Age- and size-corrected kicking speed and accuracy in elite junior soccer players.

Kicking powerfully and accurately is essential in soccer, and players who kick proficiently with both feet are highly sought after. Assessing performance in youth players is often confounded by more physically developed players outperforming their smaller peers. To alleviate such bias, we present a testing protocol and normative data developed with an elite Brazilian soccer academy that controls for players' age and size to assess kick performance with both feet. We measured kick speed and kick accuracy of 178 players and recorded their age (10-20 years), height, and mass. Combining age, height, and mass into an age and size index (ASI), we developed equations describing the relationship between ASI and performance. To determine the underlying predictors of performance, we also measured sprint ability and soccer-specific motor control of each foot with ball dribbling tasks. Kicking speed with the dominant foot was predicted by ASI, sprint speed, and motor control of the nondominant foot, while kicking speed with the nondominant foot was predicted by ASI and motor control of the nondominant foot. Kick accuracy with each foot was predicted by ASI and motor control of the corresponding foot. To improve kicking performance, we suggest training programs focus on motor control.

Simple and reliable protocol for identifying talented junior players in team sports using small-sided games.

We designed and tested a protocol for measuring the performance of individuals in small-sided soccer games. We tested our protocol on three different groups of youth players from elite Brazilian football academies. Players in each group played a series of 3v3 games, in which individuals were randomly assigned into new teams and against new opponents for each game. We calculated each individual's average individual goals scored, goals scored by teammates, goals conceded, and net team goals per game. Our protocol was consistent across days and repeatable across groups, with intraclass correlation coefficients (ICCs) of 0.57-0.69 for average net goals per game across testing days. Players could achieve high success by scoring goals or ensuring their team concede few goals. We also calculated the first and second dimension of a principal component analysis based on each player's number of goals scored, goals scored by teammates, and number of goals conceded per game. Players that were overall high performers had higher PC1 scores, while PC2 scores represented the type of contribution made by a player to overall performance. Positive PC2 values were indicative of high number of individual goals while negative values were associated with more goals from teammates and fewer conceded goals. Our design allows coaches and scouts to easily collect a robust metric of individual performance using randomly designed, small-sided games. We also provide simulations that allow one to apply our methodology for individual talent identification to other small-sided games in any team sport.

Effect of dual-task and visual manipulation on the balance of older physical exercise practitioners and sedentary older and young adults / Efeito da dupla-tarefa e da manipulação visual no equilíbrio de idosos praticantes de exercícios físicos, idosos e adultos jovens não praticantes

The objective was to compare the effect of dual-task and visual manipulation on postural balance of older physical activity practitioners and older and young adult non-practitioners. Fifty-one subjects were divided into four groups: Older Practitioners of Karate (OPK), Older Practitioners of Func-tional Gymnastics (OPG), Non-practicing Older Adult Group (ONP), and Non-practicing Young Adult Group (YNP). The task was to remain in an upright, static position on a force platform, for 40 seconds, with and without a cognitive dual-task, by means of an arithmetic sum, and visual manipulation, with and without a blindfold. The analyzed variables of the Center of Pressure (COP) were: area of oscillation and mean amplitude of oscillation, in the mediolateral and anteroposterior directions. The results showed similar performances among the physical exercise groups (OPK and OPG) and the young adults (YNP), while the ONP presented greater postural oscillation in all conditions. In the visual condition, blindfolded, in the condition with the dual-task, the OPK, OPG, and YNP groups oscillated less, when compared to the condition without dual-task. Thus, it can be inferred that the practice of physical exercises, regardless of the modality, is effective in improving the postural control of older adults, with similar performances to the group of young adults, even in conditions with dual-task and sensory manipulation of vision

