Raw acceleration can be used as a proxy measure representing external forces experienced at the hip. Peak vertical acceleration at the hip was measured (ActiGraph GT3X+ - BT) in 30 premenopausal women during common exercises (walking, running, stairs and jumping) and while they went about their normal routine (7 days). Accelerations experienced during running and jumping activities were consistently ≥3.2g, whereas only accelerations during box jumps were greater than the higher recommended threshold of ≥ 4.9g proposed to improve bone mineral density in premenopausal women. Peak jerk experienced during jumping activities was greater than the recommended threshold of 100g/s. The median number of accelerations/day ≥3.2g was 30.4, whereas only 3.5 incidences/day were observed at ≥4.9g. Running and jumping resulted in vertical accelerations that met or exceeded the thresholds proposed to be beneficial for bone, however, participants rarely experienced high magnitude vertical accelerations during daily life. / October 2016

Le processus de fabrication des pièces usinées arrive à maturité concernant la fabrication assistée par ordinateur et la maîtrise du procédé d’usinage. Aujourd’hui, les perspectives d’améliorations importantes sont liées à l’optimisation de la commande numérique et de ses interactions avec le reste du processus de fabrication. L’objectif de cette thèse est donc de maîtriser les briques de base de la commande numérique pour optimiser le processus d’usinage 5 axes grande vitesse des surfaces complexes. La création d’une commande numérique ouverte nécessite le développement des algorithmes qui transforment le programme d’usinage en consignes échantillonnées pour les axes de la machine. La première partie des travaux consiste à rendre la géométrie suffisamment continue notamment pour les trajets interpolés linéairement en 5 axes qui présentent des discontinuités en tangence. Ensuite, l’interpolation temporelle du trajet crée la trajectoire d’usinage respectant les contraintes cinématiques et en particulier le jerk de chacun des 5 axes de la machine. L’implémentation matérielle de ces algorithmes permet de piloter une machine d’usinage grande vitesse 5 axes avec une commande numérique ouverte. Ainsi, les verrous technologiques associés aux commandes numériques industrielles sont levés et la chaîne numérique est entièrement contrôlée de la CFAO jusqu’au déplacement des axes. La maîtrise complète de la commande numérique offre la possibilité de définir exactement le trajet d’usinage à partir de la CAO sans introduire les écarts géométriques inhérents aux formats de description standards. L’interpolation de la trajectoire d’usinage directement sur la surface à usiner améliore de manière significative la qualité et la productivité de l’usinage des surfaces complexes. La commande numérique PREMIUM-OpenCNC permet la validation expérimentale de ces travaux et ouvre de nombreuses autres voies d’amélioration du processus de fabrication. / The manufacturing process reaches maturity concerning Computer Aided Manufacturing and cutting process performances. Nowadays, major improvements are linked to the optimization of the Computer Numerical Control and its interactions with the rest of the manufacturing process. The aim of this thesis is to control the basic components of a CNC in order to optimize the 5-axis high speed machining process of complex surfaces. The realization of an open CNC requires the development of algorithms which transform the machining program into command setpoints for the machine drives. The first part of this thesis allows to round the 5-axis discontinuities caused by the linear tool path interpolation commonly used. Then, a feedrate interpolation algorithm computes the trajectory while respecting the kinematical constraints of the machine and especially the jerk of each axis. The implementation of this work allows to control a 5-axis high speed machine with an open CNC. Hence, the technological barriers that prevent CNC optimizations are removed and the manufacturing process is under control from CAD/CAM to axis displacement. The complete control over the CNC offers the possibility to define the tool path exactly from Computer Aided Design entities without introducing any geometrical deviation generally induced by standard NC code. The direct interpolation of the trajectory on the machined surface significantly improves the quality and the productivity of complex surface machining. The PREMIUM-OpenCNC allows to prove experimentally the efficiency of this work and opens new ways for future manufacturing process improvements.

Thesis (M. Sc.)--York University, 2001. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references. Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ71585.

