Добірка наукової літератури з теми "Punt kicking"

Context:Flexibility tests are sometimes thought to be related to range of motion in dynamic activities, but such a relationship remains to be determined.Objective:To determine the correlation between flexibility and hip and knee angles in Australian football kicking.Design:Correlation.Setting:Biomechanics laboratory.Participants:16 Australian Rules football players.Main Outcome Measures:Hip and knee angles of the preferred kicking leg in a relaxed position were determined with a modified Thomas test. Maximum hip extension, the knee-flexion angle in this position, the maximum knee-flexion angle, and the hip angle at this position during the swing phase of maximum-effort drop-punt kicks were determined.Results:Significant correlations were found between hip flexibility and maximum hip extension (r = .65, P < .01) and hip angle at the maximum knee-flexion angle (r = .70, P < .01).Conclusions:The data indicate a moderate association between hip flexibility and hip angles during kicking.

The types of kick that are performed in the football codes fall into two broad categories: punt kick and place kick. One type of punt kick is the major means of ball movement in Australian Rules football – the drop punt kick. Past studies have investigated the biomechanics of kicking. The pattern of segmental interaction during the kicking motion – known as the proximal to distal sequence (PDS) – is the most consistent finding that is reported in the biomechanics of kicking literature. In this sequence the proximal segment (thigh) initiates the forward swing of the kicking limb towards the ball and the forward rotation of the distal segment (shank) follows. PDS motions are also typified by a higher angular velocity of the distal segment (shank). Studies that have compared the difference between skilled and less skilled kickers in Australian Rules football have found that the difference in performance is the result of 1) the position of the shank at the end of the backswing is higher above horizontal (further in the clockwise direction) for the skilled than it is for the less skilled, 2) the maximum angular velocity of the thigh during the forward swing is greater for the skilled than it is for the less skilled and 3) the skilled kickers demonstrate greater mean maximum angular velocity of the shank at foot – ball contact. Apart from these findings there is inadequate information about the mechanical features of a skillful drop punt kick. The objective of this study was to quantify and compare the kinematics of skilled and less skilled kicking. A general profile of the drop punt kick and the reliability of the kinematic variables were also reported. The reliability study was conducted first. Six subjects were tested on two occasions to establish the reliability of the equipment and methods. Variables were deemed to be reliable if they demonstrated an ICC equal or greater than r = 0.80. Of the 95 variables that were analysed 42% had an ICC greater than r = 0.79 and 25% were classified as having questionable to moderate reliability because r = 0.50 – 0.79. Only reliable variables were used to compare the skilled and less skilled groups. Six elite skilled kickers and six elite less skilled kickers were used in the main study. All subjects used were AFL players at the time of the data collection. Two-dimensional video footage was taken of each kick using a high speed camera (200Hz). The camera was positioned so that its line of sight was perpendicular to the sagittal plane of motion. The video footage of each trial was processed through the Peak Motus motion analysis system. The start of the kicking motion was identified by the maximum cw angle of the thigh. The time of foot – ball contact was the end of the motion. There were two phases that were identified during this time; transition and forward swing. The duration of each was 50% of movement time. The results of the current study showed that the skilled kickers held the ankle in a more plantarflexed position than did the less skilled kickers (skilled 46.7 degrees, less skilled 39.21 degrees, r = 0.70, ES = – 1.06, p = .071) at the time of foot – ball contact. This result indicates that a common trait amongst skilled kickers is the presence of a taut instep at foot – ball contact. This is one trait of skilled kickers that is often referred to by skills coaches within the AFL. The maximum angular velocity of the shank (1402 degrees/second) was higher than that of the thigh (805 degrees/second). The mean knee extension angle at foot – ball contact was 50 degrees and the maximum knee extension angle occurred after foot – ball contact (150% movement time). There was no difference between groups in the magnitude of the angles or angular velocities (p > 0.2). There was a difference in the time between the maximum angular velocity of the thigh and the maximum angular velocity of the shank (p < 0.05). From this result we suggested that skilled kickers are distinguished from less skilled kickers based on the timing of the critical events not the magnitude of critical events.