O objetivo do estudo foi comparar o efeito da dupla-tarefa e da manipulação visual no equilíbrio postural em idosos praticantes de diferentes modalidades de exercícios físicos, idosos e adultos jovens não praticantes. Participaram do estudo 51 indivíduos, subdivididos em quatro grupos: grupo de idosos praticantes de karatê (GPK), grupo de idosos praticantes de ginástica funcional (GPF), grupo de idosos não praticantes (GNP) e grupo de adultos jovens (GNP). A tarefa consistiu em permanecer, na posição ereta, sob plataforma de força, por 40 segundos, sem e com dupla-tarefa, por meio de soma aritmética e com manipulação visual, com e sem visão. As variáveis analisadas do Centro de Pressão (COP) foram: área de oscilação e amplitude média de oscilação, nos sentidos médio-lateral e ântero-posterior. Os resultados foram desempenhos semelhantes entre os grupos que praticavam exercícios físicos (OPK e OPG) e o de adultos jovens ( YNP), enquanto o ONP apresentou maior oscilação postural, nas variáveis área e amplitude de oscilação. Na condição visual, com vi-são e com a dupla-tarefa, os grupos OPK, OPG e YNP oscilaram menos, quando comparados a condição sem dupla-tarefa. Dessa forma, pode-se inferir que a prática de exercícios físicos, independente da modalidade, é eficaz no equilíbrio postural de idosos, com desempenho semelhante no grupo de adultos jovens, mesmo em condições com dupla-tarefa e manipulação sensorial da visão

Predicting the defensive performance of individual players in one vs. one soccer games.

The aim of this study was to use technical skill and physical performance and coaches' rankings to predict the defensive performance of junior soccer players. Twenty-one male players (mean age 17.2 years, SD = 1.1) were recruited from the Londrina Junior Team Football Academy in Brazil. Data were collected during regular training sessions. After participants had warmed up, players were asked to either dribble the ball or sprint through five custom circuits that varied in average curvature (0-1.37 radians.m-1). In addition, four coaches were asked to rank the players from best to worst in defensive ability. Dribbling, sprinting, and coaches' rankings were then compared with defending performance as assessed in the one vs. one competitions (N = 1090 paired-trials: 40-65 trials per individual), in which they acted as defender or attacker in turn. When defending, the objective was to steal the ball or prevent the attacker from running around them with the ball into a scoring zone. Testing occurred over three days. Overall, dribbling performance (r = 0.56; P = 0.008) and coaches' ranking (r = 0.59; P = 0.004) were significantly related to defensive ability; sprinting performance was not (r = 0.20; P = 0.38). Though dribbling performance and coaches' ranking each explained 30% and 37% of the variance in defensive performance, respectively, the two predictors were not related (r = 0.27; P = 0.23), so combined these traits explained more than half the variance in defensive performance. In conclusion, the current study demonstrates that including only one metric of closed-skill performance-dribbling speed-doubles the ability of coaches to identify their best defensive players in one vs. one scenarios.

Efeito da oclusão temporal na ação de ataque sobre a tomada de decisão defensiva na modalidade de voleibol / Effect of temporal occlusion of the attack action on defensive decision making in volleyball

O presente estudo analisou o efeito da oclusão temporal na cortada do voleibol sobre a tomada de decisão defensiva em atletas com diferentes níveis de experiência. Os participantes foram divididos em três grupos: adulto (GAD; n = 16), infanto/mirim (GIM; n =16) e adulto novato (GNO; n = 16). Imagens da finalização de jogadas de ataque realizadas por quatro atletas foram editadas em cinco diferentes momentos: (OT1) a 399 ms (12 quadros) antes do contato do atacante com a bola; (OT2) a 266 ms (oito quadros) antes; (OT3) a 133 ms (quatro quadros) antes; (OT4) no momento do contato atacante/bola e; (OT5) a 133 ms (quatro quadros) após o contato do atacante com a bola. Ao assistirem os vídeos editados, os participantes deveriam informar o local de aterrissagem da bola seguido da confiança com a qual emitiam suas respostas. Foi mensurada a precisão na predição da trajetória da bola (acerto/erro) e a confiança da resposta (escala Likert 1-5). Quanto à frequência de acertos, o grupo GAD (X = 63,67 ± 10,38%) apresentou maior frequência de acertos que GIM (X = 55,46 ± 10,17%) em OT2 (p = 0,001). A frequência de acertos de GAD (X = 79,29 ± 10,38%) também foi maior que a de GNO (X = 71,87 ± 10,43%) em OT3 (p = 0,012). As condições mostraram-se diferentes entre si (Bonferroni's p < 0,005), com a frequência de acertos aumentando de OT1 (X = 36,06 ± 12,44%) à OT5 (X = 98,17 ± 4,81%). Para confiança, GAD e GIM apresentaram-se mais confiantes que GNO (Bonferroni's p < 0,016) em OT1, OT2, OT3. Novamente, as condições diferiram entre si (Bonferroni's p < 0,005), com os grupos mostrando-se mais confiantes em OT5. Concluiu-se que, independente da experiência, os grupos se mostraram capazes de predizer a localização de aterrissagem da bola. Contudo, grupos com maior experiência mostraram-se superior quanto à sua capacidade antecipatória.

