In Bicycle Motocross (BMX) racing, a fast gate start is crucial for overall race performance (Rylands2014). The goal of this study was to (1) provide a better understanding of how cyclists effectively propel the bicycle during BMX gate start, and (2) identify pedalling variables which are good predictors of a fast start."

On all levels of rowing, a general rule is that you have to row together. Rowing together has no clear-cut definition. However, it is known that each rower has his or her own style, which can be registered in movement patterns and force curves. The big question is how to combine these individual styles such that the crew works together in the best way. The Dutch Rowing Federation showed interest in this topic, wanting to know how to adjust the rigging dimensions of the boat to allow the best racing performance. The goal of this thesis is to provide advice on what features of the rowing stroke should be synchronized and whether and how this could be promoted by individualized rigging. The theoretical foundation for this study was a literature study about the current knowledge on the rowing stroke and differences within and between individuals and crews. Current used measures on performance and synchronization of rowers were described, and finally a proposal was done for which methods to use in the ongoing of the study. Data was obtained from five female athletes of elite level, doing trials in a quadruple sculls of approximately 30 seconds at 30 SPM and 32 SPM in four different combinations. The strokes were identified and analyzed, based on performance and synchronization measures. Performance measured as Average Speed, Work per Stroke, Blade Losses, Velocity Fluctuation Losses and their respective and combined efficiencies. Synchronization measures were defined as Mean Standard Deviation of the Phase, Standard Deviation of the Time to Half Impulse and Standard Deviation of the Time to Half Work. The chosen synchronization measures were not completely independent. Standard deviations of time to half impulse and half work were found to be highly similar (r = 0.970). An opposite effect was found between kinematic synchronization and the other two, Mean Standard deviation of the Phase was not in line with the empirical rule that better synchronization leads to better performance. The kinetic and energetic measures did show this effect: Lower standard deviations of time to half impulse and time to half work meant higher average speed (r = −0.193) and higher Work per Stroke (r = −0.574). The best performing synchronization measure was time to half impulse synchrony. A drawback on this measure was that the sampling period was long, compared to the interpolated time differences. Athletes were found to achieve their half impulse moments in a consistent order. To find out whether it is possible to promote synchronization and thus performance by individualizing rigging, the oar angles at the time to half impulse were analyzed. This new measure correlated moderately (r = 0.624), meaning it quantifies more or less the same effect. The kinetic similarity actually worked better (r = −0.292 with Average Speed and r = −0.748 with Work per Stroke) than the synchronization measure. Similarity of half impulse angles enables the coach to adjust the rigging such that the timing should improve too. However, this should be tested in a follow-up study.

Running-specific prostheses enable amputee athletes to perform at the highest level. However, current prosthesis design still impairs sprinting performance in multiple ways. An example is the constant mechanical stiffness of the prosthetic devices. The dynamic behaviour of the blade is determined by this property, but it is static and cannot change according to the gait phase-specific sprinting dynamics. During acceleration a different stiffness might be required as opposed to steady state running. Therefore, it is hypothesised that amputee athletes can improve their performance with prostheses that have a gait phase-specific stiffness. In order to investigate the effect of stiffness on amputee sprinting performance a novel and unprecedented modelling approached is used. Modelling is economical and straightforward in comparison to other research methods such as laboratory experiments. In this thesis, an extension of the established Spring-Loaded Inverted Pendulum model is proposed that qualitatively describes amputee sprinting motion. The Actuated Spring-Loaded Inverted Pendulum (ASLIP) is capable of predicting stable forwardly integrated sprinting motion with the inclusion of the start and acceleration phase. Optimisation of the model predicts that phase-specific spring stiffness leads to a significant time reduction on the 100m sprint for given physiological parameters. In general it can be said that a stiffer spring results in better performance. More specifically, the model benefits from a stiff spring during acceleration and a more compliant one in steady state. Although it has its limitations, the ASLIP model additionally provides a valuable insight into the mechanics of amputee sprinting. For example, it seems that optimal phase-specific stiffness is strongly dependent on biomechanical parameters such as touchdown angle, force angle and CoM velocity. Future work in this direction can provide a better understanding of the underlying mechanisms that determine amputee sprinting performance. The outcomes of this study suggest that amputee sprinters might be able to achieve a reduction in finishing time with prosthetic devices that have a phase-specific stiffness. The modelling approach used in this thesis is promising and lends itself well to investigate this opportunity in more detail.

