Determinants of the half-turn with the ball in sub-elite youth soccer players

We explored the biomechanics of the 180° change-of-direction with the ball (half-turn) in soccer. We aimed at identifying movement strategies which enhance the players’ half-turning performance, by characterising technique kinematics and understanding the structure of biomechanical and anthropometrics variables. Ten Under-13 sub-elite male players were recorded with an optoelectronic motion analyser while performing a 5-m straight dribbling followed by a half-turn with the sole. Joints kinematics differences between faster and slower trials were found in support-side hip rotation, driving-side hip adduction, trunk flexion and rotation, and arms abduction. To unveil the data-set structure, a principal component (PC) analysis and a stepwise linear discriminant analysis were performed using 30 biomechanical parameters and four anthropometric variables for each trial. Seven retained PCs explained 79% of the overall variability, featuring combinations of original variables that help in understanding the factors facilitating fast half-turns: keeping short steps, minimising lateral and forward body movements, and centre-of-mass lowering, even with ample lower limbs ranges of motion (RoM); abducting the upper limbs while limiting trunk flexion and pelvic inclination RoM. Balance and task-constrained exercises may be proposed to improve this technique. Moreover, a quantitative knowledge of the movement structure could give coaches objective insights to better instruct young players.     

Fundamental aerodynamics of the soccer ball

When the boundary layer of a sports ball undergoes the transition from laminar to turbulent flow, a drag crisis occurs whereby the drag coefficient (C _d) rapidly decreases. However, the aerodynamic properties and boundary-layer dynamics of a soccer ball are not yet well understood. In this study we showed that the critical Reynolds number (Re _crit) of soccer balls ranged from 2.2 × 10⁵ to 3.0 × 10⁵. Wind-tunnel testing, along with visualisation of the dynamics of the boundary layer and the trailing vortex of a ball in flight, demonstrated that both non-spinning and spinning (curved) balls had lowC _d values in the super-critical region. In addition, theRe _crit values of the soccer balls were lower than those of smooth spheres, ranging from ∼ 3.5 × 10⁵ to 4.0 × 10⁵, due to the effects of their panels. This indicated that the aerodynamic properties of a soccer ball were intermediate between those of a smooth ball and a golf ball. In a flow visualisation experiment, the separation point retreated and theC _d decreased in a super-critical regime compared with those in a sub-critical regime, suggesting a phenomenon similar to that observed in other sports balls. With some non-spinning and spinning soccer balls, the wake varied over time. In general, the high-frequency component of an eddy dissipated, while the low-frequency component increased as the downstream vortex increased. The causes of the large-scale fluctuations in the vortex observed in the present study were unclear; however, it is possible that a ‘knuckle-ball effect’ of the non-rotating ball played a role in this phenomenon.     

得分进攻活动获得球阶段的分析

采用文献资料，调查访谈和数理统计等方法对得分进攻活动获得球阶段进行了分析，发现其存在的特点和规律，并对男子足球运动和女子足球运动间的异同点进行了较为详细的探讨。     

The influence of situational variables on ball possession in the English Premier League

Abstract

The aims of this study were twofold: (1) to examine the influence of situational variables on ball possession in elite soccer and (2) to quantify the variables that discriminate between high or low percentage ball possession teams (HPBPT and LPBPT) across different playing positions. Match performance data were collected from English Premier League matches using a multiple-camera system. Data were examined using linear regression, a 2 × 5 factorial analysis of variance and discriminant analysis. Playing against weak opposition was associated with an increase (P < 0.01) in time spent in possession while playing away decreased (P < 0.01) the time spent in possession by ~3%. Possession was increased (P < 0.01) when losing than winning or drawing. Finally, the better the ranking of a team, the higher (P < 0.01) the time spent in possession. The playing position effect was significant for all variables (P < 0.05); however, there were only interactions with team ball possession in some cases. The discriminant analysis identified functions for all five playing positions (P < 0.01). The variables that discriminated performance between HPBPT and LPBPT were different for various playing positions, although the number of successful passes was the most common discriminating variable. The results demonstrate that HPBPT and LPBPT developed different possession strategies during matches and that selected variables such as successful passes were identified to explain these data trends across various playing positions. Combinations of variables could be used to develop a probabilistic model for predicting time spent in possession by teams.     

Modelling the flight of a soccer ball in a direct free kick

This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m·s^?1, the ball's initial elevation must be constrained between 16.5° and 17.5° and the ball kicked with almost perfect sidespin.     

