Construction and industrial workers are at high risk for work-related musculoskeletal disorders, often caused by repetitive tasks and lifting heavy loads. To reduce these work-related musculoskeletal disorders, guidelines on human strength capabilities should be followed to help mitigate injuries by reducing muscle overloading. Current solutions focus on rehabilitation and are often focused on the shoulder, elbow, and fingers, leaving the wrist vulnerable. In work-related injuries, the wrist is one of the most commonly injured body parts and is associated with high cost; both medical costs and cost due to productivity, as the median absence of work is 13 days. Injuries can be the result of bone impact forces, but more commonly muscle tissue and central nervous system damage resulting from repetitive tasks. Research shows that injuries are most common at workstations with frequent wrist deviation. Therefore, the goal of this paper is to design an orthosis to support employees in construction or industry work when working with a drill.

For the orthosis to be accepted by the users it has to be easy to use and should not limit freedom of movement. A force analysis of the wrist when holding the drill, and when using the drill against a vertical wall indicates that both the ulnar deviation and the radial deviation must be supported. To clarify which requirements are a basic necessity for the orthosis to be functional and which can be scored on functionality, they are divided into product requirements and user requirements, respectively.

Five concepts are presented to help support both the ulnar deviation and the radial deviation. Three of them are passive solutions, the other two are active. A prototype of all concepts is made and they are scored following the User Requirements utilizing a Harris Profile. During testing it is clear that the ulnar deviation support has little to no impact on the experienced muscle force. Therefore, this requirement is ignored and the orthosis ar scored with the other requirements. Both the concept using Bowden cables and the Support Arm scored well. Since the Support Arm is less complex and functional for the purpose of this research, the Support Arm is further developed.

A force analysis confirmed that the Support Arm can assist in lifting the drill by generating a configurable support force, adjustable via the spring constant or position of the attachment point. Testing the orthosis indicated that the forearm is not in line with the drill, as was expected, reducing the force on the drill. To resolve this, the attachment points of the spring and beam are angled 20 degrees to counteract the angle of the forearm compared to the drill.

The calculation in this paper are simplified, further analysis is needed to determine the effects excluded in this paper. The prototype of the orthosis should also be tested using EMG and a musculoskeletal model. This can give an indication on the effect of the orthosis on muscle activation an muscle force. More improvements of the orthosis are needed to improve user comfort and increase the force transfer. The Support Arm functions only to help lift an object. For more general wrist support and with further research, the Bowden Cable concept is promising. While more complex, the concept can help with dynamic forces to assist to the wrist movements.

In conclusion, the Support Arm orthosis effectively reduces the experienced muscle load during radial deviation when a drill is being lifted. The supporting force of the orthosis can be easily modified depending on the task. For the goal of this research, to support employees in construction and industry work when working with a drill, the Support Arm is a functional solution that can decrease the necessary muscle force and, in doing so, also decrease the bone contact forces in the wrist.

This research focuses on the design and evaluation of a fully passive variable damping transfemoral prosthesis, aiming to provide a low-cost alternative to existing microprocessor-controlled prosthetic knees (MPKs). Current MPKs, such as the Otto Bock C-Leg 4 and Össur Rheo Knee XC, offer advanced functionality by adjusting knee damping based on sensory input. However, their high cost make them inaccessible to many individuals, particularly in low-income regions. This study addresses this issue by developing a fully passive low-cost transfemoral prothesis with variable knee damping in the swing phase.

The design process involved defining functional requirements, identifying key subfunctions, and generating three concept designs.

The final design provides stability in the stance phase and controlled motion during the swing phase. The main innovation of this design is a centrifugal force-based damping mechanism. The foot’s centrifugal acceleration generates a force that is transmitted through a cable system to a friction brake in the knee joint, effectuating velocity-dependent damping. Additionally, knee stability in the stance phase is ensured by a spring latch lock mechanism, which engages at the end of the swing phase and disengages at the end of the stance phase through ankle dorsiflexion. An ankle spring mechanism provides ankle stability in the stance phase, and it provides energy for push-off. The final design is produced using laser-cut metal, 3D-printed components, and off-the-shelf parts to keep production costs low.

The evaluation phase included two key tests:

\textit{Swing phase test} – Assessed the velocity-dependent damping mechanism by suspending the prosthesis and measuring knee moment at various angular velocities. The results showed some velocity-dependent damping, but inconsistencies due to hysteresis were observed.

\textit{Ankle stiffness test} – Evaluated the rotational stiffness of the ankle joint using force and displacement measurements. The results showed slightly lower than expected ankle stiffness.

While the prototype shows the feasibility of a fully passive variable damping knee, several limitations were identified. The main limitation was that significant hysteresis was present the damping mechanism, leading to inconsistent results. Furthermore, the swing phase was performed only at walking speeds lower than occur at natural gait, so no conclusion can be drawn on its effectiveness in real world use.

