Isoperformance curves: An application in team selection     

R. Hugh Morton 《Journal of sports sciences》2013,31(14):1601-1605

Abstract

An isoperformance curve (or surface) defines combinations of two (or more) physiological attributes of individuals such that equal performances for a specified event would be expected of them. Parameters from the two- and three-parameter critical power models are used to illustrate the concept. There are a number of sporting races where teams of individuals compete simultaneously as a unit. Rowing and team pursuit cycling are two well-known examples. Team selection may be difficult if there are more candidates available than places in the team. Based on the assumption that team members should be evenly matched with respect to performance rather than physiological attributes, proximity to a particular isoperformance curve (or surface) may suggest an obvious grouping of individuals. Isoperformance lines also enable identification of an athlete's individual training needs, since the components of the isoperformance lines can be affected by specific training interventions.  相似文献   

Longitudinal monitoring of power output and heart rate profiles in elite cyclists     

Alfred Nimmerichter  Roger G. Eston  Norbert Bachl  Craig Williams 《Journal of sports sciences》2013,31(8):831-839

Abstract

Power output and heart rate were monitored for 11 months in one female ([Vdot]O_2max: 71.5 mL · kg^?1 · min^?1) and ten male ([Vdot]O_2max: 66.5 ± 7.1 mL · kg^?1 · min^?1) cyclists using SRM power-meters to quantify power output and heart rate distributions in an attempt to assess exercise intensity and to relate training variables to performance. In total, 1802 data sets were divided into workout categories according to training goals, and power output and heart rate intensity zones were calculated. The ratio of mean power output to respiratory compensation point power output was calculated as an intensity factor for each training session and for each interval during the training sessions. Variability of power output was calculated as a coefficient of variation. There was no difference in the distribution of power output and heart rate for the total season (P = 0.15). Significant differences were observed during high-intensity workouts (P < 0.001). Performance improvements across the season were related to low-cadence strength workouts (P < 0.05). The intensity factor for intervals was related to performance (P < 0.01). The variability in power output was inversely associated with performance (P < 0.01). Better performance by cyclists was characterized by lower variability in power output and higher exercise intensities during intervals.  相似文献   

Physiological demands of downhill mountain biking     

Jamie F. Burr  C. Taylor Drury  Adam C. Ivey  Darren E.R. Warburton 《Journal of sports sciences》2013,31(16):1777-1785

Abstract

Mountain biking is a popular recreational pursuit and the physiological demands of cross-country style riding have been well documented. However, little is known regarding the growing discipline of gravity-assisted downhill cycling. We characterised the physiological demands of downhill mountain biking under typical riding conditions. Riding oxygen consumption ([Vdot]O₂) and heart rate (HR) were measured on 11 male and eight female experienced downhill cyclists and compared with data during a standardised incremental to maximum ([Vdot]O_2max) exercise test. The mean [Vdot]O₂ while riding was 23.1 ± 6.9 ml · kg^?1 · min^?1 or 52 ± 14% of [Vdot]O_2max with corresponding heart rates of 146 ± 11 bpm (80 ± 6% HRmax). Over 65% of the ride was in a zone at or above an intensity level associated with improvements in health-related fitness. However, the participants’ heart rates and ratings of perceived exertion were artificially inflated in comparison with the actual metabolic demands of the downhill ride. Substantial muscular fatigue was evident in grip strength, which decreased 5.4 ± 9.4 kg (5.5 ± 11.2%, P = 0.03) post-ride. Participation in downhill mountain biking is associated with significant physiological demands, which are in a range associated with beneficial effects on health-related fitness.  相似文献   

Modelling and analysing track cycling Omnium performances using statistical and machine learning techniques     

Bahadorreza Ofoghi  John Zeleznikow  Dan Dwyer  Clare Macmahon 《Journal of sports sciences》2013,31(9):954-962

