The effects of jumping distance on the landing mechanics after a volleyball spike

The purpose of this study was to assess the effects of jumping distance on the landing mechanics after a volleyball spike, to help in injury prevention and training for safer landing. Ground reaction forces and three-dimensional kinematic data were collected from six male university right-handed volleyball players under “Normal” and “Long” jumping distance conditions of landing after a spike. The results revealed that the landings under the Long jumping distance condition produced significantly greater centre of gravity velocities and larger mean loading rates. Although data were collected for bilateral landings with the two feet contacting the force platform at the same time, landing motion was asymmetric and the left leg was considered to play a more critical role in the absorption of the landing impact. The trunk and hip positions at the initial contact with the floor and the range of motions of the knee and ankle were key kinematic parameters for reducing the vertical peak ground reaction forces and extending the time from the initial contact to the occurrence of this peak force, which consequently reduced the mean loading rate upon landing.     

A pitcher injury risk assessment study analyzing composite,titanium, aluminum and wood softball bat performance

Abstract

Over the past few years, there has been a significant increase in the performance of softball bats from the Olympics down to the recreational level. It is theorized that the introduction of composite-based material bats has been the largest contributor to the increase in batted-ball performance, which directly corresponds to a decrease in available pitcher reaction time that can lead to an increase in injury potential. To test this theory, a controlled field-test study comparing all of the different bat model types currently available was conducted. The performance of ten bat model types; two composite-based, two titanium-based, two aluminum-based multi-wall, two aluminum-based single-wall and two wood-based bats were measured using 1686 N/0.64 cm (379 lbs/0.25”) compression softballs in order to calculate available pitcher reaction times when using a specific bat model type. Over 1000 Batted-ball velocity measurements were analyzed using two calibrated radar devices and five experienced test subjects. The results of this study indicate that when titanium-based or composite-based softball bat performance results are compared to published safety studies in the sports of softball and baseball, available pitcher reaction times are unsafe, which can lead to a higher injury risk potential. The significance of this research is to provide experimental field-test data on the possible safety risks to pitchers that can be used to reduce the injury potential and promote safety awareness in the sport of softball.     

The effects of anxiety upon psychomotor performance

This paper describes an experiment which examined the effects of anxiety on choice reaction time and movement time. A balanced repeated measures design was adopted in which eight female subjects performed a six‐choice visual reaction task in ‘no anxiety’ and ‘anxiety’ conditions. The anxiety condition required subjects to jump from a balcony 15 feet (4.57 m) into a foam‐filled pit below. Subjects in the anxiety condition demonstrated significantly higher levels of cognitive anxiety and longer reaction times than those in the no anxiety condition. The analysis of the reaction time data also revealed a significant interaction between anxiety and block. No significant effects emerged in the case of movement time.     

Focusing of visual attention at rest and during physical exercise in soccer players

Abstract

In this study, we investigated the focus of visual attention in expert soccer players together with the effects of acute bouts of physical exercise on performance. In two discriminative reaction time experiments, which were performed both at rest and under submaximal physical workload, visual attention was cued by means of spatial cues of different size followed by compound stimuli with local and global target features. Soccer players were slower than non-athletes in reacting to local compared with global targets, but were faster in switching from local to global attending. Thus, soccer players appear to be less skilled in local attending, but better able than non-athletes to rapidly “zoom out” the focus of attention. Non-athletes generally showed faster performance under physical load, as expected according to the hypothesis of exercise-induced increases in arousal and/or activation and in resource allocation. In contrast, soccer players showed a more differentiated pattern of exercise-induced facilitation that selectively affects specific components of the attentional performance and is interpreted by referring to the role played by individual expertise and cognitive effort.     

A biomechanical analysis of common lunge tasks in badminton

Abstract

The lunge is regularly used in badminton and is recognized for the high physical demands it places on the lower limbs. Despite its common occurrence, little information is available on the biomechanics of lunging in the singles game. A video-based pilot study confirmed the relatively high frequency of lunging, ～15% of all movements, in competitive singles games. The biomechanics and performance characteristics of three badminton-specific lunge tasks (kick, step-in, and hop lunge) were investigated in the laboratory with nine experienced male badminton players. Ground reaction forces and kinematic data were collected and lower limb joint kinetics calculated using an inverse dynamics approach. The step-in lunge was characterized by significantly lower mean horizontal reaction force at drive-off and lower mean peak hip joint power than the kick lunge. The hop lunge resulted in significantly larger mean reaction forces during loading and drive-off phases, as well as significantly larger mean peak ankle joint moments and knee and ankle joint powers than the kick or step-in lunges. These findings indicate that, within the setting of this investigation, the step-in lunge may be beneficial for reducing the muscular demands of lunge recovery and that the hop lunge allows for higher positive power output, thereby presenting an efficient lunging method.     