Future research should focus on improving the robustness of the damping mechanism, reducing the hysteresis and conducting full gait cycle tests on human subjects. Additionally, implementing a delay between force sensing and damping activation could enhance the resemblance to natural gait.

In conclusion, this study demonstrates that a low-cost, fully passive variable damping prosthetic knee is possible, demonstrating a promising initial step towards the development of low-cost \textit{K3} prostheses. However, further development and testing is required before the design can be classified as a functional \textit{K3} prosthesis.

Despite the recognized impact of sex on biomechanics, research remains biased toward male anatomy, raising concerns about the validity of musculoskeletal (MSK) model predictions for females. This study investigated whether sex-specific bone geometry variations predict differences in the proportional volumes of the Gluteus Maximus (GMAX) and Rectus Femoris (RFEM). Using an MRI-based nnU-Net segmentation model trained in this thesis, bone metrics were extracted, and muscle volumes were normalized to derive proportional volumes for 16 young adults (9F/7M). The segmentation model demonstrated high accuracy (DSC: 0.926 for bones, 0.954 for muscles), revealing significant sexual dimorphism in bone geometry. Males exhibited greater femoral offsets and knee widths, while females had larger posterior pelvic widths and depths. %RFEM was significantly higher in males (p = 0.01), but %GMAX showed no sex-related differences. Regression analysis identified femoral offset and femur length as partial predictors of %RFEM (R^2 = 0.478), with pelvis-femur length weakly predicting %GMAX (R^2 = 0.151). However, the low predictive power suggests limitations in using bone metrics to estimate muscle volume proportions. These findings indicate that femoral dimorphism may partially explain sex-related %RFEM differences, but its role in %GMAX remains unclear. Future research integrating additional biomechanical factors could enhance sex-specific MSK modeling accuracy.

The Shoulder Elbow Perturbator (SEP) is a robotic diagnostic device developed to assess multiple forms of motor impairment common in stroke patients. As an active medical device, the SEP would be bound to strict regulations if brought to market. By replacing its motor with a passive power source, this regulatory burden can be minimized, with the added advantage of greatly minimizing its cost. As a first step in developing this passive SEP, a prototype capable of reproducing one of the SEP’s basic tests was conceptualized. After evaluating multiple options for the passive energy source and associated components, a cost-effective design was developed using a spring, a variable radius winding drum to convert the spring’s force output to a constant torque, and a bicycle disc brake. A simulation of this design was then modeled and run through a variety of scenarios as a theoretical validation of the concept. The results of this process are promising, though testing with a physical prototype is needed for further validation.

Age-related decline in physical and neural capacity can make the sit-to-stand (STS) motion increasingly difficult for older adults, significantly impacting their quality of life. Despite these declines, humans adopt compensatory movement strategies to mitigate the effects of reduced capacity, maintaining functional mobility. Predictive simulations offer a tool for studying the relationship between capacity decline and compensation strategies. However, previous predictive studies have omitted the modeling and control of arm movements, thus neglecting key arm compensation strategies relevant to the STS motion. Therefore, this study aimed to develop a neuromuscular controller for a three-dimensional musculoskeletal model that includes the arms, enabling the simulation of STS arm compensation strategies. STS arm strategies were successfully simulated and displayed comparable joint kinematics with experimental data. However, the simulations revealed elevated leg muscle activations and an overestimated vertical ground reaction force. Additional simulations with changed conditions demonstrated the effective use of the armrest and thigh push-off strategies to adapt to lower seat heights and reduce peak knee joint load. Overall, the neuromuscular controller in this study provides a new basis for future STS research into uncovering the link between capacity decline and compensation strategies, potentially leading to improved methods for assessing and addressing age-related declines in crucial movements.

Work-related musculoskeletal disorders (WRMSDs) are prevalent among sonographers, particularly affecting the shoulder region due to repetitive and static movements. This study introduced an ergonomic posture and a mobile arm support (MAS) to reduce the load of muscles contributing to the stabilization of the shoulder. The experimental setup replicated a conventional cardiac ultrasound examination, using a phantom model and simulations to mimic cardiac ultrasound procedures. Professional cardiac sonographers were instructed to acquire three cardiac views (parasternal long-axis view (PLAX), apical four-chamber view (A4C), and subcostal window(SCW)) while surface EMG and joint angles of the shoulder, elbow, and back were measured. Additionally, subjects were tasked with completing a questionnaire to gather subjective outcomes of usability and satisfaction with the support and ergonomic posture. Muscular activity of the middle deltoid muscular activity (PLAX; F(3,12)10.15,p=.001,η2 p=.717, A4C; F(3,12)=5.75,p=.011,η2 p=.590) and superior trapezius (PLAX; F(3,12)=7.05,p=.005,η2 p=.638) decreased significantly during examinations with postural changes but increased significantly while only support was provided. The support was considered slightly useful (SUS=65.0±6.9, α=.585), but the ergonomic change was considered poor (SUS=43.0.0±14.4, α=.813). The increase in muscular activity was likely caused by incorrect placement of the MAS on the upper extremity and incorrect levels of support. Besides, sonographers reported a MAS would be useful when there is an additional functionality that applies contact force through the MAS. The addition of support to postural changes did not significantly reduce muscular load compared to examinations with only postural changes. Therefore, ergonomic postural change is a sufficient solution for mitigating WRMSDs development due to the only significant decrease in muscular activity.