The types of kick that are performed in the football codes fall into two broad categories: punt kick and place kick. One type of punt kick is the major means of ball movement in Australian Rules football – the drop punt kick. Past studies have investigated the biomechanics of kicking. The pattern of segmental interaction during the kicking motion – known as the proximal to distal sequence (PDS) – is the most consistent finding that is reported in the biomechanics of kicking literature. In this sequence the proximal segment (thigh) initiates the forward swing of the kicking limb towards the ball and the forward rotation of the distal segment (shank) follows. PDS motions are also typified by a higher angular velocity of the distal segment (shank). Studies that have compared the difference between skilled and less skilled kickers in Australian Rules football have found that the difference in performance is the result of 1) the position of the shank at the end of the backswing is higher above horizontal (further in the clockwise direction) for the skilled than it is for the less skilled, 2) the maximum angular velocity of the thigh during the forward swing is greater for the skilled than it is for the less skilled and 3) the skilled kickers demonstrate greater mean maximum angular velocity of the shank at foot – ball contact. Apart from these findings there is inadequate information about the mechanical features of a skillful drop punt kick. The objective of this study was to quantify and compare the kinematics of skilled and less skilled kicking. A general profile of the drop punt kick and the reliability of the kinematic variables were also reported. The reliability study was conducted first. Six subjects were tested on two occasions to establish the reliability of the equipment and methods. Variables were deemed to be reliable if they demonstrated an ICC equal or greater than r = 0.80. Of the 95 variables that were analysed 42% had an ICC greater than r = 0.79 and 25% were classified as having questionable to moderate reliability because r = 0.50 – 0.79. Only reliable variables were used to compare the skilled and less skilled groups. Six elite skilled kickers and six elite less skilled kickers were used in the main study. All subjects used were AFL players at the time of the data collection. Two-dimensional video footage was taken of each kick using a high speed camera (200Hz). The camera was positioned so that its line of sight was perpendicular to the sagittal plane of motion. The video footage of each trial was processed through the Peak Motus motion analysis system. The start of the kicking motion was identified by the maximum cw angle of the thigh. The time of foot – ball contact was the end of the motion. There were two phases that were identified during this time; transition and forward swing. The duration of each was 50% of movement time. The results of the current study showed that the skilled kickers held the ankle in a more plantarflexed position than did the less skilled kickers (skilled 46.7 degrees, less skilled 39.21 degrees, r = 0.70, ES = – 1.06, p = .071) at the time of foot – ball contact. This result indicates that a common trait amongst skilled kickers is the presence of a taut instep at foot – ball contact. This is one trait of skilled kickers that is often referred to by skills coaches within the AFL. The maximum angular velocity of the shank (1402 degrees/second) was higher than that of the thigh (805 degrees/second). The mean knee extension angle at foot – ball contact was 50 degrees and the maximum knee extension angle occurred after foot – ball contact (150% movement time). There was no difference between groups in the magnitude of the angles or angular velocities (p > 0.2). There was a difference in the time between the maximum angular velocity of the thigh and the maximum angular velocity of the shank (p < 0.05). From this result we suggested that skilled kickers are distinguished from less skilled kickers based on the timing of the critical events not the magnitude of critical events.

