Background: Running is one of the most popular branches of athletics. Running has several physiological benefits, such as a higher maximal oxygen consumption, increased muscle mass and reduced blood pressure. There have been plenty of discussions about what the most efficient running technique might be, should you use a short step length and a high step frequency or vice versa. It is generally known that you can increase your running speed by increasing your step frequency or your step length, and also both. However, maximal speed is achieved by increasing your step frequency rather than your step length. For endurance runners it is important to have a good running economy, because runners with a good running economy use less energy while running, and therefore require less oxygen than a runner with poor running economy. Previous research have not found any correlations between the length of the leg with step frequency or step length.  Aim: The aim of this study was to examine whether there are any significant correlations between the length of the leg in relation to the step frequency or the step length while running in different speeds.  Method: 15 trained males participated in this correlation study. All participants’ leg length were measured with a measuring tape. Three running trials, with the speeds of 12, 16 and 20 km/h were performed on a treadmill during 1 minute each. Between each trial the participants rested for 3 minutes. The trials were recorded with a video camera, and the participants individual step frequency, step length and heel or fore foot strike were collected. Persons coefficient of correlation test was used to analyze if there were any significant correlations between the length of the leg with step frequency and step length. Also a paired samples T test was performed to see if there was a significant increase between step frequency and step length with the speeds.  Result: There were no significant correlations (p>0,05) found between the length of the leg and the step frequency or the length of the leg and step length in any of the different speeds. The paired samples t-test showed a significant (p<0,001) increase in step frequency and step length with the different speeds.  Conclusion: In conclusion, according to the present study, there were no significant correlations found between the length of the leg with step frequency or step length, which is in consensus with previous research.  Therefore, it is not advisable to predict an individual’s step length based on their leg length. There are various factors involved in determining a person’s step length and step frequency, and this study showed that running speed is one important factor. This information may be useful for runners and their coaches to apply, so they avoid making interventions involving alternations in the runners step length based on their body dimensions, such as leg length.

Music appears to have advantageous effects during exercise as it has been shown to increase motivation, decrease ratings of perceived exertion (RPE), and improve exercise performance. The improvement of running performance in particular, is the main effect recreational runners want to focus on as many want to improve their time in road races. Running velocity, indicated by a faster time to completion is thought to improve with an increase in step frequency, step length, or a combination of these variables. Currently, there is limited research that observes methods to help increase step frequency or step length. The manipulation of music cadence may be considered an effective training method that influences step frequency. The purpose of this study was to observe the effect of music cadence on step frequency in the recreational runner. A total of 30 recreational runners (15 male, 15 female) with a mean age of 31.0 ± 5.8 (range= 20-39), a BMI of 24.0 ± 3.3 (range= 19-32), and an estimated VO2 max of 49.6 ± 5.4 (range= 41-60) participated in this study. Individually, runners completed four 1600-meter time trials on an outdoor track at maximal effort. The first trial was a familiarization trial where participants ran 1600 meters with no music. Two music conditions were then created for each runner based on their natural step frequency obtained during the familiarization trial. The first condition represented music at natural step cadence and the second condition represented music at increased step cadence. The next three 1600 meter time trials were randomized and included a control condition of no music, a natural cadence music condition at the runner's natural step frequency, and an increased cadence music condition of 10-20 beats per minute (bpm) above the natural cadence music condition. Results indicated that step frequency was significantly higher during the increased cadence music condition compared to both the natural cadence music and no music conditions (p < 0.05). Additionally, time to completion was significantly lower in the increased cadence music condition compared to both the natural cadence music and no music conditions (p < 0.05). Lastly, there was no significant difference in step length among music conditions. These results indicate that music cadence had a positive influence on running performance as it was able to increase step frequency and improve time to completion in a group of recreational runners. Therefore, for practical application, recreational runners can alter music cadence to help improve running performance.

Magister Scientiae (Physiotherapy) - MSc(Physio) / Sprinting can be described as the ability to cover a short distance in the fastest possible time. It requires enormous stability, strength and speed to achieve this goal. Any improvements in technique or speed can be the difference between winning and losing and ultimately gold or silver. Many coaches focus their training on improving the mechanics of the lower limb in order to achieve their goal. They often neglect to consider the effect the upper limb, head, neck and trunk has on the sprinters technique. This study aimed to determine the effect the muscles that assist in stabilising the head and neck namely the deep neck flexors, has on sprinting technique. A systematic review was conducted to determine the factors that influence the acquisition of the correct and most efficient sprint technique. Thereafter assessments were done to determine the prevalence of neck discomfort and how it impacts the athlete’s life by use of the Disability Neck Index. In addition, the endurance of the participant’s deep neck flexors using the Craniocervical Flexion Test and an analysis of their sprinting technique through video analysis were conducted. Variables for each assessment were coded and analysed with Chisquared tests to determine statistically significant relationships. Results show that there was to prevalence of neck pain among participants and although the participants have poor deep neck flexor endurance and an inadequate sprinting technique, no statistically significant relationships could be found between these two variables. Thus poor endurance in the deep neck flexors has no effect on sprinting technique. The results of the study was limited due to a small sample size and lack of equipment, thus further research is required in order to completely reject the possibility that the deep neck flexors effects a sprinters ability to acquire an efficient sprinting technique.

