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1.
The varying results reported in response to β-alanine supplementation may be related to the duration and nature of the exercise protocol employed. We investigated the effects of β-alanine supplementation on a wide range of cycling performance tests in order to produce a clear concise set of criteria for its efficacy. Fourteen trained cyclists (Age?=?24.8?±?6.7?years; VO2max?=?65.4?±?10.2 mL·kg·min?1) participated in this placebo-controlled, double-blind study. Prior to supplementation, subjects completed two (familiarization and baseline) supramaximal cycling bouts until exhaustion (120% pre-supplementation VO2max) and two 1-, 4- and 10-km cycling time trial (TT). Subjects then supplemented orally for 4 weeks with 6.4?g/d placebo or β-alanine and repeated the battery of performance tests. Blood lactate was measured pre-exercise, post-exercise and 5 min post-exercise. β-alanine supplementation elicited significant increases in time to exhaustion (TTE) (17.6?±?11.5 s; p?=?0.013, effect compared with placebo) and was likely to be beneficial to 4-km TT performance time (?7.8?±?8.1 s; 94% likelihood), despite not being statistically different (p?=?0.060). Performance times in the 1- and 10-km TT were not affected by treatment. For the highly trained cyclists in the current study, β-alanine supplementation significantly extended supramaximal cycling TTE and may have provided a worthwhile improvement to 4-km TT performance. However, 1- and 10-km cycling TT performance appears to be unaffected by β-alanine supplementation. 相似文献
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Abstract In this study, we used recently developed technology to determine the force–time profile of elite swimmers, which enabled coaches to make informed decisions on technique modifications. Eight elite male swimmers with a FINA (Federation Internationale de Natation) rank of 900+ completed five passive (streamline tow) and five net force (arms and leg swimming) trials. Three 50-Hz cameras were used to video each trial and were synchronized to the kinetic data output from a force-platform, upon which a motorized towing device was mounted. Passive and net force trials were completed at the participant's maximal front crawl swimming velocity. For the constant tow velocity, the net force profile was presented as a force–time graph, and the limitation of a constant velocity assumption was acknowledged. This allowed minimum and maximum net forces and arm symmetry to be identified. At a mean velocity of 1.92 ± 0.06 m · s?1, the mean passive drag for the swimmers was 80.3 ± 4.0 N, and the mean net force was 262.4 ± 33.4 N. The mean location in the stroke cycle for minimum and maximum net force production was at 45% (insweep phase) and 75% (upsweep phase) of the stroke, respectively. This force–time profile also identified any stroke asymmetry. 相似文献
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桑普拉斯和阿加西毕竟都没能阻拦住库尔腾赢取大师杯奖杯，这样的结局多少都让人觉得有些伤感——毕竟他们这一代曾经带给我们太多的感动。阿加西曾是长发飘飘，牛仔短裤又包含着多少不羁的才情，狂放的步姿吸引了太多的尖叫声，直至他和波姬·小丝双双飞离球场，几经沉浮。天注定阿加西是一章不朽的传奇，当他和好莱坞的灯红酒绿挥手作别时，光着头的阿加西只身复出，续写当年的传奇，同时这个大眼睛的超级男孩也带来了他的谦谦君子风，幽默的谈吐，率直的行为，虔诚的谢幕，让球迷把他的形象珍藏于心底。球迷的心底还会有那令人钦佩的桑普… 相似文献
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Ricardo Peterson Silveira Pro Stergiou Pedro Figueiredo Flávio de S. Castro Larry Katz Darren J. Stefanyshyn 《European Journal of Sport Science》2018,18(10):1317-1326
The aim of this study was to determine the biomechanical parameters that explain ventral start performance in swimming. For this purpose, 13 elite swimmers performed different variants of the ventral start technique. Two-dimensional video analyses of the aerial and underwater phases were used to assess 16 kinematic parameters from the starting signal to 5?m, and an instrumented starting block was used to assess kinetic data. A Lasso regression was used to reduce the number of parameters, providing the main determinants to starting performance, revealing different combinations of key determinants, depending on the variant (r²?≥?0.90), with flight distance being the most relevant to all variants (r?≤??0.80; p?r?=??0.79; p?r?≤?0.61; p?r²?=?0.66) or block time and flight distance (r²?=?0.83). These data provide relevant contributions to the further understanding of the biomechanics of swimming starts as well as insights for performance analysis and targeted interventions to improve athlete performance. 相似文献
