This dissertation describes the development and results of a physiological rigid body forward solution mathematical model that can be used to predict normal knee and total knee arthroplasty (TKA) kinematics and kinetics. The simulated activities include active extension and weight-bearing deep knee bend. The model includes both the patellofemoral and tibiofemoral joints. Geometry of the normal or implanted knee is represented by multivariate polynomials and modeled by constraining the velocity of lateral and medial tibiofemoral and patellofemoral contact points in a direction normal to the geometry surface. Center of mass, ligament and muscle attachment points and normal knee geometry were found using computer aided design (CAD) models built from computer tomography (CT) scans of a single subject. Quadriceps forces were the input for this model and were adjusted using a unique controller to control the rate of flexion, embedded with a controller which stabilizes the patellofemoral joint. The model was developed first using normal knee parameters. Once the normal knee model was validated, different total knee arthroplasty (TKA) designs were virtually implanted. The model was validated using in vivo data obtained through fluoroscopic analysis. In vivo data of the extension and deep knee bend activities from five non-implanted knees were used to validate the normal model kinematics. In vivo kinematic and kinetic data from a telemetric TKA with a tibia component instrumented with strain gauges was used to validate the kinematic and kinetic results of the model implanted with the TKA geometry. The tibiofemoral contact movement matched the trend seen in the in vivo data from the one patient available with this implant. The maximum axial tibiofemoral force calculated with the model was in 3.1% error with the maximum force seen in the in vivo data, and the trend of the contact forces matched well. Several other TKA designs were virtually implanted and analyzed to determine kinematics and bearing surface kinetics. The comparison between the model results and those previously assessed under in vivo conditions validates the effectiveness of the model and proves that it can be used to predict the in vivo kinematic and kinetic behavior of a TKA.

The aim of this thesis was to study different aspects of the soft tissues of the shoulder joint. The variation in the quality of the tendons and ligaments can be explained by genetic factors. To test the hypothesis that collagen 1 α1 Sp1 polymorphism is related to the occurrence of cruciate ligament ruptures and shoulder dislocations, a total of 358 patients (233 patients with cruciate ligament ruptures and 126 with shoulder dislocations) were included in the study. We found a decreased risk of these injuries associated with collagen type 1 α1 Sp1 polymorphism. To study the mechanical properties of a better type of fixation of soft tissue to bone, 10 skeletally mature New Zealand white rabbits were operated bilaterally on the knees. The medial collateral ligaments were fixed by two types of plates one with a flat undersurface and the other with a pegged undersurface. After 4 weeks the force at failure, stiffness and energy uptake was almost double in the knees operated with the pegged plates. The prevalence and dysfunction of rotator cuff tears was investigated in 106 subjects who had never sought for their shoulder complaints, using Constant score, ultrasound and plain x-ray. The prevalence of full-thickness cuff tears was 30% (21% of all shoulders). The Constant score was lower in subjects with full-thickness tears. Partial-thickness tears and acromioclavicular joint osteoarthritis had no impact on shoulder complaints or Constant score. The subacromial index was lower for shoulders with full-thickness tears. Forty-eight patients with median age 56 years underwent subacromial decompression with or without acromioclavicular joint resection, investigated with MRI pre- and 3 months postoperatively. The Constant score and subjective shoulder value were measured preoperatively and at 3 and 6 months after surgery and even 2 years for subjective shoulder value. Two raters investigated the MRI. The results showed poor inter-rater reliability for MRI. However, both Constant score and subjective shoulder value improved over time. MRI is not a reliable method to study the capsular reaction after subacromial decompression due to high subjectivity of the radiologists.

