Variable versus constant power strategies during cycling time-trials: Prediction of time savings using an up-to-date mathematical model

Abstract

Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) employed the mathematical model of Di Prampero et al. (1979 Di Prampero, P. E., Cortili, G., Mognoni, P. and Saibene, F. 1979. Equation of motion of a cyclist. Journal of Applied Physiology, 47: 201–206. [PubMed], [Web of Science ®] , [Google Scholar]) to predict that, for cycling time-trials, the optimal pacing strategy is to vary power in parallel with the changes experienced in gradient and wind speed. We used a more up-to-date mathematical model with validated coefficients (Martin et al., 1998 Martin, J. C., Milliken, D. L., Cobb, J. E., McFadden, K. L. and Coggan, A. R. 1998. Validation of a mathematical model for road cycling power. Journal of Applied Biomechanics, 14: 276–291. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) to quantify the time savings that would result from such optimization of pacing strategy. A hypothetical cyclist (mass = 70 kg) and bicycle (mass = 10 kg) were studied under varying hypothetical wind velocities (?10 to 10 m · s^?1), gradients (?10 to 10%), and pacing strategies. Mean rider power outputs of 164, 289, and 394 W were chosen to mirror baseline performances studied previously. The three race scenarios were: (i) a 10-km time-trial with alternating 1-km sections of 10% and ?10% gradient; (ii) a 40-km time-trial with alternating 5-km sections of 4.4 and ?4.4 m · s^?1 wind (Swain, 1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]); and (iii) the 40-km time-trial delimited by Jeukendrup and Martin (2001 Jeukendrup, A. E. and Martin, J. 2001. Improving cycling performance: How should we spend our time and money?. Sports Medicine, 31: 559–569. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Varying a mean power of 289 W by ± 10% during Swain's (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) hilly and windy courses resulted in time savings of 126 and 51 s, respectively. Time savings for most race scenarios were greater than those suggested by Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). For a mean power of 289 W over the “standard” 40-km time-trial, a time saving of 26 s was observed with a power variability of 10%. The largest time savings were found for the hypothetical riders with the lowest mean power output who could vary power to the greatest extent. Our findings confirm that time savings are possible in cycling time-trials if the rider varies power in parallel with hill gradient and wind direction. With a more recent mathematical model, we found slightly greater time savings than those reported by Swain (1997 Swain, D. P. 1997. A model for optimizing cycling performance by varying power on hills and in wind. Medicine and Science in Sports and Exercise, 29: 1104–1108. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). These time savings compared favourably with the predicted benefits of interventions such as altitude training or ingestion of carbohydrate-electrolyte drinks. Nevertheless, the extent to which such power output variations can be tolerated by a cyclist during a time-trial is still unclear.     

Hip extension during the come-out of multiple forward and inward pike somersaulting dives is controlled by eccentric contraction of the hip flexors

Abstract

A modelling approach was used in the present study to investigate the role of the hip muscles during the come-out of forward and inward multiple somersaulting dives in a pike position. A planar two-segment model was used to simulate the somersault and come-out of three commonly performed dives from a 3-m springboard: forward two-and-one-half somersault pike dive (105B), forward three-and-one-half somersault pike dive (107B), and inward two-and-one-half somersault pike dive (405B). Three simulations were run for each dive: (1) hip angle was constrained to be constant, (2) hip torque was removed after 0.1 s, and (3) hip angle was constrained to a typical come-out time history used by elite divers. Simulation results indicated that hip flexion torque was required both to maintain a rigid pike position during somersault (range = 205.5–282.3 Nm) and to control the hip extension movement during the come-out (peak torque range = 355.8–548.1 Nm) in forward and inward multiple somersaulting dives. Coaches and divers should be aware that dry-land exercise drills producing hip extension movement by concentric actions of the hip extensor muscles do not replicate the neuromuscular control during the come-out of fast rotating dives.     