A paucity of research exists investigating the potential relationship between the technical and temporal strategy of accurate and inaccurate kickers in response to physical parameters modifiable by athletic conditioning. While recent studies have produced improvements in performance when kicking for distance following structured resistance training interventions, no studies have examined the influence of such interventions on the enhancement of kicking accuracy. It was therefore the purpose of this thesis to extend scientific understanding of those mechanisms which might underpin accurate kicking performances through examining kinanthropometric, strength and muscularity profiles of accurate and inaccurate kickers in Australian Football using a series of research studies. In particular, studies one and two established valid and reliable measurement protocols, while studies three, four and five quantified whole-body composition, anthropometrics, segmental masses of the lower limbs, unilateral and bilateral lower-body strength, and lower limb kinematics during the drop punt. Study one established a standardised and reliable body positioning and scan analysis model using Dual Energy X-ray Absorptiometry (DEXA) to accurately identify and assess appendicular segmental mass components (upper arm, forearm, hand, thigh, shank and foot segments); producing very high intra-tester reliability (CV ≤ 2.6%; ICC ≥ 0.941) and very high inter-tester reliability (CV ≤ 2.4%; ICC ≥ 0.961). This methodological determination of intralimb and interlimb quantities of lean, fat and total mass could be used by strength and conditioning practitioners to monitor the efficacy of training interventions; track athletes during long-term athletic development programs; or identify potential deficiencies acquired through-out injury onset and during rehabilitation. Study two assessed a portable isometric lower-body strength testing device, successfully demonstrating its ability to derive valid and reliable representations of maximal isometric force (peak force) under bilateral and unilateral conditions (CV ≤ 4.7%; ICC ≥ 0.961). This device was unable to reliably determine rate of force development across either bilateral or unilateral conditions (CV: 14.5% - 45.5%; ICC: 0.360 – 0.943); and required an extra second of contraction time to achieve peak force (p < 0.001). The portable apparatus may provide a more sport-specific assessment of maximal strength in sports where balance is an important component; such as the support leg during the kicking motion. Using the methodological approach established in study one; study three was a descriptive study which assessed the lower limb segmental profile of accurate and inaccurate kickers. A noticeable difference in leg mass characteristics was evident, with accurate kickers containing significantly greater quantities of relative lean mass (p ≤ 0.004; r = 0.426 to 0.698), significantly lower quantities of relative fat mass (p ≤ 0.024; r = -0.431 to -0.585), and significantly higher lean-to-fat mass ratios (p ≤ 0.009; r = 0.482 to 0.622) across all segments within both kicking and support limbs. To examine how these lower limb characteristics might adjust biomechanical strategy; study four used the methodological approach from study one in conjunction with three-dimensional kinematic data. No relationship was found between foot velocity and kicking accuracy (r = -0.035 to -0.083). Instead, it was the co-contribution of leg mass and foot velocity which were discriminatory factors between accurate and inaccurate kickers. A significant and strong correlation was also found between relative lean mass and kicking accuracy (p ≤ 0.001; r = 0.631). Greater relative lean mass within accurate kickers may heighten limb control due to reduced volitional effort and lower relative muscular impulses required to generate limb velocity. Study five - the final study of the thesis - assessed lower limb strength and muscularity using methodologies presented in studies one and two. Study five was able to successfully demonstrate a positive relationship between relative bilateral strength and support-leg unilateral strength with kicking accuracy outcomes (r = 0.379 to 0.401). A significant negative relationship was established between strength imbalances and kicking accuracy (p = 0.002; r = 0.516), supported by the significant positive relationship between the limb symmetry index for lean mass quantities and kicking accuracy outcomes (p = 0.003 to 0.029; r = 0.312 to 0.402). This highlighted the potential benefit of greater limb symmetry for strength and muscularity between kicking and support limbs within Australian Footballers, with particular emphasis placed toward support leg strength. The general conclusion provided by the thesis promotes the importance and positive influence of relative lean mass and lower body strength to kicking accuracy production during the drop punt. The findings provide a valid rationale for strength and conditioning professionals and skill acquisition coaches to properly consider an athlete’s strength, muscularity and body mass profiles when attempting to improve kicking performance. Given the cross-sectional nature of the Thesis, longitudinal resistance training studies should be attempted in future, to establish interventions which may heighten athletic conditioning and technical proficiency in football sports, with an express aim to improve drop punt kicking accuracy.

