Sergio Augusto Cunha

A spectral analysis of team dynamics and tactics in Brazilian football

Abstract The purposes of this study were to characterise the total space covered and the distances between players within teams over ten Brazilian First Division Championship matches. Filmed recordings, combined with a tracking system, were used to obtain the trajectories of the players (n = 277), before and after half-time. The team surface area (the area of the convex hull formed by the positions of the players) and spread (the Frobenius norm of the distance-between-player matrix) were calculated as functions of time. A Fast Fourier Transform (FFT) was applied to each time series. The median frequency was then calculated. The results of the surface area time series median frequencies for the first half (0.63 ± 0.10 cycles · min−1) were significantly greater (P < 0.01) than the second-half values (0.47 ± 0.14 cycles · min−1). Similarly, the spread variable median frequencies for the first half (0.60 ± 0.14 cycles · min−1) were significantly greater (P < 0.01) than the second-half values (0.46 ± 0.16 cycles · min−1). The median frequencies allowed the characterisation of the time series oscillations that represent the speed at which players distribute and then compact their team formation during a match. This analysis can provide insights that allow coaches to better control the team organisation on the pitch.

Analysis of the distance covered by Brazilian professional futsal players during official matches

The purpose of this study was to measure and characterise the distances covered by Brazilian professional futsal players. The trajectories of 93 players during five matches were obtained using an automatic tracking method. The distances covered were analysed for different game conditions: over the entire game and during the times when the ball was out of play and in play separately. When the entire game was considered, the results showed that there was a reduction in the total distance covered per minute from the first [median ± IQR (interquartile range): 97.9 ± 16.2 m/min] to the second half (median = 90.3 m/min; IQR = 12.0), and when only the in-play time was considered (first half: 136.6 ± 17.2 m/min; second half: 129.2 ± 16.7 m/min). The percentage of distance covered in the standing and walking velocity range was higher in the second half than in the first when considering the entire game (30.8% and 28.0%, respectively) and during the in-play time (19.3% and 16.2%, respectively). In conclusion, this study verified that futsal players reduced the physical performance during the second half.

Analysis of football game-related statistics using multivariate techniques

Abstract The purpose of this study was to explore football game-related statistics during a competition, using principal component and cluster analyses to determine if it is possible to distinguish the winning teams from the drawing and losing ones. We collected the game-related statistics of the group phase matches of the 2006 World Cup and organised them into a matrix. The principal components of the covariance matrix were calculated. The scores of the first and second components were used to represent the new data, and cluster analysis was applied to separate the elements in two groups (G1 and G2). To analyse the degree of separation between the groups, we calculated the Silhouette Coefficient for each group. Finally, we checked if the winning teams were classified into the same group. The Silhouette Coefficients found for G1 and G2 were 0.54 and 0.55, respectively. Results showed that 70.3% of the winning teams were classified into the same group (G1). Similarly, 67.8% of the drawing and losing teams were classified in G2. This study presented a different way to analyse game-related statistics that allowed the multivariate differences to be shown between successful and unsuccessful teams.

Performance comparisons of the kicking of stationary and rolling balls in a futsal context

Angular kinematics of the hip, knee, and ankle joints, as well as ball velocity and accuracy for stationary and rolling balls were compared in a futsal (Five-a-Side Indoor soccer) context. Ten futsal athletes performed five kicks each on stationary and rolling futsal balls. Six digital cameras (120 Hz) recorded the kicks. For both kick types, angles for hip, knee, and ankle joints were calculated using Euler angle conventions. Angular velocity, ball velocity, foot linear velocity, relative velocity, and accuracy also were analyzed. The kicking of both stationary and rolling balls showed similarities for ball velocity (24.2 ± 2.2 m/s and 23.8 ± 2.7 m/s, respectively), foot velocity (17.6 ± 1.8 m/s and 17.2 ± 2.2 m/s, respectively), and accuracy (26% and 24% target hits, respectively). We observed few differences in angular kinematics and angular joint velocities between kick types. Elite players can make online adjustments in the preparatory phase so that kicking a rolling ball is almost exactly like kicking a stationary ball.

