Ecological dynamics of continuous and categorical decision-making: The regatta start in sailing

Abstract

Ecological dynamics of decision-making in the sport of sailing exemplifies emergent, conditionally coupled, co-adaptive behaviours. In this study, observation of the coupling dynamics of paired boats during competitive sailing showed that decision-making can be modelled as a self-sustained, co-adapting system of informationally coupled oscillators (boats). Bytracing the spatial–temporal displacements of the boats, time series analyses (autocorrelations, periodograms and running correlations) revealed that trajectories of match racing boats are coupled more than 88% of the time during a pre-start race, via continuous, competing co-adaptions between boats. Results showed that both the continuously selected trajectories of the sailors (12 years of age) and their categorical starting point locations were examples of emergent decisions. In this dynamical conception of decision-making behaviours, strategic positioning (categorical) and continuous displacement of a boat over the course in match-race sailing emerged as a function of interacting task, personal and environmental constraints. Results suggest how key interacting constraints could be manipulated in practice to enhance sailors' perceptual attunement to them in competition.     

The effects of a single reminder trial on retention of a motor skill

Two experiments investigated the effects of a single reminder trial on immediate and delayed retention. Experiment 1 determined if beneficial effects of a reminder trial were a function of task order immediate retention performance benefited only when the reminder trial was practiced in the first block of trials. Experiment 2 added a 24-hr delayed retention test to examine the long-term benefits of a reminder trial. Retention performance was enhanced over both delay intervals. The long-term effect extended previous research (Shea & Titzer, 1993) that documented effects after 10 min. The use of a single reminder trial established that intertask comparisons between multiple reminder trials were not a precondition for the reminder trial effect as postulated by Shea and Titzer.     

Effects of repeated retention tests on learning a single timing task

The purpose of the present study was to investigate the possibility that administering an initial retention test would influence any subsequent retention tests administered to the same participants. Participants performed 40 practice trials of a four-segment key-pressing task with a movement time goal of 925 ms. Participants were then administered either two retention tests (Day 1-Day 1 group, 10 min and 20 min after practice; Day 1-Day 2 group, 10 min and 24 hr after practice; Day 2-Day 2 group, 23 hr 50 min and 24 hr after practice) or one retention test (Day 1-Control group, 20 min after practice; Day 2-Control group, 24 hr after practice). The first test had a deleterious effect on performing the second test for the Day 2-Day 2 group, which would be expected if the task representation was updated and re-encoded at the time of recall using diminished information. This finding suggests that researchers should be cautious about using repeated retention tests that are administered 1 day after practice. In addition, teachers and coaches should consider administering a test under gamelike conditions following practice of a new technique. Otherwise, performance of the new technique may be degraded or perturbed at the time of later performances.     

我国优秀帆板运动员大负荷陆地摇帆训练期间代谢特点研究

为研究我国优秀帆板运动员大负荷陆地摇帆训练期间的代谢特点,建立陆地摇帆训练模式,对16名男子帆板专业运动员分组进行训练。试验结果显示:大负荷陆地摇帆训练使运动员血清睾酮和游离睾酮出现明显下降;大负荷陆地摇帆训练会造成血清皮质醇和血尿素明显升高,血色素含量下降;建议血清睾酮、游离睾酮和皮质醇可以作为阶段性机能监控指标,血色素和血尿素可以作为小周期机能监控指标。帆板运动员FT/C和T/C的变化与运动成绩呈现较为一致的趋势,可以作为优秀帆板运动员的机能评定指标之一。     

Numerical simulations of the frictional collisions of solid balls on a rough surface

Three-dimensional simulations of the frictional collision between solid balls moving on a rough surface are analyzed in this paper. The analysis is performed in the context of pool and snooker, two popular games in the pocket billiards family. Accurate simulations of ball motion in billiard games are useful for television broadcasts, training systems and any robotic game playing systems. Studying solid ball collisions in a three-dimensional space requires careful consideration of the different phenomena involved in ball motion such as rolling, sliding and ball spin about a general axis. A set of differential equations are derived describing ball dynamics during collisions. In the absence of explicit analytical solutions to the differential equations, a numerical procedure is performed to determine post-collision ball velocities and spins after collision. In addition, the paper also presents a methodology to analyze the curved, slip trajectories of balls immediately after impact. The results presented here, when compared with some experimental shots, show that the percentile errors in post-collision velocities are reduced by the proposed method. The prediction accuracies for ball travel direction are increased twofold by the proposed impact simulation algorithm.     

