Acute Responses of Youth Elite Players to a Football Match in Terms of Blood Markers.

The current study verified the acute responses of participants to a football match in terms of blood markers. Sixteen elite U-18 male football players were divided into two groups: experimental (EG, n = 10), who played a friendly football match; and control (CG), who were not exposed to any physical exertion. Intravenous blood samples were collected from both groups at baseline, pre-match, half-time, and post-match. The blood analysis consisted of four groups: immunological (leukocytes, platelets, and cortisol), muscle damage (creatine kinase and lactate dehydrogenase), metabolic (lactate, glucose, erythrocytes, hematocrit, hemoglobin, and urea), and electrolytic (sodium, calcium, and potassium). Edwards' training impulse demonstrated that the first half was more demanding than the second half (p = 0.020). Significant changes between time points and groups were observed for leukocytes (pre-match: 6920 ± 1949; post-match: 13,890 ± 3292; p ≤ 0.05) and cortisol (pre-match: 10.78 ± 3.63; post-match: 19.15 ± 7.40; p ≤ 0.05). CK (pre-match: 516.50 ± 248.38; post-match: 713.70 ± 308.20; p ≤ 0.05) and LDH (pre-match: 348.80 ± 36.49; post-match: 414.80 ± 26.55; p ≤ 0.05) increased significantly across the time points for the EG, with no difference between the groups, however. Raised lactate (pre-match: 1.05 ± 0.32; post-match: 3.24 ± 1.60; p ≤ 0.05) and glucose (pre-match: 72.54 ± 9.76; post-match: 101.42 ± 19.87; p ≤ 0.05) differences between the groups at half-time were also observed. These current findings provide helpful information to better understand football match demands regarding physiological effects.

How Positional Constraints Affect Footedness in Football: A Notational Analysis of Five Leagues in Europe.

In elite-level soccer, the ability to take shots with both limbs from different positions in the pitch may be key to success. This research aimed to: 1) analyze footedness of elite-football players in European leagues during shooting by computing frequency of right- and left-foot use and accuracy; and 2) investigate whether an athlete's distance from the target (goal, penalty, and outside penalty area) and pitch zone (center, left, or right from the goal) can constrain foot selection during shooting. We analyzed 1826 games from the 2017/18 season, divided between: Spanish LaLiga (380 matches); Italian Serie A (380 matches); English Premier League (380 matches); German Bundesliga (306 matches); and French Ligue 1 (380 matches). Results revealed asymmetrical proportions of foot selection, favoring the preferred foot for right- and left-footed athletes. Frequency of preferred foot selection increased as a function of distance from the target (i.e., the farther the athlete, higher the percentage of preferred foot selection). Shots taken from the left side were more often performed with the right foot and vice-versa, for both left- and right-footed athletes. Interestingly, asymmetries were observed only in foot selection, but not in performance, as success rate did not vary between limbs in any position.

Design and Validation of an Observational System for Penalty Kick Analysis in Football (OSPAF).

The analysis of penalty kick has played an important role in performance analysis. The study aims are to get formal feedback on the relevance of variables for penalty kick analysis, to design and validate an observational system; and to assess experts' opinion on the optimum video footage in penalty kick analysis. A structured development process was adopted for content validity, reliability and agreement on video usage. All observational variables included in OSPAF showed Aiken's V values above the cut-off (for 5-scale V> 0.64; for 2-scale = V > 0.75; p < 0.05). Cohen's Kappa resulted in mean intra- and inter-rater reliability values of 0.90 and 0.86, respectively. It is recommended to combine at least three different viewing angles (V = 0.90; p = 0.006) with standardization of video quality (V = 0.95; p = 0.006). Changing the viewing angles may influence the observer perception (V = 0.86; p = 0.006). The aerial and pitch-level viewing angle behind the penalty taker and pitch-level viewing angle behind the goalkeeper were indicated as most appropriate for observational analysis (V = 0.97; p = 0.01). The OSPAF met all requirements of instrument validation. It may be recommended as basis of future observational systems on penalty kicks.

Time-course of changes in indirect markers of muscle damage responses following a 130-km cycling race / Comportamento das respostas dos marcadores indiretos de dano muscular após uma competição de ciclismo de 130-km

Abstract The purpose of the present investigation was to identify the effects of a 130-km cycling race on indices of biochemical indirect markers of muscle damage and muscle soreness responses during a 72-hour recovery period. Fifteen endurance-trained male cyclists which were competing for more than 2 years and were involved in systematic training at least of 3 days/wk underwent a collection of indirect biochemical markers of muscle damage (CK, LDH, Myo) and delayed onset of muscle soreness (DOMS), at five different moments of data collection: before (PRE) and immediately after (POST) a 130-km cycling race, and 24, 48, 72 hours following the cycling race. CK and LDH plasma concentrations significantly increased POST-race (p < 0.001) and remained high throughout the 72 hour recover period (CK: p < 0.05; LDH: p < 0.001). Myo increased significantly POST-race (p < 0.001) and returned to the PRE-race values 24 hours thereafter (p < 0.05). DOMS increased significantly POST-race (p < 0.001) and returned to the PRE-race values at 48 hours after (p > 0.05). A 130-km cycling race has a noteworthy effect on indices of biochemical indirect markers of muscle damage and muscle soreness responses, indicating that 72 hour recovery period do not seems to be enough for long-distance cyclist, and reinforce the propositions of scientific literature about the need of a sufficient recovery period for cycling endurance athletes.