Access technologies often deal with the classification of several physiological and biomechanical signals. In most previous studies involving access technologies, a single classifier has been trained. Despite reported success of these single classifiers, classification accuracies are often below clinically viable levels. One approach to improve upon the performance of these classifiers is to utilize the state of- the-art multiple classifier systems (MCS). Because MCS invoke more than one classifier, more information can be exploited from the signals, potentially leading to higher classification performance than that achievable with single classifiers. Moreover, by decreasing the feature space dimensionality of each classifier, the speed of the system can be increased. MCSs may combine classifiers on three levels: abstract, rank, or measurement level. Among them, abstract-level MCSs have been the most widely applied in the literature given the flexibility of the abstract level output, i.e., class labels may be derived from any type of classifier and outputs from multiple classifiers, each designed within a different context, can be easily combined. In this thesis, we develop two new abstract-level MCSs based on "reputation" values of individual classifiers: the static reputation-based algorithm (SRB) and the dynamic reputation-based algorithm (DRB). In SRB, each individual classifier is applied to a “validation set”, which is disjoint from training and test sets, to estimate its reputation value. Then, each individual classifier is assigned a weight proportional to its reputation value. Finally, the total decision of the classification system is computed using Bayes rule. We have applied this method to the problem of dysphagia detection in adults with neurogenic swallowing difficulties. The aim was to discriminate between safe and unsafe swallows. The weighted classification accuracy exceeded 85% and, because of its high sensitivity, the SRB approach was deemed suitable for screening purposes. In the next step of this dissertation, I analyzed the SRB algorithm mathematically and examined its asymptotic behavior. Specifically, I contrasted the SRB performance against that of majority voting, the benchmark abstract-level MCS, in the presence of different types of noise. In the second phase of this thesis, I exploited the idea of the Dirichlet reputation system to develop a new MCS method, the dynamic reputation-based algorithm, which is suitable for the classification of non-stationary signals. In this method, the reputation of each classifier is updated dynamically whenever a new sample is classified. At any point in time, a classifier’s reputation reflects the classifier’s performance on both the validation and the test sets. Therefore, the effect of random high-performance of weak classifiers is appropriately moderated and likewise, the effect of a poorly performing individual classifier is mitigated as its reputation value, and hence overall influence on the final decision is diminished. We applied DRB to the challenging problem of discerning physiological responses from nonverbal youth with severe disabilities. The promising experimental results encourage further development of reputation-based multi-classifier systems in the domain of access technology research.

Access technologies often deal with the classification of several physiological and biomechanical signals. In most previous studies involving access technologies, a single classifier has been trained. Despite reported success of these single classifiers, classification accuracies are often below clinically viable levels. One approach to improve upon the performance of these classifiers is to utilize the state of- the-art multiple classifier systems (MCS). Because MCS invoke more than one classifier, more information can be exploited from the signals, potentially leading to higher classification performance than that achievable with single classifiers. Moreover, by decreasing the feature space dimensionality of each classifier, the speed of the system can be increased. MCSs may combine classifiers on three levels: abstract, rank, or measurement level. Among them, abstract-level MCSs have been the most widely applied in the literature given the flexibility of the abstract level output, i.e., class labels may be derived from any type of classifier and outputs from multiple classifiers, each designed within a different context, can be easily combined. In this thesis, we develop two new abstract-level MCSs based on "reputation" values of individual classifiers: the static reputation-based algorithm (SRB) and the dynamic reputation-based algorithm (DRB). In SRB, each individual classifier is applied to a “validation set”, which is disjoint from training and test sets, to estimate its reputation value. Then, each individual classifier is assigned a weight proportional to its reputation value. Finally, the total decision of the classification system is computed using Bayes rule. We have applied this method to the problem of dysphagia detection in adults with neurogenic swallowing difficulties. The aim was to discriminate between safe and unsafe swallows. The weighted classification accuracy exceeded 85% and, because of its high sensitivity, the SRB approach was deemed suitable for screening purposes. In the next step of this dissertation, I analyzed the SRB algorithm mathematically and examined its asymptotic behavior. Specifically, I contrasted the SRB performance against that of majority voting, the benchmark abstract-level MCS, in the presence of different types of noise. In the second phase of this thesis, I exploited the idea of the Dirichlet reputation system to develop a new MCS method, the dynamic reputation-based algorithm, which is suitable for the classification of non-stationary signals. In this method, the reputation of each classifier is updated dynamically whenever a new sample is classified. At any point in time, a classifier’s reputation reflects the classifier’s performance on both the validation and the test sets. Therefore, the effect of random high-performance of weak classifiers is appropriately moderated and likewise, the effect of a poorly performing individual classifier is mitigated as its reputation value, and hence overall influence on the final decision is diminished. We applied DRB to the challenging problem of discerning physiological responses from nonverbal youth with severe disabilities. The promising experimental results encourage further development of reputation-based multi-classifier systems in the domain of access technology research.

