The New Arm Coordination Trainer in 3D (NACT-3D) is a mechatronic device developed to investigate upper limb movement and quantify human proprioceptive reflexes through haptic interaction. This thesis evaluates whether the NACT-3D meets the technical requirements necessary to perturb the human arm at frequencies suitable for system identification, while simultaneously generating realistic 3D haptic environments. The NACT-3D integrates admittance and impedance control with multimodal sensing, offering capabilities beyond existing robotic platforms. Experimental testing was conducted using perturbation signals and optical tracking to assess the device's bandwidth, while SPACAR simulations were used to model theoretical performance under various conditions. Results show that the NACT-3D’s actuation system has sufficient force output and bandwidth; however, the current manipulator's high inertia and mechanical play significantly limit performance. Without the manipulator, the system achieves bandwidths above 40 Hz, but with the manipulator attached, performance drops below 6 Hz. Simulation results indicate that a redesigned manipulator can restore performance, enabling the system to meet its operational target. These findings demonstrate that although the current configuration is inadequate for high-speed perturbations, targeted improvements to the manipulator can enable the NACT-3D to become a robust tool for studying neuromechanical control and reflex modulation. ... Read more

Background: Anterior cruciate ligament (ACL) injuries commonly reduce knee stability and increase joint loading, often leading to compensatory gait alterations that may increase injury risk. Functional electrical stimulation (FES) of the biceps femoris long head (BFLH) during the gait stance may improve knee stability by reducing harmful joint loading, but the effects on voluntary muscle control remain unclear.

Research question: This study examined whether FES of the BFLH during the stance phase of the gait reduces ACL-relevant knee joint loading in healthy adults and whether it alters voluntary muscle control. Additionally, the use of gluteus maximus (GLMAX) sEMG as a proxy for BFLH activation was assessed.

Method: Nine healthy participants walked on a treadmill under control and FES-assisted conditions. Kinematic, kinetic, and sEMG data were analyzed using statistical parametric mapping and linear mixed-effects models.

Results: FES of the BFLH significantly reduced internal knee rotation moment (KRM) with 9.37% during 42–48% of the gait cycle (p = 0.0002; d = 0.42). Knee adduction moment (KAM) showed non-significant reductions in both legs (non-stimulated: p = 0.0317, d = 0.18; stimulated: p = 0.0492, d = 0.37). Knee abduction angle (KAA) and knee rotation angle (KRA) showed no significant changes (p > 0.05). In sEMG analysis, inconsistent timing between GLMAX and BFLH activation indicated GLMAX is not a reliable surrogate for estimating BFLH activity. Regarding voluntary control, only peak KAM increased slightly over strides during FES-assisted walking (p = 0.006), possibly due to muscle fatigue. No significant retention or after-effects were observed.

Conclusion: Targeted FES of the BFLH can reduce ACL-relevant knee loading without impairing voluntary motor control. sEMG results highlight the need for direct BFLH monitoring, as GLMAX is an unreliable proxy. These findings support further exploration of FES strategies for ACL injury prevention and rehabilitation.
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The goal of this dissertation was to develop an approach to safely and proactively evaluate cyclist fall prevention interventions, addressing a significant gap in cycling safety research. While bicycle dynamics and cyclist control models present a promising solution, they have yet to be applied in the context of cycling safety.... ... Read more

This paper investigates the effect of intrinsic muscle stiffness on neural control parameters in biological musculoskeletal control of stabilisation or reaching tasks. Current model implementations of intrinsic muscle properties are highly simplified, limiting their accuracy in replicating experimental short-range stiffness (SRS) behaviour, which appears to be important for stabilisation tasks. The Hill model, often used in musculoskeletal simulations, cannot account for SRS, while the Huxley model, which can account for non-linear muscle phenomena such as SRS , has a higher computational burden. The study compares a simplified Huxley-type model to two Hill-type models and determines the effect of intrinsic SRS on the control parameters of stabilizing 1- and 2-Degree of Freedom musculoskeletal models over various positive and negative stiffness positions in the force-length curve. Furthermore, the effect of the intrinsic muscle stiffness on the robustness of the feedback parameters of simple individual muscle feedback systems is determined in reaching experiments similar to classic experiments.