Introduction: A prosthesis can be used to regain function after an amputation of the lower limbs. Conventionally, the prosthesis is connected to the stump using a tight fitting socket. The socket often leads to sweating, skin problems or discomfort while sitting. A new way of prosthetic attachment is by osseointegration. During osseointegration surgery a titanium implant is fixed to the remainder of the femur. The prosthesis can be attached to the extra- corporeal part of the implant called the abutment. In this way, socket related problems can be avoided. Qualitative analyses have reported improved walking ability, prosthetic use and a higher prosthesis related quality of life in patients using an osseointegrated prosthesis, but not much is known yet on quantitative improvements in gait measured in a clinical setting. Therefore this study mainly aims to compose and execute a measurement protocol for clin- ical quantitative gait analysis of unilateral transfemoral amputees using an osseointegrated prostheses. Furthermore, a biomechanical model will be created using OpenSim and will be validated using the data recorded using the clinical measurements.
Method: A measurement protocol for quantative gait analysis in a clinical setting was cre- ated and carried out by measuring one participant using an osseointegrated prosthesis. The participant walked at self selected walking speed across a runway with force plates built in and walked on the floor next to the runway with equal conditions around. The protocol also included measurements for stability and direction of attention during gait trials. A biome- chanical model of a unilateral transfemoral amputee with an osseointegrated prosthesis was developed using OpenSim. Bones and muscles of one leg were replaced by prosthetic ge- ometry and settings were altered. The model was used to analyse kinematics and kinetics. Results: Spatiotemporal differences were found between the floor and runway condition. Kinematic comparison showed significantly different knee flexion for the intact leg for a small phase in the gait cycle. Despite the spatiotemporal differences were significant, these were mostly small. Together with the lack of kinematic differences, the difference between the two was not considered clinically relevant and only the runway condition was included in the results section. Kinematic and kinetic results were plotted against control values mea- sured with healthy controls. Compared to these controls the prosthetic side showed a larger hip extension peak, no ankle plantairflexion peak, a larger hip flexion moment, absence of a characteristic knee flexion moment and a lower ankle plantairflexion moment. For the intact side the most noticeable differences were a knee flexion and ankle plantairflexion peak later in the gait cycle, lower hip extension moment and a higher knee flexion moment. Further- more, prosthetic side Margin of Stability was higher, around 60% of the bodyweight was carried by the intact leg during standing up from and sitting down on a chair and the direc- tion of attention was more focused downwards during the floor condition measurement. Conclusion: The aim of that the development of a measurement protocol including a biome- chanical model to measure and analyse the gait of a transfemoral amputee using an os- seointegrated prosthesis is achieved. The results from several analyses were compareable to results found in literature, which served as a validation for the model developed in this study.

Wheelchair basketball has become increasingly popular, leading to a rise in professionalism. While performance measures exist, they lack objective metrics directly related to an athlete’s individual load that can be measured during games. An objective measure related to the athlete’s load can provide information about fatigue and the total load of training or matches. A recent study presented a theoretical framework for calculating power during games. This study aims to examine the utilization of power metrics derived from Inertial Measurement Units (IMUs) in wheelchair basketball using the theoretical framework, focusing on power produced during straight-line sprinting in matches. This will be done by answering the main question of this paper: How can
individualized power metrics for performance monitoring be derived during wheelchair basketball match play using IMUs? Eight female participants from the Dutch national wheelchair basketball team were assessed in twelve international practice games using
IMUs on their wheelchairs. Power profiles were created based on sprint power, offering insight into sprint powers and their distribution. Work done, determined from power output and push duration, provided insights into athlete fatigue during games.
Power profiles can be used to monitor long-term performance, either between games or between seasons. Regression analysis showed a significant positive effect of classification scores on single push power output, with an R-squared value of 0.75. This study
proposes areas for future research, including integrating trunk motion analysis and exploring the effects of different player positions on power profiles. By enhancing the understanding of player performance, these findings contribute to the professionalization of wheelchair basketball, aiming to optimize performance and reduce injury risks.