Simulation to clarify the effect of paddling motion on the hull behavior of a single kayak in a sprint race

The cause and effect relationship between the paddling motion and the hull behavior of a kayak in a sprint race has not been sufficiently investigated. The objective of this study was to investigate the effect of the paddling motion on the hull behavior by numerical simulation. A dynamic simulation model of a paddler, paddle and hull in a single kayak, which was previously developed, was used for the simulation. One standard paddling motion and three modified motions were prepared for the simulation. Three modified motions were created based on suggestions by coaches of the Japan Olympic team. These motions were thought to be often seen in paddlers of lower skill level and, therefore, empirically considered to be typically bad motions. From the simulation results, the following findings were obtained: in the simulation of the standard paddling motion, the averaged hull velocity was 5.4 m/s. This was consistent with the actual hull velocity of 5.5 m/s. Typically bad motions which induced undesirable hull fluctuations reduced the propulsive efficiency.     

Multitrait-multimethod investigation of a novel body image measurement technique

A multitrait-multimethod (MTMM) matrix was used to evaluate validity evidence for a digital image manipulation (DIM) body image measurement technique in young women. One hundred one young women completed the DIM procedure and the Thompson and Gray (1995) Contour Drawing Rating Scale to measure self-ideal discrepancy and size perception accuracy components of body image. Seven-day test-retest reliability was acceptable (R = .81-.95). Convergent validity for self-ideal discrepancy was higher (r = .74) than the corresponding heterotrait, monomethod coefficients (r = .46, r = .23) and heterotrait-heteromethod coefficients (r = .18, r = .12). However, the convergent validity coefficient for size perception accuracy was r = .12. The pattern of correlations in the MTMM matrix met the criteria of Campbell and Fiske (1959) for validity of these procedures to measure self-ideal discrepancy but not size perception accuracy. The DIM procedure addresses some of the criticisms associated with figure-rating scales, such as unrepresentativeness of the figures, scale coarseness, and restriction of range in responses. DIM, therefore, represents a realistic, valid alternative to figure-rating scales for measuring self-ideal discrepancy.     

基于数值模拟的运动双人帆船船体与稳向板操控优化

470级帆船是奥运会双人操控的帆船级别,为了优化船体与稳向板操控策略,利用数值模拟方法开展了470级帆船船体与稳向板相互影响时船体系统的水动力性能特性研究,得到了阻力随航速(2 m/s、4 m/s、6 m/s、8 m/s、10 m/s)变化的规律,数值模拟控制方程为RANS方程和连续方程,模拟中采用RNG eke-湍流模型。研究发现:稳向板和船体水动力会相互影响,两者配合时阻力特性相比单独时发生改变;不同航速下对水动力影响程度不相同,在较低航速时,稳向板对船体阻力影响程度较明显;航速越高船体对稳向板的阻力影响程度越大。因此,稳向板对470级帆船船体阻力的影响不可忽略;由于470级帆船是双人操控,在比赛过程中运动员可以根据实际需要适当调节稳向板,减小船体总阻力从而改变船体的航速,提高比赛成绩。     

The effects of a unilateral gluteal activation protocol on single leg drop jump performance

Warm-up protocols are commonly used to acutely enhance the performance of dynamic activities. This study examined the acute effect of low-load gluteal exercises on the biomechanics of single-leg drop jumps. Eight men and seven women (18–22 years old) performed 10 single-leg drop jumps on three separate days. The gluteal exercises were performed within the warm-up on day 2. Contact time, flight time, peak vertical ground reaction force (GRF), rate of force development, vertical leg-spring stiffness, and reactive strength index were determined. A repeated measures analysis of variance was used to examine differences on all variables across days. Significant differences were found for contact time, peak GRF, and flight time between days 1 and 2 and for flight time between days 1 and 3 (p ≤ 0.05) with no significant difference in any variables between days 2 and 3. This suggested that the improvements in day 2 were due to practice effects rather than the gluteal activation exercises. In addition, a typical error analysis was used to determine individual responses to the gluteal exercises. The results using this analysis showed no discernible response pattern of enhancement or fatigue for any participant.     

