Effect of gear ratio on peak power and time to peak power in BMX cyclists

The aim of this study was to ascertain if gear ratio selection would have an effect on peak power and time to peak power production in elite Bicycle Motocross (BMX) cyclists. Eight male elite BMX riders volunteered for the study. Each rider performed three, 10-s maximal sprints on an Olympic standard indoor BMX track. The riders’ bicycles were fitted with a portable SRM power meter. Each rider performed the three sprints using gear ratios of 41/16, 43/16 and 45/16 tooth. The results from the 41/16 and 45/16 gear ratios were compared to the current standard 43/16 gear ratio. Statistically, significant differences were found between the gear ratios for peak power (F(2,14)?=?6.448; p?=?.010) and peak torque (F(2,14)?=?4.777; p?=?.026), but no significant difference was found for time to peak power (F(2,14)?=?0.200; p?=?.821). When comparing gear ratios, the results showed a 45/16 gear ratio elicited the highest peak power,1658?±?221?W, compared to 1436?±?129?W and 1380?±?56?W, for the 43/16 and 41/16 ratios, respectively. The time to peak power showed a 41/16 tooth gear ratio attained peak power in ?0.01?s and a 45/16 in 0.22?s compared to the 43/16. The findings of this study suggest that gear ratio choice has a significant effect on peak power production, though time to peak power output is not significantly affected. Therefore, selecting a higher gear ratio results in riders attaining higher power outputs without reducing their start time.     

Metabolic cost of running is greater on a treadmill with a stiffer running platform

Exercise testing on motorised treadmills provides valuable information about running performance and metabolism; however, the impact of treadmill type on these tests has not been investigated. This study compared the energy demand of running on two laboratory treadmills: an HP Cosmos (C) and a Quinton (Q) model, with the latter having a 4.5 times stiffer running platform. Twelve experienced runners ran identical bouts on these treadmills at a range of four submaximal velocities (reported data is for the velocity that approximated 75–81% VO_2max). The stiffer treadmill elicited higher oxygen consumption (C: 46.7 ± 3.8; Q: 50.1 ± 4.3 ml·kg^?1 · min^?1), energy expenditure (C: 16.0 ± 2.5; Q: 17.7 ± 2.9 kcal · min^?1), carbohydrate oxidation (C: 9.6 ± 3.1; Q: 13.0 ± 3.9 kcal · min^?1), heart rate (C: 155 ± 16; Q: 163 ± 16 beats · min^?1) and rating of perceived exertion (C: 13.8 ± 1.2; Q: 14.7 ± 1.2), but lower fat oxidation (C: 6.4 ± 2.3; Q: 4.6 ± 2.5 kcal · min^?1) (all analysis of variance treadmill comparisons P < 0.01). This study confirms that caution is required when comparing performance and metabolic results between different treadmills and suggests that treadmills will vary in their comparability to over-ground running depending on the running platform stiffness.     

Performing under pressure: Exploring the psychological state underlying clutch performance in sport

Clutch performance is improved performance under pressure. However, little research has examined the psychological state experienced by athletes in these situations. Therefore, this study qualitatively examined the subjective experience underlying clutch performance across a range of sports (e.g., team, individual) and standards (Olympic to recreational athletes). Sixteen athletes (M_age = 27.08 years; SD = 6.48) took part in in-depth, semi-structured interviews primarily after an exceptional performance (M = 4.38 days later; SD = 3.14). Data were analysed inductively and thematically. Clutch states involved 12 characteristics, including heightened and deliberate concentration, intense effort, and heightened awareness, which distinguished the experience of clutch from other optimal psychological states such as flow. Other characteristics, such as perceptions of control, were also reported and supported previous experimental research on clutch. These findings present in-depth qualitative insights into the psychological state underlying clutch performance, and are discussed in relation to the existing literature on optimal psychological states in sport.     

脑力、体力劳动者足底压力参数分布特征及评定

通过分析脑力、体力劳动者自然行走过程中峰力值（maxforce,MF）、达峰力值时间（time to max force）、冲量（impulse）等参数特征,探讨职业对足底压力分布的影响。采用比利时Footscan USB2平板式足底压测试系统对50名普通健康脑力劳动者和63名普通健康体力劳动者进行自然行走过程中动态足底压力测试。结果显示：脑力、体力劳动者左脚Toel、Toe2-5、Heel Lateral区域平均峰值（MF）存在显著性差异,右脚Mid foot、Meta5区域MF差异存在非常显著性（P〈0．01）,左、右双足平均峰力值（MF）最大值均出现在足跟内侧（Heel Medial）。脑力、体力劳动者足底各区域达峰力值的时间（TMF）,左右双足差异均存在非常显著性（P〈0．01）。脑力劳动者与体力劳动者行走过程中左足在Toel、Toe2-5、Meta1、Heel Medial、Heel Lateral区域的冲量（Impulse,IP）,体力劳动者明显大于脑力劳动者且具有显著性差异〈0．01）,体力劳动者与脑力劳动者的足底MF与足弓接触面积及足角度存在不同程度的相关。结果说明：脑力劳动者与体力劳动者行走过程中左右双足的平均峰力值、接触面积、冲量等参数都存在不同程度的差异,可能与长期从事的职业不同有关,建议经常进行体育锻炼或定制矫形鞋垫,可以缓解足底压力高压区的过度集中,不断维护足健康水平。     