The late stage of Parkinson’s disease (PD) is accompanied by unpredictable motor fluctuations which cannot be treated sufficiently with a medication schedule with fixed time intervals. At this point, feedback-based medication timing based on the medication state would satisfy the needs of persons with PD. Wearable sensors offer the ability to objectively and continuously monitor PD-related features in an unsupervised way during daily life. Sensor fusion of a shank-worn accelerometer (Cue2walk wearable device) and a heart rate sensor enables comprehensive state monitoring through the integration of physical and physiological parameters. This study aimed to identify features, retrieved from the Cue2walk wearable device and/or a heart rate sensor, correlated with the medication state in PD, in an unsupervised way during daily life. Triaxial accelerometer and heart rate data were collected from nine persons with PD for seven days. Features in the time and frequency domain were extracted and a value was assigned to each stride. The frequency features were calculated by including walking bouts of at least 10 s. The feature values were averaged over seven block sizes. The medication state was modelled by assuming a sinusoidal form and was based on the medication intake schedule. For each averaging block size, the correlation between the features and the medication state was calculated. Due to a hardware problem, only data from one participant could be included. Stride time variability and displacement, velocity, acceleration, and covariance features resulted in the largest significant correlation with the medication state in this participant. The reliability of the correlations was limited by the short walking bout duration in the calculation of the frequency features and by the simplified model of the medication state. Therefore, future research should collect data on a longer term and include walking bouts of 25 s in the calculation of the frequency features. Moreover, medication intake should be logged by the participants. Consequently, personalised digital biomarkers for medication state monitoring can be developed in an unsupervised way, by taking into account multicollinearity.

Abstract— Objective: The objective of this exploratory study is to investigate how AI speech and text technologies, specifically Whisper and ChatGPT-4, can help reduce the administrative burden in occupational health consultations, with a focus on accuracy, efficiency, and user satisfaction.
Methods: A quantitative research approach was employed, utilizing a controlled trial design. Fourteen occupational health doctors participated in simulations using Whisper for transcription and customized ChatGPT-4 modules for generating medical summaries (Medical Summarizer), letters (Letter Generator), and documents (Document Generator), and providing medical protocol-based replies on participants’ questions (Medical Protocol Assistant). The accuracy, efficiency, and user satisfaction of these technologies were compared against traditional administrative methods, with descriptive statistics and paired samples t-tests conducted to assess performance differences.
Findings: The study revealed that Whisper transcriptions had a word error rate (WER) of 13.1%, with an average transcription time of 18.4 minutes, which was 6.6 minutes faster
than human transcription. ChatGPT-4's Medical Summarizer generated summaries 29 times faster than human participants, with an average generation time of 0.5 minutes but had a 38.6%
error rate in element generation. The Letter Generator and Document Generator exhibited error rates of 90.4% and 17.5%, respectively, although both were significantly more efficient
than manual processes, with average generation times of 0.4 and 3.9 minutes, respectively. The Medical Protocol Assistant provided protocol-based replies with an 86.7% accuracy, achieving the highest user satisfaction score (4.4 out of 5) among all modules.
Conclusion: AI speech and text technologies show potential in reducing administrative tasks in occupational health settings, particularly in terms of efficiency. However, the moderate accuracy and varying satisfaction rates indicate that further refinement is necessary to enhance their applicability in clinical practice. Future research should focus on improving accuracy, evaluation of the technologies in actual patient-physician consultations and developing robust privacy safeguards.

