Reflexiones sobre los factores que pueden condicionar el desarrollo de los deportistas de alto nivel

A raíz de una nueva orientación en el estudio de los deportistas expertos, desde una perspectiva sociocrítica, en los últimos años han surgido líneas de investigación cuyo objeto de estudio han sido las distintas variables que influyen en la formación del deportista experto. El objetivo del presente artículo es presentar los resultados de dichas investigaciones, analizando cómo deben ser contemplados dichos aspectos en el entrenamiento

The Casimir spectrum revisited

We examine the mathematical and physical significance of the spectral density sigma(w) introduced by Ford in Phys. Rev. D38, 528 (1988), defining the contribution of each frequency to the renormalised energy density of a quantum field. Firstly, by considering a simple example, we argue that sigma(w) is well defined, in the sense of being regulator independent, despite an apparently regulator dependent definition. We then suggest that sigma(w) is a spectral distribution, rather than a function, which only produces physically meaningful results when integrated over a sufficiently large range of frequencies and with a high energy smooth enough regulator. Moreover, sigma(w) is seen to be simply the difference between the bare spectral density and the spectral density of the reference background. This interpretation yields a simple `rule of thumb' to writing down a (formal) expression for sigma(w) as shown in an explicit example. Finally, by considering an example in which the sign of the Casimir force varies, we show that the spectrum carries no manifest information about this sign; it can only be inferred by integrating sigma(w).Comment: 10 pages, 4 figure

Effects of fatigue and time-out on physiological, time-motion indicators and in patterns of spatial organization of the teams in basketball

The aim of this study was to identify the effects of fatigue on physiological variables, time-motion indicators and patterns of spatial organization of the teams in basketball. The study sample consisted of 10 basketball players of the under-18 with a mean age of 17.5 ± 0.3 years. There were two sessions: session a) game continuous (C1) 10 minutes - yo-yo intermittent recovery test (level 1) - 1 minute timeout - game continuous (C2) 10 minutes. Session b) game interrupted (I1) 5 minutes - 1 minute timeout - 5 minutes game - yo-yo intermittent recovery test (level 1) -1 minute timeout -game interrupted (I2) - 5 minutes - 1 minute timeout - 5 minutes game. HR values were determinate by the YYIRTL1 and registered by short range radiotelemetry heart-rate monitors (Polar Team System, Polar Electro, Finland), time-motion analysis were registered with GPS (SPI Elite. GPSports Systems, Australia), and a digital camera was used to record the game. The results suggest that the fatigue and the time-outs promote betters patterns of spatial organization. Additionally the results showed that with the accumulated fatigue the players covered a less total distance and in a slower way

Power, heart rate and perceived exertion responses to 3x3 and 4x4 basketball small-sided games

Despite the interest drawn by game adaptations in players' performance development, no study examined the effects of these task constraints in basketball games exercise intensity. Therefore, the aim of this study is to identify differences in power, heart rate and perceived exertion responses to 3x3 and 4x4 basketball small-sided games. Eight young male basketball players participated in this study. Player's individual peak heart rate value and global perceived exertion was registered immediately after two small-sided games, 3x3 and 4x4. Additionally, squat jump and countermovement jump were used to assess power. Our results show that both small-sided games promoted high physiological demands, whereas the players performed the tasks above 80% of HRmax. Nevertheless, another interesting finding of this study is related to the fact that 3x3 contributed to higher physiological demands than the 4x4. The significant increase in the countermovement jump posttest jump results could suggest that the 4x4 were not played as quickly nor intensely as the 3x3. Decreases of the space and number of players in game allow greater self-recreation of players and greater intervention in game. Therefore, the heart rate response during the series displays a higher physiologic impact in 3x3 than in 4x4

Analysis of critical moments in the league ACB 2007-08

The aim of this paper was to identify the variables that determine winning or losing in the critical moments of the basketball games. A total of forty one critical moments were analyzed, corresponding to 30 games of the regular season from the Spanish Professional League (ACB, season 2007-2008). Games were selected according to the definition of critical moments (described in the available literature), which corresponded to overtime and the last 5 minutes of games with score differences equal or below to six points. The results revealed better values in the winners in defensive rebounds and successful free-throws