This study examined the effect of temporal occlusion of a volleyball spike on the defensive decision-making of athletes with different levels of experience. The participants were divided in three groups: adult (GAD; n = 16), sub-17 (GIM; n = 16) and novice adult (GNO; n = 16). Images of attacks performed by 4 athletes were edited in five different moments: (OT1) 399 ms (12 frames) before the hitter's contact with the ball, (OT2) 266 ms (eight frames) before contact; (OT3) 133 ms (four frames) before contact; (OT4) at the moment of hitter's contact with the ball and; (OT5) 133 ms (four frames) after the hitter's contact with the ball. After watching the edited videos, participants were asked to predict the landing site of the ball, followed by the confidence with which they issued their responses. The precision in the prediction of the ball's trajectory (correct/incorrect) and the confidence of the response (1-5 Likert scale) were measured. Regarding the correct response frequency, the GAD (X = 63.67 ± 10.38%) group showed a greater frequency of correct responses than GIM (X = 55.46 ± 10.17%) in OT2 (p = 0.001) and the frequency of correct responses of GAD (X = 79.29 ± 10.38%) was also greater than GNO (X = 71.87 ± 10.43%) in OT3 (p = 0.012). The conditions were different from each other, with the frequency of correct responses increasing from OT1 (X = 36.06 ± 12.44%) to OT5 (X = 98.17 ± 4.81%). Regarding confidence, GAD and GIM were more confident than GNO in OT1, OT2 and OT3. Again, the conditions were different from each other, with the groups showing more confidence in OT5. We conclude that, regardless of experience, all groups were able to predict the landing site of the ball. However, groups with more experience were superior in their anticipatory ability.

Algumas reflexões sobre o exercicio da pesquisa na educação física / Some reflections on the research activity in physical education / Algunas reflexiones sobre el ejercicio de la investigación en educación física

O objetivo foi realizar algumas reflexões sobre o que tem sido discutido pela comunidade científica em geral, e da área da Educação Física, sobre as práticas questionáveis (PQs) empregadas no exercício da pesquisa científica. Dentre as inúmeras estratégias para levar vantagem no sistema que avalia a produtividade em pesquisa, as PQs aparecem com pouca frequência como principal objeto de investigação em pesquisas na área da Educação Física. A abordagem qualitativa e tipo de pesquisa bibliográfica caracterizam a metodologia utilizada. A análise de conteúdo foi empregada para análise dos documentos selecionados. Consideramos que é preciso ampliar os estudos sobre a temática, visando elaborar meios efetivos para prevenção de práticas questionáveis na pesquisa.

The objective was to present some reflections about what has been discussed by the scientific community in general, and in the field of Physical Education in special, on the theme of questionable practices used in scientific research. Among the numerous strategies to take advantage of the system that evaluates research productivity, the questionable practices rarely appear as the a main objective of research in the field of Physical Education. We conducted a bibliographical research with a qualitative approach, employing content analysis in the selected documents.We believe that more studies about the theme are necessary with the objective of creating effective strategies to prevent questionable practices in research.

El objetivo fue reflexionar sobre lo que ha sido discutido por la comunidad cientí¬ fica en general y el área de Educación Física, sobre las prácticas cuestionables empleados en la realización de investigaciones científicas. Entre las numerosas estrategias para tomar ventaja em el sistema que evalúa la productividad de la investigación, las prácticas cuestionables aparecen con poca frecuencia como el objeto principal de la investigación en el área de Educación Física. El estudio se caracteriza por un enfoque cualitativo, como la literatura. El análisis de contenido se utilizó para analizar los artículos y libros científicos seleccionados. Consideramos que es necesario ampliar los estudios sobre el tema, para encontrar formas efectivas de prevenir prácticas cuestionables en la investigación científica.