Ground Reaction Force Symmetry during Walking and Running

Abstract

The purpose of this study was to determine the effect of triathlon training using multiple, short cycle-run sequences (multicycle-run training) on cycle-run performance. Twelve competitive triathletes, randomized into two groups, underwent multicycle-run training or normal training for 6 weeks. During this period, baseline training remained the same for both groups, and only the high-intensity component differed. The differentiated exercises were performed at or above 100% maximal aerobic velocity. The improvements in overall cycle-run performance were similar (3.3 ± 1.4 % and 6.1 ± 1.7 % rise in performance in multicycle-run and normal training, respectively). However, the improvement in performance was significantly greater for the multicycle-run training (- 11.2 ± 6.8 s versus ?1.2 ± 7.7 s for multicycle-run training and normal training, respectively) during both the cycle-run change and the first 333-m lap, which together are termed the cycle-run transition. We concluded that 6 weeks of multicycle-run training did not induce greater improvement in cycle-run performance than did normal training in competitive triathletes. However, it did induce significant improvement in the cycle-run transition. This finding indicates that multicycle-run training may help competitive triathletes to develop greater skill and better physiological adaptations during this critical transition period of the triathlon race.     

Postcontraction Influences on Reaction Time

Abstract

The purpose of this study was to compare reaction time (RT) and fractionated RT components (premotor and motor times) between normal and postcontraction conditions. Twelve participants performed 20 trials each of control and postcontraction RT conditions. For the control condition, participants executed a learned, rapid, knee-extension contraction response to an auditory stimulus. The postcontraction condition was identical to the control condition except that the participants performed a 3-s isometric contraction of the knee extensor muscles prior to an auditory stimulus. Muscle activity was recorded from the quadriceps muscle group. Results indicated that the postcontraction condition was significantly faster than the control condition for the average RT, premotor time, and motor time. It was concluded that reaction time, processing time, and muscle contraction time for a learned task could be significantly reduced following an isometric contraction.     

社会责任、绩效评价与市场反应

以发布公司社会责任报告的上市公司为研究对象,运用因子分析法将16个社会责任绩效评价指标降维至债权人因子、股东因子、员工消费者因子、供应商因子、公共关系因子及政府因子6个主因子,采用事件研究法检验社会责任绩效评价主因子和综合绩效对累计平均超额回报率的影响,尝试在公司社会责任绩效评价与市场反应之间构建联系。研究结果显示,资本市场对公司发布社会责任报告事件反应显著敏感,公司对供应商、政府和公共关系承担的社会责任绩效评价越高,引起的正面市场反应比债权人、股东和员工消费者因子越为灵敏。进一步研究发现,相对于配对样本公司,量化披露环境责任公司的社会责任绩效评价信息引起的市场反应更为敏感。     

田径短跑中电子起跑监测系统测量方法有效性的研究

研究采用统计分析法,以第16届亚运会短跑项目354名男、女运动员的起跑后蹬的时间-压力曲线为研究对象,将起跑反应时分成实际反应时和反应动作时进行研究分析。结果表明:反应动作时存在着显著的个体差异,其个体差异明显大于起跑反应时和实际反应时,对反应时的测量结果有着显著的影响;反应动作时与实际反应时无相关性,反应速度和动作速度测量互相不能替代;起跑反应时无法反映出运动员真正的起跑反应时间以及运动员反应时间的差异;使用固定的压力阈值来测量运动员的反应时间,没有考虑运动员的个体差异,违背了国际田径规则中的公平原则;应以实际反应时作为运动员的起跑反应时的测量值,以确保竞赛的公平性。     

《化学反应工程》网络课件的设计与开发

《化学反应工程》是化工类专业的核心课程,根据教学大纲的要求,应用计算机网络技术,开发了《化学反应工程》网络课件。网络课件采用文本、图像、声音、动画、视频等媒体组合在一起,为学生提供了丰富的教学资料,生动形象地表现了用文字难以描述的难点以及抽象内容。文章论述了开发《化学反应工程》网络课件的意义、方法以及网络课件特点及应用。