548 research outputs found
Match running performance during fixture congestion in elite soccer: Research issues and future directions
Match congestion in elite soccer has been proposed to result in residual fatigue and underperformance in ensuing competition due to insufficient recovery time. In this article, matters relating to match congestion and running performance in elite soccer competition are discussed. The authors suggest a need to determine the extent to which elite players are in reality exposed to periods of match congestion hence to potential declines in performance. Despite evidence of exercise-induced muscle damage combined with a decline in physical performance up to 72-hours post-match, research using time-motion analyses suggest running performance represented by distances covered is unaffected over periods of match congestion. The authors recommend analysis of alternative movement variables including accelerations, decelerations and turns that are taxing metabolically and contribute greatly to muscle damage. Moreover, a holistic approach combining subjective ratings with biochemical, hormonal and immunological responses to exercise would be pertinent especially in players frequently exposed to match congestion. Contemporary practitioners typically implement various post-match recovery treatments during dense schedules in an attempt to accelerate recovery and ensure that subsequent running performance is not unduly affected. However, empirical evidence to support their efficacy in maintaining running performance is lacking and the authors recommend controlled intervention studies using match simulations in an attempt to verify their effectiveness. These points are critically addressed using findings from the current scientific literature while gaps in the current body of knowledge and future directions for research are highlighted
Spinning strings, cosmic dislocations and chronology protection
A massless scalar field is quantized in the background of a spinning string
with cosmic dislocation. By increasing the spin density toward the dislocation
parameter, a region containing closed timelike curves (CTCs) eventually forms
around the defect. Correspondingly, the propagator tends to the ordinary cosmic
string propagator, leading therefore to a mean-square field fluctuation, which
remains well behaved throughout the process, unlike the vacuum expectation
value of the energy-momentum tensor, which diverges due to a subtle mechanism.
These results suggest that back reaction leads to the formation of a "horizon"
that protects from the appearance of CTCs.Comment: Published version, 4 pages, REVTeX
Monitoring training loads in professional basketball players engaged in a periodized training programme
The aims of this study were to investigate the dynamics of external (eTL) and internal (iTL) training loads during seasonal periods and examine the effect of a periodized training programme on physical performance in professional basketball players. Repeated measures for 9 players (28±6 yr; 199±8 cm; 101±12 kg) were collected from 45 training sessions, over a 6-wk pre-season phase and a 5-wk in-season phase. Physical tests were conducted at baseline (T1), week 4 (T2) and week 9 (T3). Differences in means are presented as % ± Confident Limits (CL). A very likely difference was observed during in-season compared to pre-season for the eTL variables measured by GPS: mechanical load (13.5±8.8) and peak acceleration (11.0±11.2) respectively. Regarding iTL responses, a very large decrement in TRIMP (most likely difference, -20.6±3.8) and in session-RPE training load (very likely difference, -14.2±9.0) was detected from pre-season to in-season. Physical performance improved from T1 to T3 for: Yo-Yo Intermittent-Recovery Test 1, 62.2±34.3, ES>1.2; Countermovement Jump, 8.8±6.1, ES>0.6; and Squat Jump, 14.8±10.2, ES>0.8. Heart rate (HR; % HRpeak) exercise responses during a submaximal running test decreased from T1 to T3 (3.2±4.3, ES1.2). These results provide valuable information to coaches about training loads and physical performance across different seasonal periods. The data demonstrate that both eTL and iTL measures should be monitored in association with physical tests to provide a comprehensive understanding of the training process
Effect of a congested match schedule on immune-endocrine responses, technical performance, and session-RPE in elite youth soccer players
This study investigated the effects of a congested match schedule (7 matches played in 7 days) on steroid hormone concentrations, mucosal immunity, session rating of perceived exertion (S-RPE) and technical performance in 16 elite youth soccer players (14.8 ± 0.4 yr; 170.6 ± 9.4 cm; 64.9 ± 7 kg). No change was observed for salivary cortisol concentration across multiple matches (p=0.33; Effect size [ES]=0.13-0.48). In contrast, there was a decrease in salivary testosterone and IgA concentrations (SIgA) from the 1st compared to the last time-point (p=0.01 and 0.001, ES=0.42 and 0.67, respectively). The SIgA concentration varied across time points (p 0.05). A higher number of tackles and interceptions were observed during the 4th match vs. 1st and 7th matches (p<0.001; ES=2.25 and 1.90, respectively). The present data demonstrate that accumulated fatigue related to participation in a congested match schedule might induce a decrease in testosterone concentration in youth playersâ and negatively affect their mucosal immunity and capacity to perform certain technical actions
Temporal Changes in Technical and Physical Performances During a Small-Sided Game in Elite Youth Soccer Players
Background: There have been claims that small-sided games (SSG) may generate an appropriate environment to develop youth playersâ technical performance associated to game-related problem solving. However, the temporal change in technical performance parameters of youth players during SSG is still unknown..
