Effect of expertise on butterfly stroke coordination

The aim of this study was to compare the arm-to-leg coordination in the butterfly stroke of three groups of male swimmers of varying skill (10 elite, 10 non-elite, and 10 young swimmers) at four race paces (400-m, 200-m, 100-m, and 50-m paces). Using qualitative video analysis and a hip velocity-video system (50 Hz), key events of the arm and leg movement cycles were defined and four-point estimates of relative phase were used to estimate the arm-to-leg coordination between the propulsive (pull and push of arms and downward movement of leg undulation) and non-propulsive phases (entry, catch, and recovery of arms and upward movement of leg undulation). With increasing race pace, the velocity, stroke rate, and synchronization between the arm and leg key points also increased, indicating that velocity and stroke rate may operate as control parameters. Finally, these changes led to greater continuity between the propulsive actions, which is favourable for improving the swim velocity, suggesting that coaches and swimmers should monitor arm-to-leg coordination.     

Thoracoabdominal breathing motion pattern and coordination of professional ballet dancers

Ballet training includes exercises of high and moderate intensities, which require breathing control for a good performance. This study describes the thoracoabdominal motion of professional dancers and compares the breathing patterns between professional dancers and non-dancers. Participants of this study were four male and four female (30.33 ± 4.64 years) professional dancers and four male and four female (22.75 ± 1.49 years) non-dancers. The participants executed two breathing manoeuvres while sitting motionless: quiet breathing (QB) and vital capacity (VC). The 3D coordinates of 32 retro-reflective markers positioned on the trunk were used to calculate the volume of the superior thorax, inferior thorax and abdomen. Principal component analysis was applied in the volume variation of each trunk compartment to search for dominant independent variables in a breathing motion pattern. The correlation coefficient was calculated to verify the coordination between the compartments during the breathing manoeuvres. A predominance of the superior thorax or abdomen movement was found in both groups. The professional ballet dancers have an efficient breathing pattern and maintain the same breathing pattern in QB and VC manoeuvres. On the other hand, the non-dancers group showed relevant changes of the breathing pattern to respond to a greater breathing effort, like in VC.     

Effect of hand paddles and parachute on butterfly coordination

This study investigated the effects of hand paddles, parachute and hand paddles plus parachute on the inter-limb coordination of butterfly swimming. Thirteen male swimmers were evaluated in four random maximal intensity conditions: without equipment, with hand paddles, with parachute and with hand paddles + parachute. Arm and leg stroke phases were identified by 2D video analysis to calculate the total time gap (T1: time between hands’ entry in the water and high break-even point of the first undulation; T2: time between the beginning of the hand’s backward movement and low break-even point of the first undulation; T3: time between the hand’s arrival in a vertical plane to the shoulders and high break-even point of the second undulation; T4: time between the hand’s release from the water and low break-even point of the second undulation). The swimming velocity was reduced and T1, T2 and T3 increased in parachute and hand paddles + parachute. No changes were observed in T4. Total time gap decreased in parachute and hand paddles + parachute. It is concluded that hand paddles do not influence the arm-to-leg coordination in butterfly, while parachute and hand paddles + parachute do change it, providing a greater propulsive continuity.     

The influence of live- vs. video-model presentation on the early acquisition of a new complex coordination

Background: Demonstration is a widely used method in sports teaching and coaching, based on the assumption that it is more beneficial than verbal instructions or trial-and-error methods for skill acquisition. Although in teaching/coaching situations, the demonstration is usually carried out in front of the learners, in a research context, it is most often presented via a video. However, a direct comparison between these two types of model has rarely been undertaken in a motor context.

Purpose: In this study, we aimed to compare the effectiveness of the observation of a live and a videomodel for the early acquisition of a complex judo movement.

Research Design: Participants observed either a live or a videomodel executing the task. After observation, they practised for three minutes taking five trials and then performed it for analysis. This procedure was repeated three times. The form and technique of each participant's execution were evaluated using a technical score.

Main results: The results indicated a significant improvement in the task execution by the end of the practice session. However, this improvement occurred only for the video-model group between the second and third blocks of practice.

Conclusions: The video demonstration seems more effective than the live one for the early acquisition of a completely new complex coordination. This may be due to the simplification of the visual information in the former condition because of its two-dimensionality. This simplification may allow the observer to identify the more key elements that would guide him/her for the subsequent performance of the task.     