运动对中等职业学校学生骨密度的影响

采用文献法资料法和实验法调查119名中等职业学校学生（以下简称中职生）（16～18岁）的骨密度（bone mineral density,BMD）和参加运动的情况。结果显示男性运动组与不运动组BMD值有显著差异性。女性中职生运动组有使骨密度增加的趋势。运动时间长、运动频率高的组别BMD也高。男性每日运动时间大于1h组与小于1h组的BMD值具有显著性差异。结论：运动对BMD有积极影响,运动频率大于3次／周及每日运动时间超过1h对BMD的影响最为明显。     

高强度运动对心脏的冲击影响及信号提取研究

设计实时的肌肉组织血氧量和瞬时心率无损同步检测方案与设备,为研究高强度运动心脏的冲击影响、探讨高强度运动中代谢规律提供测试手段。方法:采用连续双波长近红外光测量肌肉中血红蛋白与肌红蛋白含氧量的变化情况;采用芬兰SUUNTO心率带和自行设计的转发器及配套PC软件测量瞬时心率,进行了100m跑同步实测试验。结果:100m跑以无氧代谢为主。起跑后的前7s为无氧代谢的非乳酸功能,肌氧饱和度曲线变化不大。7s后开始消耗肌肉中储存的氧。结论:双波长近红外光组织氧测试法和运动心率无线实时采集系统能够正确实时同步地检测高强度运动时血氧和心率,揭示了高强度运动过程中肌肉中氧的运输与消耗及心率之间的动力学过程。     

Impact absorption of tennis shoe-surface combinations

The aim of this study was to investigate, for typical shoes and surfaces used in tennis, the relative role of the shoe and surface in providing cushioning during running. Five test surfaces ranging from concrete to artificial turf were selected, together with two shoe models. Impact absorbing ability was assessed mechanically using drop test procedures and biomechanically using peak magnitude and rate of loading of impact force and peak in-shoe pressure data at the lateral heel. Differences in biomechanical variables between shoe-surface combinations were identified using a two-way ANOVA (p < 0.05). Mechanical test results were found to rank the surfaces in the same order regardless of the shoe model, suggesting that the surface is influential in providing cushioning. However, for all mechanical and biomechanical (p < 0.05) variables representing impact absorbing ability, it was found that the difference between shoes was markedly greater than the differences between surfaces. The peak heel pressure data were found to rank the surfaces in the same order as the mechanical tests, while impact force data were not as sensitive to the changes in surface. Correlations between mechanical and biomechanical impact absorption highlighted the importance of testing the shoe-surface combination in mechanical tests, rather than the surface alone. In conclusion, mechanical testing of the shoe-surface combination was found to provide a strong predictor of the impact absorbing ability during running if pressure data were used. In addition, for typical shoe-surface combinations in tennis, the shoe was found to have more potential than the surface to influence impact loading during running. Finally, in-shoe pressure data were found to be more sensitive than force plate data to changes in material cushioning.     

最大吸氧量间接测算全新通用方程及其应用

作者论证了最大吸氧量间接测算全新通用议程组男VO2m,Ka;女,VO2mKa.式中：P,运动强度,单位,瓦;f,运动心率,次／分;n＝0.16－0．21,人机效率;Ka＝1．25~0．01A,A,年龄系数。在A＝25、P＝50~200瓦、f＝120~170次／分之间,方程组VO2m测算范围（1．6~6．0）升／分,包括体力弱者及世界级马拉松运动员,与奥斯特兰德实测数序表偏差不大于3％。     

日粮不同蛋氨酸水平对山鸡产蛋高峰期生产性能的影响

试验选取46～48周龄,健康无病、体型、体重基本一致的产蛋高峰期山鸡200只,随机均分为5组,1个对照组(Ⅴ组),4个试验组(Ⅰ、Ⅱ、Ⅲ、Ⅳ组),对照组蛋氨酸水平为0.22%,每组设10个重复,每个重复4只山鸡。每组基础日粮相同,蛋氨酸水平为0.22%,各组蛋氨酸添加量分别为0、0.05%、0.10%、0.15%、0.20%(每组添加量递增0.05%),试验期2个月。结果表明,日粮中添加适宜蛋氨酸水平不仅维持较长时间的产蛋高峰期和理想的产蛋峰值,显著地提高产蛋量和蛋重,而且还能提高饲料报酬和经济效益。试验结果表明:山鸡产蛋高峰期日粮蛋氨酸水平为0.37%。     

人体心肺机能第二拐点与某些生理生化指标的关系

通过采用放射免疫分析（ＲＩＡ）和乳酸分析等方法，对２０名优秀运动员的实验研究，探讨人体心肺机能达到第二拐点时，血中环－磷酸腺苷（ｃＡＭＰ）、环磷酸鸟苷（ｃＧＭＰ）、乳酸水平、以及吸氧量（绝对值和相对值）、氧脉博等指标的变化，以初步揭示人体机能第二拐点与某些生理生化指标的关系。实验结果表明：人体机能达第二拐点时，以上指标各参数值均明显高于运动起始时刻的数值（Ｐ＜０．００１）。此刻人体所承受的生理负荷强度已达到无氧阈平均水平以上，机体已由有氧供能为主过渡到无氧代谢占优势。