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The purpose of the present study was to examine the acute effects of resting, aerobic exercise practised alone, and aerobic exercise with active video games (AVG), on complex reaction time (CRT) and the post-exercise acute rate of perceived exertion (RPE) in young healthy adults. The experimental group was composed of 92 healthy young adults, 78 males and 13 females (age M?=?21.9?±?2.7 years) who completed two sessions, A and B. In session A, participants rode 30?min on an ergometer, while in session B they exercised for 30?min on an ergometer while playing an AVG on a Wii. The control group was composed of 30 young adults, 26 males and 4 females (age M?=?21.4?±?2.9 years) who rested for 30?min. In each session, a CRT task was performed before and after exercising or resting, and post-exercise global RPE was noted. Repeated measures general linear model (GLM) and Wilcoxon tests were performed. (1) Both aerobic exercise alone and aerobic exercise combined with AVG improved CRT, while resting did not; (2) aerobic exercise combined with AVG did not improve CRT more than aerobic exercise only; and (3) RPE was lower after aerobic exercise combined with AVG compared with aerobic exercise only. In young adults, exercise produces acute benefits on CRT, and practising exercise with AVG helps to decrease RPE. 相似文献
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Nicholas P. Linthorne 《Sports Engineering》2013,16(2):61-70
This study used a mathematical model to examine the effects of the sled, the running surface, and the athlete on sprint time when towing a weighted sled. Simulations showed that ratio scaling is an appropriate method of normalising the weight of the sled for athletes of different body size. The relationship between sprint time and the weight of the sled was almost linear, as long as the sled was not excessively heavy. The athlete’s sprint time and rate of increase in sprint time were greater on running surfaces with a greater coefficient of friction, and on any given running surface an athlete with a greater power-to-weight ratio had a lower rate of increase in sprint time. The angle of the tow cord did not have a substantial effect on an athlete’s sprint time. This greater understanding should help coaches set the training intensity experienced by an athlete when performing a sled-towing exercise. 相似文献
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Corrado Lupo Antonio Tessitore Cristina Cortis Antonio Ammendolia Franceso Figura 《Journal of sports sciences》2013,31(8):823-831
Abstract The aims of this study were to provide a profile of young water polo players and to compare technical and tactical aspects, movement patterns, and cardiac loads of youth water polo and Acquagoal codes. Ten young (age 12.3 years, s = 0.6) male water polo players underwent anthropometric (stature, body mass, body mass index, chest circumference, hand breadth, and length), strength, and [Vdot]O2max evaluations. Friendly youth water polo and Acquagoal matches were arranged to evaluate heart rates and swimming patterns (horizontal and vertical, with and without the ball) of players, and technical and tactical aspects of matches (number of actions, passes, player involved in an action, lost possessions, shots, goals, and the origin and types of shot). Independent of code, matches imposed a high cardiac load on players. Vertical swimming occurred more frequently (P < 0.05) in Acquagoal (71%) than youth water polo (45%). Technical and tactical measures also differed (P < 0.05), with players performing more passes and shots inside the penalty area and showing a higher goal-to-shot ratio during youth water polo than during Acquagoal. These results indicate that youth water polo better resembles the swimming patterns of adult water polo and facilitates the technical and tactical aspects of play better than Acquagoal. 相似文献
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ABSTRACTIt is clear that sport coaches learn from multiple interconnected learning experiences, yet there is limited direct evidence to elucidate what is learned and how these combined experiences shape coaches’ knowledge and day-to-day practice. This research aimed to investigate the impact of the learning of two groups of English youth soccer coaches over a period of a year and a half. Using the Coach Analysis and Intervention System (CAIS) and associated video-stimulated recall interviews, changes in the practice behaviours and knowledge use of coaches completing a formal coach education course, and equivalent coaches not undertaking formal education, were compared. Data indicated that the learning period had a different effect on coaches taking part in formal coach education versus those not in education. Changes in the use of knowledge about individual players and tactics were reflected in increased behaviours directed towards individuals, and an altered proportion of technical to tactically related questioning, linked to coaches’ participation in education. Overall, more change was evident in coaching knowledge than in practice behaviours, suggesting an absence of deep learning that bridged the knowledge-practice gap. 相似文献