Thesis (MAppSc in Physiotherapy)--University of South Australia, 1996

The split jerk and power jerk are two commonly used lifts among strength and conditioning coaches, as well as lifts included in the sport of Olympic weightlifting. However, it is unknown which of these jerk techniques exhibit more advantageous barbell kinematics. PURPOSE: To compare the barbell kinematics between a power jerk and a split jerk at a constant load. METHODS: Twelve men were recruited for this study (height = 1.8 ± 0.1 m; mass = 85.3 ± 10.2 kg; age = 23.4 ± 2.4 years). All subjects had been completing the jerk for a minimum of six months, and reported their split jerk 1 repetition maximum (1-RM: 105.3 ± 19.1 kg). Subjects completed 3 repetitions of each jerk technique, at 85% of their split jerk 1-RM. The data were collected using 6 3D video cameras, with a sampling rate of 200Hz and were analyzed using Vicon software. A multivariate paired t-test was used to determine the effect of jerk technique on all kinematic variables. Paired samples t-tests were used as post hoc analyses when necessary. An alpha level of (p<0.05) was used for all inferential statistics. RESULTS: No significant differences were found between the two techniques for starting barbell position, lowest barbell position and maximum concentric velocity. Peak barbell height, range and displacement were all found to be significantly greater in the power jerk when compared to the split jerk (p<0.05). CONCLUSIONS: Results suggest that more work is done on the barbell, and greater range of motion, occur during the power jerk. The results suggest that more work may be done on the body during the split jerk due to the technique of dropping quickly under the bar for the catch. Less work done on the barbell could result in higher absolute loads, making the split jerk the superior technique for populations such as weightlifting athletes.

Smoothness is a hallmark of healthy movement and has the potential to be used as a marker of recovery in rehabilitation settings. While much past research has focused on shoulder and elbow movements (reaching), little is known about movements of the wrist despite its importance in everyday life and its impairment in many neurological and biomechanical disorders. Our current lack of knowledge regarding wrist movement prevents us from improving current models, diagnosis, and treatment of wrist disorders. In particular, while movement smoothness is a well-known characteristic of reaching movements and may potentially be used to diagnose and monitor recovery from neurological impairments, little is known about the smoothness of wrist rotations. Therefore, because the smoothness of wrist rotations has not been characterized, it cannot be used as a marker for diagnosis and evaluation. This study examines the smoothness of wrist rotations in comparison to the known baseline of reaching movements. Subjects were asked to perform wrist and reaching movements under a variety of conditions, including different speed and direction. To measure movement smoothness, this study used an established metric of speed profile number of maxima and presents a novel method for characterizing smoothness by fitting a minimum-jerk trajectory to real movement data.The results show that 1) wrist rotations are significantly less smooth than reaching movements (p≤0.0016), 2) smoothness decreases significantly as speed decreases (p<0.0001), and 3) wrist movements exhibit a pattern of smoothness that varies significantly between targets and outbound/inbound movement directions (p<0.0001). Potential causes for results 1 and 3 are presented and tested by simulation or reference to prior studies, because these findings were previously unknown. The decrease in smoothness with speed (result 2) has been found in prior studies of smoothness in reaching and finger movements. The reasoning behind the first result is explored by testing whether the difference in smoothness between wrist and reaching movements was due to differences in mechanical, muscular, neural, or protocol-related properties. The reasoning behind the third result is explored by testing whether the difference in wrist direction was due to anisotropy in musculoskeletal dynamics or anisotropy in movement duration. The simulations show that the wrist’s bandwidth is greater than that of the arm, and that there is nonvoluntary power in the bandwidth of the wrist that would be low-pass filtered in reaching movements, indicating that at least some of the difference in smoothness between wrist and reaching movements is due to differences in mechanical properties. Differences in muscular, neural, or protocol-related properties (signal-dependent noise, proprioceptive acuity, and the speed requirements of the task, respectively) do not appear to be the cause of the difference in smoothness between wrist and reaching movements. Differences in wrist smoothness between movement directions appears to be related to differences in movement duration between directions.