A mathematical analysis of the motion of an in-flight soccer ball

In this paper, an analytical and numerical study of the three-dimensional equations describing the motion through the air of a spinning ball is presented. The initial analysis involves constant drag coefficients, but is later extended to involve drag varying with the spin ratio. Excellent agreement is demonstrated between numerical, analytical and experimental results. The analytical solution shows explicitly how the ball’s motion depends on parameters such as ball roughness, velocity and atmospheric conditions. The importance of applying three-dimensional models, rather than two-dimensional approximations, is demonstrated.     

Modelling the flight of a soccer ball in a direct free kick

This study involved a theoretical and an experimental investigation of the direct free kick in soccer. Our aim was to develop a mathematical model of the ball's flight incorporating aerodynamic lift and drag forces to explore this important 'set-play'. Trajectories derived from the model have been compared with those obtained from detailed video analysis of experimental kicks. Representative values for the drag and lift coefficients have been obtained, together with the implied orientation of the ball's spin axis in flight. The drag coefficient varied from 0.25 to 0.30 and the lift coefficient from 0.23 to 0.29. These values, used with a simple model of a defensive wall, have enabled free kicks to be simulated under realistic conditions, typical of match-play. The results reveal how carefully attackers must engineer the dynamics of a successful kick. For a central free kick some 18.3 m (20 yards) from goal with a conventional wall, and initial speed of 25 m x s(-1), the ball's initial elevation must be constrained between 16.5 degrees and 17.5 degrees and the ball kicked with almost perfect sidespin.     

The effect of surface geometry on soccer ball trajectories

Two different measurement techniques are used to examine the effect of surface geometry on soccer ball trajectories. Five professional players are observed using high-speed video when taking curling free kicks with four different soccer balls. The input conditions are measured and the average launch velocity and spin are found to be approximately 24 m/s and 106 rad/s. It is found that the players can apply more spin (~50%) on average to one ball, which has a slightly rougher surface than the other balls. The trajectories for the same four balls fired at various velocities and spin rates across a sports hall using a bespoke firing device are captured using high-speed video cameras, and their drag and lift coefficients estimated. Balls with more panels are found to experience a higher lift coefficient. The drag coefficient results show a large amount of scatter, and it is difficult to distinguish between the balls. Using the results in a trajectory prediction programme it is found that increasing the number of panels from 14 to 32 can significantly alter the final position of a 20 m-curling free kick by up to 1 m.     

Finite element modelling and experimental study of oblique soccer ball bounce

In this study, we develop a finite element model to examine the oblique soccer ball bounce. A careful simulation of the interaction between the ball membrane and air pressure in the ball makes the model more realistic than analytical models, and helps us to conduct an accurate study on the effect of different parameters on a bouncing ball. This finite element model includes a surface-based fluid cavity to model the mechanical response between the ball carcass and the internal air of the ball. An experimental set-up was devised to study the bounce of the ball in game-relevant impact conditions. Ball speed, angle, and spin were measured before and after the bounce, as well as ball deformation and the forces during the impact. The finite element model has been validated with three different sets of data, and the results demonstrate that the finite element model reported here is a valuable tool for the study of ball bounce. After validation of the model, the effect of the friction coefficient on soccer ball bounce was studied numerically. Simulation results show that increasing the friction coefficient may result in reversal of the horizontal impact force.     

A dynamic model of the head acceleration associated with heading a soccer ball

This study develops a dynamic model of head acceleration, which incorporates physiologically related neck muscle contributions, to further the understanding of the mechanical behaviour of the head-neck system during soccer heading. An inverted pendulum is combined with a linear visco-elastic element to model the head-neck system following a half-sine input force. Model parameter values were varied to obtain agreement with previously published experimental data (Naunheimet al., 2003), and were subsequently compared to literature values. The model predicted the same mechanical angular kinematics as observed experimentally both during and post impact. The greatest acceleration was in the anterior direction at the instant the ball left the head, attributed to the elastic stiffness of the neck musculature. The head-neck stiffness and damping coefficients determined from the model (350 N m rad^-1 and 4 N m s rad^-1, respectively) were similar to those reported elsewhere when subjects were asked to resist maximally. The model may be subsequently used to investigate differences in technique and ability with respect to the salient model parameters to further our biomechanical understanding of soccer heading.     

