade of life exhibit annular tears and fissures with different orientations and extents. On the other hand, in vitro biomechanical investigations of the disc surgery treatment, sometimes requires collaterals lesions, such as incision or disc material removal to recreate biological injuries, as in discoplastly. These lesions could have a mechanical impact on the spine flexibility and in the surrounding tissue and could alter the final outcomes of in vitro studies. The influence of the presence of lesions on the biomechanics of the segment is still a debated research question. Thus, this in vitro study aims to evaluate changes in spine biomechanics, in terms of stiffness, range of motion and disc height, induced by an increasing damage of human disc. In order to assess the impact of the annulus damage on the surrounding tissues, principal strain distributions were investigated in the lateral side opposite than the damaged region. Eight fresh cadaver thoraco-lumbar FSUs were used in this study. The specimens were tested sequentially in flexion and extension in five different configurations: a) with the intact disc; b) with two vertical cuts; c) with four cuts, forming a square, without removing any part of the annulus; d) after having removed the cut part of the AF; e) after having removed the nucleus pulposus. Image analysis and surface strain distribution were performed on the lateral disc by means of the Digital Image Correlation.

Glutaraldehyde is a fixing agent for heterologus pericardium used in cardiac surgery. It is known to sterilize and stabilize the material and change its properties. However, it is uncertain whether fixation of autologous tissue is necessary. Fresh human pericardium specimens were harvested from cardiac surgery and cut into four smaller samples: two were kept in the native (fresh) state and two chemically treated with Carpentier's Solution (0.625% glutaraldehyde) for 10 min. The equi-biaxial response of each sample was tested with a biaxial tensile machine. Samples of other patch materials (bovine pericardium, Dacron) were also tested. Fresh tissue was significantly stiffer than fixed tissue but was then shown to be the result of significant tissue swelling due to the treatment. The fresh and fixed pericardium tissue displayed anisotropy, with the longitudinal direction being stiffer than the transverse. Comparing human pericardium (fresh and fixed) to Dacron and bovine pericardium (commercially obtained), Dacron was found to be the stiffest material followed by bovine pericardium. Surgeons should be aware of the mechanical differences of patch materials when planning surgery
Le glutaraldéhyde est un agent fixateur utilisé dans la cardiochirurgie pour stériliser et stabiliser les péricardes hétérologues. Cependant, il n'est pas certain quant à savoir si la fixation du tissu autologue est nécessaire. Des spécimens humains du péricarde ont été recueillis de patients de cardiochirurgie et coupés en quatre petits échantillons. L'état initial de deux d'entre eux a été conservé alors que les deux autres ont baignés dans une solution de Carpentier (0.625% glutaraldéhyde) pendant 10 minutes. La tension équibiaxiale de chaque échantillon a été mesurée avec une machine à tension biaxiale. Il a été fait de même pour des échantillons de matériaux substituts (péricarde de bovin, Dacron). Le tissu conservé était manifestement plus rigide que le tissu fixé. Il a été établi que l'écart des résultats s'explique par le gonflement que le tissu fixé a subi lorsqu'il a été immergé dans l'agent fixateur. De plus, il a été démontré que les deux tissus sont anisotropes. Les mesures de tension en direction longitudinale étaient plus élevées que celles en direction transversale. En comparant les échantillons de péricardes humains à deux autres matériaux substituts disponibles sur le marché, il a été établi que le Dacron suivi du péricarde de bovin sont plus rigides. Les chirurgiens doivent connaître les propriétés de ces matériaux afin d'utiliser celui le mieux adapté à leur diagnostic.