Les changements dans le contexte du traitement radar aéroporté impliquent de plus en plus d'améliorations qui justifient la recherche d'une alternative au filtrage adapté, qui est le processus utilisé classiquement pour estimer les paramètres des cibles détectées. Le Compressed Sensing ouvre la perspective d'un nouveau traitement, également efficace dans les configurations de cibles multiples, avec de meilleures performances de suivi et de reconnaissance que l'approche classique. Nous cherchons à appliquer ce traitement aux formes d'onde dites à évasion de fréquence. Le choix intégral des paramètres de définition du signal transmis déterminee entièrement la matrice de mesure de la procédure du Compressed Sensing, laquelle solution fournit toutes les informations recherchées sur la scène observée. Pour chaque signal à évasion de fréquence, et d'amplitude constante, la matrice de mesure correspondante est obtenue en extrayant certaines lignes d'une matrice de Fourier étendue particulière, la matrice de Fourier 2D. La construction de la génération de la matrice de mesure est importante car le succès de la reconstruction dépend des propriétés algébriques de cette matrice. / Changes in the context of airborne radar processing implie more and more improvements that justify to look for an alternative to Matched Filtering, the process conventionally used to estimate the parameters of detected targets. Compressed Sensing suggests a new treatment, also performing in multi-target cases, with better tracking and recognition performances than classical approach. We seek to apply this treatment to step frequency waveforms. The whole choice of definition parameters for the transmitted signal entirely builds the measurement matrix of the Compressed Sensing procedure which solution gives all the sought information of the observed scene. For each step frequency signal with constant amplitude, the resulting measurement matrix is obtained by extracting some lines from a particular extended Fourier matrix, the 2D Fourier matrix. The construction of the measurement matrix generation is important since the success of the reconstruction depends on the algebraic properties of this matrix.

La première partie de la thèse étudie le balayage des gradients de conductivité électrique avec la force de Lorentz induite par ultrasons (SECG-UILF). Pour réduire la puissance de stimulation instantanée du transducteur émetteur et en même temps la pression acoustique maximale du transducteur, cette thèse propose d'appliquer l'excitation de l'impulsion ultrasonore à la modulation de fréquence linéaire ou l'excitation de l'impulsion ultrasonore à fréquence sinusoïdale dans SECG-UILF. Pour les gradients de conductivité électrique à balayage avec la force de Lorentz induite par l’ultrasons à la modulation de fréquence linéaire (SECG-LFM-UILF), un signal électrique de puissance instantanée maximale de 39,54 dBm est utilisé pour exciter le transducteur de transmission, ce qui est inférieur de 25,5 dB à la puissance instantanée maximale de l'impulsion étroite haute tension négative (65,05 dBm) adopté dans le SECG-UILF traditionnel. Et en temps, la pression acoustique d'émission maximale dans le SECG-LFM-UILF est inférieure de 0,44 MPa à celle du SECG-UILF traditionnel. Des expériences de SECG-LFM-UILF sont effectuées en utilisant des fantômes de conductivité à la gélose saline à plusieurs formes de conductivité allant de 0,2 S/m à 0,5 S/m, ce qui montre que: (1) le SECG-LFM-UILF peut détecter avec précision la distance longitudinale des gradients de conductivité électrique; (2) le rapport signal sur bruit des images de balayage B reconstituées de la distribution de gradient de conductivité électrique par le SECG-LFM-UILF est comparable à celui obtenu par le biais du SECG-UILF traditionnel; et (3) en utilisant une largeur de bande de fréquence de modulation de 2 MHz et une durée de modulation de 500 μs, une résolution longitudinale de 1 mm est obtenue. Pour balayer des gradients de conductivité électrique avec une force de Lorentz induite par ultrasons à fréquence fréquentielle (SECG-SF-UILF), le schéma de démodulation en phase présente une implémentation matérielle plus simple que le schéma de démodulation IQ, mais ne peut détecter que la moitié de la plage longitudinale. Des expériences de SECG-SF-UILF sont effectuées sur un échantillon de feuille de cuivre à deux couches, qui démontrent qu’en utilisant une largeur de bande de fréquences de 2 MHz et 64 fréquences discrètes, la plage longitudinale de l’échantillon peut être détectée avec précision. La deuxième partie de la thèse étudie l'élastographie à base d'approche de corrélation croisée. Pour élargir la largeur de bande de fréquence du champ de déplacement de l’onde de cisaillement afin d’améliorer la qualité de la carte de vitesse de l’onde de cisaillement, cette partie étudie l’application de la force de