Three-dimensional kinematic correlates of ball velocity during maximal instep soccer kicking in males

Abstract

Achieving a high ball velocity is important during soccer shooting, as it gives the goalkeeper less time to react, thus improving a player's chance of scoring. This study aimed to identify important technical aspects of kicking linked to the generation of ball velocity using regression analyses. Maximal instep kicks were obtained from 22 academy-level soccer players using a 10-camera motion capture system sampling at 500 Hz. Three-dimensional kinematics of the lower extremity segments were obtained. Regression analysis was used to identify the kinematic parameters associated with the development of ball velocity. A single biomechanical parameter; knee extension velocity of the kicking limb at ball contact Adjusted R² = 0.39, p ≤ 0.01 was obtained as a significant predictor of ball-velocity. This study suggests that sagittal plane knee extension velocity is the strongest contributor to ball velocity and potentially overall kicking performance. It is conceivable therefore that players may benefit from exposure to coaching and strength techniques geared towards the improvement of knee extension angular velocity as highlighted in this study.     

足球运动踢球腿摆动阶段的不同时相运动特征

运用生物力学手段对5名高水平足球运动员摆动腿进行研究发现:根据摆动腿环节摆动顺序与环节摆动速度相结合的方法可将其划分为用力蹬伸、主动后摆、大腿前摆、小腿前摆,脚触球5个阶段.其中,用力蹬伸阶段是不可忽视的重要阶段之一,主动后摆阶段摆动腿应在不影响前摆速度的前提下尽力后摆;大腿前摆阶段摆动腿应在大腿摆到一定幅度时进行积极制动,摆动幅度不宜过大;小腿前摆阶段摆动腿除了膝关节的积极制动外还应主动施力.     

我国足球产业化进程中足球精神的缺失

20世纪90年代以来,我国足球产业化逐步展开,并得到了比较稳定的发展。但是在足球产业化的同时,暴露出足球精神严重缺失的问题,包括运动员体育精神的沦丧,裁判等工作人员公平公正精神的模糊与球迷缺乏健康向上、理智成熟的素养。我国足球精神的缺失主要由于功利主义思想泛滥和精神文明建设的松懈。     

Goalkeeping in the soccer penalty kick

The goalkeeper’s difficulty in the soccer penalty kick originates from the extreme spatiotemporal constraints of the situation. The present review claims that the current understanding is biased toward attributing a goalkeeper’s success in saving a penalty kick to perceptual–cognitive skill. To investigate the goalkeeper’s skill, researchers have often adopted video tasks. In doing so, they studied perceptual skill in isolation from action. We use affordance-based control theory to propose an alternative understanding and research methodology. We argue that goalkeepers in the penalty kick situation should regulate their actions in ways that sustain the perception of stoppability. To capture this, we outline the building blocks for a required lateral velocity model, in which the goalkeepers’ required actions are scaled to their maximum capabilities. In doing so, we provide new directions for research.     

现代足球的民族精神与中国足球的文化缺失

对现代足球与民族精神的关系以及我国足球发展中存在的问题进行了分析研究。结果认为,民族精神是支持现代足球发展的重要社会文化条件,传承与弘扬民族精神是现代足球的基本价值取向;当前我国足球的发展存在着深刻的文化缺失问题,关于优秀的传统文化精神以及改革时代的民族精神的缺失则是我国足球文化建设中的突出问题。     

Concussion management in soccer

Brain injuries in sports drew more and more public attentions in recent years. Brain injuries vary by name, type, and severity in the athletic setting. It should be noted, however, that these injuries are not isolated to only the athletic arena, as non-athletic mechanisms (e.g., motor vehicle accidents) are more common causes of traumatic brain injuries (TBI) among teenagers. Notwithstanding, as many as 1.6 to 3.8 million TBI result from sports and recreation each year in the United States alone. These injuries are extremely costly to the global health care system, and make TBI among the most expensive conditions to treat in children. This article serves to define common brain injuries in sport; describe their prevalence, what happens to the brain following injury, how to recognize and manage these injuries, and what you can expect as the athlete recovers. Some return-to-activity considerations for the brain-injured athlete will also be discussed.     