The study finds that the Huxley model shows positive SRS in the negative flank of the force-length curve, achieves stabilisation through only co-contraction using a lower level of required muscle excitation than both Hill-type models and stabilises both musculoskeletal systems at a larger muscle range than the Hill-type models, including in the negative stiffness flank. The feedback parameters dominantly responsible for muscle activation patterns are also more robust to change in the Huxley model. These findings suggest that intrinsic muscle stiffness impacts neural control parameters in stabilisation and reaching tasks, and further musculoskeletal modelling should consider using more complex muscle stiffness calculations for improved accuracy. ... Read more

Various source localization algorithms exist to perform localization with High Density (HD)-ElectroEncephaloGraphy (EEG). However, validation of these EEG source localization algorithms is lacking. The current gold standard for source localization in the brain is functional Magnetic Resonance Imaging (fMRI) by calculating the difference in hemodynamic response to different stimuli. This study aims to validate HD-EEG source localization with fMRI using an MR compatible haptic robot. Participants performed several tasks with the robot to activate cortex patches and allow localization of source activity under various circumstances. These hypothesized patches are the somatosensory, motor and visual cortex. No comparison is made with fMRI due to time constraints. As no comparison could be made, we aim to validate the experimental methodology.
Activation of the somatosensory cortex is clearly visible. The visual cortex is often localized, but lacks power in some settings. Activity during the torque task can be localized, but not conclusively to the motor cortex. In all, the experiment was a success, as it was able to induce verifiable different brain states. Hypothesized task contrasts contained different activity distributions. Improvements can be made by generating a more detailed leadfield and by applying a linear manipulator ... Read more

Muscle fatigue's indirect link to higher athletic injury risks is a key focus of this study. It highlights how fatigue-induced shifts in muscle resource allocation and movement patterns can lead to biomechanical imbalances, subsequently heightening injury susceptibility. Addressing high injury rates in athletics, this study was conducted in two pivotal phases: the development of a wearable, textile-integrated surface electromyography (sEMG) garment, and the identification of the most effective real-time fatigue metric for true wireless detection for dynamic exercise. While traditional sEMG methods provide valuable insights in laboratory settings, they fall short in dynamically and individually monitoring muscle fatigue in real-world scenarios.

The initial phase focused on creating a smart garment with integrated textile-based electrodes named the RunWave. The second phase concentrated on analyzing muscle fatigue during dynamic running activities, employing an incremental treadmill exercise test. Fatigue was assessed using cardiorespiratory metrics and Borg's Rate of Perceived Exertion (RPE), alongside the evaluation of six fatigue metrics: Average Rectified Value (ARV), approximate and sample entropy, instantaneous mean and median frequencies, and Dimitrov's Spectral Fatigue Index. Significant differences between fatigued and non-fatigued states were observed, especially noted in shifts in entropy, mean and median frequencies, and most prominently in ARV. These findings underscored the necessity for personalized fatigue monitoring strategies, given the variation in fatigue onset and subjective exhaustion experiences among individuals.

The RunWave, with its focus on the ARV metric, emerged as particularly promising for fatigue detection. ARV's computational simplicity and interpretability make it ideal for real-world applications. Despite initial challenges such as fitment issues, electronic limitations, and garment robustness, the RunWave garment was positively received for its comfort and practicality. With targeted improvements, the RunWave garment, leveraging ARV, shows great potential for effectively monitoring muscle fatigue in runners, suggesting a substantial step forward in reducing injury risks in athletic contexts. ... Read more

Background: Amyotrophic lateral sclerosis (ALS) is a motor neuron disease that is characterized by the degeneration of upper and lower motor neuron (UMN, LMN). A defining feature of ALS is its heterogeneous presentation, with varying sites of disease onset and progression rate. Diagnosing ALS requires the observation of both UMN and LMN degeneration in multiple regions of the body. Signs of UMN degeneration are difficult to observe in ALS. The goal of this study was to determine if reflexive parameters were related to UMN dysfunction in ALS patients.