Optimal control methods are applied to mechanical models in order to predict the control strategies in human arm movements. Optimality criteria are used to determine unique controls for a biomechanical model of the human upper-limb with redundant actuators. The motivation for this thesis is to provide a non-task-specific method of motion prediction as a tool for movement researchers and for controlling human models within virtual prototyping environments. The current strategy is based on determining the muscle activation levels (control signals) necessary to perform a task that optimizes several physical determinants of the model such as muscular and joint stresses, as well as performance timing. Currently, the initial and final location, orientation, and velocity of the hand define the desired task. Several models of the human arm were generated using a graph-theoretical method in order to take advantage of similar system topology through the evolution of arm models. Within this framework, muscles were modelled as non-linear actuator components acting between origin and insertion points on rigid body segments. Activation levels of the muscle actuators are considered the control inputs to the arm model. Optimization of the activation levels is performed via a hybrid genetic algorithm (GA) and a sequential quadratic programming (SQP) technique, which provides a globally optimal solution without sacrificing numerical precision, unlike traditional genetic algorithms. Advantages of the underlying genetic algorithm approach are that it does not require any prior knowledge of what might be a 'good' approximation in order for the method to converge, and it enables several objectives to be included in the evaluation of the fitness function. Results indicate that this approach can predict optimal strategies when compared to benchmark minimum-time maneuvers of a robot manipulator. The formulation and integration of the aforementioned components into a working model and the simulation of reaching and lifting tasks represents the bulk of the thesis. Results are compared to motion data collected in the laboratory from a test subject performing the same tasks. Discrepancies in the results are primarily due to model fidelity. However, more complex models are not evaluated due to the additional computational time required. The theoretical approach provides an excellent foundation, but further work is required to increase the computational efficiency of the numerical implementation before proceeding to more complex models.

Optimal control methods are applied to mechanical models in order to predict the control strategies in human arm movements. Optimality criteria are used to determine unique controls for a biomechanical model of the human upper-limb with redundant actuators. The motivation for this thesis is to provide a non-task-specific method of motion prediction as a tool for movement researchers and for controlling human models within virtual prototyping environments. The current strategy is based on determining the muscle activation levels (control signals) necessary to perform a task that optimizes several physical determinants of the model such as muscular and joint stresses, as well as performance timing. Currently, the initial and final location, orientation, and velocity of the hand define the desired task. Several models of the human arm were generated using a graph-theoretical method in order to take advantage of similar system topology through the evolution of arm models. Within this framework, muscles were modelled as non-linear actuator components acting between origin and insertion points on rigid body segments. Activation levels of the muscle actuators are considered the control inputs to the arm model. Optimization of the activation levels is performed via a hybrid genetic algorithm (GA) and a sequential quadratic programming (SQP) technique, which provides a globally optimal solution without sacrificing numerical precision, unlike traditional genetic algorithms. Advantages of the underlying genetic algorithm approach are that it does not require any prior knowledge of what might be a 'good' approximation in order for the method to converge, and it enables several objectives to be included in the evaluation of the fitness function. Results indicate that this approach can predict optimal strategies when compared to benchmark minimum-time maneuvers of a robot manipulator. The formulation and integration of the aforementioned components into a working model and the simulation of reaching and lifting tasks represents the bulk of the thesis. Results are compared to motion data collected in the laboratory from a test subject performing the same tasks. Discrepancies in the results are primarily due to model fidelity. However, more complex models are not evaluated due to the additional computational time required. The theoretical approach provides an excellent foundation, but further work is required to increase the computational efficiency of the numerical implementation before proceeding to more complex models.