How do humans generate and resist repetitive impact forces beneath the heel during walking and heel strike running? Due to the evolution of long day ranges and larger body sizes in the hominin lineage modern human hunter-gatherers must resist millions of high magnitude impact forces per foot per year. As such, impact forces may have been a selective pressure on many aspects of human morphology, including skeletal structure. This thesis therefore examines how humans generate impact forces under a variety of conditions and how variation in skeletal structure influences impact resistance. This thesis includes four studies that can be separated into two parts. In the first part, I test two models of how variation in the stiffness and height of footwear affect the generation of impact peaks during walking and heel strike running. The first model predicts that variation in the stiffness of footwear introduces tradeoffs between three crucial impact force related variables: impact loading rate, vertical impulse and effective mass. The prediction of the second model is that higher heels have the same effects on impact forces as do footwear of lower stiffness. These hypotheses were tested using 3D motion data and force data in human walkers and runners wearing a variety of footwear. Experimental results show that soft footwear introduces tradeoffs between impact loading rate, vertical impulse and effective mass, and that high heeled shoes influence impact duration, loading rate and vertical impulse in predictable ways. In the second part of this thesis, I document variation in hominoid skeletal structure and experimentally test how this variation affects function during impact forces. In particular, I examine trabecular bone volume fraction in the calcaneus of gorillas, chimpanzees and several H. sapiens populations that vary widely in geologic age and subsistence strategy. I then develop and test a model of how variation in trabecular bone volume fraction affects several mechanical properties of trabecular bone tissue, including the stiffness, strength and energy dissipation. The comparative data indicates that trabecular bone volume fraction in the human calcaneus has declined after the Pleistocene. The experimental data shows that larger trabecular bone volume fraction results in increased stiffness and strength but reduced energy dissipation of trabecular bone tissue. A final examination of the comparative data relative to the experimental data suggests that the human calcaneus resists impacts by being stiff strong rather than by dissipating mechanical energy. The results of this thesis suggest that way in which impacts are both generated and resisted has changed in recent human history, as modern footwear alters impact loading rate and vertical impulse and decline in trabecular bone volume fraction negatively influence trabecular bone strength. These results also have implications for how bones evolve to resist impacts, suggesting that bone structures than favor stiffness and strength are favored to cope with impacts. Finally, the results of this thesis are important for understanding the etiology of osteoarthritis, and musculoskeletal disease that has been linked to both repetitive impact forces during human locomotion and to variation in trabecular bone volume fraction.
Human Evolutionary Biology

Motion analysis allows for the collection and quantification of movement, and has long been used for the assessment of gait. In more recent years, models have been developed to accurately track the kinematics of the upper extremity, however, current methods are limited due to the small number of validated kinematic models. Over time, multiple models have developed for shoulder joint center (SJC) calculation, however, few are validated, with most difficult to implement.

Currently, approximately 3.7 million wheelchair users reside in the USA. The repetitive cyclic propulsion pattern required for wheelchair mobility places high loads on the wrist, elbow, and shoulder and often results in overuse injuries with an estimated 30% to 69% prevalence. Quantification of the shoulder complex using 3D kinematics allows for the assessment of ranges of motion, forces, and moments which may allow for better prescription and training, and propulsion biomechanics in wheelchair users.

Schnorenberg et al. developed and validated a wheelchair model whereby the SJC was calculated using multiple linear regression of the positions of the scapula, clavicle, and humerus. While this model more accurately tracks the glenohumeral joint center as compared to previous models, it requires advanced training and custom Matlab code which limit application for adoption by low resourced clinics and facilities. A simplified model using Visual 3D was developed to allow for local and international clinical and research applications in conjunction with a previously develop low-cost motion tracking system. Motion data during the wheelchair stroke cycle, was obtained using 12 Vicon cameras and Vicon Nexus software. The 3D motion files were processed using both models.

The wrist joint center and glenohumeral joint center yielded sub 2 mm mean error. While the wrist, elbow, and glenohumeral joints had an average error of less than 10° during the grasp and vertical events. Through the development and validation of a simplified model utilizing Visual3D, upper extremity motion analysis may be easily applied in international and outreach clinics. This work presents new methodology to augment current paradigms for evaluation of wheelchair biomechanics.

Due to the rising number of stroke victims, the demand for reduced cost and effective treatments for recovering patients increases. To offset this need, previous studies introduced robotic assistance to rehabilitation treatments. This study investigates how much robotic assistance affects the patient by analyzing the differences in muscle activity. From the collected experimental data of ten healthy subjects, the results initially inferred that the end position of the reaching movements affected the muscle activity in biceps and triceps only, while the deltoid was not affected. However, after applying ANOVA one-way analyses, robotic assistance was found to have an impact on the deltoid, triceps, and bicep muscles when subjects moved their hands along an indirect trajectory towards nine targets. Meanwhile, only the bicep was affected when subjects moved their arm in a direct path with assistance. Lastly, the impact that the trajectory of the hand movement had on muscle activity was undetermined.