Across the football codes, kicking is the main skill used to score goals and pass between team members. Kicking with high ball velocity and high accuracy is required to kick to targets at far distances or reach a submaximal target in less time. The impact phase is the most important component of the kicking action: it is the only time a player forcefully contacts the ball to produce the flight path. Ensuring high impact efficiency and the appropriate combination of flight characteristics are imparted onto the ball during foot-ball impact is important for successful kicking. The aim of this thesis was to determine how foot-ball impact characteristics influences impact efficiency, ankle plantarflexion, ball flight characteristics and kicking accuracy. By using a mechanical kicking machine to systematically explore impact characteristics and performing an intra-individual analysis of human kickers, high-speed-video analysis of foot-ball impact found impact characteristics influenced impact efficiency, ankle plantarflexion, ball flight characteristics, and kicking accuracy. Increasing ankle joint stiffness, impact locations on the foot closer to the ankle joint, altering foot-ball angle and reducing foot velocity each increased impact efficiency. These results supported the coaching cue ‘maintaining a firm ankle’ during impact as effective at increasing impact efficiency. The impact location between the foot and ball across the medial-lateral direction, foot-ball angle and foot trajectory were each identified as influential to ball flight characteristics and/ or kicking accuracy. The oblique impact theory applied to the duration of impact provided a theoretical framework underpinning how each impact characteristic influenced ball flight characteristics. More consistent performing players produced less kick-to-kick variability in their impact characteristics, while lower kick accuracy was due to errors produced in the combination of impact characteristics. In conclusion, foot-ball impact characteristics were influential to impact efficiency, ankle plantarflexion, ball flight characteristics, and kicking accuracy.

In Australian Rules football (AF), kick skill performance involvements, notably the drop punt, are statistically strong contributors towards team match success. The start of a National women’s AF competition (AFLW) in 2017 created opportunity for new knowledge to be established around the characteristics of AFLW athletes’ skilled performances. Using developments in inertial measurement unit (IMU) technology and analytical methods, this thesis takes a multi-disciplinary approach to analysing AFLW skilled performances and subsequently proposes a concept of a semi-automated AF kick type classification system for skill monitoring in an applied environment. Specifically, the thesis: 1) evaluates the research literature on machine learning for sport-specific movement recognition, 2) determines the importance of AFLW athlete skilled performance indicator contributions during match play, 3) defines AFLW drop punt kick kinematics, and 4) evaluates AF kick type classification models using IMUs as a proof-of-concept to support further developments in the area. Understanding analytical methods previously implemented with IMU or computer vision data and the evaluated capacity of these models in sport-specific movement recognition literature, is important in the adaptation for, and application towards new problems in sport. The first part of this thesis focuses on the experimental set-up, data pre-processing, and model development methods in the relevant literature on recognition of sport-specific movements in-field using IMU or computer vision technology. Of the 52 studies identified, 29 used IMUs, 22 used vision data and one study integrated both technologies. Supervised machine learning models were the dominant approach for developing sport specific movements recognition systems. Although nine studies implemented deep learning algorithms which comparatively indicated superior results to machine learning models, and demonstrated the advantages and potential of these model types. This study also highlights the importance of considering the model and overall system development in relation to the targeted sports movement(s) when progressing future research in the field. The applications of IMUs for sport skill recognition and subsequently performance analysis in-situation demonstrated in the literature may be beneficial in AF. As AF matches are technically skilled in nature, this thesis sought to investigate relationships of AFLW athlete skill performances in explaining team quarter and match success which knowledge was previously limited. Performance indicator distributions in explaining match quarter outcomes show the strongest skilled contributions from key high performing athletes, and the overall team strongest features related to kick performance indicators. Considering the importance of the kick in AF, the thesis then continued to define the kinematics of AFLW athlete’s drop punt kicks across leg preferences which was unknown. Several key differences from men’s AF kicks were found, also, women’s kick movement patterns quantified which is beneficial for specific coaching practices. Developments in IMU use for sport-specific movement recognition through machine learning models demonstrate advantages in sporting performance analysis applications. In the final section, these technological developments are investigated for the concept of a semi-automated AF kick monitoring system using IMUs. The work is applied in an AFLW training environment as a unique study for capturing the importance kick skill performance towards team match success and differentiation from men’s AF kick biomechanics. The findings indicate that kick types can be sufficiently distinguished from one another which creates scope for further applied work in AF training sessions. Overall, the work in this thesis is the first to establish the biomechanical characteristics of elite women’s AF kicks and enhances the knowledge of skilled performances in the AFLW. Furthermore, it is the first to implement IMUs for on-field AF kick recognition. Increasing automation in sport-specific movement recognition can be applied in AF kick skill monitoring; particularly as a unique forefront in AFLW sport science applications towards kick performance improvement. The methods used and findings of this thesis can also be transferred to other elite women’s team sporting leagues involving kicking actions such as Rugby and Gaelic football.