On winning the penalty shoot-out in soccer

The penalty shoot-out is used to break tied games in the knock-out stages of soccer competition. The shoot-out, which consists of an alternating series of penalty kicks, is won by the team with the highest goal tally after n kicks per team (n = 5). In the event of a tie after five penalty kicks each, the shoot-out progresses to 'sudden death' by increasing n in iterative fashion (i.e. n = n + 1) until one team obtains a higher goal tally than the other after an equal number of kicks per team. The team to strike first is determined at the end of extra time by the toss of a coin. As each on-field player can be awarded only a single penalty kick, the line-up order in which the penalty kicks are taken allows for the possibility of tactical influence on the final outcome. Consequently, we report a probability analysis of the penalty shoot-out in soccer from which we identify the following pre- and post-game strategies. The best five ranked penalty takers from the on-field players should be assigned to the first five penalty kicks in their reverse order of ability. That is, the fifth best penalty taker should take the first penalty kick, the fourth best penalty taker should take the second penalty kick, and so on. In the event of sudden death, the next highest ranked on-field player should be assigned to the next penalty kick until the shoot-out ends. For this tactic to be successful, players should be ranked a priori on their penalty-taking ability. Similarly, goalkeepers should be ranked a priori on their penalty-stopping ability. These findings indicate that the tactical substitution of on-field players for higher ranked penalty takers, including higher ranked penalty stoppers (i.e. goalkeepers), with a view to an impending penalty shoot-out should be given due consideration. These results are of practical importance in that they are shown to maximize the likelihood of winning the penalty shoot-out under certain initial conditions.     

On winning the penalty shoot-out in soccer

The penalty shoot-out is used to break tied games in the knock-out stages of soccer competition. The shoot-out, which consists of an alternating series of penalty kicks, is won by the team with the highest goal tally after n kicks per team (n = 5). In the event of a tie after five penalty kicks each, the shoot-out progresses to 'sudden death' by increasing n in iterative fashion (i.e. n = n + 1) until one team obtains a higher goal tally than the other after an equal number of kicks per team. The team to strike first is determined at the end of extra time by the toss of a coin. As each on-field player can be awarded only a single penalty kick, the line-up order in which the penalty kicks are taken allows for the possibility of tactical influence on the final outcome. Consequently, we report a probability analysis of the penalty shoot-out in soccer from which we identify the following pre- and post-game strategies. The best five ranked penalty takers from the on-field players should be assigned to the first five penalty kicks in their reverse order of ability. That is, the fifth best penalty taker should take the first penalty kick, the fourth best penalty taker should take the second penalty kick, and so on. In the event of sudden death, the next highest ranked on-field player should be assigned to the next penalty kick until the shoot-out ends. For this tactic to be successful, players should be ranked a priori on their penalty-taking ability. Similarly, goalkeepers should be ranked a priori on their penalty-stopping ability. These findings indicate that the tactical substitution of on-field players for higher ranked penalty takers, including higher ranked penalty stoppers (i.e. goalkeepers), with a view to an impending penalty shoot-out should be given due consideration. These results are of practical importance in that they are shown to maximize the likelihood of winning the penalty shoot-out under certain initial conditions.     

Measuring the effectiveness of offensive match-play in professional soccer

Abstract

The broader measures of offensive effectiveness, such as scoring opportunities and shots at goal, are commonly used as an alternative to goals scored due to the naturally low probability of scoring (about 1%) in soccer match-play. These measures may enable soccer practitioners to objectively see behind single match results, which are often influenced by chance. The purpose of this study was to examine the relationship between broader measures (scoring opportunities and score box possessions) and the ultimate measure (goals scored) of offensive effectiveness. We analysed data from videotapes of 163 of 182 (90%) matches played in the Norwegian men's professional league during the 2004 season. Multiple logistic regression analyses showed very similar results when comparing the effectiveness of different offensive tactics, regardless of which outcome was used. For example, counterattacks were more effective than elaborate attacks in producing goals (odds ratio OR=2.07, 95% confidence interval: 1.40 to 3.05), scoring opportunities (OR=2.30, 95% confidence interval: 1.28 to 4.15), and score box possessions (OR=2.12, 95% confidence interval: 1.39 to 3.25). The receiver-operating characteristic function statistical procedure was used to examine the association between each of the three measures of offensive effectiveness: scoring opportunities, score box possessions, and goals scored. No significant difference was observed between the area under the curve (AUC) for the broader measures (scoring opportunities and score box possessions) and the ultimate measure (goals scored) of offensive effectiveness. The 95% confidence interval of the AUC for both scoring opportunities (0.74–0.84) and score box possessions (0.68–0.76) includes the AUC for goals scored (0.74). Thus, the results are very similar regardless of which outcome measure for offensive effectiveness is used. This indicates that scoring opportunities and score box possessions (shooting opportunities) can be used as a proxy for goals scored when comparing the effectiveness of different playing tactics in soccer. Compared with goals scored, using scoring opportunities or score box possessions requires smaller match samples for meaningful analyses, and may therefore be more feasible alternatives.     

试论中国足球球迷文化

运用社会学、文化学、哲学的理论与方法，从历史背景、民族心理、体育文化、体育产业等多角度、多方位全面系统地研究球迷这一业余体育团体文化，为促进我国群众性体育团体开展体育文化创建工作提供参考意见。