Every movement has a goal. For reaching, the goal is to move the hand to a specific location. For locomotion, however, goals for each step cycle are unclear and veiled by the automatic nature of lower limb control. What mechanical variables does the nervous system "care" about during locomotion? Abundant evidence from the biomechanics literature suggests that the force generated on the ground, or endpoint force, is an important task variable during hopping and running. Hopping and running are called bouncing gaits for the reason that the endpoint force trajectory is like that of bouncing on a pogo stick. In this work, I captured kinematics and kinetics of human bouncing gaits, and tested whether structure in the inherent step-to-step variability is consistent with control of endpoint force. I found that joint torques covary from step to step to stabilize only peak force. When two limbs are used to generate force on the ground at the same time, individual forces of the limbs are not stabilized, but the total peak force is stabilized. Moreover, passive dynamics may be exploited during forward progression. These results suggest that the number of kinetic goals is minimal, and this simple control scheme involves goals for discrete times during the gait cycle. Uncovering biomechanical goals of locomotion provides a functional context for understanding how complex joints, muscles, and neural circuits are coordinated.

Throwing with power and accuracy is a uniquely human behavior and a potentially important mode of early hunting. Chimpanzees, our closest living relatives, do occasionally throw, although with much less velocity. At some point in our evolutionary history, hominins developed the ability to produce high performance throws. The anatomical changes that enable increased throwing ability are poorly understood and the antiquity of this behavior is unknown. In this thesis, I examine how anatomical shifts in the upper body known to occur during human evolution affect throwing performance. I propose a new biomechanical model for how humans amplify power during high-speed throwing using elastic energy stored and released in the throwing shoulder. I also propose and experimentally test a series of functional hypotheses regarding how four key shifts in upper body anatomy affect throwing performance: increased torso rotational mobility, laterally oriented shoulders, lower humeral torsion, and increased wrist hyperextensability. These hypotheses are tested by collecting 3D body motion data during throws performed by human subjects in whom I varied anatomical parameters using restrictive braces to examine their effects on throwing kinematics. These data are broken down using inverse dynamics analysis into the individual motions, velocities, and forces acting around each joint axis. I compare performance at each joint across experimental conditions to test hypotheses regarding the relationship between skeletal features and throwing performance. I also developed and tested a method for predicting humeral torsion using range of motion data, allowing me to calculate torsion in my subjects and determine its effect on throwing performance. My results strongly support an important role for elastic energy storage in powering humans’ uniquely rapid throwing motion. I also found strong performance effects related to anatomical shifts in the torso, shoulder, and arm. When used to interpret the hominin fossil record, my data suggest high-speed throwing ability arose in a mosaic-like fashion, with all relevant features first present in Homo erectus. What drove the evolution of these anatomical shifts is unknown, but as a result the ability to produce high-speed throws was available for early hunting and likely provided an adaptive advantage in this context.
Anthropology

Nearly 27,000 vehicle occupants are killed annually in the United States, with passenger car and light truck occupants amassing 25,000 of these. Over 50% of passenger car and light truck occupant fatalities are due to frontal crashes. Although advancements in safety technology have reduced the number of fatalities and injuries, motor vehicle collisions are still a major issue in the United States. Continued development of computational models and biofidelic anthropomorphic test devices (ATDs) necessitates benchmarking of current surrogates and further analysis of an occupantâ s biomechanical response in automobile collisions. This thesis presents data from low-speed frontal sled tests performed with human volunteers, a Hybrid III 50th percentile male ATD, and post mortem human surrogates (PMHSs). The first study sought to investigate the effects of muscle bracing by human volunteers. The second study sought to compare the responses of the relaxed and braced volunteers in the first study to those of the Hybrid III and PMHS subjects. Overall, these two studies provide novel biomechanical data that can be used to refine and validate computational models and ATDs used to assess injury risk in automotive collisions. The third study was focused on quantifying the ability for children to swing a sword-like toy. Over 200,000 toy-related injuries occur every year in the United States. Currently, data is unavailable with regard to sword-like toys. Incorporating the knowledge gained by this study will allow manufacturers to reduce the inherent risks associated with their products as well as market them to the correct target age groups.
Master of Science

Human upper limb motion analysis with sensing by way of consumer-off-the-shelf (COTS) devices presents a rich set of scientific, technological, and practical implementation challenges. The need for such systems is motivated by the popular trend toward the development of home based rehabilitative motor therapy systems in which patients perform therapy alone while a technological solution connects the patient to a therapist by performing data acquisition, analysis, and the reporting of evaluation results remotely. The choice to use COTS devices mirrors the reasons why they have become universally accepted in society in recent times. They are inexpensive, easy to use, manufactured to be deployable at large scale, and satisfactorily performant for their intended applications. These claims for the use of COTS devices also resound with requirements that make them suitable for use as low-cost equipment in academic research.