Drop punt kicking is considered the most important skill in Australian Football (AF) and impact is the most crucial element in performance. Previous research on impact in AF kicking has used pre and post ball contact data to calculate average foot-ball characteristics but there has been no evaluation of the phase during impact. Important information has been found in soccer performing this analysis and importantly some parameters such as force have been found to be two times average force. The aims of the study were to evaluate foot and ball velocity during impact and compare impact differences between distance and accuracy kicks. Eleven elite AF players were fitted with reflective markers on the kick leg and foot and kicked drop punt kicks with their preferred foot attempting to hit a 20m target (accuracy) and performing maximal distance kicks. Two-dimensional 4000Hz video recorded impact and from this footage, shank, foot and ball markers were tracked using ProAnalyst software. Distance kicks displayed significantly larger foot and ball velocity, contact distance, average and peak force, work and impulse while accuracy kicks exhibited larger contact time and greater plantarflexion at the ankle throughout impact. Foot to ball ratio did not differ between accuracy and distance kicks. The profile of impact was successfully described where many similarities with soccer kicking existed. It was suggested that throughout the deformation phase of impact foot is applying force to the ball while during the reformation phase ball was applying force to the foot. Peak deformation did not occur at the crossover point of foot and ball velocity as seen in soccer kicking. Active changes in ankle angle were exhibited as accuracy kicks displayed a greater range of movement. The results of distance kicking suggested that decreasing ankle rigidity led to increases in performance which is in contrast to previous literature.

This chapter focuses on how the new doctrines and technologies developed after Vietnam were put to the test in Iraq in 1991. Operation Desert Storm was based on extensive use of the technologies and strategies that the Fighter Mafia and the Reformers had opposed. John Boyd and his fellow Reformers had predicted a future war in which large fleets of aircraft battled for air superiority in ferocious dogfights. They argued that this hypothetical scenario demanded smaller, simpler aircraft, relying on the flying skill of the individual pilot. Furthermore, they assumed that the large all-weather radar of the F-15 Eagle was unnecessary and made it vulnerable. The Reformers also assumed that missiles would be useless. However, the skies over Iraq in 1991 debunked these assumptions as radar played a key role in gaining and maintaining air superiority; air-to-air combat did not involve the types of aircraft that the Reformers thought it should; and according to Western intelligence sources, Iraqi fighter pilots were poorly trained and inexperienced. For many observers, the Gulf War proved the Reformers wrong. On the other hand, the Reformers themselves took it as a validation. Most of the Reformers' ideas went untested in the Gulf War. What is clear is that the Reformers' vision was not applicable to all wars.

This chapter focuses on Bob Thomas's experience of training camp at Lake Forest in July of 1976. A second harvest of draft picks and free agents joined Jack Pardee's evolving ranks. Brought into camp to compete with Thomas was free agent kicker Rick Danmeier from the University of Sioux Falls, who had received a tryout with Minnesota as a rookie the previous year. By the time of the last exhibition game of the season on September 3 in Washington, Thomas had put an indelible stamp on the kicking job. The young Bears were ready to conquer new territory and got off to a strong start in 1976. However, abuse continued to be delivered toward Thomas from the segment of fans who chose to focus on the memory of the Oakland game. Thomas generally managed to ignore the mistreatment, as he looked forward to a long NFL tenure yet to come. It did not prevent him, however, from making plans for a second career. The chapter then looks at his enrolment for law school at Loyola University in Chicago.