Anterior cruciate ligament tears are a common injury, with over two million people affected annually. Typically, magnetic resonance imaging is used to diagnose the injury, but this technique is less sensitive in evaluating incomplete or concomitant injuries. Four-dimensional computed tomography is a relatively new technique that can become commonly available in the clinical setting. It allows for dynamic imaging, which may be suited for evaluating a change in knee kinematics after ACL in movements like flexion/extension. This may be used to gain insight into the function of the anterior cruciate ligament or surrounding ligaments which informs surgical decision-making and might prevent or alter intended surgeries.
This thesis aims to answer the following research question; How can four-dimensional computed tomography scans of the tibiofemoral joint made during unloaded flexion/extension movements be meaningfully visualized and can it be used to detect kinematic differences between a knee with a complete anterior cruciate ligament tear and an uninjured one? To do so, both knees of eight patients with a unilateral complete anterior cruciate ligament tear were scanned during a simultaneous flexion/ex- tension movement in the four-dimensional computed tomography scanner. A workflow was created that consists of four steps; the segmentation, the registration, the definition of anatomical coordinate systems, and the visualization of the kinematic measures in three different ways. Almost all steps of this workflow were automated and open-source programs were used where possible throughout the workflow to facilitate easy usage. However, some manual steps are still required. The kinematic measures were expressed in three different ways. First, the rotations between the anatomical coordinate systems of the femur and tibia were calculated using Euler decomposition alongside the translations. In addition, a plot of the intercondylar axes was made, which shows the movement of the mediolateral axis of the femur relative to the tibia during flexion/extension. Finally, to obtain the kinematics at the articulation surface, an OpenSim Joint and Articular Mechanics simulation was set up to simulate the movement using the patient-specific information obtained from the four-dimensional computed tomography scans. Based on this simulation, the centres of proximity were plotted for both the tibia and the femur. The distances between the subsequent centres of proximity were then evaluated for a set of flexion angles to gain insight into the type of movement occurring (e.g., roll or slip).
Minor differences for the mean translations and rotations were seen between the anterior cruciate ligament deficient and the uninjured knees. Only in the anterior-posterior translation a statistically significant (p=0.023) increase could be seen at extension and the lower flexion angles (±-5∘ to ±15∘) for the anterior cruciate ligament deficient knees. No noteworthy differences were present for all other degrees of freedom. Differences were more apparent in the plots of the intercondylar axes. Here, the increased anterior-posterior translation was more prominent for anterior cruciate ligament deficient knees than for uninjured ones. Lastly, the centres of proximity showed substantial differences among patients, obscuring the determination of a pattern to distinguish between anterior cruciate ligament deficient and uninjured knees. However, these plots did show a substantial difference compared to the plots of the intercondylar axes. This may be due to slip occurring at the articulation surface and would mean that plotting the intercondylar axes does not adequately represent the kinematics of the articular surface throughout the whole range of motion of the knee.
Overall, some minor kinematic differences during flexion/extension can be seen in the graphs of the translations and rotations and the plots of the intercondylar axes. The plots of the intercondylar axes showed the most apparent differences, but they may not represent the situation at the articulation surface. Therefore the centres of proximity are better suited to gain information about the articulation surface. Still, due to the differences among patients, a pattern to distinguish between anterior cruciate ligament deficient and uninjured knees could not be determined. Altogether, this technique may not be suited as a tool to evaluate knee injuries in all patients, but only in patients that are expected to cope very well with the injury or where a concomitant injury is expected. However, future research should still evaluate the performance of the workflow for these situations.

As the indoor cycling trainer industry keeps innovating, a cycling trainer that has a similar longitudinal motion to outdoor cycling does not yet exist. Therefore, this thesis aimed to design a simulator controller that can actively simulate longitudinal cycling motion and assess its performance in translating outdoor longitudinal cycling dynamics to the indoor cycling trainer setup. Since the thesis concerned an indoor cycling setup the amount of allowed longitudinal motion was ± 20 cm.
We performed a literature review and motion study on the topic of longitudinal bicycling dynamics, whereafter equations of motion of outdoor cycling were defined to address the difference between inand outdoor cycling. The gathered knowledge was then used to design a simulator controller for an indoor cycling setup that is actuated in the longitudinal direction through a linear actuator. To evaluate the performance of the simulator controller torque data of 4 different test subjects was collected and used as the input signal for the controller to theoretically assess its simulation performance.
The simulator controller simulations, of 7 different slope angles for both seated and standing cycling, resulted in minimal longitudinal motion of the simulated trainer setup during low-resistance cycling situations and maximal motion during high-resistance cycling situations. During the simulations, the simulated cycling trainer setup stayed well within the maximal allowable ± 20 cm from its initial position. The intra-pedal stroke range of motion of the simulations was similar to the intra-pedal stroke range of motion measured on a cycling treadmill through a motion capture study.
This thesis concludes that it is possible to translate outdoor longitudinal cycling dynamics to an indoor cycling simulator with torque as the only input. The theoretical assessment of the simulator controller shows that the metrics meet the requirements and are similar to real-world cycling.

Introduction: During the sit-to-stand (STS) motion, thigh push-of (TP) is frequently used, yet the biomechanical advantage for the upper extremity, is relatively unknown. In this thesis, the STS motion is analyzed for three different techniques; TP, armrest push-off (AP), and no arm aid (NA). The aim of this study is to determine the biomechanical advantage of the TP strategy through examining the joint moments (JM), and muscle forces (MF). Furthermore, the study aims to find whether age or gender affects the JM and MF generated in the TP, AP, and NA strategies. Method: Time to stand (TTS), JM and MF exerted on the upper extremity were examined for TP, AP and NA strategies for 34 participants across 3 groups: EM, elderly female (EF), and young males (YM). The metrics were obtained through inverse kinematic (IK), inverse dynamic (ID), and static optimization (SO) simulations in a 3D musculoskeletal model. Results: The time-to-stand (TTS) in elderly participants is significantly longer in the TP strategy than in the AP and NA strategies. For elderly people, the TP strategy results in upper extremity JM lower than during AP and equal as in NA. Similarly, the TP strategy results in significantly lower MF than the AP strategy, and equal MF as in the NA strategy. Conclusion: The TP strategy takes longer than AP and reduces the JM and MF for elderly participants. Moreover, the TP strategy does not yield higher JM and MF than the NA strategy for any participant group. Thus, the biomechanical advantage of the TP strategy for elderly people, are lowered JM and MF in the upper extremity

