Movement variability in the golf swing

Traditionally, golf biomechanics has focused upon achieving consistency in swing kinematics and kinetics, whilst variability was considered to be noise and dysfunctional. There has been a growing argument that variability is an intrinsic aspect of skilled motor performance and plays a functional role. Two types of variability are described: 'strategic shot selection' and 'movement variability'. In 'strategic shot selection', the outcome remains consistent, but the swing kinematics/kinetics (resulting in the desired ball flight) are free to vary; 'movement variability' is the changes in swing kinematics and kinetics from trial to trial when the golfer attempts to hit the same shot. These changes will emerge due to constraints of the golfer's body, the environment, and the task. Biomechanical research has focused upon aspects of technique such as elite versus non-elite kinematics, kinetics, kinematic sequencing, peak angular velocities of body segments, wrist function, ground reaction forces, and electromyography, mainly in the search for greater distance and clubhead velocity. To date very little is known about the impact of variability on this complex motor skill, and it has yet to be fully researched to determine where the trade-off between functional and detrimental variability lies when in pursuit of enhanced performance outcomes.     

The influence of short-term fixture congestion on position specific match running performance and external loading patterns in English professional soccer

The aim of the current study was to investigate positional specific physical performance and external load responses to short term fixture congestion in English professional soccer. A total of 515 match observations were categorised as G1: the first game in a week with >4 days following a previous game, G2: the second game in a week played <4 days since G1, and G3: the third game in a week played with <4 days between each of the previous games. Global positioning system and accelerometer-based metrics were partitioned into fifteen-minute epochs. These data were then analysed using a linear mixed model to assess both the within and between game positional differences. Total, low-intensity (<4.0 m·s^?1), medium-intensity (MID; 4.0–5.5 m·s^?1), and sprint distance (>7.0 m·s^?1) were significantly different across games. No between game positional differences were identified; however, within match position specific differences were observed for measures of MID and HID. No significant differences were evident for accelerometer derived metrics between games or across positions. The current data suggests that the use of fifteen minute within game epochs enables the detection of alterations in physical output during congested schedules. The observed within game positional differences has implications for player specific conditioning and squad rotation strategies.     

An investigation of the in-game behaviours of professional, top-level youth soccer coaches

Although research into coaching has increased considerably during the last two decades, an area of neglect has been that of the professional youth coach. The aim of this study was to investigate the working behaviours of six top-level professional soccer coaches. Data were collected using a modified version of the Arizona State University Observation Instrument and semi-structured interviews. The triangulation of the data ensured that both the "what" and the "why" of the coaches' behaviour were considered. Results revealed a conscious and well thought out pattern of behaviour: silently monitoring, interspersed with clips of instruction coupled with praise and encouragement. The interviews revealed three themes underpinning this behaviour: developing game understanding, support and encouragement, and coaches' role and influences. The use of silence was the largest single behaviour, the efficacy of which was considered in light of theories of experiential and discovery learning.     

网络技术:改进数据访问的性能

谈起网格,肯定要涉及数据、信息以及如何在分布式的基础设施上对二者进行智能化处理.而这个时候似乎更让大家着迷的是网格的计算能力,而数据在以计算为重点的网格中仅能占据次席.