Abstract

This article describes the utilisation of an unsupervised machine learning technique and statistical approaches (e.g., the Kolmogorov-Smirnov test) that assist cycling experts in the crucial decision-making processes for athlete selection, training, and strategic planning in the track cycling Omnium. The Omnium is a multi-event competition that will be included in the summer Olympic Games for the first time in 2012. Presently, selectors and cycling coaches make decisions based on experience and intuition. They rarely have access to objective data. We analysed both the old five-event (first raced internationally in 2007) and new six-event (first raced internationally in 2011) Omniums and found that the addition of the elimination race component to the Omnium has, contrary to expectations, not favoured track endurance riders. We analysed the Omnium data and also determined the inter-relationships between different individual events as well as between those events and the final standings of riders. In further analysis, we found that there is no maximum ranking (poorest performance) in each individual event that riders can afford whilst still winning a medal. We also found the required times for riders to finish the timed components that are necessary for medal winning. The results of this study consider the scoring system of the Omnium and inform decision-making toward successful participation in future major Omnium competitions.  相似文献   

Effects of magnitude and frequency of variations in external power output on simulated cycling time-trial performance     

Marc Wells  Greg Atkinson 《Journal of sports sciences》2013,31(15):1639-1646

Abstract

Mechanical models of cycling time-trial performance have indicated adverse effects of variations in external power output on overall performance times. Nevertheless, the precise influences of the magnitude and number of these variations over different distances of time trial are unclear. A hypothetical cyclist (body mass 70 kg, bicycle mass 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance times were modelled over distances of 4–40 km, mean power outputs of 200–600 W, power variation amplitudes of 5–15% and variation frequencies of 2–32 per time-trial. Effects of a “fast-start” strategy were compared with those of a constant-power strategy. Varying power improved 4-km performance at all power outputs, with the greatest improvement being 0.90 s for ± 15% power variation. For distances of 16.1, 20 and 40 km, varying power by ± 15% increased times by 3.29, 4.46 and 10.43 s respectively, suggesting that in long-duration cycling in constant environmental conditions, cyclists should strive to reduce power variation to maximise performance. The novel finding of the present study is that these effects are augmented with increasing event distance, amplitude and period of variation. These two latter factors reflect a poor adherence to a constant speed.  相似文献   

‘The finances stagger these fellows’: the Great American Bicycle Trust, 1899–1903     

Bruce D. Epperson 《国际体育史杂志》2013,30(18):2633-2652

Between 1895 and 1904, over 1,800 separate businesses merged into approximately 150 ‘trusts’, most of them simple horizontal combinations. Less than a third succeeded. One of the more spectacular failures was the American Bicycle Company. Formed by combining 45 bicycle and cycle-parts makers, it lasted less than three years. Various theories have been advanced to explain this abysmal performance, but there appears to have been no single deterministic cause. The firm was inadequate in size and scope, poorly organised, and lacking a clear goal. Its participating owners had disparate, often contradictory, objectives. Its demise left the American industry with a decentralised structure fragmented into competing sub-industries for cycle parts, bicycle fabrication and assembly, and the distribution and marketing of completed cycles. This structure led to market dominance by component firms, minimal profits and high failure rates for cycle makers, and a low overall level of innovation.  相似文献   

马氏体相变对P91钢焊接残余应力的影响          下载免费PDF全文

蔡宝杰  龚凌诸  徐火力 《福建工程学院学报》2022,(1):27-34

基于仿真模拟软件SYSWELD,建立了P91钢材料属性数据库,设计开发了考虑马氏体相变的“热-冶金-力学”耦合计算方法,采用热循环曲线法对P91钢平板对接接头残余应力场进行数值模拟仿真分析。参照原始焊接工艺方案进行上下0.5mm/s焊接速度的调整,并进行残余应力仿真计算。结果表明,马氏体相变能抵消焊缝热收缩时产生的拉应力。后道焊缝焊接过程中施加的热载荷对前道焊缝应力变化和平板角变形有着显著的影响。考虑后道焊缝焊接过程中施加的热载荷对前道焊缝组织变化的影响时,焊接接头整体的拉应力大幅度下降,热影响区的拉应力上升,角变形起缓和作用。焊接速度越大,Von Mises残余应力和横向残余应力越大,纵向残余压应力越小。  相似文献   