Les systèmes de navigation par satellites permettent les applications de positionnement en extérieur, dont la navigation routière. Dans les environnements contraints, comme l'intérieur des bâtiments où ces signaux satellitaires sont dégradés, la continuité du service de positionnement est nécessaire. Les applications adaptées aux citoyens modernes avec leurs appareils nomades posent des contraintes fortes de mobilité, de coûts et de limitations des infrastructures existantes. Les larges possibilités de déplacements dans des environnements hétérogènes accroissent les difficultés. Un état de l'art alimenté par une décennie de travaux académiques et industriels présente un ensemble de technologies qui visent disponibilité et performance. L'accent porte ensuite sur les systèmes inertiels pédestres à bas coût, avec une première contribution permettant d'abandonner la détection de pas au profit d'une mobilité facilitée, mais reste limitée par la connaissance de la distance parcourue pendant une phase de calibration. Cette approche nouvelle est confrontée à celle classique au pied, puis éprouvée pour différents capteurs et piétons au travers d'expérimentations répétées en conditions réalistes. Une seconde contribution décline une constellation radio locale pour estimer la distance avec une infrastructure allégée à deux émetteurs. Elle s’inspire d’une conception satellitaire sur radio programmable pour faciliter sa compatibilité avec l’existant et explorer ses performances. Une surveillance du rapport signal à bruit inter-canal améliore la précision du positionnement. Le couplage de ces systèmes asynchrones et distribués est évalué en intérieur sur une plateforme automatisée / The global navigation satellite systems allow outdoor positioning applications, including car navigation. In challenging environments, such as the buildings where satellite signals are mitigated, georeferenced points of interest or navigation applications require a continuity of the positioning service. The applications adapted to modern citizens and their mobile devices raise strong constraints on mobility, costs and limitations of the existing infrastructure. The wide variety of displacements in heterogeneous environments increases the challenge. A state of the art fed by a decade of academic and industrial works presents a set of technologies that target availability and performance. The emphasis follows on the low cost pedestrian inertial systems, with a first contribution allowing to give up the step detection for the benefit of an easier mobility, but remains limited to the knowledge of the distance traveled during a calibration phase. This new approach is compared with the classical foot-mounted approach, and then benchmarked with several sensors and pedestrians through repeated experiments in real conditions. A second contribution operates a local radio constellation to estimate the distance with a minimal infrastructure with two emitters. The signals and the algorithm are based on a reproduction of satellite systems to ease the compatibility but are implemented on a programmable radio to explore the performances. A monitoring of the difference of carrier to noise ratio between the radio channels improves the distance estimation. The hybridization of these distributed, asynchronous and multi-rates inertial and radio systems is evaluated indoor on a motorized platform

No description available.

Preparing for a national weightlifting championship: A case series. J Strength Cond Res XX(X): 000–000, 2019—This study aimed to characterize psychological, physiological, and performance changes of a high-level female (24.5 years; 53.8 ± 0.3 kg; 155.4 cm) and male (25.8 years; 92.7 ± 1.2 kg; 189 cm) weightlifter over 28 weeks while preparing for a national championship. Body mass, hydration, psychological inventories, serum biomarkers, vastus lateralis muscle cross-sectional area (CSA), and squat jump (SJ) performance were assessed weekly beginning 11 weeks from the competition date. Weightlifting performance goals were met for the female athlete (actual total = 159 kg) but not for the male athlete (actual total = 292 kg). Reductions in vastus lateralis CSA possibly took place the week leading into competition for both athletes. Both athletes reported positive recovery-stress states on the day of competition relative to baseline values. Fluctuations between steroid hormone concentrations and inflammatory markers were unpredictable and inconsistent for both athletes throughout the training program. Unloaded SJ height and rate of force development were the highest on competition day for both athletes. Based on these findings, it is possible for high-level male and female weightlifters to achieve and maintain peak preparedness 3–4 days before competition following a 1-week overreach and 3-week exponential taper, where training volume-load is reduced by half and intensity maintained or slightly increased relative to pretaper values. Furthermore, the short recovery and stress scale and SJ testing seem to be useful tools for sport scientists and coaches when monitoring high-level weightlifters preparing for competition.

Some seabirds (such as Northern Gannets and Brown Boobies) can dive from heights as high as 30 m reaching speeds of up to 24 m/s as they impact the water surface. It is perceived that physical geometry, particularly of the beak, allows them to endure relatively high impact forces that could otherwise kill non-diving birds. Acceleration data from simplified models of diving birds agree with simulated data for one species (Northern Gannet), however, no reliable experimental data with real bird geometries exist for comparison purposes. This study utilizes eleven 3D printed diving birds (five plunge-diving, five surface-diving and one dipper) with embedded accelerometers to measure water-entry impact accelerations for impact velocities ranging between 4.4 - 23.2 m/s. Impact forces for all bird types are found to be comparable under similar impact conditions and well within the safe zone characterized by neck strength as found in recent studies. However, the time each bird requires to reach maximum impact acceleration and its effect represented here by the derivative of acceleration (i.e., jerk), is different based on its beak and head shape. We show that surface diving birds cannot dive at high speeds as the non-dimensional jerk experienced exceeds a safe limit estimated from human impact analysis, whereas those by plunge divers do not.