Methods: A robot applied continuous torque perturbations to the right wrist of the subjects. Subject were asked to perform 4 different tasks, each provoking different control strategies. Closed-loop system identification was used to estimate the joint dynamics. A neuromuscular model was then fitted to the estimated joint dynamics to express the contribution of intrinsic and reflexive pathways in physiologically relevant parameters.

Results: We show that patients are able to alter their joint dynamics in order to comply with the tasks. During the relax task patients had visibly higher admittance than controls, in the active tasks the patients were able to lower their admittance similar as controls. Patients with pathologically increased reflexes had significantly increased reflexive feedback during the force tasks compared to controls.

Conclusion: In this study we have demonstrated the ability of neuromechanical parameters to detect hyperreflexia in patients diagnosed in ALS. Therefore the proposed method of closed-loop system identification and parameters estimation could be used to monitor the progression of ALS.
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Injury to the Ulnar Collateral Ligament (UCL) is common among baseball pitchers, due to high external valgus torques applied around the elbow during pitching. Literature shows that elbow muscles and the osseous articulation can lower the load imposed to the UCL by countering the external valgus moment. As the contribution of the individual elbow muscles and the osseous articulation to the UCL load during pitching remains unclear, this study aims to identify the muscles capable of (un)loading the UCL during baseball pitching. Muscle-driven simulations for ten baseball pitches were generated using a musculoskeletal (MSK) model of the upper extremity. The simulations were run twice: ones without any constrictions to the model and ones with the wrist motion locked. The flexor digitorum superficialis (FDS) was identified as biggest contributors to the internal muscle moment during the wrist-included simulations. The external valgus torque was 10% countered by the elbow muscles, 59% by the osseous articulation and 31% by the UCL. The UCL had to resist a moment of 25.6 Nm. During the wrist-excluded simulations, the flexor carpi radialis (FCR) and was identified as biggest contributors to the internal muscle moment. The external valgus torque was 10% countered by the elbow muscles, 42% by the osseous articulation and 48% by the UCL, resulting in a UCL moment of 39.4 Nm. Further research should focus on the influence of wrist and finger motion on UCL load and concentrate more on the osseous articulation as main elbow stabilizer during pitching. ... Read more

The combination of the high number and the consequences of falls in older adults led to the development of fall risk assessments; non-sensor-based and sensor-based. Multiple studies used ML for older adults' fall risk prediction using raw IMU data. This study's objective was to develop a DL algorithm that predicts the fall risk of people living in a geriatric rehabilitation department using raw data collected from IMUs positioned at the ankles during the 10-m walk test.
Raw IMU data of 97 participants were used. The participants were classified as low, increased or high fall risk based on the Performance Oriented Mobility Assessment (POMA). Accelerometer and gyroscope's resultant time-series sequences (n=1037) were used as input for the Convolutional Neural Network (CNN) that was optimised and trained with 80% and tested with 20% of the participants. The results were compared with the performance of an existing portable sensor-based fall risk assessment called the Smart Floor (SF). The macro F1 of the unweighted (40%) and weighted (41%) multiclass classification CNNs was lower than the macro F1 of the SF (49%). The binary classification CNN's macro F1 (56%) was slightly lower than the SF's performance. All CNNs were better at predicting high-risk sequences. All models had poor performance when all three POMA fall risk categories should have been predicted. Adjustments to the data collection and CNN optimisation methods should be performed to study the possibility of predicting fall risk using raw IMU data in geriatric rehabilitation centres.
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Hamstring injuries in field hockey are very common. Accurate estimates of muscle tendon unit lengths (MTU) and elongation velocities could give insight into the risk of injury during field hockey specific movements. For accurate measurements the hockey field would be best suited. Inertial measurement technology allows for such measurements; however, a method of applying this technology to hockey must first be developed and applied to athletes. The goal of this study is to develop this method and indicate what field hockey-related activities might be accompanied with a higher risk for hamstring injuries. Three elite female field hockey athletes participated in this study, performing ten field hockey-specific exercises. The results obtained with inertial measurement technology were compared to the results obtained with the commonly used optoelectric motion capture system. This method showed very good (0.850 - 0.950) to excellent (0.960 - 1.000) coefficients of multiple correlation values. Furthermore, absolute peak values for MTU lengths and elongation velocities were obtained. The results showed that the MTU length and elongation velocity were higher during running while dragging the ball on the hockey stick than during running without ball. The MTU length was also higher during various types of hits than during running. Additionally, the MTU length and elongation velocity were higher on the left leg compared to the right leg. Excessive stretch and high elongation velocities could indicate a greater chance of muscle injuries. This study shows that MTU lengths and elongation velocities can be obtained with inertial measurements and could in part, explain the relatively high hamstring injury rate among female field hockey athletes. ... Read more