Efeito da ingestão de cafeína sobre o desempenho físico e estado de humor de ciclistas / Effects of caffeine on performance and mood of cyclists

O objetivo do estudo foi analisar os efeitos da ingestão de cafeína sobre o desempenho físico e estado de humor de ciclistas em teste contrarrelógio de 1 km. Dez ciclistas do sexo masculino realizaram aleatoriamente um teste contrarrelógio de 1 km em duas condições experimentais: ingestão de cafeína (CAF - 6 mg.kg-1) e placebo (PL) 60 min antes do teste. Durante os testes foram obtidas as medidas de tempo total e estado de humor pelo questionário de Brunel (BRUMS). Para comparações dos parâmetros tempo total e estado de humor, foi utilizado o teste t de Student pareado e teste Wilcoxon, respectivamente. Nenhuma diferença estatisticamente significante foi encontrada no tempo total e no estado de humor nas condições CAF e PL (P>0,05). Os resultados sugerem que a cafeína não melhora o desempenho físico e nem altera o estado de humor dos atletas em um teste contrarrelógio de 1 km.

This study analyzed the effects of caffeine ingestion on physical performance and mood state of cyclists in a 1km time trial test. Ten male cyclists performed randomly a 1km time-trial test under two experimental conditions: Caffeine (CAF - 6 mg.kg-1) and placebo (PL) 60 min before the test. During the test were obtained the total time and the mood using the Brunel questionnaire (BRUMS). For comparisons of total time and mood states it was applied the paired Student's t-test and Wilcoxon test, respectively. No significant differences were found in the total time to complete tests and in the mood states between CAF and PL conditions (P>0.05). The results suggested that caffeine does not improve performance or change the mood of cyclists in a 1km time trial test.

EMG spectral analysis of incremental exercise in cyclists and non-cyclists using Fourier and Wavelet transforms / Análise espectral do sinal emg de exercício incremental em ciclistas e não ciclistas usando as transformadas de Fourier e Wavelet

The aim of this study was to compare the electromyographic indices of fatigue (slope of median frequency) calculated with the fast Fourier transform (FFT) and wavelet transform (WT) in trained and untrained individuals during cycle exercise. A second objective was to compare the variance of the spectral parameters (median frequency - MF) obtained by the FFT and WT during exercise. Twelve cyclists and non-cyclists performed a maximal incremental test to determine the peak power (Wp) and electromyographic activity of the vastus lateralis (VL), rectus femoris (RF), biceps femoris (BF), semitendinous (ST) and tibialis anterior (TA). Mean values of median frequency, determined by the FFT and WT, were used for the spectral analysis of the electromyographic signals of the studied muscles. The analyzed parameters were obtained for each time period corresponding to 0, 25, 50, 75, and 100% of total duration of the maximal incremental test. No statistically significant differences were found in the values of MF and electromyographic indices of fatigue between the two techniques (FT and WT) both in the cyclists and non-cyclists group (P>0.05). Regarding the MF variance, statistically significant differences were found in all analyzed muscles, as well as in different time periods, both in the cyclists and non-cyclists groups when comparing the FFT and WT techniques (P<0.05). The WT seems to be more adequate to dynamic tasks, since it does not require the signal to be quasi-stationary, unlike the limitation imposed upon the use of the FFT.