Objectives: The aim of this study was to examine temporal changes in technical and physical performances during a small-sided game (SSG) in elite soccer players..
Methods: Sixty elite youth players (age 14.8 ± 0.2 yr; stature 177 ± 5 cm; body mass 66.2 ± 4.7 kg) completed a 5 v 5 SSG using two repetitions of 8 minutes interspersed by 3 minutes of passive recovery. To evaluate temporal changes in performance, the data were analysed across 4 minutes quarters. Physical performance parameters included the total distance covered (TDC), the frequency of sprints (>18 kmâąh-1), accelerations and decelerations (> 2.0 mâąs-2 and - 2.0 mâąs-2), metabolic power (Wâąkg-1), training impulse (TRIMP), TDC: TRIMP, number of impacts, and body load. Technical performance parameters included goal attempts, total number of tackles, tackles and interceptions, total number of passes, and passes effectiveness..
Results: All physical performance parameters decreased from the first to the last quarter with notable declines in TDC, metabolic power and the frequency of sprints, accelerations and decelerations (P 0.05; trivial ES for 1st v 4th quarters: 0.15 - 0.33)..
Conclusions: The data demonstrate that technical performance is maintained despite substantial declines in physical performance during a SSG in elite youth players. This finding may have implications for designing SSGâs for elite youth players to ensure physical, technical and tactical capabilities are optimized. Modifications in player number, pitch dimensions, rules, coach encouragement, for instance, should be included taking into account the main aim of a given session and then focused on overloading physical or technical elements.
The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters
The role of the bridging ligand on the effective Heisenberg coupling
parameters is analyzed in detail. This analysis strongly suggests that the
ligand-to-metal charge transfer excitations are responsible for a large part of
the final value of the magnetic coupling constant. This permits to suggest a
new variant of the Difference Dedicated Configuration Interaction (DDCI)
method, presently one of the most accurate and reliable for the evaluation of
magnetic effective interactions. This new method treats the bridging ligand
orbitals mediating the interaction at the same level than the magnetic orbitals
and preserves the high quality of the DDCI results while being much less
computationally demanding. The numerical accuracy of the new approach is
illustrated on various systems with one or two magnetic electrons per magnetic
center. The fact that accurate results can be obtained using a rather reduced
configuration interaction space opens the possibility to study more complex
systems with many magnetic centers and/or many electrons per center.Comment: 7 pages, 4 figure
Financial indicators to evaluate the economic performance of feedlot steers with different slaughter weights
Unravelling the size distribution of social groups with information theory on complex networks
The minimization of Fisher's information (MFI) approach of Frieden et al.
[Phys. Rev. E {\bf 60} 48 (1999)] is applied to the study of size distributions
in social groups on the basis of a recently established analogy between scale
invariant systems and classical gases [arXiv:0908.0504]. Going beyond the ideal
gas scenario is seen to be tantamount to simulating the interactions taking
place in a network's competitive cluster growth process. We find a scaling rule
that allows to classify the final cluster-size distributions using only one
parameter that we call the competitiveness. Empirical city-size distributions
and electoral results can be thus reproduced and classified according to this
competitiveness, which also allows to correctly predict well-established
assessments such as the "six-degrees of separation", which is shown here to be
a direct consequence of the maximum number of stable social relationships that
one person can maintain, known as Dunbar's number. Finally, we show that scaled
city-size distributions of large countries follow the same universal
distribution
Geographic Information Systems (GIS) in Assessing Dental Health
The present study investigated the distribution profile of dental caries and its association with areas of social deprivation at the individual and contextual level. The cluster sample consisted of 1,002 12-year-old schoolchildren from Piracicaba, SP, Brazil. The DMFT Index was used for dental caries and the Care Index was used to determine access to dental services. On the individual level, variables were associated with a better oral status. On the contextual level, areas were not associated with oral status. However, maps enabled determining that the central districts have better social and oral conditions than the deprived outlying districts
Movement of Heterorhabditis amazonensis and Steinernema arenarium in search of corn fall armyworm larvae in artificial conditions
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