自行车短距离项目场地专项力量训练方法的比较          下载免费PDF全文

梁效忠  倪大海 《体育科研》2014,(5):24-29

目的：通过运动学指标分析,对自行车短距离项目几种力量耐力和速度力量训练方法的专项性和有效性进行对比研究。方法：选择上海自行车队短组3名男子优秀运动员为对象。选择2011年全国比赛8场1km计时赛,以及期间分别进行的8节原地750m和蓝线行进750m训练课进行力量耐力训练方法分析;选择同期进行的12场争先赛200m资格赛,以及12节大坡行进200m和牵引125＋200m训练课进行速度力量训练方法分析。采用德国SRM系统采集运动学指标,分析数据包括各训练比赛中的功率、频率、速度,同时记录运动成绩。结果：（1）原地750m训练的前两个250m分段及总平均功率（Pmean）和平均频率（Cmean）均显著低于1km计时赛;蓝线行进750m各分段Pmean、Cmean和即刻速度均高于原地750m,且总Pmean和Cmean与1km计时赛相比无明显差异。（2）牵引125＋200m训练的两个100m分段的Pmax和Cmean、200m总Cmean和50m分段即刻速度均显著高于大坡行进200m训练和争先资格赛。结论：蓝线20km/h行进出发750m和摩托车牵引125＋200m训练方法可能是更加符合专项要求的自行车短距离专项力量耐力和速度力量训练。  相似文献   

Performance effects of acute β-alanine induced paresthesia in competitive cyclists     

Phillip M. Bellinger  Clare L. Minahan 《European Journal of Sport Science》2016,16(1):88-95

β-alanine is a common ingredient in supplements consumed by athletes. Indeed, athletes may believe that the β-alanine induced paresthesia, experienced shortly after ingestion, is associated with its ergogenic effect despite no scientific mechanism supporting this notion. The present study examined changes in cycling performance under conditions of β-alanine induced paresthesia. Eight competitive cyclists (VO_2max = 61.8 ± 4.2 mL·kg·min^?1) performed three practices, one baseline and four experimental trials. The experimental trials comprised a 1-km cycling time trial under four conditions with varying information (i.e., athlete informed β-alanine or placebo) and supplement content (athlete received β-alanine or placebo) delivered to the cyclist: informed β-alanine/received β-alanine, informed placebo/received β-alanine, informed β-alanine/received placebo and informed placebo/received placebo. Questionnaires were undertaken exploring the cyclists’ experience of the effects of the experimental conditions. A possibly likely increase in mean power was associated with conditions in which β-alanine was administered (±95% CL: 2.2% ± 4.0%), but these results were inconclusive for performance enhancement (p = 0.32, effect size = 0.18, smallest worthwhile change = 56% beneficial). A possibly harmful effect was observed when cyclists were correctly informed that they had ingested a placebo (–1.0% ± 1.9%). Questionnaire data suggested that β-alanine ingestion resulted in evident sensory side effects and six cyclists reported placebo effects. Acute ingestion of β-alanine is not associated with improved 1-km TT performance in competitive cyclists. These findings are in contrast to the athlete’s “belief” as cyclists reported improved energy and the ability to sustain a higher power output under conditions of β-alanine induced paresthesia.  相似文献   

The understanding and development of cycling aerodynamics   总被引：1，自引：1，他引：0  

R. A. Lukes  S. B. Chin  S. J. Haake 《Sports Engineering》2005,8(2):59-74

In elite cycling the resistive force is dominated by aerodynamics. Be it on the roads or in the velodrome, the sport has many examples where aerodynamics has won and lost races. Since the invention of the bicycle, engineers have strived to improve performance, often by reducing aerodynamic drag. Over the last 50 years a number of authors have presented their efforts in journals, books and magazines. This review summarises the publications that show the continued development in the aerodynamics of cycling. The review concludes by examining the shortcomings of the current understanding and making suggestions for future research and development.  相似文献