Running economy,mechanics, and marathon racing shoes     

Iain Hunter  Aubree McLeod  Dru Valentine  Tyler Low  Jared Ward  Ron Hager 《Journal of sports sciences》2013,31(20):2367-2373

ABSTRACT

The choice of marathon racing shoes can greatly affect performance. The purpose of this study is to metabolically and mechanically compare the consumer version of the Nike Vaporfly 4% shoe to two other popular marathon shoes, and determine differences in running economy. Nineteen subjects performed two 5-minute trials at 4.44m/s wearing the Adidas Adios Boost (AB), Nike Zoom Streak (ZS), and Nike Vaporfly 4% (VP) in random order. Oxygen uptake was recorded during minutes 3–5 and averaged across both shoe trials. On a second day, subjects wore reflective markers, and performed a 3-minute trial in each shoe. Motion and force data were collected over the final 30 seconds of each trial. VP oxygen uptake was 2.8% and 1.9% lower than the AB and ZS. Stride length, plantar flexion velocity, and center of mass vertical oscillation were significantly different in the VP. The percent benefit of the VP over AB shoe was predicted by subject ground time. These results indicate that use of the VP shoe results in improved running economy, partially due to differences in running mechanics. Subject variation in running economy improvement is only partially explained by variation in ground time.  相似文献   

Analysis of lower limb internal kinetics and electromyography in elite race walking     

Brian Hanley  Athanassios Bissas 《Journal of sports sciences》2013,31(11):1222-1232

Abstract

The aim of this study was to analyse lower limb joint moments, powers and electromyography patterns in elite race walking. Twenty international male and female race walkers performed at their competitive pace in a laboratory setting. The collection of ground reaction forces (1000 Hz) was synchronised with two-dimensional high-speed videography (100 Hz) and electromyography of seven lower limb muscles (1000 Hz). As well as measuring key performance variables such as speed and stride length, normalised joint moments and powers were calculated. The rule in race walking which requires the knee to be extended from initial contact to midstance effectively made the knee redundant during stance with regard to energy generation. Instead, the leg functioned as a rigid lever which affected the role of the hip and ankle joints. The main contributors to energy generation were the hip extensors during late swing and early stance, and the ankle plantarflexors during late stance. The restricted functioning of the knee during stance meant that the importance of the swing leg in contributing to forward momentum was increased. The knee flexors underwent a phase of great energy absorption during the swing phase and this could increase the risk of injury to the hamstring muscles.  相似文献   

The Kinematics and Kinetics of the Running Pattern of Two-, Four-, and Six-Year-Old Children     

Virginia L. Fortney 《Research quarterly for exercise and sport》2013,84(2):126-135

Abstract

Selected kinematic and kinetic variables in the running pattern of 2-, 4-, and 6-year-old children were investigated. Cinematographic records and force-plate tracings were used to study the running patterns of the 28 Caucasian subjects, 15 male and 13 female. A 2 × 3 (sex × age) factorial analysis of variance was used to determine whether effects of variation between and within age and sex factors for each of the dependent variables of selected kinematic (displacement and velocity) and kinetic (ground reaction force) variables were significant. The running speeds improved with age. Although height and weight gains influenced the improvement shown in performance, certain biomechanical variables also contributed to the development of the running pattern. In the majority of the selected kinematic and kinetic variables there were significant differences between the 2-year-old group and the other two groups. Where there were significant differences in the variables, the differences tended to be in displacement, velocity, and magnitude of force measures, rather than in time of occurrence measures. Significant differences between male and female subjects appeared in five kinematic variables related to the swing leg.  相似文献   

System Analysis for Oxygen Uptake Kinetics with Step and Pseudorandom Binary Sequence Exercise in Endurance Athletes     

Takayoshi Yoshida  Yoshiyuki Fukuoka  Richard L. Hughson 《Measurement in physical education and exercise science》2013,17(1):1-9

We examined whether the system analysis for step and pseudorandom binary sequence (PRBS) exercises could be useful to characterize oxygen uptake (VO₂) kinetics of female sedentary subjects and endurance athletes. Breath-by-breath VO₂ was determined during step- and PRBS-cycle ergometer exercises. The time course of the VO₂ kinetics was evaluated by the time constant of the second phase, which should reflect the adjustment of the oxidative metabolism at the skeletal muscle level. The VO₂ kinetics were significantly faster in long-distance runners than in sedentary subjects for both exercises. A significant relationship was observed in the VO₂ kinetics obtained from step and PRBS exercises. In each group, there was no significant difference in the VO₂ kinetics for step and PRBS exercises. These results indicated that the system analysis with PRBS exercises revealed the faster VO₂ kinetics in endurance athletes than in sedentary subjects.  相似文献   

Tennis     

John Blackwell  Duane Knudson 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(2):187-191