Homeless people are among the most marginalized in the UK, where homelessness—or vagrancy—has been ‘the classic crime of social status, the social crime par excellence’ since the 1349 Vagrancy Statute sought to deal specifically with the ‘wandering poor’. People who are homeless are those ‘swept into the vortex of political practices, socioeconomic assumptions, values and expectations bearing on the phenomenon of “home” as we understand it today and negatively put on “homelessness”’. But regardless of how they are legally and politically defined, homeless people have to exist somewhere. They have to find shelter, food, and other resources. They have the same physical, bodily and emotional needs as everyone else. It isn’t pretty or polite but homelessness has been documented in the UK for over eight hundred years, and it continues to shape and inform the world around us. Homelessness leaves material traces and a rich intangible heritage in the form of lexicon, folklore, and memories, making it an appropriate subject for archaeological study. The practice of applying archaeological approaches to the contemporary world—or, contemporary archaeology—is a comparatively recent development in the history of the discipline of archaeology. As Graves-Brown, Harrison, and Piccini note in the introduction to their edited volume, the contemporary archaeologist’s subject matter is ‘not just the buried remains of past societies, but as often as not the circumstances of living people’. An important question to bear in mind is this: For whom do archaeologists practise archaeology and what right do they have to make claims about the past or decisions about what should happen to data in the future? Archaeologists have a moral responsibility to ‘bear witness’ to other human lives regardless of whether the people concerned have been dead for thousands of years or they stand beside us, alive and kicking. To undertake an archaeological investigation of contemporary homelessness is to consider the ways in which homeless memory is constituted through objects (places and landscapes) as a form of bearing witness to the human experiences to which they testify.

A storm blew up in Berlin in 1989 not far from the spot where much of this book was written. It all began in a small way with people attending weekly services at the local church to pray for peace. When the communist East German regime used violence to break up a demonstration, the church became a refuge for hundreds, and later thousands, of people. The society in question had grown rigid. To express it in the language of complexity, the social network became so tautly stretched that any shock was readily propagated throughout the system. The police repeatedly beat up the churchgoers, but the multitude failed to respond in the expected way. Instead of kicking and punching, they prayed and sang. They didn’t display the anticipated logic of action and reaction, eventually causing the police to withdraw in confusion. The demonstrators created positive feedback, and as a result, the mass of people grew even bigger. “We were prepared for everything but not for candles,” a police commander later commented. The protests also confused the GDR’s inflexible leaders. At the peak of the protests, an East German minister declared that citizens would be permitted to travel to the West. The chaos that ensued was so great that historians are still trying to unravel the precise sequence of events. On the brink of a critical transition, old forces dissipate and unpredictable movements can occur. This is a typical example of a small movement that can lead to much greater things, as we have also seen in other complex systems. Tens of thousands of people laid siege to the Wall. Exactly who eventually decided to raise the barriers has been lost in the fog of history. It was most likely a low-ranking officer at a border crossing who was no longer able to cope with the mass of people. To ease the pressure, he allowed a few citizens through the barrier. The effect was to throw gasoline onto the fire or, to put it another way, to create positive feedback that tipped the situation into transition. Within minutes, the crowd could no longer be restrained.

The starting field position is often a deciding factor in an American football game. In the case of a defensive stop, a kick, known as a punt, is used to give the receiving team a field position that is more advantageous to the kicking team when possession changes. The goal of the punter is to kick the ball along a desired flight path, where a delicate balance between the distance traveled before impact, hang time in the air, and the distance traveled after bouncing is favorable for the kicking team. However, the punter has only imprecise control over the initial conditions, such as the angular velocity, linear velocity, and orientation of the football. Due to the highly nonlinear behavior of the football, from aerodynamic and impact forces, even small changes in initial conditions can produce large changes in the final position of the football, but there may be regions of initial conditions with relatively consistent results. If punters could target such large contiguous regions of initial conditions with desirable football paths, they could improve their chances of successful kicks. For nonlinear systems, basins of attraction diagrams are often used to graphically display the initial conditions that lead to different final attractors. In this case, the regions of initial conditions that lead to a desirable final field position can be grouped and shown graphically. A numerical simulation program was developed including models for aerodynamic flight and bouncing of the irregularly shaped football. The flight model used fourth order Runge-Kutta integration of the equations of motion of the football, including gravitational and aerodynamic forces and moments with empirical lift, drag, and yaw coefficients in three dimensions. The bounce model was based on an empirical two-dimensional coefficient of restitution model that was published in the literature. The behavior of a football in flight and during bouncing was simulated for a range of initial angular velocities and launch angles, and the characteristics of the flight paths were analyzed. The characteristics of some regions of initial conditions were relatively sensitive to small changes, while other regions were relatively uniform. This shows that this approach, with a quantitatively accurate bounce model, could be practically applied to develop a guide for punters to optimize their kicks. With such a guide and sufficient practice, punters could select and target the larger regions of initial conditions that produced desirable behavior, which would improve their chances of successful punts.