Characterization of the Sprint and Repeated-Sprint Sequences Performed by Professional Futsal Players, According to Playing Position, During Official Matches

The purposes of this study were to investigate sprints and to characterize repeated-sprint sequences (RS) performed by athletes during professional futsal matches. We analyzed 97 players during 5 official matches using the DVideo automatic tracking system. The sprints were analyzed during the first and second halves according to playing position, and RS were categorized according to the number of sprints and the time between them. The results showed an increase (F[1, 2520] = 3.96; P = .046) in the sprint duration from the first (mean = 3.1 ± 1.3) to the second half (mean = 3.2 ± 1.2). However, no differences were found for other variables (distance covered, peak velocity, initial velocity, recovery time between sprints, and sprints performed per minute) or among playing positions. In addition, when considering RS, the results showed that RS comprising two sprints interspersed with a maximum of 15 seconds of recovery were significantly more frequent than other RS. The findings of this study characterizing the sprinting features of futsal players can help coaches to plan physical training and assessments according to the requirements of the sport.The purposes of this study were to investigate sprints and to characterize repeated-sprint sequences (RS) performed by athletes during professional futsal matches. We analyzed 97 players during 5 official matches using the DVideo automatic tracking system. The sprints were analyzed during the first and second halves according to playing position, and RS were categorized according to the number of sprints and the time between them. The results showed an increase (F[1, 2520] = 3.96; P = .046) in the sprint duration from the first (mean = 3.1 ± 1.3) to the second half (mean = 3.2 ± 1.2). However, no differences were found for other variables (distance covered, peak velocity, initial velocity, recovery time between sprints, and sprints performed per minute) or among playing positions. In addition, when considering RS, the results showed that RS comprising two sprints interspersed with a maximum of 15 seconds of recovery were significantly more frequent than other RS. The findings of this study characterizing the sprinting features of futsal players can help coaches to plan physical training and assessments according to the requirements of the sport.

Utilização do intercepto-y na avaliação da aptidão anaeróbia e predição da performance de nadadores treinados

The objective of this study was to verify the use of y-intercept from the critical velocity model in the evaluation of the anaerobic fitness and prediction of maximal performance in trained swimmers in crawl style. Fourteen swimmers with ages ranging from 15 to 18 years participated in this study. The athletes performed the tied swimming test, maximal performances tests and critical velocity (CV) for the determination of anaerobic swimming capacity (AWC). 1) The tied swimming test was applied through maximal effort during 30 seconds fixed to the equipment with load cells for the measurement of the peak force, anaerobic fitness and peak lactate. 2) The subjects also performed maximal performances at distances of 100, 200, 300, 400 and 600 meters with two hours interval between each swim. 3) AWC at CV model was determined utilizing all possible combinations by maximal performances applying the distance-time linear regression model. The AWC value obtained was of 25.07 ± 4.22 m, with linear regression coefficient between 0.99 and 1.00, and linear coefficient error of 19.30 ± 5.9%. AWC was not correlated with all maximal performances, peak force (227.81 ± 63.02 N), anaerobic fitness (85.55 ± 13.05 N), and peak lactate (6.80 ± 1.08 mM). However, the anaerobic fitness was correlated with all maximal performances. Thus, it was concluded that the AWC obtained by y-intercept of the distance/time of swim relation does not seem to be a good parameter for the anaerobic fitness evaluation neither to predict the maximal performances between 100 and 600 meters in crawl style.O objetivo desse estudo foi verificar a utilizacao do intercepto-y na avaliacao da aptidao anaerobia e predicao da performance de nadadores treinados. Foram participantes do estudo 14 nadadores com idade entre 15 e 18 anos. Os atletas realizaram o teste de nado atado, performance maxima e velocidade critica (VC) para determinacao da capacidade de nado anaerobio (CTA), todos em nado crawl em um periodo de tres dias. 1) O teste de nado atado consistiu em realizar esforco maximo durante 30 segundos amarrado a um aparato de medicao com celulas de carga para mensuracao da forca pico (Fpic), aptidao anaerobia (APANA) e concentracao de lactato pico ([la-]pic) conforme Papoti et al. (11); 2) Os participantes realizaram tambem performances maximas nas distâncias de 100, 200, 300, 400 e 600 m, com intervalo minimo de duas horas entre cada nado; 3) E o teste de VC foi aplicado para determinacao da CTA utilizando todas as combinacoes possiveis dos resultados das performances maximas, atraves do modelo de regressao linear entre distância versus tempo. Foi encontrada media de 25,07± 4,22 m nas 16 combinacoes de CTAs encontradas e coeficiente de regressao linear variando entre 0,99 e 1,00 e erro de coeficiente linear de 19,30± 5,9%. Nao foram encontradas correlacoes significativas entre as CTAs e performances maximas, Fpic (227,81± 63,02 N), APANA (86,55± 13,05 N) e [la-]pic (6,80± 1,03 mM). Contudo, foram encontradas correlacoes significativas entre a APANA e as performances maximas. Desse modo, e possivel concluir que a CTA representada pelo intercepto-y da relacao distância versus tempo de nado, parece nao ser um bom parâmetro na avaliacao da aptidao anaerobia e predicao de performances entre 100 m e 600 m nado crawl.