The first aim of this master thesis is to explore whether the normal force on the castor wheels can be estimated from IMU data using a machine learning approach. The second aim is to evaluate whether incorporating the changing load distribution due to trunk movement could improve the friction power estimation compared with neglecting changes in load distribution. Twenty-five subjects performed forward handrim wheelchair propulsions with no trunk, moderate and fast trunk movement on a treadmill in a wheelchair with six conditions regarding wheelchair mass and tire pressure. Two IMUs were placed on the trunk and wheelchair and two load pins in each castor wheel measured the normal force. After feature, model and hyperparameter selection, a model was trained to estimate the normal force on the castor wheels in percentage of the total weight from the IMU data. Accordingly, the predicted instantaneous normal force is used to calculate the friction power including changing mass distribution. When using the linear velocity and acceleration of the wheelchair and the, linear acceleration of forward movement of the trunk, adequate estimations (MAE of 3.69% total weight) of the normal force from an LSTM model can be obtained for unseen subjects. This model is robust for wheelchair settings regarding wheelchair mass and tire pressure and for propulsions with no, moderate and fast trunk movement. The instantaneous friction power prediction incorporating the changing load distribution is proven to more accurate during propulsions with moderate and especially fast trunk movement. Coaches, sport scientists, and athletes may find this model useful for analysing the effect of different propulsion techniques or wheelchair conditions on the friction power. As part of a larger context, this research will contribute to the process of filling the technological gap of in-field monitoring mechanical power. Future research must validate the robustness of the model during game situations

BACKGROUND: Rising UCL injury rates at both amateur and professional levels have been linked to fatigue in baseball pitchers. Repeated pitching has been associated with changes to kinematics, kinetics, and perceived fatigue, but no statistical model exists which incorporates all the most common aspects of fatigue into one framework. Confirmatory factor analysis (CFA) can be used to investigate possible fatigue frameworks and their plausibility in explaining the multivariate nature of observed changes occurring with repeated pitching. AIM: To investigate how multiple fatigue manifestations could be associated with a shared factor in baseball pitching. METHOD: Two CFA models were proposed; one a priori model based solely on previous findings and literature linking commonly found variables which change with repeated pitching, and one a posteriori model with added correlation factors between maximum external shoulder rotation (MER) with perceived fatigue and MER with triceps EMG activity. RESULTS: Model fitness test performed on the first a priori model proved plausible, with it passing some of the tests but failing others. The a posteriori model showed to be an excellent model for explaining the covariance of the data, passing all model fitness tests. CONCLUSIONS: Confirmatory factor analysis can serve to provide a plausible framework for explaining the covariance measured in kinematic, kinetic, and other fatigue related changes to baseball pitching data. Both models would suggest that the shared latent variable represents an underlying aspect of physiological fatigue. Changes to MER were determined to not be directly caused by fatigue. A proper understanding of different fatigue manifestations can potentially reduce the amount of fatigue related UCL injuries plaguing baseball pitchers by providing a more accurate proxy for measuring physiological fatigue.

The ability of musculoskeletal models to acquire metrics and simulate human motion enables researchers to perform biomechanical analysis of daily activities. The improved analysis of human motion could for instance help recognize physical decline early. The sit-to-stand movement, which is performed 60 times daily on average, is one greatly affected by physical decline. Predictive simulation could enhance comprehension of the influence of physical decline, but most musculoskeletal models are not suitable for predictive simulation as they lack computational speed. In this project, a simplified musculoskeletal model called the H1126 with 11 joints and 26 muscular actuators suitable for sit-to-walk simulations is developed. Muscle moment arms at vertebral levels T12 through S1 are based on literature and optimized in OpenSimCreator using via points. Muscle-tendon minus tendon slack length, normalized fiber length, and maximum joint moments of the H1126 are compared to three state-of-the-art OpenSim models containing torso musculature. Results show that the H1126 performs well in terms of muscle geometry and force output. The H1126 muscle moment arms are within a 2 SD margin compared to the literature. The H1126 muscle-tendon length minus tendon slack length and normalized fiber length are within a 10\% margin compared to the state-of-the-art comparison models. Maximum joint moments of the H1126 are also within a 2 SD margin compared to the state-of-the-art torso models and literature. The H1126 is more suitable for predictive simulation than the comparison models as it is computationally faster due to the minimized number of muscle fascicles and the use of purely via points while performing similarly in terms of force output.