Effect of swimming velocity on arm coordination in the front crawl: a dynamic analysis

We examined the preferred mode of arm coordination in 14 elite male front-crawl swimmers. Each swimmer performed eight successive swim trials in which target velocity increased from the swimmer's usual 3000-m velocity to his maximal velocity. Actual swim velocity, stroke rate, stroke length and the different arm stroke phases were then calculated from video analysis. Arm coordination was quantified by an index of coordination based on the lag time between the propulsive phases of each arm. The index expressed the three coordination modes in the front crawl: opposition, catch-up and superposition. First, in line with the dynamic approach to movement coordination, the index of coordination could be considered as an order parameter that qualitatively captured arm coordination. Second, two coordination modes were observed: a catch-up pattern (index of coordination= -8.43%) consisting of a lag time between the propulsive phases of each arm, and a relative opposition pattern (index of coordination= 0.89%) in which the propulsive phase of one arm ended when the propulsive phase of the other arm began. An abrupt change in the coordination pattern occurred at the critical velocity of 1.8 m. s(-1), which corresponded to the 100-m pace: the swimmers switched from catch-up to relative opposition. This change in coordination resulted in a reorganization of the arm phases: the duration of the entry and catch phase decreased, while the duration of the pull and push phases increased in relation to the whole stroke. Third, these changes were coupled to increased stroke rate and decreased stroke length, indicating that stroke rate, stroke length, the stroke rate/stroke length ratio, as well as velocity, could be considered as control parameters. The control parameters can be manipulated to facilitate the emergence of specific coordination modes, which is highly relevant to training and learning. By adjusting the control and order parameters within the context of a specific race distance, both coach and swimmer will be able to detect the best adapted pattern for a given race pace and follow how arm coordination changes over the course of training.     

Effect of swimming velocity on arm coordination in the front crawl: a dynamic analysis

We examined the preferred mode of arm coordination in 14 elite male front-crawl swimmers. Each swimmer performed eight successive swim trials in which target velocity increased from the swimmer's usual 3000-m velocity to his maximal velocity. Actual swim velocity, stroke rate, stroke length and the different arm stroke phases were then calculated from video analysis. Arm coordination was quantified by an index of coordination based on the lag time between the propulsive phases of each arm. The index expressed the three coordination modes in the front crawl: opposition, catch-up and superposition. First, in line with the dynamic approach to movement coordination, the index of coordination could be considered as an order parameter that qualitatively captured arm coordination. Second, two coordination modes were observed: a catch-up pattern (index of coordination?=??8.43%) consisting of a lag time between the propulsive phases of each arm, and a relative opposition pattern (index of coordination?=?0.89%) in which the propulsive phase of one arm ended when the propulsive phase of the other arm began. An abrupt change in the coordination pattern occurred at the critical velocity of 1.8?m?·?s^?1, which corresponded to the 100-m pace: the swimmers switched from catch-up to relative opposition. This change in coordination resulted in a reorganization of the arm phases: the duration of the entry and catch phase decreased, while the duration of the pull and push phases increased in relation to the whole stroke. Third, these changes were coupled to increased stroke rate and decreased stroke length, indicating that stroke rate, stroke length, the stroke rate/stroke length ratio, as well as velocity, could be considered as control parameters. The control parameters can be manipulated to facilitate the emergence of specific coordination modes, which is highly relevant to training and learning. By adjusting the control and order parameters within the context of a specific race distance, both coach and swimmer will be able to detect the best adapted pattern for a given race pace and follow how arm coordination changes over the course of training.     

论新型体育教学模式的构建

通过分析传统体育教学模式的弊端,探索体育教学的新路子,提出构建新型体育教学模式的途径:创建和谐情境,鼓励师生合作学习;鼓励学生积极参与;为学生创设自我表现机会;让学生进行自选练习。     

Effect of string bed pattern on ball spin generation from a tennis racket

Topspin has become a vital component of modern day tennis. Ball-to-string bed and inter-string friction coefficients can affect topspin generation from a racket. The aim of this research was to determine the effect of string bed pattern on topspin generation. Tennis balls were projected onto nine head-clamped rackets with different string bed patterns. The balls were fired at 24 m/s, at an angle of 26° to the string bed normal with a backspin rate of 218 rad/s and outbound velocity, spin and angle were measured. Outbound velocity was shown to be independent of string bed pattern. Outbound angle increased with the number of cross strings, while outbound topspin decreased. In the most extreme case, decreasing the number of cross strings from 19 to 13 increased rebound topspin from 117 to 170 rad/s.     