During team time trials in road cycling changing schemes are used to spread the workload over the cyclists in the team. Models that provide predictions of race performance already exist for individual time trials. It is proposed that with a performance model for team time trials, the performance of different strategies can be compared and optimised. In literature combinations of mechanical resistance models and physiological models are used to determine the performance of individual time trials. The aerodynamic interaction between cyclists is very important to the effectiveness of a strategy. Coefficients of drag reduction between cyclists in a team time trial are presented in several studies, however most studies use groups of only four cyclists, which is not useful for a team time trial with eight cyclists. Only two studies report data for groups up to eight cyclists. These two models show different behaviour and are both used to asses the performance of strategies. Also two physiological models were used. In the model provided in this study the resistances are calculated from the kinematics resulting from the evaluated strategy. The mechanical resistance model, including the aerodynamic interaction model calculates the power required to perform the strategy. The physiological model calculates the physiology during the race, which determines if the cyclists are able to sustain the prescribed strategy. Genetic algorithm optimisation is used to optimise the strategy parameters, such as initial position and times spend in first position. The velocity is optimised for each evaluated strategy configuration. A convergence test was performed to determine the parameters for the genetic algorithm, which are used in the optimisation of strategy. Using the standard strategy, where cyclists only change from first to last position, different orders are compared. From this study it was determined that the mean velocity over a 30 km team time trial could be raised by a maximum of 0.228 m/s by improving the order, depending on the model configuration. It was found that the best performing orders were those where the mean performance difference of following cyclists was lowest. Two different strategies have been assessed where cyclists still always change from first, but not necessarily last position have been assessed on their performance. With those more complex strategies the mean velocity could be increased with 0.358 m/s over a 30 km team time trial. The model still lacks validity, but gives a relevant insight in the performance of different team time trial strategies. The validity can either improved by using track test to validate the drag reduction coefficients or by using power data from a team time trial to show that the model predicts realistic physiology. Of those two methods the last is preferred.

In football, a lot of hip and thigh muscle injuries occur as a result of high muscular loads due to accelerative leg movements. To prevent muscle damage and optimise performance, it is essential to continuously identify when and how frequent local hip and thigh muscular loads develop in the explosive and dynamic football environment. The currently used method is an acceleration index based on two-dimensional position data of the whole global body measured by the Local Positioning Measurement system. The problem is that this system does not correspond with the experienced load of players because leg movements are excluded. Therefore, this study introduces a new local concept of gathering local three-dimensional leg acceleration data by inertial measurement units. This pilot study aims to use a big data analysis approach to translate leg acceleration data into a measure to indicate local muscle load and compare this new local and the current global method to the players’ experienced load. Five participants performed specific football drills with an intensity increase from jogging to sprinting and by adding a pass and shot. Measures are developed, based on the pelvis, upper leg, and lower leg accelerations, by a peak and cumulative data analysis approach. By evaluating trend percentages of the intensity increase, it is obtained that a local acceleration measure is comparable to the players’ experienced load if it considers the sum of normal or peak data points weighted per zone and per travelled distance. Furthermore, a similar result is obtained when only the upper leg or lower leg accelerations are considered. It can be concluded that local three-dimensional acceleration of the lower extremities, processed with a big data analysis approach, represent the football players’ experienced muscular load more accurate than the current global method. Further research, including a higher number of participants, should prove the significance.

Performance in wheelchair court sports is to a large extent determined by the wheelchair mobility performance, the performance measure for the wheelchair-athlete combination. So far, wheelchair mobility performance is mostly utilized as concept, rather than a well quantified measure. However, in order to gain insight in the interaction between athlete, wheelchair and sport, it should be an objective and well quantified outcome that is easily measured. An inertial sensor-based “Wheelchair Mobility Performance Monitor” (WMPM) was developed that met the demands of objective quantification of mobility performance in an easy to use manner. This WMPM is believed to be a valuable tool for wheelchair court sports practice and research. All research done with the WMPM showcases its opportunities and commenced the unravelling of the complex interactions between athlete, wheelchair and sport. It will be a matter of time before the use of the WMPM will be common practice in wheelchair sports and sports research.@en

Technology is being used more and more to aid elite athletes in improving their performance. Recently there have been promising developments in the research using IMUs regarding wheelchair rugby and basketball. Applying this same measurement setup to wheelchair tennis could give better insight in the wheelchair mobility of wheelchair tennis athletes. This knowledge could aid the athletes in causing less sport related injuries, altering the focus of their training or even training entirely new aspects of the sport. This is why this research will be answering the research question: “What is/are the most influential factor(s) regarding the mobility of wheelchair tennis athletes to discriminate between the winning and losing player?”. We define the wheelchair mobility performance as all the measurable parameters related to the movements of the athlete. These mainly consist of the velocities and accelerations reached by the athletes. The measurements resulted in three different ways to output variables. Match statistics, these include information about the distance travelled, turns made and points played during the match. This was chosen to give general insight into the match. The wheelchair mobility performance (WMP), shows information about the velocities and accelerations during the match. This was chosen to compare the velocities and accelerations of athletes, they are plotted against the average value of the entire database of all measurements, this will be a standardized baseline to compare the results to. Lastly the speed zone plots, the plots give an indication of how long the athlete has been driving within a certain velocity range. To give better insight in the dynamic of the match all outputs also includes the constraints of winning/losing and serving/receiving. It is therefore possible to compare the differences between won and lost points and served and received points. There was also experimented with the possibility of making a plot that shows the location of the athlete on the field as a heatmap. However, because the IMUs only record accelerations the cumulative error to distance had to be manually adjusted for, therefore this was only done for one match as a pilot case. The match statistics, WMP plots and speed zone plots showed no significant differences between winning and losing points. Therefore, this study found that the mobility performance has no deciding effect on the outcome of a tennis match. The technique used to hit the ball and place it on the right spot in the field will probably be the determining factor here. This said, the mobility does however have to be above a certain threshold for the player to compete at a certain level of play, so neglecting it completely is not recommended, however the focus should be on the technique that involves hitting the ball. The heatmap case shows that the winning player plays more aggressive, but whether he is playing aggressive because he is winning or winning because he is playing aggressive cannot be concluded by this research.

