The relationship between peak height velocity and physical performance in youth soccer players

Longitudinal changes in height, weight and physical performance were studied in 33 Flemish male youth soccer players from the Ghent Youth Soccer Project. The players' ages at the start of the study ranged from 10.4 to 13.7 years, with a mean age of 12.2 +/- 0.7 years. Longitudinal changes were studied over a 5 year period. Peak height velocity and peak weight velocity were determined using non-smoothed polynomials. The estimations of peak height velocity, peak weight velocity and age at peak height velocity were 9.7 +/- 1.5 cm x year-1, 8.4 +/- 3.0 kg x year-1 and 13.8 +/- 0.8 years, respectively. Peak weight velocity occurred, on average, at the same age as peak height velocity. Balance, speed of limb movement, trunk strength, upper-body muscular endurance, explosive strength, running speed and agility, cardiorespiratory endurance and anaerobic capacity showed peak development at peak height velocity. A plateau in the velocity curves was observed after peak height velocity for upper-body muscular endurance, explosive strength and running speed. Flexibility exhibited peak development during the tear after peak height velocity. Trainers and coaches should be aware of the individual characteristics of the adolescent growth spurt and the training load should also be individualized at this time.     

Identification with sport teams as a function of the search for certainty

Based on ideas from subjective uncertainty reduction theory, we examined the extent to which individuals hold similar sport team preferences to their family and friends. We also assessed the extent to which perceived sport importance and personal need for structure are influential in the development of team identification. Australian high school students aged 15.5+/-1.0 years (mean+/-s) completed questionnaires containing the Personal Need for Structure Scale, the Relational-Interdependent Self-Construal scale, a Team Identification Scale, and items assessing perceptions of sport importance and team preferences. As expected, correlations indicated that preferences for sport teams were significantly related to the preferences of family and friends. Separate analyses of variance confirmed the remaining hypotheses. More specifically, individuals who perceived that sport was important identified with the team more than individuals who perceived sport to be less important. Also, individuals high in personal need for structure scored higher in cognitive/affective team identification than those low in this need. Individuals with differing needs for structure did not differ in their scores on other dimensions of team identification. The results support the notion that cognitive/emotional attachments to sport teams are influenced by perceptions of the importance of sport and by needs for subjective structure. It is possible that other psychological motives, such as the desire for self-esteem, facilitate the development of evaluative dimensions of team identification.     

Food attitudes in female athletes: association with menstrual cycle length

The aim of this study was to examine the relationship between indicators of risk of disordered eating, body image and varied menstrual cycle lengths. Altogether, 151 female athletes were invited from 16 sports and 70 female non-athletic controls were recruited from a university lecture class. The participants completed several surveys, including demographics, menstrual cycle history, physical activity, Eating Disorder Inventory (EDI) and the Three Factor Eating Questionnaire (TFEQ). Selected EDI subscales were summed to reflect eating disorder risk and body image. Menstrual cyclicity was based on self-reported cycle length for the last 6 months (normal cycles = 26-32 days, irregular cycles < or =26 or >32 days). Athletes overall had more irregular cycles (29.1%) than the non-athletes (15.7%) (P < 0.05). There were significant differences in scores for eating disorder risk, body dissatisfaction, drive for thinness, cognitive restraint (TFEQ) and disinhibition (TFEQ), only when athletes were divided based on menstrual cyclicity (i.e. irregularly cycling athletes had higher scores than athletes with normal menstrual cycle lengths). No differences in these scores were found between non-athletes with normal or irregular menstrual cycle lengths. In conclusion, irregularly short or long menstrual cycle length is associated with subtle indications of higher risk of disordered eating in female athletes.     

The graph-theoretic field model— II. application of multi-terminal representations to field problems

This paper is a sequel to a paper entitled “The Graph-Theoretic Field Model—I: Modelling and Formulations” (1). Herein, the Theory of Multi-Terminal Representations is applied to the Graph-Theoretic Field Model to provide mathematical models of finite elements. The element models are obtained solely from the algebraic building blocks of the Graph-Theoretic Field Model, without recourse to any functional mathematics. The theory of Multi-Terminal Representations is developed for both linear and non-linear problems. Examples of the application of the theory to one- and two-dimensional field problems are presented from heat conduction and electrostatics.     

A control problem with structural choices

The case is considered in which, during the operation of an optimal control system, the optimizer, in addition to applying his usual control, may switch structures. Necessary and sufficient conditions are derived and emphasis is placed on the special characteristics of this problem. Continuous and discrete time set-ups are considered and the separation principle is shown not to hold for the linear quadratic case in the presence of noise.     

Dimensions of R&D location in the United States

R&D activities in the United States, as in other advanced economies, are geographically concentrated in certain types of locations. This study presents data on the location of four dimensions of R&D in the U.S.: industrial R&D laboratories, scientists and engineers engaged in R&D, scientists and engineers employed by the federal government, and research universities. Industrial R&D is much more concentrated in large urban areas than the other dimensions, and appears to locate more in response to the location of manufacturing activity than to the location of research universities and federal research facilities. The location of R&D employment, which includes government university, and industrial employees, is associated with facilities for all three types of R&D. Because of these factors, R&D in the U.S. is found on a significant per capita basis in 44 of 177 urban areas, most of them in the northeastern portion of the country. When two dimensions, industrial R&D laboratories and R&D employees, are combined as a measure of R&D concentration, the locational pattern is less clustered regionally. Ten urban areas in all regions of the U.S. are identified as important complexes of R&D. Since the location of R&D is a major indicator of comparative advantage for technological activities and the economic potential of urban regions, only a few areas of the U.S. are likely to remain important in the generation of innovations.     

The physics of brass wind instruments

The design of musical instruments owes more to art than to science and assessment of their quality is essentially subjective. Nevertheless, the physical principles of their operation are very interesting and may be of practical importance. This article reviews the acoustics of brass wind instruments, regarding the player and his instrument as an entity, and compares experimental and theoretical results.     

Structural aspects of controllability and observability—I. tensorial aggregation

The classical criteria for controllability and observability are given a tensorial formulation which is then extended into Boolean form directly related to a digraph interpretation of system structure. This is examined in detail with particular reference to group theoretic aspects, invariant properties under transformation, the term rank test and the existence of zero eigenvalues.Within this framework the structural design concepts of potential controllability and observability are presented in generalised terms.