This study investigated the effect of the larger diameter (Type 3) tennis ball on performance and muscle activation in the serve. Sixteen male advanced tennis players performed serves using regular size and Type 3 tennis balls. Ball speed, surface electromyography, and serve accuracy were measured. There were no significant differences in mean initial serve speeds between balls, but accuracy was significantly greater (19.3%) with the Type 3 ball than with the regular ball. A consistent temporal sequence of muscle activation and significant differences in mean activation of different muscles were observed. However, ball type had no effect on mean arm muscle activation. These data, combined with a previous study, suggest that play with the larger ball is not likely to increase the risk of overuse injury, but serving accuracy may increase compared to play with the regular ball.  相似文献   

List of Reviewers     

Coral Falco  Javier Molina-García  Octavio Álvarez  Isaac Estevan 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(4):381-382

The aim of this study was to investigate the effects of target distance on temporal and impact force parameters that are important performance factors in taekwondo kicks. Forty-nine taekwondo athletes (age = 24.5 ± 5.9 years; mass = 79.9 ± 10.8 kg) were recruited: 13 male experts, 21 male novices, 8 female experts, and 6 female novices. Impact force, reaction time, and execution time were computed. Three-way repeated measure ANOVAs revealed significant ‘distance’ effect on impact force, reaction time, and execution time (p = 0.001). Comparisons between distance conditions revealed that taekwondo athletes kicked with higher impact force from short distance (17.6 ± 7.5 N/kg) than from long distance (13.1 ± 5.7 N/kg) (p < 0.001), had lower reaction time from short distance (498 ± 90 ms) and normal distance (521 ± 111 ms) than from long distance (602 ± 121 ms) (p < 0.001), and had lower execution time from short distance (261 ± 69 ms/m) than from normal distance (306 ± 105 ms/m) or from long distance (350 ± 106 ms/m) (p = 0.003 and p < 0.001, respectively). In conclusion, target distance affected the kick performance; as distance increases, impact force decreased and reaction time increased. Therefore, when reaction to a simple visual stimulus is needed, kicking from a long distance is not recommended, as longer time is required to respond.  相似文献   

Biomechanics of the ski cross start indoors on a customised training ramp and outdoors on snow     

Niels Jensby Nedergaard  Frederik Heinen  Simon Sloth  Hans-Christer Holmberg 《Sports biomechanics / International Society of Biomechanics in Sports》2013,12(3):273-286

An effective start enhances an athlete's chances of success in ski cross competitions. Accordingly, this study was designed to investigate the biomechanics of start techniques used by elite athletes and assess the influence of different start environments. Seven elite ski cross athletes performed starts indoors on a custom-built ramp; six of these also performed starts on an outdoor slope. Horizontal and vertical forces were measured by force transducers located in the handles of the start gate and a 12-camera motion capture system allowed monitoring of the sagittal knee, hip, shoulder, and elbow kinematics. The starting movement involved Pre, Pull, and Push phases. Significant differences between body sides were observed for peak vertical and resultant forces, resultant impulse, and peak angular velocity of the shoulder joint. Significantly lower peak vertical forces (44 N), higher resultant impulse (0.114 Ns/kg), and knee joint range of motion (12°) were observed indoors. Although movement in the ski cross start is generally symmetrical, asymmetric patterns of force were observed among the athletes. Two different movement strategies, i.e. pronounced hip extension or more accentuated elbow flexion, were utilised in the Pull phase. The patterns of force and movement during the indoor and outdoor starts were similar.  相似文献   

水分胁迫对茶树叶绿素a荧光动力学的影响   总被引：9，自引：0，他引：9  

王怀玉  罗英 《绵阳师范学院学报》2003,22(2):61-63

水分胁迫下，茶树叶片及叶绿体的光系统Ⅱ(PSⅡ)原初光能转换效率(Fv／Fm)和PSⅡ潜在活性(Fv／Fo)降低，而且随着水分胁迫的加强，降低越明显。三个茶树品种对水分胁迫的响应，也存在一定的差异。表明它们的抗旱性不同，其中福鼎大白茶和黔湄809抗旱性较强。黔湄303较差。  相似文献   

Modeling the kinetics of methane conversion in steam reforming process of coke-oven gas based on experimental data     

ZHANG Jia-yuan ZHOU Jie-min 《重庆大学学报(英文版)》2007,6(3):155-160

Steam-reforming is an effective approach for upgrading methane and hydrocarbon of coke-oven gas into CO and H2, but the kinetic behavior needs more study. We investigated the conversion of methane in coke-oven gas by steam reforming process in an electric tubular flow at 14 kPa with temperature varying from 500 °C to 950 °C, and developed a kenetic model for , ignoring the effects of adsorption and diffusion. The optimal dynamic conditions for methane conversion 14 kPa are as follows:the ratio of the amount of water to the amount of methane is from 1.1 to 1.3;the reaction temperature is from 1 223 K to 1 273 K. The methane conversion rate is larger than 95% when the ratio of the amount of water to the amount of methane is 1.2 at a temperature above 1 223 K with the residence time up to 0.75 s.  相似文献   

催化动力学光度法测定微量铁     

么琳 《唐山学院学报》2002,(4)

根据铁对过氧化氢氧化酸性铬蓝 K有强烈的催化作用 ,并使之褪色明显的特性 ,研究了最佳实验条件和动力学参数 ,建立了测定痕量铁的新方法。  相似文献