Colored nanoparticles for ecological dyeing of cellulosic fibers

Dyeing cellulosic fibres with reactive dyes wastes great quantities of salt and water. The objective of this work is to dye cellulosic fibers using colored nanoparticles (CNPs) as an alternative to dyeing with reactive dyes. CNPs do not need salt nor soaping after dyeing, consuming less than 50% of water

Diffusion of coloured silica nanoparticles into human hair

A novel method for dyeing human hair fibres using coloured silica nanoparticles of 206 nm has been developed. Diffusion of coloured silica nanoparticles into hair fibres has been investigated; silica nanoparticles do not penetrate at all, or do so only sparingly, into the structure of Caucasian virgin hair. However, coloured silica nanoparticles diffused readily into bleached hair fibres. Scanning electron microscopy showed that coloured silica nanoparticles were present mainly in the outer regions of the hair structure (the inner layers of the cuticle and the outer region of the cortex). It was found that the silica nanoparticles were physically entrapped in the hair fibres and results showed a good shampoo fastness to washing

Sol-gel technology for ecological dyeing cellulosic of fibres

Dyeing cellulosic fibres with reactive dyes wastes great quantities of salt and water. The objective of this work is to dye cellulosic fibers using coloured nanoparticles (CNPs) as an alternative to dyeing with reactive dyes, without salt and with only a short washing-off procedure at the end of dyeing. Samples of cotton were dyed by exhaustion with CNPs at light to medium colours. Washfastness results are given. Complete Washing-off sequence after dyeing was not necessary for the red and yellow colours, only one rinsing. The blue colour needs some washing off since the fastness is lower than for the other colours even though soaping is not necessary, saving energy and time relative to dyeing with reactive dyes

Short- and long-term effects of using shooting straps on free-throw accuracy of young female basketball players

This study identified the short- and long-term effects of using a shooting strap on the accuracy of freethrows performed by U15 female basketball players during training and competition. Thirty six female basketball player volunteers (aged 14.3±0.5 years) from the Lithuanian Schoolchildren Basketball League were randomly assigned to either an experimental or control group. The experimental group used a shooting strap that immobilized movements of the supporting hand while shooting. The control group performed freethrows without any training aid. Learning and transfer of performance was assessed before and after the intervention training sessions (4-week intervention program applied 4 times per week), and on a retention test after one year. Results showed that: (a) free-throw accuracy was higher after one month and after one year of intervention than before the intervention training program in both practice and competition; (b) the experimental group scored better in practice and competition than the control group after one month and one year of the intervention; and (c) free-throw accuracy was higher during training sessions than during competition. The identified short-term and long-term improvements in free-throw shooting accuracy support the usage of shooting straps. The use of shooting straps and external assisting devices might allow adjusting programs of training to provide fluent free-throw accuracy progresses from youth to senior categories

Coaches perceived importance of tactical items in basketball players' long term development

One of the topics of sport sciences that have not been adequately investigated is the importance that specialists dedicate to tactical skills in long-term players development. The purpose of this study was to evaluate the importance that basketball coaches give to the development of these abilities in both sexes. Data were collected using a questionnaire. Items tapped six areas tactic related to: small sided games, offensive superiority games, defensive superiority games, formal game, offense and defense. The sample was divided according to team's sex and stage of long-term development: initiation, orientation, specialization, or high-performance. No significant differences were found in small sided games and formal game. Significant differences in assigned importance between coaches of boys to offensive superiority and defensive superiority games were found, supporting that these items should be the subject of more intense development primarily until 14 years of age. Significant differences in assigned importance between coaches of girls to defense were found. Coaches reinforced the importance of developing team offensive aspects, primarily at highperformance stage. Finally, significant differences in assigned importance between coaches of both sexes to defensive tactical work were found. Results confirmed that defensive tactical work should be the subject of more intense development between 11 and 14 years old but mostly after 19 years of age, reinforcing the importance of tactical work in later stages of development, i.e., high-level performance