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《European Journal of Sport Science》2013,13(7):876-884
AbstractObjectives: The aim of this study was to: (a) examine the time courses of runners’ recovery-stress states within the month following a demanding Mountain Ultra-Marathon (MUM) race; and (b) explore the role of primary and secondary appraisals in these trajectories. Design: A seven-wave one-month longitudinal design was used with one measurement point within two days before the race to measure appraisals and six time points within the month following the race to assess recovery-stress states experienced by athletes. Method: A multilevel growth curve analysis approach was used among a sample of 29 MUM runners. Results: Recovery-stress states were characterized by distinct trajectories during the month following MUM race. Results of multilevel growth curve analyses showed significant linear increases of general and total recovery, significant linear decreases of general, sport-specific and total stress and a positive quadratic effect of squared time (U shape over time) on specific recovery. Primary appraisal significantly positively predicted levels of sport-specific recovery, total, general and sport-specific stress and significantly negatively predicted total and general recovery. Secondary appraisal significantly negatively predicted total and general stress. Conclusions: This study provided insights into the role played by appraisals on the recovery-stress states experienced by MUM runners the month following a demanding MUM race. Operational strategies were suggested in order to optimize the recovery-stress balance and in turn psychological adaptation processes in response to an ultra-endurance race. 相似文献
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Dionne Matthew 《Journal of sports sciences》2013,31(8):813-821
Abstract The aim of this study was to examine the physiological demands and movement patterns of female basketball players after changes in the rules of the game. Nine varsity players were studied during nine official games. Each game was videotaped to identify the frequencies of the main movements performed, heart rate was recorded continuously, and blood samples were collected to determine blood lactate concentration when the competition rules allowed. The main results showed that the players performed on average 652 ± 128 movements per game, which corresponded to a change in activity every 2.82 s. Mean heart rate was 165 ± 9 beats · min?1 (89.1% of maximum heart rate) for total time and 170 ± 8 beats · min?1 (92.5% of maximum) for live time. Mean blood lactate concentration was 5.2 ± 2.7 mmol · l?1 (55.9% of maximum blood lactate concentration). In addition, heart rates were significantly higher in the first half than the second half of games. These results indicate: (1) a greater physiological load compared with previous studies on female players tested before the rules modification (Beam & Merrill, 1994; McArdle et al., 1971) and (2) lower movement frequencies compared with male players competing under modern rules (Ben Abdelkrim et al., 2007). These observations must be taken into account by coaches and conditioning specialists working with female players. 相似文献
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《Sport Management Review》2014,17(1):65-77
Disability sport in Great Britain has, since its genesis over sixty years ago, gained greater public profile with each passing decade. Arguably, this is a result of a more direct, interventionist approach from the British government and the Sport Councils into the field of disability sport over the past twenty years. In this paper we highlight a case of integration within sport by examining the process of mainstreaming disability cricket within England and Wales. Following a review of the extant literature in this area we will draw upon Bourdieu's practice theory in order to examine the impact of the implementation of policy on the management of issues of disability in mainstream cricket. Longitudinal ethnographic data (including participant observation and semi-structured interviews) was collected on the organizations involved in this mainstreaming process. Informants were either involved in the delivery of disability cricket or in the management of disability sports partnerships. Preliminary findings suggest that true integration is still unrealized. Whether the policy seeks true integration or whether mainstreaming is simply another modernizing process seeking greater efficiencies from sport organizations is unclear. Nevertheless a number of institutional pressures from the proximal and distal external environments have provided support for generating mainstreaming initiatives at management levels. In addition to these findings we argue that an additional outcome of this research is to demonstrate the suitability of a relational approach for conceptualizing policy, its interpretation by sport managers and the implementation strategies that follow. 相似文献
