Strategies to improve impact efficiency in football kicking

In football, kicking with high ball velocity can increase scoring opportunities and reduce the likelihood of interception. Efficient energy transfer from foot to ball during impact is important to attain a high ball velocity. It is considered impact efficiency can be increased by reducing the change in ankle plantarflexion during foot–ball impact. However, conflicting evidence exists, questioning its effectiveness as a coaching cue. The aim of the present study was to systematically analyse joint stiffness, foot velocity and impact location with a mechanical kicking machine to determine if change in ankle plantarflexion during foot–ball impact and ball velocity are influenced. Sagittal plane data of the shank, foot and ball were measured using high-speed video (4,000 Hz). Increasing joint stiffness reduced change in ankle plantarflexion and increased ball velocity from a greater effective mass. Increasing foot velocity increased change in ankle plantarflexion and increased ball velocity. Distal impact locations increased change in ankle plantarflexion and reduced ball velocity as coefficient of restitution decreased. These results identify that change in ankle plantarflexion is a dependent variable during foot–ball impact and does not directly influence ball velocity. Coaches can assess ankle motion during impact to provide feedback to athletes on their impact efficiency.     

A review of models of vertical,leg, and knee stiffness in adults for running,jumping or hopping tasks

Abstract

The ‘stiffness’ concept originates from Hooke's law which states that the force required to deform an object is related to a spring constant and the distance that object is deformed. Research into stiffness in the human body is undergoing unprecedented popularity; possibly because stiffness has been associated with sporting performance and some lower limb injuries. However, some inconsistencies surrounding stiffness measurement exists bringing into question the integrity of some research related to stiffness. The aim of this study was to review literature which describes how vertical, leg and knee stiffness has been measured in adult populations while running, jumping or hopping. A search of the entire MEDLINE, PubMed and SPORTDiscus databases and an iterative reference check was performed. Sixty-seven articles were retrieved; 21 measured vertical stiffness, 51 measured leg stiffness, and 22 measured knee stiffness. Thus, some studies measured several ‘types’ of stiffness. Vertical stiffness was typically the quotient of ground reaction force and centre of mass displacement. For leg stiffness it was and change in leg length, and for the knee it was the quotient of knee joint moments and change in joint angle. Sample size issues and measurement techniques were identified as limitations to current research.     

奶奶家的早餐

I listen to her hum as she slowly scurries around the kitchen preparing breakfast. Well,she's scurrying in HER mind anyway.She snaps her fingers as she remembers she almost forgot the butter.While she turns to get it,I enter the kitchen area and take a seat.She reaches for the pepper and I appreciatively examine the table.She's made the coffee,and the creamer sits patiently in the tiny pitcher waiting to be poured.It ripples with her every step as they vibrate through the     

Assessment of progressively delayed prompts on guided skill learning in rats

We examined the controlling factors that allow a prompted skill to become autonomous in a discrete-trials implementation of Touchette’s (1971) progressively delayed prompting procedure, but our subjects were rats rather than children with disabilities. Our prompted skill was a left-right lever-press sequence guided by two panel lights. We manipulated (a) the effectiveness of the guiding lights prompt and (b) the presence or absence of a progressively delayed prompt in four groups of rats. The less effective prompt yielded greater autonomy than the more effective prompt. The ability of the progressively delayed prompt procedure to produce behavioral autonomy depended upon characteristics of the obtained delay (trial duration) rather than on the pending prompt. Sequence accuracy was reliably higher in unprompted trials than in prompted trials, and this difference was maintained in the 2 groups that received no prompts but yielded equivalent trial durations. Overall sequence accuracy decreased systematically as trial duration increased. Shorter trials and their greater accuracy were correlated with higher overall reinforcement rates for faster responding. Waiting for delayed prompts (even if no actual prompt was provided) was associated with lower overall reinforcement rate by decreasing accuracy and by lengthening trials. These findings extend results from previous studies regarding the controlling factors in delayed prompting procedures applied to children with disabilities.     

Nomadic Subjects: Young black women in Britain

This paper reads the fragmented life stories of four young black women in the UK, at a transitional point of their lives, when they are making decisions about their post-compulsory education. We argue that the notion of nomadism is a useful, albeit not unproblematic, tool to theorize the multifarious ways that these black young women negotiate subject positions, make choices and shape their lives. We further trace how these women are struggling against fixity and unity and attempting to speak and act outside or beyond the positions available within the collectivities to which they belong. Finally, we point out that in travelling around unstable and contradictory subject positions they are sometimes caught up within fears of distortion, and ultimately choose to remain 'at home'. This 'home', however, is rather formless and uncentred and, far from being easily localizable and defined, interrogates ideas and perceptions about territories and borders. It is through this 'new image', that we can perhaps start thinking about 'being at home' in different ways, beyond restrictions and limitations of families, classes, gender groups, races or nations.     

The Necessity and Violence of Theory

This paper offers a personal view of the need for and uses of theory in educational research. It draws on the work of two exemplary theorists to point up the epistemological role of theory in making research possible and making it reflexive. The second section of the paper deploys some recent ideas and research from class theory and class analysis to suggest some of the limitations of the use of social class in current educational research and some ways of thinking differently about class.     

Following My Head and My Heart: Integrating Preschoolers' Empathy,Theory of Mind,and Moral Judgments

Associations among hypothetical, prototypic moral, and conventional judgments; theory of mind (ToM); empathy; and personal distress were examined in 108 socioeconomically diverse preschoolers (M_age = 42.94 months, SD = 1.42). Repeated measures analysis of covariance with empathy, false beliefs, and their interaction as covariates indicated that empathy was significantly associated with judgments of greater moral but not conventional transgression severity, particularly for psychological harm, and with deserved punishment for unfairness. False beliefs were associated with (combined) moral criterion judgments of rule and authority independence and inalterability. Empathy also was positively associated with criterion judgments but only for children low in ToM. Personal distress was unrelated to judgments. Results demonstrate the importance of both affective and cognitive processes in preschoolers' moral judgments.     

Kinematics of preferred and non-preferred handballing in Australian football

In Australian football (AF), handballing proficiently with both the preferred and non-preferred arm is important at elite levels; yet, little information is available for handballing on the non-preferred arm. This study compared preferred and non-preferred arm handballing techniques. Optotrak Certus (100 Hz) collected three-dimensional data for 19 elite AF players performing handballs with the preferred and non-preferred arms. Position data, range of motion (ROM), and linear and angular velocities were collected and compared between preferred and non-preferred arms using dependent t-tests. The preferred arm exhibited significantly greater forearm and humerus ROM and angular velocity and significantly greater shoulder angular velocity at ball contact compared to the non-preferred arm. In addition, the preferred arm produced a significantly greater range of lateral bend and maximum lower-trunk speed, maximum strike-side hip speed and hand speed at ball contact than the non-preferred arm. The non-preferred arm exhibited a significantly greater shoulder angle and lower- and upper-trunk orientation angle, but significantly lower support-elbow angle, trunk ROM, and trunk rotation velocity compared to the preferred arm. Reduced ROM and angular velocities found in non-preferred arm handballs indicates a reduction in the degrees of freedom and a less developed skill. Findings have implication for development of handballing on the non-preferred arm.