谈青少年山地自行车运动员的科学选材

从青少年运动员的身体形态、生理机能、运动素质、心理素质、专项成绩、教练员评定等因素对山地自行车运动项目的影响进行分析,试图为青少年山地自行车运动员选材提供必要的科学依据。     

Physical characteristics and resistance parameters of typical urban cyclists

This study investigates the rolling and drag resistance parameters and bicycle and cargo masses of typical urban cyclists. These factors are important for modelling of cyclist speed, power and energy expenditure, with applications including exercise performance, health and safety assessments and transportation network analysis. However, representative values for diverse urban travellers have not been established. Resistance parameters were measured utilizing a field coast-down test for 557 intercepted cyclists in Vancouver, Canada. Masses were also measured, along with other bicycle attributes such as tire pressure and size. The average (standard deviation) of coefficient of rolling resistance, effective frontal area, bicycle plus cargo mass, and bicycle-only mass were 0.0077 (0.0036), 0.559 (0.170) m², 18.3 (4.1) kg, and 13.7 (3.3) kg, respectively. The range of measured values is wider and higher than suggested in existing literature, which focusses on sport cyclists. Significant correlations are identified between resistance parameters and rider and bicycle attributes, indicating higher resistance parameters for less sport-oriented cyclists. The findings of this study are important for appropriately characterising the full range of urban cyclists, including commuters and casual riders.     

基于STAR-CCM+的帆板帆翼空气动力性能数值模拟

利用计算流体力学软件STAR-CCM+对奥运会比赛用帆板及帆船帆翼的空气动力性能进行了数值模拟,得到了不同攻角下的帆翼在粘性流场下的数值模拟结果和相应的升力系数及阻力系数。对不同攻角下的升力系数和阻力系数计算结果与实验结果进行了对比,通过比较可以看出利用STAR-CCM+软件能够快速有效地预报帆翼空气动力性能和流场。     

Field and laboratory correlates of performance in competitive cross-country mountain bikers

Abstract

We designed a laboratory test with variable fixed intensities to simulate cross-country mountain biking and compared this to more commonly used laboratory tests and mountain bike performance. Eight competitive male mountain bikers participated in a cross-country race and subsequently did six performance tests: an individual outdoor time trial on the same course as the race and five laboratory tests. The laboratory tests were as follows: an incremental cycle test to fatigue to determine peak power output; a 26-min variable fixed-intensity protocol using an electronically braked ergometer followed immediately by a 1-km time trial using the cyclist's own bike on an electronically braked roller ergometer; two 52-min variable fixed-intensity protocols each followed by a 1-km time trial; and a 1-km time trial done on its own. Outdoor competition time and outdoor time trial time correlated significantly (r = 0.79, P < 0.05). Both outdoor tests correlated better with peak power output relative to body mass (both r = ?0.83, P < 0.05) than absolute peak power output (outdoor competition: r = ?0.65; outdoor time trial: r = ?0.66; non-significant). Outdoor performance times did not correlate with the laboratory tests. We conclude that cross-country mountain biking is similar to uphill or hilly road cycling. Further research is required to design sport-specific tests to determine the remaining unexplained variance in performance.     

Saddle height effects on pedal forces,joint mechanical work and kinematics of cyclists and triathletes

Abstract

The effects of saddle height on pedal forces and joint kinetics (e.g. mechanical work) are unclear. Therefore, we assessed the effects of saddle height on pedal forces, joint mechanical work and kinematics in 12 cyclists and 12 triathletes. Four sub-maximal 2-min cycling trials (3.4 W/kg and 90 rpm) were conducted using preferred, low and high saddle heights (±10° knee flexion at 6 o'clock crank position from the individual preferred height) and an advocated optimal saddle height (25° knee flexion at 6 o'clock crank position). Right pedal forces and lower limb kinematics were compared using effect sizes (ES). Increases in saddle height (5% of preferred height, ES=4.6) resulted in large increases in index of effectiveness (7%, ES=1.2) at the optimal compared to the preferred saddle height for cyclists. Greater knee (11–15%, ES=1.6) and smaller hip (6–8%, ES=1.7) angles were observed at the low (cyclists and triathletes) and preferred (triathletes only) saddle heights compared to high and optimal saddle heights. Smaller hip angle (5%, ES=1.0) and greater hip range of motion (9%, ES=1.0) were observed at the preferred saddle height for triathletes compared to cyclists. Changes in saddle height up to 5% of preferred saddle height for cyclists and 7% for triathletes affected hip and knee angles but not joint mechanical work. Cyclists and triathletes would opt for saddle heights <5 and <7%, respectively, within a range of their existing saddle height.     