The focus of this work is on the development of a proof of concept human upper limb motion capture system using Myo and Sphero. The end-to-end development of the motion capture system begins with developing the software that is required to interact with these devices in MATLAB. Each of Myo and Sphero receive a fully-featured device interface that’s easy to use in native MATLAB m-code. Then, a theoretical framework for upper limb motion capture and analysis is developed in which the devices’ inertial measurement unit data is used to determine the pose of a subject’s upper limb. The framework provides faculties for model calibration, registration of the model with a virtual world, and analysis methods that enable successful validation of the model’s correctness as well as evaluation of its accuracy as shown by the concrete example in this work.

The purpose of this study is to quantify the dynamic mechanical properties of human cervical ligaments following whiplash. Cervical ligaments function to provide spinal stability, propioception, and protection during traumatic events to the spine. The function of cervical ligaments is largely dependant on their dynamic biomechanical properties, which include force and energy resistance, elongation capability, and stiffness. Whiplash has been shown to injure human cervical spine ligaments, and ligamental injury has been shown to alter their dynamic properties, with potential clinical consequences such as joint degeneration and pain. In this study we quantified the dynamic properties of human lower cervical ligaments following whiplash and compared their properties to those of intact ligaments. Whiplash simulation was performed using biofidelic whole cervical spine with muscle force replication (WCS-MFR) models. Next, ligaments were elongated to failure at a fast elongation rate and peak force, peak elongation, peak energy, and stiffness values were calculated from non-linear force-elongation curves. Peak force was highest in the ligamentum flavum (LF) and lowest in the intraspinous and supraspinous ligaments (ISL+SSL). Elongation was smallest in middle-third disc (MTD) and greatest in ISL+SSL. Highest peak energy was found in capsular ligament (CL) and lowest in MTD. LF was the stiffest ligament and ISL+SSL least stiff. These findings were similar to those found in intact ligaments. When directly comparing ligaments following whiplash to intact ligaments in a prior study it was found that the anterior longitudinal ligament (ALL) and CL had altered dynamic properties that were statistically significant, suggesting that whiplash may alter the dynamic properties of cervical ligaments. These findings may contribute to the understanding of whiplash injuries and the development of mathematical models simulating spinal injury.

Biomechanical models provide a means to analyze movement and forces in highly complex anatomical systems. Models can be used to explain cause and effect in normal body function as well as in abnormal cases where underlying causes of dysfunction can be clarified. In addition, computer models can be used to simulate surgical changes to bone and muscle structure allowing for prediction of functional and aesthetic outcomes. This dissertation proposes a state-of-the-art model of coupled jaw-tongue-hyoid biomechanics for simulating combined jaw and tongue motor tasks, such as chewing, swallowing, and speaking. Simulation results demonstrate that mechanical coupling of tongue muscles acting on the jaw and jaw muscles acting on the tongue are significant and should be considered in orofacial modeling studies. Towards validation of the model, simulated tongue velocity and tongue-palate pressure are consistent with published measurements. Inverse simulation methods are also discussed along with the implementation of a technique to automatically compute muscle activations for tracking a target kinematic trajectory for coupled skeletal and soft-tissue models. Additional target parameters, such as dynamic constraint forces and stiffness, are included in the inverse formulation to control muscle activation predictions in redundant models. Simulation results for moving and deforming muscular-hydrostat models are consistent with published theoretical proposals. Also, muscle activations predicted for lateral jaw movement are consistent with published literature on jaw physiology. As an illustrative case study, models of segmental jaw surgery with and without reconstruction are developed. The models are used to simulate clinically observed functional deficits in movement and bite force production. The inverse simulation tools are used to predict muscle forces that could theoretically be used by a patient to compensate for functional deficits following jaw surgery. The modeling tools developed and demonstrated in this dissertation provide a foundation for future studies of orofacial function and biomedical applications in oral and maxillofacial surgery and treatment.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第19793号
人博第764号
新制||人||184(附属図書館)
27||人博||764(吉田南総合図書館)
32829
京都大学大学院人間・環境学研究科共生人間学専攻
(主査)教授 神﨑 素樹, 教授 森谷 敏夫, 教授 石原 昭彦
学位規則第4条第1項該当

This thesis contains three cross-sectional studies and an equipment development study, presented in the form of journal submissions, regarding the hydrodynamics experienced by swimmers during the various phases of the freestyle tumble turn.