The study of human motion consists of the analysis of kinematics, dealing with joint angles, velocities and accelerations, and kinetics, which deals with joint torques and interaction forces. Traditionally, kinematics and kinetics are estimated from optical marker data and sometimes measured interaction forces. Inertial measurement units (IMUs) were introduced as a low cost alternative that makes measurements outside the laboratory possible. Measurements are often used in a loosely coupled combination of marker-based inverse kinematics (IK) or orientation-based inverse kinematics (OBIK) and inverse dynamics (ID). The orientations for OBIK are first estimated from IMU data. Recently, tightly coupled estimation methods based on nonlinear state space models have been introduced for both sensor modalities to improve accuracy. Sensor fusion of marker and IMU data is a relatively unexplored area of research. Markers provide a measurement on the position level whereas IMUs measure on the velocity and acceleration levels. Fusing the two sensor modalities is hypothesized to result in the most accurate estimation of kinematics and kinetics. The objective of this thesis is to investigate the effects of the sensor modality and the estimation method on the accuracy of estimated kinematics and kinetics. An iterated extended Kalman filter (IEKF) was developed which estimates joint angles, velocities and torques using any combination of marker data, IMU data and measured interaction forces. To validate the system with respect to ground truth, two experiments (fast motion and interaction force) were carried out on a robot equipped with all three sensor types. For comparison, IK, OBIK and a marker/IMU-based kinematic extended Kalman filter (EKF) were used together with ID to estimate kinematics and kinetics as well. The IEKFs estimated joint angles with a root mean square error (RMSE) between 0.33◦ (markers and interaction forces only) and 1.58◦ (IMUs only, fast motion). The marker-based IEKF and the IMU-based IEKF outperformed IK and OBIK respectively in both experiments. The IMU-based IEKF improved joint velocity RMSE from 4.13 deg/s to 1.10 deg/s in the fast motion experiment. Sharp peaks in the joint torque signal were only estimated accurately using IMU data directly. The marker/IMU IEKF was the only method that estimated joint angles, velocities and torques with RMSEs below 1◦ , 1.5 deg/s and 1.5 Nm respectively in both experiments. It is concluded that using IMU data in a tightly coupled system improves joint velocity and torque estimation. Assuming accurate sensor registration and no soft tissue artifacts, a tightly coupled IMU-only method can be sufficiently accurate in practice.

Introduction Fractures of the diaphysis of the radius and/or ulna are most common in children from 5 to14 years old and take up to 40% of all pediatric fractures. Patients with a diaphyseal fracture of the forearm can develop a malunion: healing of the bones in non-anatomical position. This can lead to pain, cosmetic differences and a limitation of pronation and/or supination. A malunion with an angulation of at least 15degrees leads to a limitation in rotation of the forearm in 60% of the cases. However, it is not known how amalunion leads to a rotational limitation and why certain patients have a predominant supination limitation and some have a predominant pronation limitation. It is hypothesized that the distance between the bonescan explain the limitation: a too small distance leads to bone impingement and blocking the rotation, a toolarge distance leads to contracture of the central band, a ligament between the radius and ulna.AimThe aim of this research is to explain the loss of rotational function in malunited forearms by using akinematic model in which bone impingement and contracture of the central band can be recognized.MethodFifteen (n=15) patients were included who developed a malunion after a one-sided, both-bonediaphyseal fracture of the forearm during childhood (age < 18) which led to a range of pronation and/orsupination lower than 50 degrees. Their range of motion was measured and CT-scans were made of bothforearms, from which three-dimensional bone surface models were retrieved. A kinematic model for prona-tion and supination of the forearm was developed in which the patient specific anatomy was used to detectbone impingement, measure central band length (CBL) and measure minimal interosseous distance (MID)between the radius and ulna. Bone impingement and CBL were used for prediction of the range of motion ofthe malunited forearms, MID was used to compare the distance between the bones at maximum supinationand pronation between the affected and unaffected forearms of the patients. Central band length relative tothe neutral position was calculated in unaffected forearms to define a threshold for contracture. Bone im-pingement was defined as overlapping of the bone surface models. The root mean squared error (RMSE)between in vivo measured range of pronation, supination and full range and the predicted values is calcu-lated.ResultsAll fifteen patients showed bone impingement as reason for limiting pronation, fourteen patientsshowed contracture of the central band as reason for limiting supination. By setting the threshold at 103%of the relative central band length, the pronation, supination and full range of thirteen patients could bepredicted with a RMSE between 15.5 and 17.9 degrees. Bone distance was significantly lower in malunited forearms than in unaffected forearms in maximum pronation. In supination this effect was much less clear.The kinematic model showed an error less than one millimeter and one degree for translation and rotation compared to cadaveric scans in different pronation and supination positions.Conclusion The kinematic model showed that bone impingement and central band contracture are the best explanations for limiting pronation and supination of malunited forearms. Prediction is difficult because the kinematic model uses the neutral position as starting point, which is not always clear because the kinematics of forearm rotation still has some unknowns and the central band origin and insertion is now located based on a cadaveric study