Inertial measurement units (IMUs) offer the possibility to capture the lower body kinematics of players of outdoor team sports. However, various sources of error are present when using IMUs: the definition of the body frames, the soft tissue artefact (STA) and the orientation filter. Methods to minimize these errors are currently being used without knowing their exact influence on the various sources of errors. The goal of this study was to quantify each of the sources of error of an IMU. An optoelectronic system was used as a golden standard. Rigid marker clusters (RMCs) were designed to construct a rigid connection between the IMU and four markers. This allowed for the separate quantification of each of the sources of error. Ten subjects performed nine different trials, varying both in type of movement and in movement intensity. The error of the definition of the body frames (11.3-18.7 deg RMSD), the STA (3.8-9.1 deg RMSD) and the error of the orientation filter (3.0-12.7 deg RMSD) were all quantified separately. Furthermore, the type of movement, movement intensity and body segment were found to have a significant influence on the errors. This study is the first study to quantify each of these sources separately and allows future studies to quantify and optimize error reduction techniques. ... Read more

Existing wind load simulators such as wind tunnels and fans have multiple disadvantages, especially when used in a scaled-down environment. This paper proposes to simulate wind loads by using an admittance-controlled industrial robot arm rigidly attached to a research object. Admittance control should make it possible to simulate wind loads and a specific amount of inertia that is higher than the inertia of the original research object. The goal is to verify whether an admittance-controlled industrial robot arm is suitable for wind load and inertia simulations and what the limitations of this simulation method are. The scope of this research is limited to three Degrees of Freedom. First, the admittance controller is tested on a computer simulation model before execution on a Hardware-in-the-loop setup. It is found that an admittance-controlled robot arm is well capable of simulating both wind loads and a specific amount of inertia. However, there are some limitations. The motion controller of the industrial robot should be able to change the end-effector position within a frequency of 50 Hz. Frequencies above 333 Hz result in the most accurate simulations. The upper range of inertia that can be simulated is restricted by the maximum joint torques the robot can apply. The lower range is restricted by the inertia of the real object, the applied wind loads, and the sampling frequency of the admittance control loop. ... Read more