Kyoto University (京都大学)
0048
新制・課程博士
博士(人間・環境学)
甲第18353号
人博第666号
新制||人||160(附属図書館)
25||人博||666(吉田南総合図書館)
31211
京都大学大学院人間・環境学研究科共生人間学専攻
(主査)准教授 神﨑 素樹, 教授 森谷 敏夫, 准教授 久代 恵介, 教授 小田 伸午
学位規則第4条第1項該当

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.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.
Includes bibliographical references (p. 236-259).
Osteoarthritis is affecting over 20 million people in the United States, the etiology of which is still unclear. As abnormal stress is believed to be one of the factors causing the degeneration of cartilage, the combined dual-orthogonal fluoroscopic and magnetic resonance imaging technique was applied to investigate the in-vivo biomechanics of human ankle joint complex in this work. The in-vivo kinematic data showed that the talocrural joint contributes more in dorsi/plantarflexion, while the subtalar joint is more responsible for inversion/eversion and internal/external rotation of the joint. During the stance phase of walking there is a complicated combination of the motion of the talocrural and subtalar joints. Cartilage-to-cartilage contact area during the stance phase of walking was determined by quantifying the amount of overlap of the cartilage surfaces of the tibia and talus. The in-vivo cartilage contact data showed significant changes in cartilage contact areas at different positions during the stance phase of walking. The articular cartilage contact was only observed in less than 50% of the cartilage coverage areas in the talocrural joint at various positions of the simulated stance phase of walking. The 3D compressive contact strain distribution within the ankle joint was determined under full body weight based on the thickness distribution and the deformation of the cartilage layers. The mean of the average cartilage contact strain of the entire contact area was only 7.5% whereas the mean peak contact strain reached 34.5%. With Young's modulus as 7.5 MPa and Poisson's ratio as 0.4, the average peak pressure was 6.87 ± 1.76 MPa and the average joint contact force was 1.66 ± 0.12 body weight. The in-vivo creep test of human ankle joint was also carried out and the contact deformation occurred mostly in early 30 to 40 seconds after loading the ankle joints. The in-vivo material properties was calculated and compared with the in vitro data. More computational research was performed focusing on the finite element analysis of the in-vivo ankle cartilage with biphasic/poroelastic material properties. The variation of the cartilage surface layer permeability was shown to have significant effects on the biomechanics behavior of human ankle cartilage.
by Lu Wan.
Ph.D.

The Sit-to-Stand (STS) transition is a voluntary daily activity that consists of rising from a sitting position to a standing position, an activity that is typically performed by a person several times a day. To undertake the activity successfully requires the coordination of the body limbs in order to transfer the body weight between the sitting and standing positions, maintaining the balance, in order to avoid a fall. A biomechanical analysis of the STS transition provides useful information about the motor ability and control strategy of a person and as such, it is commonly employed to assess functional performance, and as an indicator of lower limb strength in the elderly and in people with disabling diseases. The aim of the work described in this thesis was to investigate and analyse the STS transition in two groups of healthy subjects, a cohort (n=10) of younger adult participants (age range 28±2 years) and a cohort (n=10) of older adult participants (age range 56±8 years), in order to identify the differences in the performances within and between the two groups when the STS transition was undertaken at different speeds. The two groups of participants performed STS transition trials at three, different, self-selected speeds (normal, slow and fast) during which data was recorded from a caption systems, consisting of a set of six infrared-cameras and two force plates. The in-vivo data obtained was applied to a link segment biomechanical model enabling the kinematic contribution of the major body segments to the STS activity to be determined for each participant. A principal component analysis (PCA) was undertaken to identify any aggregate and segmental differences in the STS transition performance between speeds. In addition, a kinetic analysis was performed to determine the torque and power contributions of the lower limb joints during the STS transition. The results from the analysis showed that younger and older participants performed the STS transition with a similar pattern, but they used different strategies to ascend according to the speed at which the activity was being performed. The younger participants used the same strategy at slow speed than the older participants used at slow and normal speeds. Likewise, the younger participants used the same strategy at normal and fast speeds as the older participants used at fast speed. From the segmental analysis it was found that the upper-body and pelvis segments presented the larger variability than the other segments. From the joint analysis, the knee and hip joints were identified as the joints that provide the greatest contribution to the STS transition as they generated most of the power and torque required for the activity. The results obtained and the methodology developed could help clinicians with the diagnosis, planning and selection of treatment for patients with a lack of mobility. This type of analysis may also find application in fields such as robotics, ergonomics and sports training.