Perfectionism and training distress in junior athletes: a longitudinal investigation

Perfectionistic athletes may train harder and for longer than non-perfectionistic athletes, leaving them susceptible to elevated levels of training distress. So far, however, no study has investigated the relationships between perfectionism and training distress, a key indicator of overtraining syndrome. Furthermore, no study has determined psychological predictors of overtraining syndrome. Using a two-wave design, the present study examined perfectionistic strivings, perfectionistic concerns and training distress in 141 junior athletes (mean age = 17.3 years, range = 16–19 years) over 3 months of active training. Multiple regression analyses were employed to test cross-sectional and longitudinal relationships between perfectionism and training distress. In all analyses, perfectionism emerged as a significant predictor, but strivings and concerns showed differential relationships. When the cross-sectional relationships were regarded, perfectionistic concerns positively predicted training distress (P < .001), whereas perfectionistic strivings negatively predicted training distress (P < .01). When the longitudinal relationships were regarded, only perfectionistic concerns predicted increases in training distress (P < .05), whereas perfectionistic strivings did not (P > .05). The findings suggest that sports scientists who wish to identify athletes at risk of overtraining syndrome may monitor athletes’ perfectionistic concerns as a possible risk factor.     

Inspiratory muscle fatigue in swimmers after a single 200 m swim

Inspiratory muscle fatigue may occur in as little as 6 min during high-intensity spontaneously breathing exercise. The aims of this study were to determine whether inspiratory muscle fatigue occurs during swimming exercise and whether inspiratory muscle strength differs between the supine and standing body positions. Seven competitive swimmers were recruited to perform a single 200 m front-crawl swim, corresponding to 90-95% of race pace. Inspiratory muscle strength was measured at residual volume using a hand-held mouth pressure meter that measured maximal inspiratory pressure in the upright and supine positions. At baseline, maximal inspiratory pressure in the supine position was significantly lower than maximal inspiratory pressure in the upright position (112 +/- 20.4 and 133 +/- 16.7 cmH2O, respectively; P < or = 0.01). Post-exercise maximal inspiratory pressure in the supine position (80 +/- 15.7 cmH2O) was significantly lower than baseline maximal inspiratory pressure in the supine position (P < or = 0.01). The results indicate that a single 200 m front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue in less than 2.7 min. Furthermore, although diaphragm muscle length is optimized when supine, our results indicate that the force output of the diaphragm and inspiratory accessory muscles is greater when upright than when supine.     

Inspiratory muscle fatigue in swimmers after a single 200 m swim

Inspiratory muscle fatigue may occur in as little as 6 min during high-intensity spontaneously breathing exercise. The aims of this study were to determine whether inspiratory muscle fatigue occurs during swimming exercise and whether inspiratory muscle strength differs between the supine and standing body positions. Seven competitive swimmers were recruited to perform a single 200 m front-crawl swim, corresponding to 90-95% of race pace. Inspiratory muscle strength was measured at residual volume using a hand-held mouth pressure meter that measured maximal inspiratory pressure in the upright and supine positions. At baseline, maximal inspiratory pressure in the supine position was significantly lower than maximal inspiratory pressure in the upright position (112±20.4 and 133±16.7 cmH₂O, respectively; P?0.01). Post-exercise maximal inspiratory pressure in the supine position (80±15.7 cmH₂O) was significantly lower than baseline maximal inspiratory pressure in the supine position (P?0.01). The results indicate that a single 200 m front-crawl swim corresponding to 90-95% of race pace was sufficient to induce inspiratory muscle fatigue in less than 2.7 min. Furthermore, although diaphragm muscle length is optimized when supine, our results indicate that the force output of the diaphragm and inspiratory accessory muscles is greater when upright than when supine.     