In vivo, biomechanical stress plays an important role in tissue physiology and pathology, affecting cell and tissue behavior. Even though conventional outflow tissues in the eye are constantly exposed to dynamic changes in intraocular pressure (IOP), the effects of such biomechanical stressors on outflow tissue function have not been analyzed. In particular, changes in IOP with each heartbeat have been measured in human eyes approximating 2.7 mmHg/sec. The purpose of this dissertation is to determine the effect(s) of ocular pulse on conventional outflow tissue regulation and the effect that contractility plays in this mechanical stress-mediated response. The central hypothesis directing this research is that cyclic intraocular pulsations (i.e. ocular pulse) play a significant role in conventional outflow facility.In order to address our hypothesis we studied the effect of biomechanical stressors on conventional outflow physiology using three different strategies: (1) by comparing conventional outflow endothelial cells to blood and lymphatic capillary endothelia, we gained a better understanding of the effects of biomechanical stress on conventional outflow tissue physiology, (2) by modifying the anterior segment perfusion model, we were able to measure the effect of ocular pulse on conventional outflow facility, and (3) by exposing trabecular meshwork cell monolayers to cyclic biomechanical pressure oscillations in the presence of compounds known to affect trabecular meshwork contractility, we were able to analyze the effect of rho-kinase-mediated contractility on the ocular pulse-associated response.Perfused human and porcine anterior segments showed a significant ocular pulse-mediated decrease in outflow facility; in addition, perfused trabecular meshwork monolayers showed an increase in intra-chamber pressure when exposed to cyclic pressure oscillations. This effect was blocked by Y27632 inhibition of rho-kinase-mediated contraction.In conclusion, the work shown in this dissertation demonstrates for the first time that trabecular outflow tissues are capable of responding to a physiologically-relevant cyclic biomechanical stress. This response can be observed as an increase in outflow resistance that translates to lower baselines in outflow facility of anterior segments and lower hydraulic conductivity of trabecular meshwork monolayers. In addition, we concluded that the observed ocular pulse-mediated response of trabecular meshwork cells is regulated by rho-kinase-induced contractility.

Background: The incidence of injuries in rugby union has increased on both professional and amateur levels since the introduction of professionalism in 1995. Although rugby union is a body contact sport with an expected high injury rate, limited research has been done regarding the postural and biomechanical characteristics of the players and the effect these variables have on the incidence and nature of rugby union injuries. Large body size is a significant predictor of success in rugby union and the body mass and mesomorphy of players has increased over the last years. It has, however, not been thoroughly investigated whether changes in body composition have any effect on the incidence of rugby union injuries. Intrinsic risk factors that have been identified to contribute to rugby union injuries are Hyper-mobility of joints, lack of dynamic mobility and core stability, previous injuries, aerobic and anaerobic fitness as well as the personalities and characteristics of players which affect their on-field awareness. The findings of studies investigating the relation between player characteristics and rugby union injuries are inconsistent because of the differences in player characteristics under investigation and playing conditions, different research methodologies used as well as differences in the way injury is defined. Therefore, the need exists to determine the differences in the biomechanical, postural and anthropometrical characteristics of injured and uninjured rugby union players by making use of a prospective design and a standardized injury definition. Objectives: The objectives of this study were firstly, to determine the incidence and nature of injuries among U/21 rugby union players at the Rugby Institute (RI) of the North-West University (NWU) (South Africa) and secondly, to determine which of the selected biomechanical, postural and anthropometrical characteristics contributed to musculoskeletal injuries obtained during the first five months of the 2005 season. Method: s A prospective once-off subject availability study was performed that included forty-nine U/21-rugby union players of the RI of the NWU. Biomechanical, postural and anthropometrical assessments were performed on all subjects before the start of the 2005- season. All the injuries sustained during the first five months of the 2005 season were recorded by means of a validated rugby union injury report questionnaire. A stepwise discriminant analysis identified the independent variables that discriminated mostly between the players with and without injuries within the different body regions. Back-classification by means of the "Jack-knife method" determined whether the independent characteristics that were selected to contribute to injuries was valid and the effect size, I ("better than chance"), was then determined, with I > 0.3 accepted as practically significant. Results: A total of 66 injuries with an injury rate of 8.611000 training hours and 61.811000 game hours were reported. Severe injuries accounted for 53% of all injuries to forward players with the ankle being the most injured anatomical region. In the backline severe injuries accounted for 11% with the shoulder being the most injured region. The tackle was the phase of play in which most injuries occurred. The statistical analysis identified uneven hips, pronated feet, tight hamstrings, anatomical leg length differences, gait pronation and a tall stature to be practically significant predictors for lower extremity injuries (I>0.3). No practical significance was obtained for the selected biomechanical, postural and anthropometrical characteristics related to shoulder girdle as well as back or spine injuries. Conclusions: The conclusions that can be drawn from this study are that the injury incidence of rugby union players of the U/21-squad of the RI of the NWU is high in comparison with those of other club level players and that postural and biomechanical imbalances of the lower extremities may increase the risk for injury in this area. / Thesis (M.A. (Human Movement Science))--North-West University, Potchefstroom Campus, 2007.