Dominant–non-dominant asymmetry of kicking a stationary and rolling ball in a futsal context

Abstract The aim of this study was to analyse the characteristics of the asymmetries in the dominant and non-dominant limbs when kicking stationary and rolling balls. Ten experienced Brazilian amateur futsal players participated in this study. Each participant performed kicks under two conditions (stationary ball vs. rolling ball) with the dominant and non-dominant limbs (five kicks per condition per limb). We analysed the kicking accuracy, ball and foot velocities, angular joint displacement and velocity. The asymmetry between the dominant and non-dominant limbs was analysed by symmetry index and two-way repeated measures ANOVA. The results did not reveal any interaction between the condition and limb for ball velocity, foot velocity and accuracy. However, kicking with the dominant limb in both kicks showed higher ball velocity (stationary ball: dominant – 24.27 ± 2.21 m · s‒1 and non-dominant – 21.62 ± 2.26 m · s‒1; rolling ball: dominant – 23.88 ± 2.71 m · s‒1 and non-dominant – 21.42 ± 2.25 m · s‒1), foot velocity (stationary ball: dominant – 17.61 ± 1.87 m · s‒1 and non-dominant – 15.58 ± 2.69 m · s‒1; rolling ball: dominant – 17.25 ± 2.26 m · s‒1 and non-dominant – 14.77 ± 2.35 m · s‒1) and accuracy (stationary ball: dominant – 1.17 ± 0.84 m and non-dominant – 1.56 ± 1.30 m; rolling ball: dominant – 1.31 ± 0.91 m and non-dominant – 1.97 ± 1.44 m). In addition, the angular joint adjustments were dependent on the limb in both kicks (the kicks with non-dominant limb showed lower hip external rotation than the kicks with the dominant limb), indicating that the hip joint is important in kick performance. In conclusion, the kicks with the non-dominant limb showed different angular adjustments in comparison to kicks with the dominant limb. In addition, kicking a rolling ball with the non-dominant limb showed higher asymmetry for accuracy, indicating that complex kicks are more asymmetric.

Acute responses of biomechanical parameters to different sizes of hand paddles in front-crawl stroke

Abstract This study investigated the acute effects of different sizes of paddles on the force-time curve during tethered swimming and swimming velocity in front-crawl stroke. Fourteen male swimmers (20.0 ± 3.7 years; 100-m best time: 53.70 ± 0.87 s) performed two 10-s maximal efforts in tethered swimming to obtain peak force, average force, impulse, rate of force development, stroke duration and time to peak force. Swimming velocity, stroke rate and stroke length were obtained from two 25-m maximal swims. Both tests were repeated in five conditions: free swimming, wearing small (280 cm 2 ), medium (352 cm 2 ), large (462 cm 2 ) and extra-large (552 cm 2 ) hand paddles. Compared to free swimming, paddles provided significant increases of peak force (medium: 11.5%, large: 16.7%, extra-large: 21.7%), impulse (medium: 15.2%, large: 22.4%, extra-large: 30.9%), average force (medium: 5.1%, large: 7.5%), rate of force development (extra-large: 11.3%), stroke duration (medium: 9.3%, large: 11.8%, extra-large: 18.5%), time to peak force (medium: 11.1%, large: 15.9%, extra-large: 22.1%), swimming velocity (medium: 2.2%, large: 3.2%, extra-large: 3.7%) and stroke length (medium: 9.0%, large: 9.0%, extra-large: 14.8%), while stroke rate decreased (medium: –6.2%, large: –5.5%, extra-large: –9.5%). It is concluded that medium, large and extra-large paddles influence the force-time curve and change swimming velocity, suggesting these sizes may be useful for force development in water.