Lorentz pour la génération de champs d’onde de cisaillement. Tout d'abord, la génération des sources des ondes de cisaillement sur la surface du support souple à travers le mécanisme de la force de Lorentz est étudiée en stimulant un anneau ou un patch conducteur non ferromagnétique avec un champ magnétique transitoire. La mesure de déplacement à l'aide d'une sonde laser interférométrique confirme les caractéristiques d'origine, de fréquence et d'amplitude de la force de Lorentz. Sous un champ magnétique transitoire dont la vitesse de changement est de 10,44 kTs-1, le patch génère une source de champ des ondes de cisaillement d'amplitude de 100 µm à la surface de l'échantillon de fantôme d'alcool polyvinylique (PVA). Ensuite, le potentiel des champs d'ondes de cisaillement générés pour la reconstruction de la vitesse des ondes de cisaillement basée sur la corrélation croisée est exploré. Sur la base de l’approche de corrélation croisée, les cartes qualitatives de la vitesse des ondes de cisaillement sont reconstruites à partir de 100 cadres des champs de déplacement, à partir desquels les interfaces ou les limites entre des régions de rigidité différente peuvent être clairement reconnues, lesquelles sont complètement dissimulées dans les images ultrasonores / The first part of the thesis studies the scanning electric conductivity gradients with ultrasonically induced Lorentz force (SECG-UILF). To reduce the instantaneous stimulation power to the transmitting transducer and at the same time the peak acoustic pressure from the transducer, this thesis proposes to apply the linearly frequency-modulated ultrasound pulse excitation or the sinusoidal step-frequency ultrasound pulse excitation in SECG-UILF. For the scanning electric conductivity gradients with linearly frequency-modulated ultrasound-induced Lorentz force (SECG-LFM-UILF), electrical signal of peak instantaneous power of 39.54 dBm is used to excite the transmitting transducer, which is 25.5 dB lower than the peak instantaneous power of the negative high-voltage narrow pulse (65.05 dBm) adopted in traditional SECG-UILF; and at the same time, the peak transmitting acoustic pressure in SECG-LFM-UILF is 0.44 MPa lower than that in traditional SECG-UILF. Experiments of SECG-LFM-UILF are done using multi-shaped saline agar phantoms of conductivity ranging from 0.2 S/m to 0.5 S/m, which show that: (1) the SECG-LFM-UILF can detect precisely the longitudinal distance of the electric conductivity gradients; (2) the signal-to-noise ratio of the reconstructed B-scan images of the electrical conductivity gradient distribution by the SECG-LFM-UILF are comparable to that obtained through the traditional SECG-UILF; and (3) using modulation frequency bandwidth of 2 MHz and modulation duration of 500 μs, a longitudinal resolution of 1 mm is achieved. For the scanning electric conductivity gradients with step-frequency ultrasound induced Lorentz force (SECG-SF-UILF), the in-phase demodulation scheme is simpler in hardware implementation than the IQ demodulation scheme but can only detect half of the longitudinal range. Experiments of SECG-SF-UILF are done on a sample of two-layer copper foil, which demonstrate that, using a frequency bandwidth of 2 MHz and 64 discrete frequencies, the longitudinal range of the sample can be detected precisely. The second part of the thesis studies the cross-correlation approach based elastography. To expand the frequency bandwidth of the shear wave displacement field so as to improve the quality of the shear wave velocity map, this part studies application of the Lorentz force for generation of shear wave fields. First, generation of shear wave sources on the soft medium surface through the mechanism of the Lorentz force is investigated by stimulating a non-ferromagnetic conductive ring or patch with a transient magnetic field. The origin and the frequency and amplitude characteristics of the Lorentz force acting on the conductive ring are confirmed by the displacement measurement using an interferometric laser probe. Under a transient magnetic field of changing rate of 10.44 kTs-1, the patch generates a shear wave field source of amplitude of 100 μm at the surface of the sample of polyvinyl alcohol (PVA) phantom. The shear wave fields created and propagating in the PVA phantom by experiments agree qualitatively well with the theoretical shear wave fields calculated through the analytical Green function solution. Then, the potential of the generated shear wave fields for the cross-correlation based shear wave velocity reconstruction is explored. Based on the cross-correlation approach, the qualitative shear wave velocity maps are reconstructed from 100 frames of the displacement fields, from which the interfaces or boundaries between regions of different stiffness can be clearly recognized, which are completely concealed in the ultrasound images