Cycling

The resistance against a cyclist while riding on rollers is due mainly to rolling resistance produced by the deformation of the tyre as it rolls against small diameter drums. Resistance is then combined with wheel speed to set power output. The effect of tyre pressure and cross‐section on power was investigated by systematically altering the pressure (552 kPa, 690 kPa, and 827 kPa) in a 20c, 23c, 25c, and 28c tyre of the same design while riding at a wheel speed of 45 kph. Average power over 1 minute was measured with a Power Tap Hub (Tune Corporation, Cambridge, Massachusetts, USA) on five occasions. Statistical significance was evaluated at p < 0.05. Power requirements increased significantly with each reduction in tyre pressure for all tyres and pressures except the 25c between 690 and 827 kPa. The 20c tyre required significantly more power from the cyclist at each tested tyre pressure when compared to the other tyres (which were not different from each other). The differences in resistance from tyre size were not observed when ridden on the road. Additionally, a slightly different tyre design from the same manufacturer responded similarly in the 20c, but was significantly different in the 23c size. It was also observed that power requirements increased significantly when both the wheels were ridden on the rollers as compared to just the rear wheel. These results indicate that the power requirements may be significantly altered by the cyclist by adjusting tyre pressure, tyre cross‐section size, tyre type, and with the number of wheels contacting the rollers. However, the magnitude of these power requirements may not be suitable for intense workouts of trained cyclists.     

Comparison of vibration rolling,nonvibration rolling,and static stretching as a warm-up exercise on flexibility,joint proprioception,muscle strength,and balance in young adults

Warm-up is an essential component for optimizing performance before an exercise session. This study investigated that the immediate effects of vibration rolling (VR), nonvibration rolling (NVR), and static stretching as a part of a warm-up regimen on the flexibility, knee joint proprioception, muscle strength, and dynamic balance of the lower extremity in young adults. Compared with the preintervention, VR induced the range of motion of knee flexion and extension significantly increased by 2.5% and 6%, respectively, and isokinetic peak torque and dynamic balance for muscle strength and dynamic balance increased by 33%–35% and 1.5%, respectively. In the three conditions, most outcomes between VR and NVR were comparable; however, the participants had a significantly higher knee joint reposition error after NVR than after VR, indicating that NVR would have a hampering knee joint proprioception effect. In particular, compared with static stretching, VR significantly increased the quadriceps muscle strength by 2-fold and dynamic balance by 1.8-fold. These findings suggest that athletic professionals may take VR into account for designing more efficient and effective preperformance routine to improve exercise performances. VR has high potential to translate into an on-field practical application.     

男子自行车4千米团体计时赛运动员的科学训练与监控

男子自行车4km团体计时赛,是我省一个新兴的项目,同时也是一个非常有希望的项目,为了这个项目能在12界全运会上有好的表现,能有一个历史性的突破.本文通过对我省4km团体的主力运动员,在训练和比赛中无氧域的运用生理生化监测等方法和手段,论证了一些训练方法的可行性,以及效果。为4km团体项目的突破指明了方向。     

筋膜自我放松效应研究进展

筋膜自我放松（Self-myofascial release,SMFR）是一种通过特殊工具不需要其他人帮助就可实现自我放松的方法,如今被运动员或普通人群广泛使用。近年来有研究成果初步证实SMFR似乎对人体有各种良好效应,比如,提升肌肉柔韧性,减少肌肉酸痛等,但目前对SMFR相关效应认识还不够全面,且机制不是很清楚。通过综述近年来国内外有关SMFR的文献,探究SMFR的急性和慢性效应与其相关机制。结论：短期而言,SMFR似乎对提高人体柔韧性和减少肌肉酸痛很有效,且不影响运动能力;SMFR可能会即刻改善动脉硬化,改善血管内皮功能,增加副交感神经系统的兴奋度;长期而言,SMFR也似乎可以提高人体柔韧性,但观点依然存在争议;SMFR的相关效应可能是通过生物力学和生理学机制实现。     

Acute adaptations and subsequent preservation of strength and speed measures following a Nordic hamstring curl intervention: a randomised controlled trial

This randomised controlled trial investigated changes in eccentric hamstring strength, 10m sprint speed, and change-of-direction (COD) performance immediately post Nordic hamstring curl (NHC) intervention and following a 3-week detraining period.

Fourteen male team sports athletes were randomised to a do-as-usual control group (CG; n = 7) or to a NHC intervention group (NHC; n = 7). Isokinetic dynamometry at 180°/s evaluated eccentric hamstring strength immediately post-intervention as the primary outcome measure. Secondary outcomes included 10 m sprint time and COD. Each outcome was measured, pre, immediately post-intervention and following a 3-week detraining period.

Immediately post-intervention significant group differences were observed in the NHC group for eccentric hamstring strength (31.81 Nm^?1 vs. 6.44 Nm^?1, P = 0.001), COD (?0.12 s vs. 0.20 s; P = 0.003) and sprint (- 0.06 s vs. 0.05 s; P = 0.024) performance. Performance improvements were maintained following a detraining period for COD (?0.11 s vs. 0.20 s; P = 0.014) and sprint (?0.05 s vs. 0.03 s, P = 0.031) but not eccentric hamstring strength (15.67 Nm^?1 vs. 6.44 Nm^?1, P = 0.145) These findings have important implications for training programmes designed to reduce hamstring injury incidence, whilst enhancing physical qualities critical to sport.