Dynamics of coordination within elite rowing crews: evidence from force pattern analysis.

For a rowing crew to be successful, the movements of the rowers need to be well coordinated. Because rowers show individual force patterns, they have to adapt their movements when rowing as a crew. In this exploratory study, these hypothesized changes in movement pattern were examined. The force graphs of six elite coxless fours crews were recorded over 11 training runs using strain gauges attached to the oars. A detailed force analysis showed that form differences, but not area differences, between force patterns decreased when force output increased as a result of two different processes. First, increasing force output reduced form differences instantaneously by reducing the individual variation in force patterns. Secondly, the kinaesthetic perception of form differences is easier than that of area differences. This better perception facilitates the adaptation of movement patterns, especially when force output is high.     

新赛制下全年训练周期的安排

通过对传统周期训练理论以及其他一些观点的剖析，认为传统周期训练理论在新赛制下并未过时，仍是全年周期安排的依据。     

Effect of hand paddles and parachute on backstroke coordination and stroke parameters

Hand paddles and parachutes have been used in order to overload swimmers, and consequently increase the propulsive force generation in swimming. However, their use may affect not only kinematical parameters (average speed, stroke length and stroke rate), but also time gaps between propulsive phases, assessed through the index of coordination (IdC). The objective of this study was to assess the effects of hand paddles and parachute use, isolated or combined, on kinematical parameters and coordination. Eleven swimmers (backstroke 50-m time: 29.16 ± 1.43 s) performed four 15-m trials in a randomised order at maximal intensity: (1) without implements (FREE), (2) with hand paddles (HPD), (3) with parachute (PCH) and (4) with hand paddles plus parachute (HPD+PCH). All trials were video-recorded (60 Hz) in order to assess average speed, stroke rate, stroke length, five stroke phases and index of coordination. When average swimming speed was compared to FREE, it was lower in PCH and HPD+PCH, and higher in HPD. Stroke rate decreased in all overloaded trials compared to FREE. The use of hand paddles and parachute increased and decreased stroke length, respectively. In addition, propulsive phase duration was increased when hand paddles were used, and time gaps shifted towards zero (no time gap), especially when hand paddles were combined with parachute. It is conceivable that the combined use of hand paddles and parachute, once allowing overloading both propulsive and resistive forces, provides a specific stimulus to improve muscle strength and propulsive continuity.     

新规则周期下世界女子竞技体操发展格局研究

运用文献资料法、录像观察法和数理统计法,对第39届、40届世界体操锦标赛和第29届奥运会女子体操比赛的团体、全能和单项决赛前8名运动员的比赛情况进行分析,结果表明：在新规则周期里世界女子体操的奖牌分布越来越集中;团体与全能的竞争越来越激烈;单项奖牌呈现出垄断性;各国充分显示出自己的特长。     

Effect of hand paddles and parachute on the index of coordination of competitive crawl-strokers

We investigated the effects of hand paddles and parachute on the relative duration of stroke phases and index of coordination of competitive crawl-strokers. Eleven male-swimmers (age: 21.9 ± 4.5 years; 50-m best time: 24.23 ± 0.75 s) were evaluated in four maximal-intensity conditions: without equipment, with hand paddles, with parachute, and with both hand paddles and parachute. Relative stroke phase duration of each arm, swimming velocity, and stroke rate were analysed from video (60 Hz). The index of coordination was quantified based on the lag time between propulsive phases of each arm, which defined the coordination mode as catch-up, opposition or superposition. The stroke rate decreased in all conditions (P < 0.05) and swimming velocity decreased with parachute and with paddles + parachutes (P < 0.05). The coordination mode changed from catch-up in free swimming (-2.3 ± 5.0%) to opposition with paddles (-0.2 ± 3.8%), parachute (0.1 ± 3.1%), and paddles + parachute (0.0 ± 3.2%). Despite these variations, no significant differences were observed in relative duration of right and left arm-stroke phases, or in index of coordination. We conclude that the external resistances analysed do not significantly influence stroke phase organization, but, as a chronic effect, may lead to greater propulsive continuity.     