Use of the y-intercept in the evaluation of the anaerobic fitness and performance prediction of trained swimmers

The objective of this study was to verify the use of y-intercept from the critical velocity model in the evaluation of the anaerobic fitness and prediction of maximal performance in trained swimmers in crawl style. Fourteen swimmers with ages ranging from 15 to 18 years participated in this study. The athletes performed the tied swimming test, maximal performances tests and critical velocity (CV) for the determination of anaerobic swimming capacity (AWC). 1) The tied swimming test was applied through maximal effort during 30 seconds fixed to the equipment with load cells for the measurement of the peak force, anaerobic fitness and peak lactate. 2) The subjects also performed maximal performances at distances of 100, 200, 300, 400 and 600 meters with two hours interval between each swim. 3) AWC at CV model was determined utilizing all possible combinations by maximal performances applying the distance-time linear regression model. The AWC value obtained was of 25.07 ± 4.22 m, with linear regression coefficient between 0.99 and 1.00, and linear coefficient error of 19.30 ± 5.9%. AWC was not correlated with all maximal performances, peak force (227.81 ± 63.02 N), anaerobic fitness (85.55 ± 13.05 N), and peak lactate (6.80 ± 1.08 mM). However, the anaerobic fitness was correlated with all maximal performances. Thus, it was concluded that the AWC obtained by y-intercept of the distance/time of swim relation does not seem to be a good parameter for the anaerobic fitness evaluation neither to predict the maximal performances between 100 and 600 meters in crawl style.O objetivo desse estudo foi verificar a utilizacao do intercepto-y na avaliacao da aptidao anaerobia e predicao da performance de nadadores treinados. Foram participantes do estudo 14 nadadores com idade entre 15 e 18 anos. Os atletas realizaram o teste de nado atado, performance maxima e velocidade critica (VC) para determinacao da capacidade de nado anaerobio (CTA), todos em nado crawl em um periodo de tres dias. 1) O teste de nado atado consistiu em realizar esforco maximo durante 30 segundos amarrado a um aparato de medicao com celulas de carga para mensuracao da forca pico (Fpic), aptidao anaerobia (APANA) e concentracao de lactato pico ([la-]pic) conforme Papoti et al. (11); 2) Os participantes realizaram tambem performances maximas nas distâncias de 100, 200, 300, 400 e 600 m, com intervalo minimo de duas horas entre cada nado; 3) E o teste de VC foi aplicado para determinacao da CTA utilizando todas as combinacoes possiveis dos resultados das performances maximas, atraves do modelo de regressao linear entre distância versus tempo. Foi encontrada media de 25,07± 4,22 m nas 16 combinacoes de CTAs encontradas e coeficiente de regressao linear variando entre 0,99 e 1,00 e erro de coeficiente linear de 19,30± 5,9%. Nao foram encontradas correlacoes significativas entre as CTAs e performances maximas, Fpic (227,81± 63,02 N), APANA (86,55± 13,05 N) e [la-]pic (6,80± 1,03 mM). Contudo, foram encontradas correlacoes significativas entre a APANA e as performances maximas. Desse modo, e possivel concluir que a CTA representada pelo intercepto-y da relacao distância versus tempo de nado, parece nao ser um bom parâmetro na avaliacao da aptidao anaerobia e predicao de performances entre 100 m e 600 m nado crawl.

Analysis of Soccer Players’ Positional Variability During the 2012 UEFA European Championship: A Case Study

Abstract The purpose of this study was to analyse players’ positional variability during the 2012 UEFA European Championship by applying principal component analysis (PCA) to data gathered from heat maps posted on the UEFA website. We analysed the teams that reached the finals and semi-finals of the competition. The players’ 2D coordinates from each match were obtained by applying an image-processing algorithm to the heat maps. With all the players’ 2D coordinates for each match, we applied PCA to identify the directions of greatest variability. Then, two orthogonal segments were centred on each player’s mean position for all matches. The segments’ directions were driven by the eigenvectors of the PCA, and the length of each segment was defined as one standard deviation around the mean. Finally, an ellipse was circumscribed around both segments. To represent player variability, segment lengths and elliptical areas were analysed. The results demonstrate that Portugal exhibited the lowest variability, followed by Germany, Spain and Italy. Additionally, a graphical representation of every player’s ellipse provided insight into the teams’ organisational features throughout the competition. The presented study provides important information regarding soccer teams’ tactical strategy in high-level championships that allows coaches to better control team organisation on the pitch.