Atherosclerosis is a cardiovascular disease in the arteries and a primary cause of death in the industrialized world. Most deaths due to atherosclerosis occur when the fibrous cap covering the necrotic core ruptures, leading to a blood clot. To determine whether an atherosclerotic plaque will rupture requires the development of accurate computational models. One of the key aspects for these models is the material model, in which collagen fibres play a major role. This study aims to contribute to the making of a numerical model which accurately represents atherosclerotic plaque by comparing the elastic and rupture behaviour of engineered collagenous micro tissues and their respective finite element models in ABAQUS. The Holzapfel-Gasser-Ogden material model of these computational models is based on a combination of global material parameters and local material parameters based on the local fibre organisation. A framework developed to measure the local fibre organisation using provided imagery of a nuclear stained tissue engineered sample shows the collagen fibres align along the loading direction and the edges of the geometry. The fibers are less dispersed along the edges of the geometry and on the left and right of a formed soft inclusion. A uniaxial tensile test was performed on four tissue engineered samples. The elastic and rupture behaviour of the samples during the uniaxial tensile tests is replicated in ABAQUS using both isotropic and homogeneous material parameters, and anisotropic heterogenous material parameters. The stresses measured in the simulations are highly dependent on both the material parameters and the geometry of the model. The strains are mostly dependent on the geometry, but are affected by the material model. Due to the higher stiffness at the edges of the geometry of the anisotropic samples, the stresses increased greatly, and the strains decreased slightly. The rupture behaviour of the cultured samples is replicated in the FEM simulations using extended finite element method (XFEM). The damage in the samples with isotropic material parameters initiates both from the soft inclusion as the left and right edges of the geometry. The damage in the samples with anisotropic material parameters initiates, similarly to the cultured samples, only from the sides of the soft inclusion. The damage in both the cultured and simulated samples propagate mostly horizontal and from the soft inclusion outward. In three out of four isotropic samples however, damage propagates to varying degrees from the edge of the geometry inward. Based on these findings it is concluded that implementing the local fibre organisation in the material model can improve the accuracy of finite element simulations of collagenous soft tissues, which includes atherosclerotic plaque, as the rupture behaviour of the simulations with anisotropic material parameters more accurately represents the rupture behaviour of the engineered fibrous tissues in comparison with simulations with isotropic material parameters.

Background:
Many professional violin players develop pain complaints in neck and shoulder regions as a result of prolonged practices containing highly repetitive motions and awkward postures. These complaints are often diagnosed as overuse syndrome, where physical changes are not apparent and of which the etiology is not yet understood. Mechanical overload might be part of the equation. Only limited research has been done to evaluate whether the biomechanics of violin playing differ between violinists with and without overuse syndrome. Muscle activity has been reported to differ between violinists with and without pain, but findings were often inconsistent. This study aims to evaluate the biomechanics of the musculoskeletal system in the neck and left shoulder region in violin players with and without pain complaints while playing different musical excerpts.

Method:
Twenty violinists, 10 with and 10 without pain complaints, were playing three musical pieces containing different wrist and bow motions. These were measured using motion capture and chin-violin force measurements. An upper body model was created by combining a neck model with a shoulder model in OpenSim, which was then used to calculate joint angles and moments of the neck and left shoulder. Differences in the kinematics and kinetics of violin playing were assessed by investigating mean values as well as the variability around these average values. The mean values of the joint angles and joint moments were compared over time during selections of bowing cycles and cycles of wrist movement. The kinematic variability was assessed with the standard deviations of the mean in each playing condition.

Findings:
Kinematic and kinetic differences were found between symptomatic and pain-free violinists during fast bowing motions. The axial rotation of the glenohumeral joint was significantly more external in violinists with overuse syndrome compared to controls. Additionally, joint moments in several degrees of freedom of the scapulothoracic and glenohumeral joints were larger in the symptomatic group compared to the asymptomatic group. Lastly, the kinematic variability of symptomatic violinists was lower than that of asymptomatic violinists.

Conclusion
These found kinematic and kinetic differences could mean that violinists with overuse syndrome play the violin with less optimal motor control, resulting in larger loads on the joints and surrounding tissues. The lower variability of kinematics in violinists with pain may indicate an increase in stiffness. Overall, these findings suggest that biomechanical differences exist between violinists with and without overuse syndrome.