构建适应"新课程标准"的体育师资培养模式管见

从基础教育改革和新课程标准的实施对高师体育教育专业人才培养的期望和要求出发,分析了当前体育教育专业人才培养中面临的困惑,并提出了构建适应新课程标准的新的人才培养模式的思路。     

以建构主义教育观建构体育教学模式初探

从建构主义教育观出发,分析学校体育教学过程的模式及其特点,提出了斩新的学生观、学习观、教师观。     

Effect of swim speed on leg-to-arm coordination in unilateral arm amputee front crawl swimmers

The aim of this study was to examine the effect of swimming speed on leg-to-arm coordination in competitive unilateral arm amputee front crawl swimmers. Thirteen well-trained swimmers were videotaped underwater during three 25-m front crawl trials (400 m, 100 m and 50 m pace). The number, duration and timing of leg kicks in relation to arm stroke phases were identified by video analysis. Within the group, a six-beat kick was predominantly used (n = 10) although some swimmers used a four-beat (n = 2) or eight-beat kick (n = 1). Swimming speed had no significant effect on the relative duration of arm stroke and leg kick phases. At all speeds, arm stroke phases were significantly different (P < 0.05) between the affected and unaffected sides. In contrast, the kicking phases of both legs were not different. Consequently, leg-to-arm coordination was asymmetrical. The instant when the leg kicks ended on the affected side corresponded with particular positions of the unaffected arm, but not with the same positions of the affected arm. In conclusion, the ability to dissociate the movements of the arms from the legs demonstrates that, because of their physical impairment, unilateral arm amputee swimmers functionally adapt their motor organisation to swim front crawl.     

Effect of environmental constraints on multi-segment coordination patterns during the tennis service in expert performers

The aims of this study were to examine the effect of different environmental constraints on kinematic multi-segment coordination patterns during the service and its coordination with service time variability. Ten expert tennis players (Age: 34.1 ± 5.3) volunteered to take part in this study. Participants served 30 times in 3 different conditions: control, target and opposition. The order of conditions was counterbalanced between participants. A wireless 3D motion capture system (STT Co, Spain) was used to measure 7 joint motions, with a 17 degrees of freedom biomechanical model created to capture the entire service action. Results of the principal component analysis showed that 4 synergies were created; however, their roles were changed relative to the perception of the environment. The results of repeated-measures analysis of variance did not show any significant difference on total variance and individual principal components between conditions; however, one synergy pattern significantly predicted the service time variability in both control and opposition conditions. In conclusion, the findings demonstrated that expert performers reduce the joint dimensionality by creating functional synergies in different phases of service and adapt the service action according to the perception of the environment.     

新规则导向下世界女子竞技体操格局及发展趋势的研究

运用文献资料法、数理统计法和专家访谈法，结合新规则对39届世界体操锦标赛女子团体、全能和单项前8名运动员的比赛成绩、动作难度和完成情况进行了比较分析。结果表明：世界女子体操的格局基本稳定；全能比赛呈现出强项突出，单项均衡发展的特点；单项比赛的竞争呈现出个性化、特长化的发展趋势，技术的发展要求在动作难度和编排上不断创新，同时注重表现的艺术性和发挥的稳定性。     

小学体育“引导──发现法”课堂教学模式的探索与实践

通过不断学习现代教学理论和《面向２１世纪上海市中小学体育与健身学科教育改革行动纲领》,提出构建小学体育“引导发现法”课堂教学模式,强调学生在教学活动中是积极参与的主体。研究旨在探索一条能提供学生自我发现,自主学习,自我完善的新的教学模式。     

新旧规则下奥运会拳击项目世界竞争格局分析

运用文献资料法、数理统计法、比较分析法,根据里约奥运会和伦敦奥运会拳击项目奖牌分布,对采用新规则下里约奥运会拳击项目世界竞争格局进行对比分析,结果显示:里约奥运会获得金牌和奖牌的国家数量减少,说明规则改变后拳击项目的优势强国更加集中;奥运拳击项目世界格局主要以美洲、欧洲、亚洲三大洲竞争为主,非洲和大洋洲在近两届奥运会中并无金牌入账;古巴依旧是美洲奥运拳击最强国,美国在女子拳击项目上保持优势;欧洲拳击则在大级别和女子拳击项目占有优势,但整体实力下降;亚洲拳击突飞猛进,未来将在奥运拳坛占有主导地位;中国拳击队在里约奥运会中获得1银3铜的成绩,未来要对新规则更加适应.