广州市小学生书包负荷的调查与分析

通过对广州市小学生书包运动负荷的初步调查与分析，发现广州部分小学生书包负荷欠合理并可能造成脊柱缺陷，提出广州市小学生要减轻书包负荷的建议。     

Validity of a single lactate measure to predict fixed lactate thresholds in athletes

This study aimed to validate the use of a single blood lactate concentration measure taken following a 12 km h^?1 running stage (BLC₁₂) to predict and monitor fixed blood lactate concentration (FBLC) thresholds. Three complementary studies were undertaken. Study I: the relationships between BLC₁₂ and the running speeds at FBLC of 3 mmol L^?1 (S3mM) and 4 mmol L^?1 (S4mM) measured during a multistage running field test were examined in 136 elite athletes. Study II: data from 30 athletes tested one year apart were used to test the predictive capacity of the equations obtained in Study I. Study III: 80 athletes were tested before and after an intensified training period to examine whether training-induced changes in FBLC thresholds could be predicted and monitored by BLC₁₂. Study I: BLC₁₂ was significantly (P < 0.001) and inversely related to S3mM (R² = 0.89) and S4mM (R² = 0.95). Study II: prediction models yielded robust correlations between the estimated and measured FBLC thresholds (r = 0.94–0.99; P < 0.001). Study III: estimated changes predicted actual training-induced changes in FBLC thresholds (r = 0.81–0.91; P < 0.001). This study gives empirical support to use a single lactate measure during a sub-maximal running field test as a simple, low-cost and practical alternative to FBLC thresholds in athletes.     

新时期城市社区体育公共服务供给问题探索

城市社区体育公共服务供给是我国社会结构与社会体系的重要组成部分,对它的研究被认为是前瞻性的课题.文章分析了城市社区体育公共服务供需主体双方关系及面临的突出矛盾,提出了新时期我国城市社区体育公共服务供给的发展路径,为大力推动城市社区体育公共服务的供给提供理论与实践的借鉴.     

基于单向流固耦合的不同风速下帆板帆翼空气动力性能仿真

目的：探究不同风速对帆板帆翼结构以及周围流场的影响。方法：以奥运女子级别的Neil Pryde RS：X帆板帆翼为研究对象，考虑空气动力与结构的流固耦合效应，利用ANSYS Workbench进行单向流固耦合分析。结果：Realizable模型适合计算帆翼周围的流场湍流度，在风速为2m/s时帆翼升阻比最大；随着风速的增大，帆翼面发生变形和振动会导致风激振现象、背风面产生明显的涡脱现象，且帆翼表面应力区增大，全帆的应变逐步增加。结论：不同风速下的帆翼迎风面和背风面的压力分布、帆翼整体空气动力有一定差异，运动员比赛中应该根据当时风况调整帆翼参数。     

高职院校学生课内课外体育活动冷热现象调查研究

采用文献资料法、调查法、数理统计法等研究方法,通过对我省部分高职院校的体育课现状进行的调查结果显示:有93%的学生喜欢体育活动,但同时又有86%的学生不喜欢体育课.针对这些现象及形成根源作出了分析,并提出体育教学模式、内容、方法等改革基本思路,旨在为体育课堂教学的良性发展和提高教学质量及体育教学整体改革提供依据.     

沈阳市部分高校乒乓球运动开展现状的调查研究

采用问卷调查和文献资料等研究法,对沈阳市部分高校学生对乒乓球的了解情况、学习途径以及学校的场地设施等方面进行调查分析,结果表明:影响沈阳市部分高校乒乓球运动发展的主要原因是学生亲身体验和了解乒乓球运动的条件受限,学校场地收费过高以及对理论知识的宣传力度不够等。针对这些问题,建议学校加强对学生乒乓球理论知识的培养,并多开展乒乓球运动活动,以及适当降低课外乒乓球场地的收费,使乒乓球运动真正融入大众,在高校中能蓬勃发展。