全方位自我保健对健康长寿关系的研究

国内外专家研究指出 :人的自然寿命应享 1 2 0岁 ,这是从细胞分裂次数与细胞分裂周期乘积计算出来的结果。但现实生活告诉我们 ,尽管人们生活的水准在日益提高 ,而享尽天年的人并不多 ,英年早逝的人却不少 ,究其原因概在于对保健意识的认知方面。养生家告诫我们 ,人生在世 ,自我保健意识不能局限于某一方面 ,而应是全方位的 ,即 :起居有常、饮食有节、摄食科学、劳逸适度、情志豁达、动静兼练 ,并要根据自己的实际情况 ,找出一条适宜自我的规律来 ,方能走上健康长寿的道路     

对高校新生身体素质状况的调查与分析

通过对新生的综合调查，了解到当前中学体育课上课的情况和学生的身体素质状况，提出几个突出性的问题，探讨解决问题的方法，供有关部门参考。     

奋起直追的亚洲田径

亚洲地区的三级跳远、马拉松与撑杆跳高等项,早在二、三十年代曾扬威过奥林匹克田坛,可是在近半个世纪中一度处于不景气的状态。自1989年我国选手黄志红为亚洲夺得金牌以来,短短四年中亚洲田径精美在奥运会、世锦赛与世界杯三大赛中,取得了较好的成绩。本外重点叙述了亚洲田径水平迅速提高的特点、原因与今后努力方向,供田径爱好者参考。     

Leveraging events to ensure enduring benefits: The legacy strategy of the 2015 AFC Asian Cup

The Asian Football Confederation (AFC) Asian Cup is the largest soccer event on the Asian continent. Australia hosted the 2015 AFC Asian Cup which provided the nation with an opportunity to not only celebrate the sport of soccer, but also leverage the event to deliver enduring legacies. This case study examines the three key legacies of the 2015 AFC Asian Cup which were tourism, trade and investment, and multicultural engagement, and considers the leveraging strategies that were implemented to achieve the stated legacies.     

行为转变理论模式在社区居民体育健身锻炼行为干预中的运用

调查沈阳市铁西区和淄博市张店区社区居民体育健身锻炼行为现况,采用行为转变理论模式对居民健身锻炼实施不同的干预措施。结果发现,社区居民在体育健身锻炼行为各阶段的情况是:打算转变前阶段的居民占45.03%,打算转变阶段占13.91%,准备行动阶段占13.41%,行动阶段占16.05%,巩固阶段占12.58%。干预前后社区居民对体育健身锻炼重要性的认识、保持锻炼的信念和参与体育健身锻炼的百分率均有较大的提高,居民参与锻炼的人数也有增加,干预组与对照组之间的差异有显著性意义(P<0.01)。     

现代科学技术与竞技武术运动发展研究

当下竞技体育领域的深入发展离不开现代科技的支撑.文章简要分析现代科学技术的基本理论,系统探讨了现代科技在促进竞技武术运动发展中的作用与价值.研究结果显示,竞技武术运动要实现国际化发展并与奥运的对接,强化科技意识,提升科技融入水平是必由之路.     

高校滑雪课程开展的现状与对策

滑雪运动从贵族运动走向平民百姓,标志着大众滑雪的开始,高校滑雪课程是普及大众滑雪的重要途径。但是近几年高校滑雪课程开设、开展过程曲折反复,其中的原因是多方面的。存在的主要问题有主管部门领导对滑雪课程认识不够充分、滑雪课程安全防范不足、滑雪课程教学体系不完善、任课教师技能有待提高等。通过对滑雪课程的现状与相关问题的深入分析,提出相应的发展对策,以期为高校滑雪课程普及提供借鉴和帮助,保障滑雪课程的顺利开展,促进滑雪运动的全面发展。     

普通高校体育保健课程个性化教学的探索与实践

长期以来针对体残病弱学生开设的体育保健课强化的是＂教＂的统一要求——统一的教学大纲、统一的课程内容、统一的评价方法等等,并没有让每一个体残病弱学生公平地获得适合其身心特点与需要的体育知识和自我体育锻炼方法。运用文献资料法、专家访谈法和问卷调查法,并结合3年的体育保健课教学实践,对高校体育保健课程实施个性化教学进行了初步探讨和具体的教学实践。结果表明,个性化体育保健课程可以较好适应体残病弱学生的生理和心理需求,通过丰富教学内容和教学手段、布置课外体育作业等形式,使他们对体育锻炼的态度在行为认知、行为习惯和主观标准方面均有明显提高。