Do aerobic characteristics explain isometric exercise-induced neuromuscular fatigue and recovery in upper and lower limbs?     

Gianluca Vernillo  John Temesi  Matthieu Martin 《Journal of sports sciences》2019,37(4):387-395

This study investigated the relationships between aerobic characteristics and (i) neuromuscular fatigue induced by 2-min sustained isometric maximal voluntary contractions (MVC) and (ii) subsequent recovery, in the upper and lower limbs. In a pseudo-randomized order, eleven healthy males completed four sessions on different days: maximal incremental cycling test (100 W + 40 W every 2 min); maximal arm-cranking test (50 W + 20 W every 2 min); and 2-min sustained isometric MVCs of the knee extensors (KE) and elbow flexors (EF). Neuromuscular assessment was performed with transcranial magnetic and peripheral nerve stimulation to evaluate central and peripheral neuromuscular factors of fatigue and the subsequent recovery. Peak oxygen uptake, gas exchange threshold and the corresponding power outputs were correlated with recovery of voluntary force after the 2-min KE MVC. Regression analysis showed that power output at the gas exchange threshold alone explained 72% of the variability in ?recovery of KE voluntary force. No relationships with fatigue or recovery in EF were observed. These results suggest that participants with greater aerobic capacities experience the same amount of fatigue and faster recovery of voluntary force in KE but not EF. The potential reasons behind the relationship in KE but not EF are discussed.  相似文献   

Influence of wheel rim width on rolling resistance and off-road speed in cross-country mountain biking     

Thomas Maier  Beat Müller  Remo Allemann  Thomas Steiner  Jon Peter Wehrlin 《Journal of sports sciences》2019,37(7):833-838

The rim width of cross-country mountain bike wheel sets has increased in recent years, but the effect of this increase on performance remains unknown. The aim of this study was to analyse the influence of rim width on rolling resistance and off-road speed. We compared 3 tubeless wheel sets: 25 mm inner width as baseline, 30 mm width with the same tyre stiffness, and 30 mm width with the same tyre pressure. Three riders conducted 75 rolling resistance tests for each wheel set on a cross-country course. We determined rolling resistance using the virtual elevation method and calculated off-road speeds for flat and uphill conditions using a mathematical model. Baseline rolling resistance (C_r) was 0.0298, 90% CI [0.0286, 0.0310], which decreased by 1.4%, [0.7, 2.2] with the wider rim and the same tyre stiffness and increased by 0.9%, [0.1, 1.6] with the wider rim and the same tyre pressure. The corresponding effects on off-road speed were most likely trivial (0.0% to 0.7% faster and 0.1% to 0.6% slower, respectively). Because the effect of rim width on off-road speed seems negligible, athletes should choose the rim width that offers the best bike handling and should experiment with low tyre pressures.  相似文献   

Physiological determinants of elite mountain bike cross-country Olympic performance     

Jacob Bejder  Thomas Christian Bonne  Michael Nyberg  Kim Anker Sjøberg 《Journal of sports sciences》2019,37(10):1154-1161

Detailed physiological phenotyping was hypothesized to have predictive value for Olympic distance cross-country mountain bike (XCO-MTB) performance. Additionally, mean (MPO) and peak power output (PPO) in 4 × 30 s all-out sprinting separated by 1 min was hypothesized as a simple measure with predictive value for XCO-MTB performance. Parameters indicative of body composition, cardiovascular function, power and strength were determined and related to XCO-MTB national championship performance (n = 11). Multiple linear regression demonstrated 98% of the variance (P < 0.001) in XCO-MTB performance (t_XCO-MTB; [min]) is explained by maximal oxygen uptake relative to body mass (VO_2peak,rel; [ml/kg/min]), 30 s all-out fatigue resistance (FI; [%]) and with a minor contribution from quadriceps femoris maximal torque (T_max; [Nm]): t_XCO-MTB = ?0.217× VO_2peak,rel.–0.201× FI+ 0.012× T_max+ 85.4. Parameters with no additional predictive value included hemoglobin mass, leg peak blood flow, femoral artery diameter, knee-extensor peak workload, jump height, quadriceps femoris maximal voluntary contraction force and rate of force development. Additionally, multiple linear regression demonstrated parameters obtained from 4x30s repeated sprinting explained 88% of XCO-MTB variance (P < 0.001) with t_XCO-MTB = ?5.7× MPO+ 5.0× PPO+ 55.9. In conclusion, XCO-MTB performance is predictable from VO_2peak,rel and 30 s all-out fatigue resistance. Additionally, power variables from a repeated sprint test provides a cost-effective way of monitoring athletes XCO-MTB performance.  相似文献   

Quantification of brake data acquired with a brake power meter during simulated cross-country mountain bike racing     

Matthew C. Miller  Philip W. Fink  Paul W. Macdermid  Stephen R. Stannard 《Sports biomechanics / International Society of Biomechanics in Sports》2019,18(4):343-353

