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The aims of this study were to investigate the energy build-up and dissipation mechanisms associated with using an arm swing in submaximal and maximal vertical jumping and to establish the energy benefit of this arm swing. Twenty adult males were asked to perform a series of submaximal and maximal vertical jumps while using an arm swing. Force, motion and electromyographic data were recorded during each performance and used to compute a range of kinematic and kinetic variables, including ankle, knee, hip, shoulder and elbow joint powers and work done. It was found that the energy benefit of using an arm swing appears to be closely related to the maximum kinetic energy of the arms during their downswing, and increases as jump height increases. As jump height increases, energy in the arms is built up by a greater range of motion at the shoulder and greater effort of the shoulder and elbow muscles but, as jump height approaches maximum, these sources are supplemented by energy supplied by the trunk due to its earlier extension in the movement. The kinetic energy developed by the arms is used to increase their potential energy at take-off but also to store and return energy from the lower limbs and to "pull" on the rest of the body. These latter two mechanisms become more important as jump height increases with the pull being the more important of the two. We conclude that an arm swing contributes to jump performance in submaximal as well as maximal jumping but the energy generation and dissipation sources change as performance approaches maximum. 相似文献
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This study replicated a previous research project addressing connections between family-of-origin communication and organizational dissent expression. We predicted that family communication patterns (FCPs), specifically conversation and conformity orientations, would predict upward, lateral, and displaced dissent. As in the original study, significant findings emerged for upward dissent and conformity orientation. This replication study indicated family type as an inconsistent predictor of expressed dissent. Contrary to the original study, we found no evidence to support a connection between pluralistic family types and upward dissent. Finally, as an extension of the original study we analyzed effects of FCPs on displaced dissent, finding an inverse association with conversation orientation. Implications for future research are discussed. 相似文献
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Robert Reed Simon Adrian Jobson Louis Passfield 《European Journal of Sport Science》2016,16(8):903-911
The cadence that maximises power output developed at the crank by an individual cyclist is conventionally determined using a laboratory test. The purpose of this study was two-fold: (i) to show that such a cadence, which we call the optimal cadence, can be determined using power output, heart-rate, and cadence measured in the field and (ii) to describe methodology to do so. For an individual cyclist's sessions, power output is related to cadence and the elicited heart-rate using a non-linear regression model. Optimal cadences are found for two riders (83 and 70 revolutions per minute, respectively); these cadences are similar to the riders’ preferred cadences (82–92?rpm and 65–75?rpm). Power output reduces by approximately 6% for cadences 20?rpm above or below optimum. Our methodology can be used by a rider to determine an optimal cadence without laboratory testing intervention: the rider will need to collect power output, heart-rate, and cadence measurements from training and racing sessions over an extended period (>6 months); ride at a range of cadences within those sessions; and calculate his/her optimal cadence using the methodology described or a software tool that implements it. 相似文献
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Wojciech Szczęsny Magdalena Kuligowska-Prusińska Stanisław Dąbrowiecki Jakub Szmytkowski Adrian Reśliński Maciej Słupski 《Journal of Zhejiang University. Science. B》2018,19(1):65-70
Purpose
Metalloproteinases are a key component of the pathogenesis of abdominal hernias. Obesity is considered a risk factor in herniogenesis and hernia recurrence. The aim of this study was to evaluate the serum concentrations of metalloproteinase-2 (MMP-2), MMP-9, MMP-13, and adiponectin in morbidly obese and nonoverweight controls.Materials and methods
The participants were recruited from among patients undergoing bariatric and non-bariatric surgery and divided into two groups: I (body mass index (BMI)≥35 kg/m2, n=40) and II (BMI<25 kg/m2, n=30). Serum concentrations of MMP-2, MMP-9, MMP-13, and adiponectin were measured using enzyme-linked immunosorbent assay (ELISA).Results
A statistically significant difference between groups was observed for MMP-2 concentration. The median MMP-9 concentration was higher in the obese group, but the difference was not statistically significant. Median MMP-13 concentrations did not differ between groups. Serum adiponectin concentration was insignificantly higher in the non-obese group.Conclusions
The elevated serum MMP-2 and MMP-9 concentrations in obese individuals may be related to the higher incidence of incisional hernias in this population.8.
Cheating on exams is a rampant and highly developed practice among youth in the Arab world, often involving elaborate networks, advanced technology and adult authorities. Rather than viewing cheating as mere laziness or immorality, this article interrogates the social meanings of cheating by comparing the practices and discourses of cheating on high-stakes high school exit exams – the tawjihi in Jordan and the Baccalauréat in Morocco. Using informal networks to obtain higher grades, and thereby better futures, cheating is one way youth contest the putative meritocracy of the state to reclaim a sense of control over their lives. Ironically, cheaters develop twenty-first century skills of collaboration, networking and creativity outside the school in order to evade the nation’s formal system of educational sorting. We argue that cheating illuminates the declining effectiveness of the public school in the nation-building project and the simultaneous emergence of the outcomes-oriented ‘neoliberal student’. 相似文献
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Mapping the knowledge structure exhibited by a cohort of students based on their understanding of how a galvanic cell produces energy 下载免费PDF全文
This study evaluates the use of an open‐ended question to determine students' knowledge structure on the topic of galvanic cells. The open‐ended question was developed and administered to 163 Grade 10 students who had earlier completed a course on electrochemistry. Students' responses were marked as well as coded on the basis of the fields identified from their responses. This was then evaluated statistically to determine the collective knowledge structure of the sample of students. The knowledge structure thus mapped contains both canonical concepts and alternative conceptions (ACs). An important finding emerging from this study is that instructors need to focus student's attention on the dynamic processes involving electrons and ions during the operation of galvanic cells. In order for students to fully understand how a galvanic cell operates, they need to see the whole picture. There are three critical components that lead to students' understanding of how an oxidation–reduction reaction can generate energy and how a circuit is complete: transfer of electrons during oxidation–reduction half‐reactions, flow of electrons within metals, and migration of ions in solution. Also, we found that it is possible for students to use correct chemistry concepts in an incorrect way by establishing linkages among these in an inappropriate manner. We reiterate that apart from evaluating students' ACs, it is also important to evaluate the links between the concepts and conceptions present in students' knowledge structure so that teaching can be made more effective. 相似文献
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