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Diana A. Santos Adilson Marques Cláudia S. Minderico Ulf Ekelund 《Journal of sports sciences》2018,36(15):1720-1726
Cardiorespiratory fitness (CRF) is associated with health benefits in children, improving cardiac morphology, cardiovascular disease risk factors, and biological outcomes. This study aimed to examine the substitution effects of displaying a fixed duration of sedentary time with a fixed duration of physical activity (PA) at different intensities on children’s CRF. A total of 315 children (136 boys) were assessed (age: 10.6 ± 0.6 years old). Outcomes at baseline and follow-up (16-months) were CRF determined using a maximal cycle test and sedentary time and PA measured with accelerometers. Data were analysed by isotemporal substitution analyses estimating the effect of reallocating 30 min/day of sedentary time by light (LPA), moderate (MPA) and vigorous physical activity (VPA) on CRF. VPA was positively and significantly associated with CRF cross-sectional (β = 0.026, p < 0.001) and prospectively (β = 0.010, p < 0.001). Reallocating 30 min/day of sedentary time into VPA was positively cross-sectionally (β = 0.780, p < 0.001) and prospectively (β = 0.303, p < 0.05) associated with CRF. Conversely, relocating 30-minutes of sedentary time into 30 minutes of LPA and MPA was not associated with CRF. These results suggest that reallocating an equal amount of time from sedentary into VPA is cross-sectional and prospectively associated with a favourable CRF. 相似文献
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F. Chan-Dewar W. Gregson G. Whyte D. Gaze J. Waterhouse J. Wen 《Journal of sports sciences》2013,31(4):414-423
Abstract Twelve healthy participants performed two identical high-intensity 40 km cycling trials (morning and evening) under controlled laboratory conditions. Echocardiograms and venous blood samples were collected before and after each exercise bout. Cardiac electro-mechanical-delay (cEMD) was measured as QRS-complex onset to peak systolic (S’) and early diastolic (E’) tissue velocities. Myocardial strain and strain rates were assessed in longitudinal, circumferential and radial planes at the left ventricular apex and base. Cardiac troponin I (cTnI) and N-terminal Pro-Brain Natriuretic Peptide (NT-proBNP) were assessed as biomarkers of cardiomyocyte damage and wall stress. cEMD was lengthened after both morning (S’: 160 ± 30 vs. 193 ± 27; E’: 478 ± 60 vs. 620 ± 87, P < 0.05) and evening (S’: 155 ± 29 vs. 195 ± 31; E’: 488 ± 42 vs. 614 ± 61, P < 0.05) trials. A reduction in peak S’ (morning: 6.96 ± 1.12 vs. 6.66 ± 0.89; evening: 7.09 ± 0.94 vs. 7.02 ± 0.76) was correlated with cEMD (r = ?0.335, P < 0.05). Peak longitudinal strain was reduced, atrial strain rates were sporadically increased in both trials post-cycling. cTnI was elevated in only two participants (0.04 µg · L?1, 0.03 µg · L?1), whilst NT-proBNP was below the clinical cut-off point in all participants. Prolonged-cycling resulted in a lengthening of cEMD, small changes in aspects of left ventricular deformation and sporadic increases in cardiac biomarkers. None of these effects were moderated by time-of-day. 相似文献
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Jonathan D. Wiles Damian Coleman Michael Tegerdine Ian L. Swaine 《Journal of sports sciences》2013,31(11):1165-1171
Abstract There is little published data in relation to the effects of caffeine upon cycling performance, speed and power in trained cyclists, especially during cycling of ～60 s duration. To address this, eight trained cyclists performed a 1 km time-trial on an electronically braked cycle ergometer under three conditions: after ingestion of 5 mg · kg?1 caffeine, after ingestion of a placebo, or a control condition. The three time-trials were performed in a randomized order and performance time, mean speed, mean power and peak power were determined. Caffeine ingestion resulted in improved performance time (caffeine vs. placebo vs. control: 71.1 ± 2.0 vs. 73.4 ± 2.3 vs. 73.3 ± 2.7 s; P = 0.02; mean ± s). This change represented a 3.1% (95% confidence interval: 0.7–5.6) improvement compared with the placebo condition. Mean speed was also higher in the caffeine than placebo and control conditions (caffeine vs. placebo vs. control: 50.7 ± 1.4 vs. 49.1 ± 1.5 vs. 49.2 ± 1.7 km · h?1; P = 0.0005). Mean power increased after caffeine ingestion (caffeine vs. placebo vs. control: 523 ± 43 vs. 505 ± 46 vs. 504 ± 38 W; P = 0.007). Peak power also increased from 864 ± 107 W (placebo) and 830 ± 87 W (control) to 940 ± 83 W after caffeine ingestion (P = 0.027). These results provide support for previous research that found improved performance after caffeine ingestion during short-duration high-intensity exercise. The magnitude of the improvements observed in our study could be due to our use of sport-specific ergometry, a tablet form and trained participants. 相似文献