There is currently a dearth of information describing cycling performance outside of propulsive and physiological variables. The aim of the present study was to utilise a brake power meter to quantify braking during a multi-lap cross-country mountain bike time trial and to determine how braking affects performance. A significant negative association was determined between lap time and brake power (800.8 ± 216.4 W, mean ± SD; r = ?0.446; p < 0.05), while the time spent braking (28.0 ± 6.4 s) was positively associated with lap time (314.3 ± 37.9 s; r = 0.477; p < 0.05). Despite propulsive power decreasing after the first lap (p < 0.05), lap time remained unchanged (p > 0.05) which was attributed to decreased brake work (p < 0.05) and brake time (p < 0.05) in both the front and rear brakes by the final lap. A multiple regression model incorporating braking and propulsion was able to explain more of the variance in lap time (r² = 0.935) than propulsion alone (r² = 0.826). The present study highlights that riders’ braking contributes to mountain bike performance. As riders repeat a cross-country mountain bike track, they are able to change braking, which in turn can counterbalance a reduction in power output. Further research is required to understand braking better.  相似文献   

短距离场地自行车专项训练强度评价方法的个案研究          下载免费PDF全文

唐琪 《体育科研》2017,(2):50-53

以备战2012年伦敦奥运会中国自行车队场地短距离项目组重点女子运动员为研究对象。在奥运会前一年的备战训练中,采用SRM系统对场地专项爆发力、最大速度和速度耐力训练进行监测,并对运动员阶段训练前后不同专项能力的变化进行了分析。同时,采用成绩与训练后血乳酸综合分析的方法,对运动员奥运赛前专项速度和力量耐力训练的完成强度进行评价,为建立场地自行车专项训练强度的测试与评价方法进行有益尝试。自行车短距离阶段训练中不同专项训练比例可决定专项能力的变化,功率是评价自行车短距离项目专项能力和训练强度的有效指标,结合乳酸变化可分析专项能力变化与供能比例、代谢产物清除之间的关系。  相似文献   

Yellow and social perceptions of racing cyclists’ sportspersonship: Proposing an inter-contextual analysis     

Yves Chantal  Iouri Bernache-Assollant 《Journal of sports sciences》2017,35(6):525-530

Through inter-contextual designs, the present set of experiments sought to explore whether the colour yellow would impact on social perceptions of sportspersonship exclusively in relation to competitive cycling. In Experiment 1 (N = 149), a silhouette image of a cyclist on a yellow background yielded lower perceptions of sportspersonship in comparison to grey or to the context of motocross, regardless of the colour. That interaction was conceptually replicated in Experiment 2 (N = 146) while changing measures (i.e., adaptation of the World Anti-Doping Code) and the context of comparison to sprinting. Furthermore, female and male observers’ scores did not differ significantly thereby suggesting that yellow impacted on perceived sportspersonship similarly across gender. On the whole, those findings suggest that yellow can generate negative impressions of racing cyclists because, with years, this colour took on a meaning of opportunism from frequent pairings with doping. We close with discussing a number of limitations and future research avenues.  相似文献   

Building an inclusive cycling “movement”: Exploring the charity-led mobilisation of recreational cycling in communities across Merseyside,England     

《Sport Management Review》2019,22(1):21-37

In this article, the authors examined the charity-led implementation of an inclusive cycling programme across Merseyside in the North West of England. The project itself is delivered via a network of cycling 'hubs' that the charity has set up and run typically in deprived communities. Using resource mobilisation theory, the authors specifically examined how the Cycling Projects charity mobilises a raft of diverse resources from the financial to the human, and from the cultural to the physical, to drive and sustain its Pedal Away product. To do this, the authors utilise qualitative data captured from 15 in-depth semi-structured interviews undertaken with stakeholders both internal and external to the charity, as well as focus group data yielded from programme participants (n = 32). The findings illustrate how the charity is able to garner and exchange resources from its partners and funders, and the ways in which it mobilises both participants and personnel from within the communities it serves. As an original contribution to the sport management field, the authors demonstrate both the value and applicability of resource mobilisation theory as a theoretical framework by which to understand how a non-profit organisation derives the resources it requires in order to deliver a network of community embedded recreational cycling programmes.  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   

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   

昆明市自行车旅游爱好者行为特征及其环境偏好分析   总被引：1，自引：0，他引：1  

万亚军  蒙睿 《昆明大学学报》2011,3(4):14-18,24

自行车旅游是国内近年来趋于流行的一种户外旅游体验形式。研究自行车旅游爱好者对骑行环境的感知与偏好对发展自行车旅游具有重要的参考价值。在对国内外自行车旅游研究现状整理的基础上,采用问卷对昆明市自行车旅游爱好者进行调查,分析自行车旅游爱好者的基本特征、骑行感知、骑行体验及骑行环境偏好。结果表明,自行车旅游爱好者男性为79％,而女性只有21％;高校大学生和公司职员是自行车旅游市场的中坚;53％的骑行活动由学生社团和地方俱乐部组织;59％的自行车旅游爱好者认为骑行活动不会对环境造成破坏;“骑行环境的空气质量”是自行车旅游爱好者最为关注的选项。认为：应尽快制定自行车旅游推广计划,设计自行车旅游线路,以此推动自行车旅游的蓬勃发展。  相似文献