Resumo O objetivo do presente estudo foi identificar os efeitos de uma competição de ciclismo de 130-km nos índices de marcadores bioquímicos indiretos de dano muscular e na dor muscular durante um período de 72 horas de recuperação. Quinze ciclistas do sexo masculino que estavam em treinamento competitivo por mais de dois anos e que estavam em treinamento sistemático, pelo menos três dias por semana, foram submetidos à coleta de marcadores bioquímicos indireto de dano muscular (CK, LDH e Mioglobina) e dor muscular em cinco momentos distintos de coleta: antes, depois, 24, 48 e, 72 horas após uma competição de ciclismo. A CK e a LDH aumentaram imediatamente após a corrida (p < 0,001) e mantiveram-se elevadas durante as 72 horas de recuperação (CK: p < 0,05; LDH: p < 0,001). A Mioglobina aumentou logo após a competição (p < 0,001) e retornou aos valores basais 24 horas após (p < 0,05). A dor muscular aumentou logo após a competição (p < 0,001) e retornou aos valores basais após 48 horas de recuperação (p > 0,05). Uma competição de ciclismo de 130-km teve efeitos notáveis sobre os índices de marcadores bioquímicos indiretos de lesão muscular e dor muscular, indicando que um período de 72 horas de recuperação pode não ser o suficiente para ciclistas de longa distância, isto também reforça as proposições da literatura científica sobre a necessidade de um período de recuperação suficiente para os atletas de ciclismo de fundo.

Distribuição de subgrupos com base nas respostas fisiológicas em jogadores profissionais de futebol pela técnica K Means Cluster / Subgroup distribution based on physiological responses in professional soccer players by K-means cluster technique

INTRODUÇÃO: A preparação física no futebol necessita estar sempre em constante atualização em virtude das exigências presentes no futebol contemporâneo. OBJETIVO: Verificar a sensibilidade da técnica estatística K Means Cluster na distribuição de grupos com base nas respostas fisiológicas pertinentes ao futebol. MÉTODOS: Os atletas foram submetidos a avaliações antropométricas para determinar o percentual de gordura (%G) e de massa magra (MM), teste incremental em esteira para obter o VO2 máximo (VO2máx) e a velocidade de limiar ventilatório (VLim), bem como testes de campo para a agilidade (AG) e o salto vertical (SV). Os dados foram analisados pelo teste de Kruskal-Wallis e a distribuição dos grupos foi desenvolvida pela técnica de K Means Cluster conforme as semelhanças dos jogadores com essas variáveis fisiológicas, assumindo o nível de significância de p < 0,05. RESULTADOS: Os grupos diferiram significativamente somente com relação ao SV (p < 0,001), MM (p < 0,001), VLim (p = 0,011) e VO2máx (p = 0,029) indicando que para estas variáveis, os atletas necessitam ser distribuídos em grupos. Entretanto, o %G e a AG (p = 0,317; p = 0,922), respectivamente, não foram diferentes, indicando que essas variáveis podem ser aprimoradas em todos os atletas de maneira coletiva. CONCLUSÃO: Tendo em vista os resultados encontrados, podemos concluir que a distribuição dos grupos pela técnica K Means Cluster pode ser realizada utilizando as respostas fisiológicas dos atletas no intuito de otimizar e priorizar o treinamento físico das principais necessidades apresentadas em comum pelos atletas, independentemente da função tática exercida em campo.

INTRODUCTION: Physical fitness in soccer needs to be constantly updated due to current demands in contemporary soccer. OBJECTIVE: To assess the sensitivity of the K Means Clustering in group distribution based on physiological responses relevant to soccer. METHODS: The athletes underwent anthropometric evaluations to determine fat percentage (%F) lean mass (LM), treadmill incremental test to obtain the VO2 maximum (VO2max) and ventilatory threshold velocity (VL), as well as a field test for agility (AG) and vertical jump (VJ). Data were analyzed by Kruskal-Wallis and distribution of groups was determined by K Means Clustering according to their similarities with these physiological variables, assuming significance level of p < 0.05. RESULTS: Showed that both groups were significantly different only concerning VJ (p < 0.001); LM (p < 0.001); VL (p = 0.011) and VO2max (p = 0.029) indicating that the athletes need to be distributed in groups for these variables. Nevertheless, %F and AG (p = 0.317; p = 0.922) respectively, were not different, indicating that these variables can be improved in all athletes collectively. CONCLUSION: The results make us conclude that group distribution by K Means Clustering technique can be performed using physiological responses of athletes in an attempt to optimize training for professional soccer players with focus on the common main training needs regardless of their tactical function played on the field.