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Abstract We analyse the evolution of the slope (critical speed) and the y-intercept (anaerobic distance capacity) of the linear distance–time relationship over a century of Olympic running performances. The distance–time relationship of each Olympic Games (1920–2004) was plotted using the performances in the 800-, 1500- and 5000-m track events. Values for critical speed and anaerobic distance capacity were determined by linear modelling. Mean performances for the 800, 1500 and 5000 m were 104.9 ± 1.5 s (1.4%), 217.2 ± 2.8 s (1.3%) and 808.9 ± 18.4 s (2.3%), respectively. Critical speed improved during the first three-quarters of the twentieth century to reach a plateau in 1984. This is in accordance with the literature (Peronnet & Thibault, 1989) and suggests that “human aerobic endurance” has improved within the century (+13.4%) and tends to stabilize. Anaerobic distance capacity was highly variable over the century (coefficient of variation = 9.4%) and did not show a linear improvement over the years as has previously been suggested (Peronnet & Thibault, 1989). This could be due to an artefact in the application of the two-parameter model to only three Olympic performances. A limitation to the use of this linear mathematical model to fit physiological data may have been demonstrated. 相似文献
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2007年9月刊《星际Ⅱ歪批第一弹》为大家送上了许多"异想天开"的理念,许多读者也对此表示了极大的兴趣。距离上次Blizzoon的Re-Aplah版,如今已经过了8个月了。在这期间,暴雪也不定期地为大家放出官方的FAQ。万众期待的Zerg虫族也终于在3月10日这天大举入侵地球。中、美、韩三地玩家都先后领略到了新生Zerg的恐怖之处。同时我们也看到了更多更详细的有关星际Ⅱ的资料,这让全世界玩家都兴奋得很。小编自然也坐不住了,我们这个对星际Ⅱ评头论足的栏目也应该继续了,这里仍然会不定期地出现最新的星际Ⅱ消息、评论和不负责任的猜想。Hell,it's about time! 相似文献
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《哈尔滨体育学院学报》2007,(6)
A州姗甲m阮F朋~ DISCu8Si佣叨win沈r olympicG~’Gene耐on and Devel叩二ni····························································……2衬刀2人泣一，川月召(1一1) D助dor FO叭口口R二二卜onT椒hing Qua 相似文献
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《运动与健康科学(英文)》2022,11(5):613-619
BackgroundWhile the relationship between sedentary time and adiposity markers may be independent of moderate-to-vigorous intensity physical activity (MVPA) among adolescents, little is known about the role of light-intensity physical activity (LIPA) in this relationship. The aim of this cross-sectional study was to examine whether device-measured LIPA and MVPA moderate the associations between objectively measured sitting time and adiposity markers (body mass index (BMI)) and waist circumference (WC)) among adolescents.MethodsThis study included accelerometer and inclinometer data obtained from 219 adolescents (age = 14.9 ± 1.6 years, mean ± SD), collected during 2014 and 2015 in Melbourne, Australia. ActiGraph GT3X accelerometers were used to determine time spent in total-LIPA (101 counts/min to 3.99 metabolic equivalents (METs)) was dichotomized into low-LIPA (101–799 counts/min) and high LIPA (800 counts/min to 3.99 METs), and MVPA (≥ 4 METs). The average time spent sitting was obtained from activPAL inclinometers. Anthropometric measures were assessed by trained staff. Interactions between sitting and total-LIPA, low-LIPA, high-LIPA, and MVPA on BMI z-score (zBMI) and WC z-score (zWC), respectively, were examined using linear regression, adjusting for age and sex; and moderation by total-LIPA, low-LIPA, high-LIPA, and MVPA were examined by adding interaction terms. Significant interaction effects were probed by comparing associations at the mean and at 1 SD below and above the mean.ResultsTotal-LIPA significantly moderated the association between sitting time and zBMI, and low-LIPA significantly moderated the association between sitting time and zBMI and zWC. No other associations were found for total-LIPA, high-LIPA, or MVPA. Specifically, at high levels of total-LIPA (+1 SD), there is a negative association between sitting time and zBMI. In addition, at high levels of low-LIPA (+1 SD), there is a negative association between sitting time and zBMI and zWC.ConclusionAssociations between sitting and adiposity depended on time spent in total-LIPA and low-LIPA, but not high-LIPA or MVPA. Results suggest that increasing time spent in LIPA may provide protection from the deleterious effects of sitting on adiposity markers among adolescents. Experimental evidence is needed to support these conclusions. 相似文献