Multiple studies indicated that the degree of muscle strain is the most relevant parameter in understanding the injury mechanism behind a hamstring strain injury. To monitor this parameter a new system is developed; the Smart Sensor Shorts. The system contains five Inertial Measurement Units (IMUs) integrated in a sports tights. The purpose of this study was to develop a methodology to estimate the muscle strain and muscle elongation velocity of the biceps femoris (BF), semimembranosus (SM) and the semitendinosus (ST) muscle in professional and recreational football athletes with the use of IMUs during different football specific movements and during different intensities. When comparing different movements and intensities, the greatest peak muscle strain was found in the BF and the lowest peak muscle strain was found in the SM during the majority of the movements. The biomechanical load was different for each hamstring muscle and was different for the running based movements and other football specific movements. The BF experienced the greatest peak muscle strain (12.12 ± 0.88%) during a maximal intensity kick in the supporting leg, while the greatest peak muscle elongation velocity was observed in the ST (3.97 ± 0.47 s-1) in the kicking leg during the maximal intensity kick. The greatest biomechanical loading was during a maximal intensity kick. Finally, it was observed that the moment of peak muscle strain was different from the time period of peak muscle elongation velocity for running based movements. It is concluded that IMUs together with the developed methodology could be used in the assessment of hamstring strain injuries in professional and recreational football by analyzing and monitoring muscle strain and muscle elongation velocity.

This exploration study focuses on the braking behaviour of World Tour cyclists during a descent. For this study, 8 riders descended over 6 trials using a ‘sensor bike’. As part of this particular study, a novel brake sensor is developed and validated in practice. The sensor package can be transferred between bicycles, allowing each rider to use his own bicycle. Results of the exploration study indicate that for the chosen descent, braking and cornering skills are not decisive for overall time over the descent. However, significant time differences are found for the corner which is analysed. Time difference reported over this corner are approximately one second. With a shortest cornering time of 10.14 seconds this is a significant difference. The brake behaviour of theWorld Tour cyclists could be split into two distinct braking strategies: • ’stop brake late’ ( where braking is stopped late and well into the turn). • ’stop brake early’ (where braking is stopped before or early in the turn). It was found in this study that the best brake strategy is ’stop brake late’. The peak brake forces measured during the descent are much lower than the maximum brake forces reported in literature. This implies, that performance can still be improved by increasing brake forces at the first part of the braking action, so the braking can start later. The results found in this study can contribute to optimise braking and cornering skills of riders by explaining and showing where improvements can be found. An additional result is that the brake sensor revealed unexpected brake rub at certain parts of the descent, especially when riders are accelerating. Eliminating this brake rub, can improve rider performance. The riders also shows clear signs of learning behaviour as can be observed in the obtained data. For future research it is recommended to add a speed sensor to the sensor package. Recommended small improvements for the brake sensor are identified. Using this improved sensor package, trials could be rehearsed on a steeper descent, such that pedalling actions have less influence, exploring braking and cornering strategies further.

The purpose of this thesis project is to design a new concept of sprinting prosthesis to enhance the acceleration phase performance of bilateral transtibial amputees (BTAs) competing in sprinting races. Amputee sprinters are hampered in the acceleration phase of a sprint race by the compliance of their prostheses. Increased contact times, and small and too vertical ground reaction forces limit the acceleration performance of BTAs. A variable stiffness prosthesis, with a higher stiffness at the initial steps of the acceleration phase, would reduce contact times and increase forward propulsion. A new variable stiffness design is proposed in this report. A prototype of this new design is created and characterized by retrieving the stiffness matrices and ellipses. Ottobock's 1E90 prosthesis is also characterized, and the results are compared. For this, a new testing methodology to obtain the stiffness ellipses of running prostheses (RPs) is proposed.