Problem: A biomarker that accurately predicts recovery of ischemic stroke for patients with poor baseline Fugl-Meyer Assessment of the Upper Extremity (FMA-UE) is lacking. Biomarkers that predict recovery while providing functional insight into the underlying neural process are highly desired for optimal clinical care. Objectives: This explorative study aims to determine potential biomarkers from Somatosensory Evoked Potentials (SEP) using ElectroEncephaloGraphy (EEG). Brain asymmetry metrics are derived from high-density EEG recordings of five longitudinal stroke patients during the first six months of stroke recovery. In addition, EEG sources and their interactions, constrained by anatomical information from (d)MRI, are explored for a potential biomarker. Results: Subjects with low baseline FMA-UE show a trend of increased recovery as the Laterality Index (LI) of the infarcted hemisphere increases, although it is not significant within this small group. The LI of the non-infarcted hemisphere shows a significant trend of high LI values at baseline that decrease to lower values during recovery. This effect was tested on a different dataset of 17 longitudinal stroke patients (without dMRI data). The results in this second group showed strong variability between subjects and measurements. The non-infarcted hemisphere is able to significantly predict the FMA-UE for both datasets. On the other hand, estimated effects for the LI of the infarcted hemisphere did not show significant values. Biomarkers were not derived from EEG sources and their interactions. Conclusion: In this study, we have demonstrated the potential of the LI as a biomarker for stroke recovery. Small sample size and absence of controls make hard clinical conclusions impossible. However, our findings show that the LI might predict recovery of the FMA-UE, even at low baseline FMA-UE. The LI of the non-infarcted hemisphere is able to significantly predict the FMA-UE of the affected hand, a surprising discovery that might be attributed to background cortical activity or ipsilateral SEP components. Derivations from EEG sources and their interactions might lead to more sensitive metrics and novel insights into stroke rehabilitation. Significance: If the discovered trends apply to a larger sample size, asymmetry metrics from SEP’s have prognostic value in stroke recovery. ... Read more

Running Specific Prosthesis (RSP) allow amputee sprinters to compare to the best able-bodied sprinters in the world. In RSP research, the current state of the art mainly focusses on highly detailed analysis of discrete moments in the sprint, but more data of the entire sprint process in terms of RSP characteristics and sprinting technique are needed for further development of RSP-design and sprinting technique. In recent research Petrone et al. [4] and Galvão et al. [2] developed instrumented RSPs for collection of Ground Reaction Force (GRF)s suring sprinting, however both methods have disadvantages for implementation of instrumented RSPs in amputee sprinting training purposes. A different instrumented RSP approach was taken in this research by measuring surface strain in Fiber Bragg Grating (FBG) sensors attached to two RSPs; one Ottobock 1E90 and one Gyromotics ArcX Sport. From the collected data the internal moments and axial forces could be approximated, from which the GRF magnitude, direction and point of application were determined. The sensor system was calibrated in a 1-DOF load-cell compression bench and was conducted to a field test in which a participant performed load shifting, walking and running trails on the instrumented Gyromotics RSP. The compression tests showed that the measurement system complied to design requirements and that it was possible to estimate the point of application of the GRF. The field test indicated that loads applied in different directions than applied in the compression bench could lead to measurement errors. Additional calibration, predominantly in the x-direction, is therefore needed. ... Read more

Background Upper limb prostheses help people with an upper limb deficiency in performing activities of daily living. They can be divided into two categories; body-powered and externally powered prostheses. The advantage of body-powered prostheses is that they provide feedback to the user. The advantage of externally powered prostheses is the low operating force required to control the prosthesis. To reduce rejection rates of upper limb prostheses control, cosmetics and comfort should be improved. To improve control, a design was proposed integrating proprioceptive force feedback into an externally powered upper limb prosthesis with a haptic interface placed on the scapula. However, the cosmetics and comfort are to be improved. The goal of this study is to design a haptic force feedback system that meets the demands regarding comfort and cosmetics. Method Design requirements and mechanical requirements are set. A conceptual design was made using SolidWorks and a prototype was built. The proposed prototype was tested on a test bench to evaluate the overall system. It was analyzed whether the design met the pre-set requirements and the results were compared to other devices. Results The designed haptic device is made out of an anchoring system, pneumatic artificial muscle (PAM), and a distance sensor. The total weight of the system is 41푔 for the anchoring system and PAM, and 29푔 for the distance sensor. The dimensions are 50푥25푥120푚푚. The maximum pressure for the actuator is 3푏푎푟. The output forces reached are 87.41푁, 79.04푁, 100.00푁, 85.38푁, and 104.8푁 for actuators with an initial length of 80푚푚, 90푚푚, 100푚푚, 110푚푚, and 120푚푚 respectively. The designed distance sensor measures a distance up to 58푚푚, with an accuracy of ±1푚푚. Compared to other devices the developed overall system is lighter in weight and smaller in size. Furthermore, it is made out of flexible materials, allowing the device to bend along the curve of the shoulder. Conclusion This study presents a new design for a haptic interface to provide proprioceptive force feedback for an upper limb prosthesis. It is an improvement in cosmetics and comfort, while still meeting the mechanical requirements. Future research should be done with users of an upper limb prosthesis to evaluate the applicability. ... Read more