The primary aim of this study was to evaluate the effectiveness of an injury prevention and training programme for elite cricketers in regard to biomechanical, physical and motor and anthropometric variables over a period of six cricketing off-seasons (1998/1999-2003/2004). A secondary aim was to investigate the injury epidemiology of elite cricket players over a six-season period (1998/1999 – 2003/2004). A total of 93 cricket players, who were part of the North-West professional cricket squad, were evaluated over a six-season period stretching from the 1998/1999 cricket season to 2003/2004 cricket season. The players were all evaluated at the end of the off-season (middle September) of the commencing season and the injury lists were compiled throughout each playing season. This included all players who needed medical attention due to injury sustained while representing the North-West cricket team in a cricket match. An analysis was done of literature sources by making use of electronic media, library search and sports medicine journals. Databases such as Pubmed, EbscoHost (Academic Search Elite), Sciencedirect, Medline, Eric, Health Source - Consumer Edition, Health Source: Nursing/Academic Edition and SPORTDiscus were used. Special consideration was given to cricket injury epidemiology, injury prevention strategies in cricket, biomechanics in cricket and general injury prevention strategies. The recorded data were statistically processed and the practical significances were calculated. Three different protocols were followed to evaluate the effectiveness of the injury prevention and training programme. The recorded data were analysed for the six off-season periods (1998/1999-2003/2004, protocol 1) of the study for the biomechanical, physical and motor and anthropometric evaluations, as well as for the injury epidemiology. The players were then divided into four exposure times (protocol 2) in the study for the biomechanical, physical and motor and anthropometric evaluations. Then the players were divided into two groups (protocol 3), with each group consisting of the same players, and over a three off-season period each evaluated for the biomechanical, physical and motor and anthropometric variables. Lastly, the results for the last three seasons of protocol 1 were compared with the result of the last three seasons of protocol 3 (group 2) for the biomechanical, physical and motor and anthropometric evaluations, as well as for the injury epidemiology. The results for this study indicate that the injury prevention and training programme was successful in improving and maintaining the biomechanical, physical and motor and anthropometric profile of the cricketers over the six off-season periods (1998/1999-2003/2004). Although all injuries could not be prevented, injuries resulting from structural vulnerability did decrease. Injuries resulting from structural vulnerability (mechanism of injury) decreased from the 1998/1999 season (67,67% of the total injuries suffered during the 1998/1999 season) to the 2003/2004 season (10% of the total injuries suffered during the 2003/2004 season), indicating that the training and prevention programme played a role in the prevention of these injuries. Injury incidence per 10 000 hours of play was 5,82 injuries for the six-season period (1998/1999- 2003/2004). The injury prevention and training programme used in this study can be utilised to improve the biomechanical, physical and motor and anthropometric profile of cricketers. The biomechanical, physical and motor and anthropometric evaluations can also be used as injury prevention strategies by identifying possible injury risk factors as a result of poor biomechanical, physical and motor and anthropometric profiles. / Thesis (Ph.D. (Education))--North-West University, Potchefstroom Campus, 2005.

Heart failure is an important medical disease and impacts millions of people throughout the world. In order to treat this problem, biomaterial injectable treatment injected into the myocardium of the failing LV are currently being developed. Through this treatment, the biomaterial material injections can reduce wall stresses during the cardiac remodeling process. By using computational techniques to analyze the effects of a treatment involving the injection of biomaterial material into the LV after MI, the material parameters of the hydrogel injections can be optimized. The results shows that the hydrogel injections could reduce the global average fiber stress and the transmural average stress seen from optimization. These results indicated that the hydrogel injections could influence the stiffness in passive LV tissue, but there is still need for more research on the active part of ventricular contraction. Conclusion: hydrogel injection is a viable way to alter ventricular mechanical properties.