O objetivo deste estudo foi comparar índices de fadiga eletromiográfica (inclinação da frequência mediana), calculado com a transformada rápida de Fourier (FFT) e transformada de wavelet (WT) em indivíduos treinados e não treinados durante o exercício de ciclismo. Um segundo objetivo foi o de comparar a variância dos parâmetros espectrais (frequência mediana - MF), obtidos por FFT e WT durante o exercício. Doze ciclistas e doze não ciclistas realizaram um teste incremental máximo, para determinar a potência pico (Wp) e atividade eletromiográfica do vasto lateral (VL), reto femoral (RF), bíceps femoral (BF), semitendíneo (ST) e tibial anterior (TA). Os valores médios da frequência mediana determinados pelo FFT e WT, foram utilizados para a análise espectral dos sinais eletromiográficos dos músculos estudados. Os parâmetros avaliados foram obtidos para cada período de tempo correspondente a 0, 25, 50, 75 e 100% da duração total do teste incremental máximo. Nenhuma diferença estatisticamente significativa foi encontrada nos valores da MF e índices eletromiográficos de fadiga entre as duas técnicas utilizadas (FT e WT), em ambos os grupos, ciclistas e não ciclistas (P> 0,05). Quanto à variância da MF, as diferenças estatisticamente significativas foram encontradas em todos os músculos analisados, bem como em diferentes períodos de tempo, tanto nos ciclistas quanto nos não ciclistas, quando se compara as técnicas FFT e WT (P <0,05). A WT parece ser mais adequada para tarefas dinâmicas, uma vez que não requer que o sinal a ser quase estacionário, ao contrário da limitação imposta ao uso da FFT.

Electromyographic activity and rate of muscle fatigue of the quadriceps femoris during cycling exercise in the severe domain.

This study compared the activation pattern and the fatigue rate among the superficial muscles of the quadriceps femoris (QF) during severe cycling exercise. Peak oxygen consumption (VO(2)peak) and maximal accumulated oxygen Deficit (MAOD) were established by 10 well-trained male cyclists (27.5 ± 4.1 years, 71.0 ± 10.3 kg, 173.4 ± 6.6 cm, mean VO(2)peak 56.7 ± 4.4 ml·kg·min(-1), mean MAOD 5.7 ± 1.1 L). Muscle activity (electromyographic [EMG] signals) was obtained during the supramaximal constant workload test (MAOD) and expressed by root mean square (RMS) and median frequency (MF slope). The RMS of the QF, vastus lateralis (VL) and vastus medialis (VM) muscles were significantly higher than at the beginning after 75% of exercise duration, whereas for the rectus femoris (RF), this was observed after 50% of exercise duration (p ≤ 0.05). The slope of the MF was significantly higher in the RF, followed by the VL and VM (-3.13 ± 0.52 vs. -2.61 ± 0.62 vs. -1.81 ±0.56, respectively; p < 0.05). We conclude that RF may play an important role in limiting performance during severe cycling exercise.

Fourier and wavelet spectral analysis of EMG signals in maximal constant load dynamic exercise.

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in maximal constant load dynamic exercise (100% W(max)). The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in maximal constant load dynamic exercise (P>0.05). However, the results of the variance was significantly lower for at least one of the muscles studied in CWT compared to STFT (P〈0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

Fourier and wavelet spectral analysis of EMG signals in supramaximal constant load dynamic exercise.

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in supramaximal constant load dynamic exercise (110% VO(2peak)). The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in supramaximal constant load dynamic exercise (P>0.05). However, the results of the variance was significantly lower for at least one of the muscles studied in CWT compared to STFT (P < 0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.

Fourier and wavelet spectral analysis of EMG signals in isometric and dynamic maximal effort exercise.

Frequency domain analyses of changes in electromyographic (EMG) signals over time are frequently used to assess muscle fatigue. Fourier based approaches are typically used in these analyses, yet Fourier analysis assumes signal stationarity, which is unlikely during dynamic contractions. Wavelet based methods of signal analysis do not assume stationarity and may be more appropriate for joint time-frequency domain analysis. The purpose of this study was to compare Short-Time Fourier Transform (STFT) and Continuous Wavelet Transform (CWT) in assessing muscle fatigue in isometric and dynamic exercise. The results of this study indicate that CWT and STFT analyses give similar fatigue estimates (slope of median frequency) in isometric and dynamic exercise (P>0.05). However, the results of the variance was lower for both types of exercise in CWT compared to STFT (P < 0.05) indicating more variability in the EMG signal analysis using STFT. Thus, the stationarity assumption may not be the sole factor responsible for affecting the Fourier based estimates.