Introduction: A thigh push-off is often used as a compensation strategy for standing up by elderly people. However, the biomechanics of this movement are not known. In this thesis the standing-up movement with the use of the thigh push-off strategy (TP), the armrest push-off strategy (AR) and the no arm aid strategy (NA) was analysed. The aim was to find out why TP for standing up is being used as a compensation strategy by elderly people. Method: We examined upper and lower limb joint moments and lower limb muscle forces in three different sit-to-stand strategies in nine healthy elderly men. Inverse dynamics and static optimisation were done in OpenSim using a 3D musculoskeletal model. Results: The lumbar extension moment in TP was significantly lower compared to NA (p=0.04). Rectus femoris force is lower in phase 2 in TP compared to AR. AR upper limb joint moments were significantly larger in dominant and non-dominant shoulder external rotation (p=0.02, p<0.01), elbow extension (p<0.001, p<0.001), and wrist flexion (p=0.04, p=0.02) compared to TP. Also, dominant shoulder abduction (p=0.04) moment was higher in AR compared to TP. Conclusion: Elderly people probably use a thigh push-off to unload the lower back, but this could also be accomplished with AR. However, AR upper limb loading is higher com- pared to TP. TP is used to unload the lower back and upper limb joints. ... Read more

The design of current skating suits is based on the assumption that the flow across the skater body parts is highly similar to cylinder flow. The latter features drag crisis behaviour, resulting in significant drag reduction at the critical Reynolds number. However, whether the aforementioned assumption is valid and whether a drag crisis along the different body parts occurs, so far remains unknown.

The goal of this study is to investigate Reynolds number effects along the leg of a skater mannequin. To do so, potential drag crisis behaviour is studied via robotic Particle Image Velocimetry and Infrared Thermography for speeds ranging between 5 m/s and 25 m/s. The boundary layer state and the critical velocity distribution along the leg, based on the wake width variation, are evaluated for the bare mannequin and the mannequin wearing a skating suit optimized for ∼ 15 m/s.

Results reveal drag crisis behaviour along the knee, lower and upper leg. Furthermore, the flow topology is not only governed by the leg geometry, but also by streamwise vortices. These streamwise vortices cause an increase of the wake width below the calf and a reduced velocity deficit behind the upper leg. Most significant differences in wake width between the bare and the dressed leg are observed at 17.5 m/s. The latter observation is also supported by the Infrared Thermography results.

