Sprint acceleration training has been highly researched and found that resistance sleds are one of the most effective tools for maximizing training adaptations. The resistance sled is being used by many of the world leaders in athletic training but has yet to be researched for the kinetic and kinematic effects some of its key components cause. The aim of this study was to better understand the effects of the attachment height on the sled and sled rail material on the user's trunk lean and jerking effect caused by the sled. This was done because it was hypothesized that the attachment height has a direct impact on trunk lean and sled rail material has a direct impact on jerk caused by the sled. To test these assumptions, experimental and theoretical data was collected using a single subject study analyzing trunk lean and acceleration values of the sled. The results presented a significant decrease in trunk lean (more horizontal line of action) when the attachment height was raised. Additionally, no significant values were attained to support the assumption that by modifying the sled rail material, jerking effects will decrease. The results indicate that there is a direct correlation between attachment height and trunk lean. More research is needed to better understand the relationship between sled rail material and jerk.

Physical tasks such as scrummaging, rucking and mauling are highly specific to rugby and also place unique physiological demands on the different playing positions within the forwards. Traditionally, the recruitment and development of talented rugby union players has focused on the assessment of motor skills and game intelligence aspects of performance, with less emphasis placed on the specific physiological requirements of playing positions in rugby. The purpose of this investigation was to measure the position-specific strength, speed and power characteristics of Premier rugby forwards in order (1) to determine whether any differences existed in the physiological characteristics of the different forward playing positions (prop, lock and loose forwards) and (2) to investigate the relationship between these physiological characteristics and coaches evaluations of football playing ability. Twenty-two male Premier level competition rugby forwards, consisting of eight prop forwards, five lock forwards and nine loose-forwards participated in the study. The Grunt 3000, a rugby specific force testing device was utilised to measure the static and dynamic horizontal strength during simulated scrummaging and rucking/mauling movements. Sprint times relating to acceleration ability (0 -10m, 0-20m) and maximum running speed (20 - 40m) were measured during a 40m sprint running test. In addition, force, power and displacement characteristics of a countermovement vertical jump were calculated from trials performed on a force plate. Also, player performance skill and physical capacity scores were determined independently by experienced coaches who assessed them based on their performances during the season. One-way analysis of variance and effect size statistics evaluated differences in the measured variables between forward playing positions and linear regression analysis evaluated the relationship between the coaches' scores of player performance skill and physical capacity and game specific measures of strength speed and power. Since there were no statistical significant differences between forward groups for horizontal force and countermovement jump variables and these analyses lacked statistical power, an effect size statistic was used to establish trends for differences in force and CMJ variables between the groups. There were moderate effect size differences between groups for horizontal impact force with prop and lock forwards producing 17.7% and 12.8% more force than the loose forwards respectively. No clear differences were apparent between forward positional groups for mean dynamic horizontal force and countermovement jump displacement of the centre of gravity. A significant difference (p =0.049) was shown between forward positional groups over the 0-40m sprint distance. Also, moderate effect size differences between pairs of groups were evident in 0-10m, 0-20m, 20-40m sprint times with both loose forwards and lock forwards on average, 6% faster than the prop forwards. A backward linear regression analysis revealed that the single best predictor of coaches' physical capacity and performance skill scores was the 20 - 40m sprint performance, accounting for 28% of the variance in player's physical capacity scores and 29% of the variance in player's performance skill scores. Whole-body horizontal static strength and impact strength in prop forwards and dynamic horizontal strength (relative to body mass) and sprint acceleration ability in loose forwards represent key factors for consideration when selecting forward players to these positions in the Premier rugby competition. The vertical jumping ability of all forward positional groups needs to be confirmed in a future study utilising a line-out specific countermovement jump test (free use of arm swing and line-out lifters in the jump) on a force plate. Monitoring of performance in rugby forwards should include an acceleration sprint test (0-10m) as this is specific to the sprinting patterns of forward players during a game, and maximum sprinting speed test (20-40m) as this test has the ability to discriminate between skilled and less-skilled rugby union forwards.

The purpose of this research was to investigate the influence of height, crosssection and metal alloy in the mechanical act of teardrop loops used in incisors retraction and in en masse retraction of incisors and canines, aiming analyze the mechanical behavior of these loops in relation to optimum forces presented in the literature. Two hundred and forty loops were submitted to a tensile load on the testing machine considered heights of 6mm, 8mm and 10mm; cross-sections of 0.018in.x 0.025in and 0.019in.x 0.025in and wire materials of stainless steel and beta-titanium alloys. It was obtained magnitudes of horizontal force (N) and load-deflection (N/mm) for each loop across activations of 0.5mm, 1mm, 1.5mm, 2mm and 2.5mm. The results showed that height (p<0.01), cross-section and metal alloy (p<0.05) were considered significant factors with reference to horizontal force and load-deflection. There was no influence of one factor but a combination of these trying to achieve very light forces. This study suggest that is necessary a large orthodontic biomechanics knowledge with respect to loops design used in incisors retraction and in en masse retraction of incisors and canines, selecting adequate height, crosssection and metal alloy. / O objetivo desta pesquisa foi investigar os efeitos da altura, secção transversal e tipo de liga no desempenho mecânico de alças confeccionadas em forma de gota, indicadas para a retração de incisivos e para a retração em massa de incisivos e caninos, buscando avaliar o comportamento das mesmas em relação às magnitudes de força ótima existentes na literatura. Foram submetidas a um ensaio mecânico 240 alças, considerando as alturas de 6mm, 8mm e 10mm; as seções transversais de 0.018 x 0.025 e de 0.019 x 0.025 e as ligas de aço inoxidável e beta-titânio (TMA). Foram obtidos valores de força horizontal (N) e carga-deflexão (N/mm) para cada alça mediante ativações de 0.5mm, 1mm, 1.5mm, 2mm e 2.5mm. Os resultados mostraram que a altura (p<0.01), a secção transversal e a liga (p<0.05) foram consideradas fatores significativos na força horizontal e cargadeflexão gerada. Não houve influência de um fator sobre os demais, mas sim, uma combinação destes, buscando atingir forças muito leves. Este estudo sugere que é necessário amplo conhecimento da biomecânica ortodôntica na confecção de alças direcionadas para a retração dos dentes anteriores, selecionando adequadamente a altura, a secção transversal e a liga.