It can be concluded that the flow across the leg partly differs from cylinder flow, mainly because of streamwise vortices that locally affect the drag crisis behaviour.
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Muscle-driven simulations performed with a musculoskeletal model of the human upper-extremity need to include closed-loop kinematics to capture the limb's full mobility and model the actions of thoracoscapular muscles. On the OpenSim platform, a single upper-extremity model with closed-loop kinematics is available: the thoracoscapular shoulder model (TSM), which only includes muscle-elements crossing the shoulder-girdle, omitting upper-extremity musculature partially. OpenSim's native algorithms for subject-specific scaling of geometric- and muscle-length parameters function insufficiently for upper-extremity models, whilst inertial- and muscle-strength parameters are rarely scaled. Subject-specific models are impossible to validate in vivo, whilst indirect validation methods are limited. The goal of this study is to enable future OpenSim users to perform muscle-driven simulations with adequately scaled, subject-specific upper-extremity models. This study develops: (1) A generic model with the closed-loop kinematic structure of the TSM and all upper-extremity musculature; the thoracoscapular Delft shoulder and elbow model (TDSEM). (2) Subject-specific scaling tools for the TSM and TDSEM, performing geometric- and muscle-length parameter scaling based on optimization procedures, and inertial- and muscle-strength scaling based on a total muscle-volume estimation. (3) A method to estimate maximum isometric directional force at an end-effector with subject-specific models to indirectly validate the maximum force-generating capacity of these models. Geometric scaling accuracy is mainly limited by the accuracy of marker-data used. Both the TSM and TDSEM reached the desired RMS marker-error of ≤2cm and an average segmental-length error of ≤5%. Muscle-length parameter optimization fit is comparable to, or better than, studies employing similar algorithms. Scaled muscle-strength-, and inertial parameters are not validated, but the accuracy of the muscle-volume estimates they are derived from was known beforehand. The indirect validation method is not able to make estimations within ±10% of measured maximum forces. The method greatly overestimates measured values, regardless of the subject modelled or model used. Including upper-extremity musculature in the TDSEM results in improved muscle-driven analyses compared to the TSM. This can be improved further by improving the accuracy of muscle-elements attached to the radius, including ligaments in the model, and using a constraint to maintain glenohumeral stability. The presented scaling methods are recommended over OpenSim's native methods when scaling the TSM or TDSEM. The indirect validation method must be improved before it can be used to inform (in)validating conclusions about subject-specific models. For this, the effect of a constrained torso, task-specific practice, and inclusion of trained subjects on measurements must be evaluated and subject pose must be recorded. When combined with the stability constraint, estimation accuracy will likely improve greatly. ... Read more

Short-track speed skates are prepared with rocker to improve cornering behavior. However, rocker also has a negative impact on ice friction. As there is currently no scientific theory for selecting optimal rocker profiles, skaters have to rely on personal experience. There is a lack of experimental data available in literature to validate current hypotheses for ice friction. A setup was designed to measure ice friction of an upright skate with varying rocker profiles and normal loads. The experiment was conducted on the artificial ice rink at Thialf, Heerenveen. A sled fitted with two parallel blades was towed at a constant speed of approximately 1.5 ms-1. A force transducer was used to measure friction forces on the sled. Short-track and long-track blades with representative rocker radii were tested. A strong correlation was found between rocker radius and ice friction. Friction forces were found to be on average greater by a factor of 1.868(±0.050) for blades with rocker radius of 10 m compared to 21 m. The results further show high repeatability between tests. This study demonstrates the impact of rocker on ice friction in speed skating. Further research is needed to establish a valid theory for optimal rocker selection. This test method can be used in the future to include different variables, such as ice temperature, sliding speed or blade inclination angle. The method is not limited to short-track speed skating, but can be applied to other disciplines. ... Read more

Nowadays the design of prosthetic hands is mainly focused on myo-electric control for more functionality. And easy producible 3d printed prosthetics to lower the costs of a custom prosthesis. As a result of this change of focus, the body powered prosthetic hands currently on the market are mainly simple clamping mechanisms with no innovative functions. Looking back into the history of hand prosthetics many body powered prosthetic hands housed a couple of innovative design choices to increase the functionality. Some examples of this are the Pringle-Kirk arm and the Despinasse hand. As a counter reaction to this movement, a new body powered prosthetic hand is designed. The new prosthetic hand will be based on the innovative solutions of the past and will bring back more functionalities to the body powered prosthetics. The new design housed fingers made out of cylindrical springs, in combination with leaf springs. This is all actuated via a dependency mechanism in the hand palm, this combination allows for very flexible fingers that can grab complexly shaped objects and still offer a multi finger grip. The first tests revealed that the leaf springs limited the motion of the fingers and further testing without the leaf springs showed a setup with only cylindrical springs was a better solution. The second test was focused on pinch force, although the maximum acquired pinch force was not high, a sturdy grip should be possible based on literature, this does need further testing to validate. For the continuing of the prototyping testing of the dependency mechanism was done, initial testing at a larger scale showed promising results, little to no loss of force. The conclusion that can be drawn based on these tests is that there are certainly parts of prosthetic hands of the past that are worth taking a closer look at. ... Read more